We report the recent progress in the development of high intensity ultrashort pulse lasers at the State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics (SIOM). Based on the concept of optical parametric chirped pulse amplification (OPCPA), a 16.7 TW/120 fs laser at 1064 nm was developed. Some new nonlinear optical materials, such as quasi-phase-match crystals, were investigated as new OPCPA gain media. The investigation of broadband OPCPA near 780 nm was also carried out. On the other hand, based on the scheme of chirped pulse amplification (CPA), the Ti:sapphire laser system with a peak power of 0.89 PW and a pulse width of ~29.0 fs has been developed. The high gain amplification was achieved in a large aperture amplifier by cladding with refractive-index matched liquid doped with absorber to suppress the parasitic lasing.

A scheme of combining smoothing by spectral dispersion (SSD) technology with lens array (LA) is introduced in laser produced shock wave experiments. The feasibility of the scheme is analyzed by numerical simulation. It is shown that the beam uniformity in near field could be improved by the phase modulation and spectral dispersion, and a smoothed pattern with flat-top and sharp-edge profile could be obtained in the focal plane. The irradiation nonuniformity of the focal pattern depends on the design of both SSD and LA but less on the incident beam in comparison with other smoothing methods. Experiments are conducted by adopting the schemes of LA and SSD, distributed phase plate (DPP) and SSD. The results are beneficial for better smoothing in laser-plasma interaction experiments in the future.

A novel method of error analysis for opto-mechanical system by considering issues of the space and time stability is proposed. According to the theory of error transfer model and the system stability requirements, the temporal parameter is introduced as the dynamic compensate to reflect the structure random response influencing the position precision in the period of working time. The error transfer model originated from our method is also put forward. Moreover, the simulation is used to analyze the error of spatial filter system in Shenguang (SG) II facility. The results show that the method can more effectively deal with the target position error induced by the system structure, and it also provides a dynamic error analysis method for the high power laser facility and other great science projects.

Thermal effects control is very critical in highly scaling the output power of diode-pumped solid-state lasers to a few watts especially for end pumping configuration. Low temperature reservation of the pumping surface and the crystal could be adopted to reduce thermal effects and improve laser performance. Diffusion bonding crystal has been demonstrated to be an effective method to relieve the thermal lensing theoretically based on the numerical heat analysis to the end-pumped anisotropic laser crystal. The temperature distribution in Nd:YVO4/YVO4 composite crystal was analyzed before the end-pumped Nd:YVO4/YVO4 composite crystal laser with V cavity was designed and set up. The maximum output powers of 9.53 W at 1064 nm, 5.01 W at 532 nm were obtained while the pumping power was 17 W. The highest optical to optical conversion efficiencies were up to 59.1% at 1064 nm and 34.4% at 532 nm, respectively.

We present a continuously tunable Alexandrite laser. By means of chromatic dispersion prisms, the output spectrum in the range of 725-781 nm has been obtained. The output energy at the center wavelength of 750 nm has achieved 1 J per pulse. To obtain the highest output energy, the best transmission rate of output mirror has been briefly studied. By reducing the transmission rate of the output mirror, the output range of spectrum has been extended to 725-791.4 nm. The difference between tuning with one and two prisms has also been analyzed experimentally.

The stability of the output of a heat capacity laser was measured. The output power dropped rapidly with the increase of lasting time. The result showed that the rise of the average temperature of laser medium was not the main reason, while the non-uniform distribution of the temperature was the main reason which resulted in depolarization and maladjustment of resonant cavity.

In order to improve the energy efficiency of high power laser system of ICF and use the optical energy sufficiently, converting Gaussian laser beam into uniform beam is important. Meanwhile, the wavefront of the laser beam in the system is also significant because it affects the imaging quality at image surface and the transfer of image in multilevel magnification laser system. Starting from the Jones matrix of spheric lenses, the intensity transmittance distribution of birefringent lenses beam shaping system has been analyzed by transmission matrix. The wavefronts of different polarized states after transmission through beam shaping system are discussed. The effecting factors, such as the distances between lenses, the lens' mechanical deviation from optical axis of system, have been considered. The uniform laser beam can be obtained. In the ninth beamline of 'SG II' device, the static beam filling factor of near field can be improved from 66% to 80% by using the birefringent lens shaping system.

Multi-kilojoule petawatt lasers using chirped-pulse amplification need large-scale compression gratings. Tiled-grating approach has been adopted in several systems to meet the size requirements, grating tiles need to be precisely phased to ensure a transform-limited focal spot when focusing high-energy laser pulses in the target. Piston error of segmented gratings induced the focal spot to split when it arrived at multiple of the half wavelength. Alignment method using ultra-short pulse capable of controlling the absolute piston phase error within one half wavelength is proposed.

We demonstrate an efficient tunable diode-end-pumped continuous wave (CW) Yb3+:Lu2SiO5 (Yb:LSO) laser. With a 5 at.-% Yb3+-doped sample, we obtained 3.24-W output at 1080 nm for 7.3 W of absorbed pump power, the corresponding slope efficiency was 55%. And the laser wavelength could be tuned from 1017 to 1084 nm.

Luminescence of Nd3+ is observed in a new undeuterated organic liquid medium. The measured lifetime 'tau' of 1060-nm emission is 460 microseconds and the emission cross section is 2.54*10^(-20) cm2. According to the spectral research results, two pumping schemes are designed and the threshold energies for outputting laser are roughly calculated. Taking 808 nm as pumping wavelength and using single-pulse-mode pumping, the threshold pumping energy of single pulse is evaluated about 250 mJ to ensure the pumped volume enough large and so the peak power of 200-microsecond pulse is about 1250 W, which is easily obtained today. The rough estimated results prove that this organic solution is a successfully potential laser media.

Ultra-thin slab with the dimension of 1*10*60 (mm) is demonstrated to acquire high-power laser output with high beam quality. The output average power of 70 W with diffraction limited beam quality is obtained, and the total optical-optical efficiency is about 32%. It can produce more than 100 W output laser when it operates with multi-mode. Cr4+:YAG is adopted as the saturable absorber, the pulse repetition rate is higher than 10 kHz, and the pulse duration is less than 10 ns. An asymmetrical composite crystal is also studied, the new crystal consists of two layers: one is undoped YAG, the other is Nd-doped YAG layer. It is shown that thermal effects of the new asymmetrical crystal are obviously reduced.

We demonstrated the measurements of attenuation constant of a multi-mode fiber with 300-micron core diameter and 1-km length at 1070 nm. The observed attenuation constant was below 0.7 dB/km, the laser power of 5 kW was coupled into the 1-km fiber at 1070 nm, and the overall transmittance was 85%, and the first Raman Stokes signal was observed in the transmitted laser spectrum. We demonstrated concrete cutting with a 4-kW fiber laser at 1070 nm. The slab thickness was 100 mm. This technique can be extended to thick concrete slabs more than 1 m without increasing laser power.

In order to get stable continuous wave (CW) mode-locked (ML) laser, conventionally, the laser cavity was designed to reach very small mode radius in the laser crystal to make the laser material saturated. While for the laser diode (LD) end pumped Nd:YVO4 without fiber coupling transmission, as long as choosing the appropriate short focus lens and making the focus area in front of the Nd:YVO4 small enough, we found even large cavity mode volume can make the laser material saturated. In addition, relatively large cavity mode volume can make high power output with single mode come true. Ideal beam quality without high order transverse mode oscillating, the CW ML state turned to be very stable. Accordingly, relatively large mode volume in the laser crystal was designed with semiconductor saturated absorber mirror (SESAM), over 1.5-W CW ML output with near diffraction limited was acquired. The optical-to-optical conversion efficiency reached 30%.

A numerical model is presented to predict the time-resolved evolution of the spatial intensity distribution of the laser pulses in the super-Gaussian mirror resonator, taking into account diffraction and stored energy depletion. The beam-quality factor M2 is calculated during the pulse evolution. Simulation results show that gain saturation affects the beam quality of the Q-switched solid-state lasers, the corresponding values of the M2 parameter increase during the pulse evolution. The spatial distribution of laser pulse first starts on the resonator axis with a Gaussian-shaped spot, then expands very quickly and forms a donut-shaped profile towards the end of the pulse.

A new method is proposed which makes it possible to produce flattened irradiance distribution by incoherent combination of cosh Gaussian beams with different parameters. Based on the Collins integral formula, the resulting irradiance distribution is derived and the corresponding beam qualities in terms of M2 factor and kurtosis parameter are given. The numerical examples illustrate that a flattened intensity distribution of the resulting beam can be obtained in the near filed if appropriate parameters are chosen. Compared with the coherent combination of the Hermite-Gaussian (HG) beams, this new method leads to better beam quality and can be more easily realized experimentally resulting from in-phase-free requirement.

This paper introduces a self-tuning fuzzy temperature control system for the diode-pumped solid-state (DPSS) blue laser at 473 nm. This temperature control system includes circuit of temperature sampling, power circuit of temperature adjusting, and fuzzy proportional-integral derivative (PID) controller. Circuit of temperature sampling adopts the precision temperature sensor for exact temperature sampling. The input signal of fuzzy PID controlling is digital signal from A/D transform chip, then the input analog signal of A/D transform chip is the differential signal of temperature sampling signal and setting temperature signal. The traditional PID control method cannot self-tune parameters of Kp, Ki, Kd in operating, this paper applies the method of combining fuzzy illation with traditional PID controlling to realize self-tuning parameter of PID. This system designs the power circuit to respond to control signal of fuzzy PID controller, that power circuit is made up of high power metal-oxide-semiconductor (MOS) field effect transistors semiconductor and Peter component. This self-tuning fuzzy temperature control system has good dynamic characteristic and static characteristic, and the system has lower over-adjusting and shorter response time. The temperature control precision of system is up to +-0.05 deg., the change range of the pump laser diode wavelength is below 0.02 nm, and the power stability of the laser at 473 nm is below +-1%.

In order to get high efficiency and high brightness laser output with single fiber coupled laser diode array, two laser diode array bars which have 40-W continuous wave (CW) output power at 980-nm wavelength are used in the experiment. The laser diode bars are collimated by two pieces of cylindrical micro lenses in the fast axis direction, and in the slow axis direction step mirrors are used to divide the beams of light to shape the output beam symmetrically. A piece of polarizing beam splitter cube is used to combine the two shaped beams. The focused output beam is coupled into a multimode fiber. More than 55-W output power is obtained from the fiber with core diameter of 400 microns and numerical aperture of 0.22, the total coupling efficiency is about 70% and the brightness is up to 10^(9) level.

In the 9th laser system of Shenguang II inertial confinement fusion (ICF) facility, tunable Fabry-Perot (F-P) filter is applied to compensate the FM-AM effect. According to the technical requirements of compensation device, a precise displacement monitor system using the capacitive displacement sensor with nanometer scale precision to stabilize the spacing of the tunable F-P filter is proposed firstly, then the basic structure and operating principle of the monitor system are analyzed. The scheme design of the driving circuit of capacitive displacement sensor, the data processing as well as the system controlling program are discussed in detail, and the precision of capacitive displacement sensor is calibrated. The experimental results show that the spacing stability of the tunable F-P filter is better than 15 nm/h and the modulation depth of the FM-AM effect is better than 4% by introducing the displacement monitor system.

Structural design and stability analysis of 'phi' 570 mm mirror mount are performed. Under the constraint conditions, the geometric parameters of cross-flexure pivot in large aperture mirror mount are determined. With finite element analysis software (ANSYS), the influences of cross-flexure pivot's setting angle on center drifting and stress distribution of flexure, and the dynamic performance of the whole mirror mount, are analyzed. When the setting angle between the direction of gravity and the setting direction of flexure is 0 or 90 deg., the center drifting of mirror mount is minimum and the stress distribution of flexure is relatively uniform. The nature frequency is 23 Hz, and the maximum amplitude of angular vibration response to random excitation input is 0.91 microrad, which is consonant with experiment results. The performance of mirror mount can satisfy the requirement of precision positioning in Shenguang (SG) II laser system.

A laser diode (LD) stack pumped solid-state laser (DPL) with different cooling conditions was reported. The thermal lens was calculated and compared under different cooling conditions. The influence of the thermal lens effect on the output energy fluctuation of the DPL was studied. The LD stacks peak power was 12 kW with 1-kHz repetition frequency and 20% duty ratio. In the examination with nothing to cool the solid-state heat capacity laser (SSHCL), the output power was 1 J at the beginning, after 1 s it fell down to 50%, and with the water cooling the output power hardly fell down.

Propulsion system using continuous-wave (CW) CO2 laser has several advantages in comparison with other systems. This system does not require strong structure compared with propulsion with chemical propellant, plasma and gas arc jet. Laser propulsion can produce high specific impulse which determines propellant efficiency since the highest energy density is limited simply by laser system capability. Furthermore, propellant selection is free from the combination of fuel and oxidizer and therefore can be made according to propulsion performance. Using system of water vapor and CO2 laser which can offer large power system and has large absorption coefficient with water molecule, we consider rocket lunching from the ground to the earth orbits. On the other hand, laser propulsion uses high temperature propellant compared to the chemical rocket and gets high specific impulse under subsonic speed. We examine the performance of propellant that is heated with laser from downstream of the flow and estimate specific impulse and thrust using numerical calculations. We found that specific impulse can be increased by selecting proper combination of laser power and propellant mass flux.

We have developed a rigid hollow fiber composed of a silver-clad stainless steel pipe. The inside wall of the pipe was polished to a mirror-smooth state, and after that a cyclic olefin polymer (COP) as a transparent dielectric material was coated on the inside of the silver layer. Transmission of CO2 laser light through the hollow fiber of 20-cm length with a 0.75-mm inside diameter was 95% under straight condition, and more than 75% under the condition of a 90 deg. bend with a 4-cm bending radius. This metallic hollow fiber is not very long or flexible, but it has great mechanical strength. For this reason, this sturdy metallic hollow fiber can be used for a laser probe mounted at the tip of a long optical transmission line.

Based on the laser rate equations in a typical four-level system, we research the temperature-dependent gain characteristics of a solid-state heat-capacity laser (SSHCL) involving the small-signal gain coefficient and the gain distribution's uniformity. The influences of doping concentration of active ions and initial operating temperature on the small-signal gain coefficient are discussed for Nd-doped glass heat-capacity laser. Furthermore, the gain distributions of a slab laser gain medium operating in SSHCL mode are discussed.

The technology of measuring high-speed optical pulse sequence is under fast development for meeting the increasing requirement in optical communication, characterization of optical pulse and other fields. We propose a chirped pulse sampling technology to measure the terahertz (THz) pulse sequence. The principle and detection resolution of this high-speed sampling technology have been discussed and analyzed. The acquisition could measure a THz sequence containing hundreds of pulses at a single-shot. With this method, THz sequence could be measured by low-speed sampling devices.

We have successfully demonstrated a single-frequency distributed-feedback Yb-doped silica fiber laser. The laser cavity is 10 cm long and is formed by a simple method called the shielded method. The phase shift in the fiber Bragg grating is introduced by shielding a small region of the fiber during fabrication by ultraviolet (UV) light from a 193-nm excimer. Without complex pump configuration, the fiber laser gives a maximum output of more than 20 mW when pumped by laser diode at 978 nm with 100 mW. The laser shows a single frequency and single polarization operation.

A refractive index profile design, which can enable us to obtain a flat-top fundamental mode field around the center, is presented. The theoretical method to analyze the four-layer large flattened mode (LFM) fibers is given. The properties of the fiber, including the fundamental and higher order modal fields, effective area, and bending loss, are discussed. The reasons forming the different modal fields are explained. By discussion, the larger effective area of the LFM fiber compared with conventional step-index fiber is proven and the feasibility to suppress the higher order modes via bending is given.

A high energy all-solid-state blue laser with wavelength of 455 nm is proposed, which can be used in laser communication underwater or in the differential absorption lidar (DIAL) system. Ti:sapphire crystal is suitable material and is pumped by the second harmonic generation (SHG) of Nd:YAG laser. The pumped laser of 1000 mJ, 10 Hz is used, and the output wavelength of Ti:sapphire resonator cavity is controlled by external injection seeding. Parameters of the resonator cavity of Ti:sapphire crystal is carefully calculated and optimized. Pulsed 455-nm blue laser exceeding 100 mJ is obtained through frequency-doubled Ti:sapphire laser.

With the advent of HDTV, the high density DVD (HD DVD) and blue-ray disk (BD) series will become the mainstream. Compared with BD, HD DVD has lower producing cost and sailing price, and it can be compatible with DVD. We design a new kind of compact optical picking-up head (PUH) based on HD DVD technology. It is simple in structure and small in size. It has two laser waves, and can be compatible with DVD downward. The PUH is mainly composed of a penta prism, a collimating lens, and an objective lens. The light route is analyzed using ZEMAX, and the results turn out to be successful. The penta prism is used to achieve a much longer optical path, so that the PUH size is reduced.

The Q-switching performance in a folded resonator containing prism reflectors is analyzed. It is shown that the performance of the Q-switch in a folded cavity is affected by its configuration. A variety of configurations are compared theoretically. The transmissivities are calculated when the Q-switch is turned on and off, respectively. The effects of the misalignments of the prisms are also calculated. The Q-switch in a folded resonator with prism reflectors is optimized. With the optimal Q-switch, the laser system is more compact and stable. The effects of the misalignments of the prisms on the Q-switching performance are reduced by using optimal Q-switching configuration.

The energy storage of solar radiation with magnesium as an energy reservoir is proposed for renewable energy cycle. Magnesium reaction with water generating hydrogen and residual MgO is used to retrieve energy. Solar pumped laser is used to reduce MgO back to magnesium. This unique reduction process is possible because highly concentrating power density of laser radiation realizes non-equilibrium states of magnesium and oxygen dissociation from MgO and quickly separates each other for avoiding recombination to MgO. The proposed energy cycle consists of three key technologies: power generation by magnesium combustion, reduction of magnesium oxide, MgO, the combustion residue, and solar pumped laser that drives the MgO reduction process. This paper describes the experimental investigation of Mg combustion engine characterization.

Development of a fiber laser pumped, compact mid-infrared (IR) difference frequency spectrometer employing a periodically poled LiNbO3 (PPLN) for next generation environmental monitoring is presented. Previous spectroscopic experiments of various gas species, performance characteristics of pump and signal lasers and PPLN-based difference frequency generation (DFG) are reviewed. The DFG spectrometers developed in our facility were carefully calibrated with concentrations between a few ppm and 500 ppm, and demonstrated with an excellent linearity. Moreover, a ratio between measurement deviation and gas concentration was approximately +-1%, which could maintain in a long-term measurement operation (~1000 h). Rapid gas detection for N2O, CH4, CO2, NO2, and NH3 with a total measurement time of less than 10 s was achieved with interference completely free from absorption spectra of other gas species, resulting in minimum detectable concentration at sub ppm level. Also, real-time NO2 monitoring of an exhaust gas of a diesel engine is demonstrated, and a simultaneous dual gas detection concept by the DFG is introduced.

A small flying object (kite plane) was successfully driven by using the laser energy transmission technology. A demonstration test was done in a large baseball dome stadium. A long-time flight of a kite plane flying at an altitude of 50 m and with a circulating radius of 10 m has been accomplished. It has been shown that the technology is applicable to practical use such as a reconnaissance flight in natural disasters.

A high peak power, high repetition rate master oscillator power amplifier (MOPA) system incorporating an Yb-doped fiber amplifier and its second harmonic generation (SHG) were investigated in detail. The oscillator is actively Q-switched microchip laser at repetition rate of 50 kHz with a pulse width of 2.8 ns. The amplifier employing Yb-doped polarization maintaining fiber and having a large mode area was excited by a laser diode with an optical power of 17 W. As results, the amplified average output power of 10 W and optical-optical conversion efficiency of 59% were achieved. In this MOPA system, experiments were performed by using KTP and LBO crystals. The conversion efficiency of 21% and 40%, SHG maximum power of 0.92 and 3.3 W were obtained for KTP and LBO crystals respectively.

A compact Q-switched laser based on Er/Yb co-doped fiber is demonstrated. Operating in repetition rate of 10-100 kHz and Q-switching window time of 100 ns to 2 microseconds, the laser is optimized in the amplitude and stability of the pulses. At the repetition rate of 100 kHz, and maximum power of 1.75 W, average output power of 264 mW and a slope efficiency of 14% were obtained. The maximum pulse energy reached to 2.6 microjoules at the repetition rate of 100 kHz.

A new physical explanation of the fringes in the high-order harmonic spectra generated by ellipticity-modulated infrared pulses is proposed, which is different from those in previous works. In this work we find that the fringes are due to the spectral interference effect induced by the two outgoing pulses with a delay, which are generated by the wave plates for ellipticity control. The visibility of interference fringes observed experimentally increases with the increase of the asymmetry of the two pulses, with the decrease of the delay and with the increase of peak intensity of the driving laser pulse. The experimental results are in good agreement with the calculated ones.

Nanohole fabrication using near electromagnetic field enhancement in vicinity of gold particles is demonstrated. Gold spherical particles with the diameters of 40, 80 and 200 nm are deposited on substrate surfaces and irradiated by a 100-fs laser pulse at the wavelength of 800 nm. The enhanced near field results in substrate surface modification and nanohole formation under the particle. The applied laser fluence ranges from the values below the ablation threshold of the substrate material without particles to the values slightly above it in order to estimate its influence on the properties of the produced structures. The morphological changes on the surface of soda lime glass, Si, and Au, and the parameters of the produced nanostructures are analyzed by scanning electron microscope and atomic force microscope. The distribution of the near electric field is analyzed by a finite difference time domain simulation code. The produced structures are found to depend strongly on the properties of the substrate and laser parameters. In the case of the metal and semiconductor substrates, the electric field is localized in the vicinity of the contact point. In the case of glass substrate the electric field is spreading in an area larger than the particle size. The enhancement factor is about an order of magnitude lower than the case of using the silicon substrate. The results indicate that this method is capable of producing precise nanostructure of a variety of materials.

The property of femtosecond laser pulse propagation in a metallic nano-slit lens, which is composed of nano-slits with variant widths, is investigated by using the finite-difference time-domain method. By appropriately setting the width profile of the arrayed nano-slits, we find that the femtosecond laser pulse can be focused on a nano-scale spot, while the pulse shape is well maintained beyond the spot location.

A simplified Coulomb explosion model is presented for the analysis of the explosion dynamics of hydrogen clusters driven by an ultrashort intense laser pulse. The scaling of the proton kinetic energy with cluster size has been studied in detail based on this model. It is found that the maximum kinetic energy the protons acquire in the laser-cluster interaction rises to a peak and then decreases slightly as the cluster size increases, which can be explained very well by investigating the temporal evolution of outer ionization rate of different-size clusters. It is also indicated that there exists an optimum cluster size to maximize the proton energy for given laser parameters. Moreover, taking the cluster-size distribution as a log-normal function distribution into account, the maximum proton energy increases sharply with the cluster size and then levels off before beginning to fall slowly. The inclusion of a cluster-size distribution into the simulations considerably improves the fit with experimental data. These discussions are useful for the optimum-match determination of laser-cluster parameters to obtain the maximum proton energy in experiments.

Experiments for the laser guiding have been carried out with the 30-fs, 100-TW Ti:sapphier laser pulse interaction with a long slab (1.2*10 (mm)) and discharged capillary of underdense plasma. Formation of an extremely long plasma channel with its length (~10 mm) 10 times above the Rayleigh length is observed when the laser pulse power is much higher than the critical power for relativistic self-focusing. The long self-guiding channel formation is accompanied by the quasi-monoenergetic electron acceleration with a low transverse emittance (<0.8'pi' mm.mrad) and high electric current (up to ~10 nC/shot). In order to continuously elongate the plasma channel, a 4-cm-scale discharged capillary was used. We successfully demonstrated the laser-plasma acceleration of high-quality electron beams up to near GeV. Our results exactly verify the prediction of laser-wakefield acceleration through a centimeter-scale plasma channel in the "blowout bubble" regime, where a micro-scale plasma cavity produced through the ultra-relativistic laser-plasma interactions plays an essential role in the self-injection and acceleration of electrons.

Laser-accelerated ion sources have exceptional properties and could stimulate development of compact ion accelerators. For many applications beam control is an essential requirement. A new and interesting technique to control proton beam characteristics has been recently developed. It consists in using an ultrafast laser-triggered micro-lens, which provides simultaneous energy selection and focusing of the incoming ion beam and is tunable. Particle-in-cell simulations coupled with particle tracing are used to model the focusing and energy selection mechanisms, and to study the symmetry of the expanding plasma inside the micro-lens. The model developed is able to reproduce and explain the experimental results obtained at the Laboratoire pour l'Utilisation des Lasers Intenses in France.

This paper reports fundamental aspects of high-order harmonic generation from N2, O2 and CO2 molecules spatially aligned with intense femtosecond laser pulses. The time-dependent harmonic signal observed with a pump and probe technique has been found to include several sets of beat frequency for pairs of coherently populated rotational states. We have shown the origin of each frequency component and its effect on the revival signal. The results demonstrate that the high-order harmonic generation provides a sensitive and useful way for an extensive study of dynamic processes in the field-free alignment of molecules.

The correlation between the gain material and the factors affecting characteristic temperature in high-power semiconductor lasers is comprehensively considered, and the AlInGaAs is adopted as the active area material. The AlInGaAs/AlGaAs/GaAs strained quantum well laser is designed and the whole structure of the device is given. Its highest operation temperature is 100 Celsius degrees and the characteristic temperature is up to about 200 K when the temperature is within 20-40 Celsius degrees. The output power is over 1 W at room temperature, and the lowest threshold current density is 126 A/cm2.

The technique of pulsed anodic oxidation is adopted in the fabrication of 980-nm bottom-emitting vertical-cavity surface-emitting lasers. A high-quality native oxide current blocking layer is formed with this method. A significant reduction of threshold current and a distinguished device performance are achieved. The threshold current of large aperture devices with active diameter up to 400 microns is as low as 0.45 A at room temperature, which is substantially lower than the lasers fabricated by SiO2 sputtering. The maximum continuous-wave output power is 0.83 W. The lasing peak wavelength is 990.2 nm, and the full width at half-maximum is 0.9 nm. Low lateral divergence angle of 15.3 deg. and vertical divergence angle of 13.8 deg. are obtained.

An optical fiber bundle array coupling module with high output power is proposed. The device integrates the coupling technique of the high power laser diode array (LDA) and the flat end-surfaces of fiber array. This module can efficiently couple the output laser of the LDA into the 19-fiber array through the flat-end surface. The fibers are ordinally fixed precisely on the V-grooves, and the fiber array has the same arrange period with the semiconductor laser units of LDA. A cylindrical fiber lens is fixed at the front of the LDA, which will greatly reduce the divergence of the laser beam and assure the laser beam to totally pass through into the end surface of fibers. High output power of 33.2 W of the fiber optic coupling of LDA is achieved, and maximal coupling efficiency is 84%.

The design, fabrication, and characteristics calculation of 980-nm optically pumped semiconductor disk laser are reported. The laser combines a vertical cavity semiconductor laser with a partically reflecting out coupler and an external cavity for mode control. Pumped by 808-nm diode laser, the disk laser directly generates a linearly polarized, circularly symmetric, diffraction-limited beam with watt-level power. Calculation shows the laser with active region of InGaAs/GaAsP/AlGaAs system can operate at near 500-mW in a single transverse mode.

High power diode array module has been fabricated. The epitaxial structure is an InGaAs/GaAsP strain compensated single quantum well. The laser bars are made with a filling factor of 84.6%. The module's quasi-continuous wave (100 microseconds, 1000 Hz) peak power can reach to 88.6 W at a current of 100 A. The central wavelength is 1050 nm and the full width at half maximum is 4.2 nm.

High power bottom-emitting In0.2Ga0.8As/GaAs 4*4 two-dimensional vertical-cavity surface-emitting laser (VCSEL) arrays, with high output power in the 980-nm wavelength regime are reported. At room temperature, the 16-element array with 200-micron aperture size of individual elements shows a continuous wave output power of 1.21 W with a lasing wavelength of 981.9 nm. Temperature dependent characteristics of VCSEL arrays with 90-micron aperture size of individual elements are investigated. The lasing wavelength, optical output power and threshold current are measured at various heatsink temperatures. With the increase of heatsink temperature, the maximum output power and slope efficiency are greatly decreased. A red shift of lasing wavelength and a widening of the lasing spectrum are also observed.

It is observed that the pulse duration of loosely focused pulses is self-compressed during the nonlinear propagation in argon when the input pulse peak power is close to the threshold power for self-focusing, and the results are confirmed by the numerical simulation. From the simulation we find that, near the lens focus the central part of the beam moves forward to the outer part owing to the plasma generation, and produces a leading peak in the temporal profile. And then, with the decrease of the plasma density, the spatio-temporal focusing and self-steepening effects predominate and promote a shock beam structure with a steep trailing edge. It is also found that, for our calculation case with the input pulse power close to the critical value of self-focusing, group velocity dispersion and multiphoton absorption effect have little influence on the propagation process, but the spatio-temporal focusing and self-steepening effects play a significant role in promoting the final pulse shortening.

We describe a Ti:sapphire multi-pass amplifier with high efficiency at the repetition rate of 1 kHz. In the amplifier, the incident pulse is 0.66 mJ with the pulse duration about 90 ps. The incident pulse is amplified to 7.2 mJ when the pump energy is 23 mJ. The energy efficiency in the amplifier is nearly 30% with extracting efficiency larger than 40% when considering about 25% static reflecting loss in the amplifier. After compressed in the compressor, 5.4-mJ, 36-fs pulses with peak power larger than 0.1 TW are obtained.

We suggest and demonstrate an approach to generate a femtosecond multi-terawatt pulse train at repetition rate of 100 MHz in a 10-Hz chirped pulse amplification Ti:sapphire laser system. With an electro-optic Q-switch regenerative amplifier, we can obtain an adjustable repetition-rate chirped pulse train. After amplification and compression, the 100-MHz pulse train with 46-fs pulse width and 1-TW peak power per pulse is obtained in our 10-TW-class Ti:sapphire laser system.

Two-dimensional particle-in-cell simulations are taken to study the interaction of a relativistic, circularly polarized laser pulse with a preformed overdense plasma channel containing a slice of micron size. The laser pulse is confined in the channel, so it can keep higher intensity on a longer time scale inside the channel than the case without a channel. The electrons, both in the slice and from the channel, are pushed forward in the channel by the large light pressure of the laser pulse, followed by the ions accelerated by the electro static field generated by the charge separation. As a result, the acceleration of the slice is more efficient and has a better collimation than in the case without a preformed channel.

We present the study of the interaction of an intense circularly polarized pulse with a solid target with one-dimensional (1D) particle-in-cell (PIC) simulation. The evolvement of ion motion with time is explained by a purely kinetic description and by the theory of electrostatic shock in collisionless plasmas. Especially the formation of the stable profile with a "double-flat-top" in ion phase space is explained and validated visually. Assuming the initial state, we find that the ion distribution in the phase space agrees qualitatively with the PIC simulation results by using the particle-tracing approach.

Space debris distribute in a large range in the space, and their size are very different. For the purpose of detecting the small space debris, the space-based laser radar is used. The characteristics of the background radiation in space are analyzed at first. Then, according to the analog and digital detection theory of laser radar, with avalanched photodiode as the detector, the minimal detectable laser powers are calculated. Based on the radar equation, the detection ability of laser radar is got. The result indicates that the space-based laser radar is effective to detect the small space debris in a specific range.

A reflecting ring focusing system for laser propulsion has been designed. A paraboloidal reflector of higher order is constructed to focus the laser energy on a ring which can produce a tire liked ignition region in the thruster. Considering the angle of laser incidence and reflector's coarseness, mathematic models of the focusing performance have been set up through ray tracking method. Moreover, numerical simulations of the shape, size, energy density and spatial characteristics of ignition wire are carried out in order to know the ring focusing system's superiority. The results show that the ring ignition region with a radius of 49 mm produced by a ring focusing system is about one order of magnitude larger than that produced by single point focusing system, which makes the heating of the work substance much more uniformly. Also, the ring focusing system has a better coarseness endurance.

We present a simple method of the spectral interference between two white light continuum spectra to measure the Gouy phase shift of the focused femtosecond laser pulses. From the spectral interference signal, the relative phase is extracted by the Fourier transform method. The minimum spot size (beam waist) of the laser pulses after the lens (focal length f=200 mm) is measured by imaging method. According to the beam radius, the curves of nonlinear fitting are drawn for comparison, which fit the data of experiments very well. The quantity of phase shift is also discussed. The result shows that this method of measuring Gouy phase shifts is available and stable.

The Technical Integration Experiment Line (TIL) prototype for Shenguang (SG) III laser facility at Research Center of Laser Fusion (RCLF) of China Academy of Engineering Physics (CAEP) has commissioned the first beam line into the diagnostic target chamber. The facility has demonstrated frequency converted Nd:glass laser energies from a single beamline of 1.43 kJ for 1.3-ns nearly flat-top pulse and 2.75 kJ for 3-ns flat-top one at 3'omega' in 2006, namely third harmonic generation (THG) efficiency of 65%-70% for two states. This paper describes comprehensive and precise theory and experiment analysis of frequency converter development and factors affecting THG efficiency for high-power laser facility.

Quantitative analysis of frequency tripling based on the transform of phase aberrations is presented to study the influence of medium-high phase errors on focal spot tails. Nine-fold increase of energy fraction of high-order spectrum caused by the noises in the "waviness-1" regime would result in power growth of 3'omega' tails and significantly enlarge the spot size from 1'omega' to 3'omega' laser. The power growth in "waviness-1-2" regime (0.1-0.4 mm^(-1)) is with main responsibility for the increment of 3'omega' spot tails, as noises in whole "waviness-1" portion answer for the growth of 1'omega' spot tails. Theoretical predictions are shown to be consistent with numerical simulations on focal spot with variant phase ripples and different B-integral values.

Electron acceleration by a propagating short ultra-intense laser pulse in a low-density plasma has been investigated. Electrons have the maximum energy when meeting the peak of the laser pulse. If a propagating laser pulse is abruptly stopped by a solid target, the highly energetic electrons will continue to move forward inertially and escape from the laser field. The envelope of the laser pulse is taken into account and there is an optimal position between the electron and the solid target. The electron maximum energy depends on the laser intensity and initial electron energy, and has nothing to do with the polarization of the pulse, but a linearly polarized laser pulse is more effective to accelerate electron than circularly polarized one under the same laser energy. The influence of the reflected light has been taken into account which makes our model more perfect and the results give good agreement with particle in cell simulations.

Pulse shaping and phase control of femtosecond pulses are shown to have effect on the dielectric breakdown of sapphire. The influence of a pulse tilt on a dielectric breakdown is demonstrated. Three-dimensional structuring of transparent dielectric and semiconducting materials at tight focusing is discussed.

We have performed a pump and probe experiment for real-time reflectivity measurements as a function of superimposed laser shots at the fluence below the ablation threshold to induce nanostructure formation on thin films of diamond-like carbon (DLC). The evolution of reflectivity resolved the bonding structure change and the nanostructure formation through coherent interaction between the probe pulse and the film surface excited with the pump pulse. The characteristic reflectivity changes observed show that the nanostructure formation is preceded by the bonding structure change to swell the film surface. Based on the experimental results, we discuss the ultrafast dynamics of the nanostructure formation.

Near infrared to ultraviolet (UV) and visible upconversion luminescence was observed in ZnO single crystalline under femtosecond laser irradiation. The optical properties of the crystal reveal that the UV and visible emission band are due to the exciton transition (D0X) bound to neutral donors and the deep luminescent centers in ZnO, respectively. The relationship between the upconversion luminescence intensity and the pump power of the femtosecond laser reveals that the UV emission belongs to three-photon simultaneous band-to-band excitation and the visible emission belongs to two-photon simultaneous defect-absorption-induced luminescence. The saturation effects are also found in the upconversion process of ZnO.

The signal-to-noise ratio (SNR) of the optical heterodyne beat between a low-power laser and an optical frequency comb with a relatively low mode power is often insufficient to exclude the possibility of frequency counter error. We develop some methods to enhance this beat SNR including the adoption of a fiber coupler, the suppression of the shot noise, and the utilization of Ti:sapphire laser output. We obtain the highest SNR ever reported with similar laser systems by these methods. With sufficiently enhanced SNR, we measure the absolute frequency of some optical frequency standards without counter error. We give some experimental criteria of beat SNR for the correct frequency count.

We designed a novel and low switching-power all-optical fiber switch. The highly nonlinear photonic crystal fiber (PCF) and the bidirectionally pumped Er3+ doped fiber amplifier are inserted into the Sagnac loop mirror simultaneously. Therefore, the symmetry of the loop is broken, and the switching function is realized for the phase shift of the reversely propagating signal. The theoretical analysis shows that the switching power is inversely proportional to the product of the amplifier gain and the PCF nonlinear coefficient. In the experiment, 40 mW switching power and 15.9 dB switching extinction are obtained, furthermore, the transmission of signal light is cosine proportional to the peak power of the pump pulse. The experimental result agrees well with that from theory.

Densely-aligned void arrays of the length of hundreds of micrometers are fabricated in SrTiO3 crystal by tightly focusing multiple femtosecond (fs) pulses and fixing the focal point at a certain depth of SrTiO3 crystal without translation. The effect of the laser energy and the laser irradiation time as the well as entrance crystal plane on the induced structures is investigated. It is possible to control these factors to achieve the desirable void strings. This kind of self-fabrication method combined with the high linear refractive index of SrTiO3 (2.30 at 800 nm) largely extends the fabrication scope which is generally limited by the short working distance of the high numerical aperture (NA) objective lens in scanning fabrication mode. The possible formation mechanism is also discussed.

We propose two dense gas schemes of four-level 'Lambda'-type and V-type atoms based on the effect of quantum coherence. It is shown that under certain conditions the dense gas can simultaneously exhibit negative permittivity and negative permeability, and thus become a negative refractive-index material. Furthermore, by analyzing the absorption property of the left-handed materials, we find that the absoption can be reduced via choosing appropriate parameters. Such schemes might be used to fabricate isotropic and homogeneous left-handed material with vanishing absorption in a wider optical frequency band.

The analyses of second harmonic generation (SHG) effects have been firstly conducted for characterizing ultrashort pulse with the spectral phase interferometry for direct electrical reconstruction (SPIDER). The results show that we should multiply a modulation function for the recorded interferometric intensity in order to avoid the effect of bandwidth of the pulses, thus we can exactly reconstruct the fundamental-pulse intensity. The root-mean-square (RMS) phase error generated by bandwidth is proportional to the nonlinear-crystal length, the intersection angle of the beams. We can also obtain greater phase-matching acceptance angle in type II phase-matching crystal.

The chirp effect in supercontinuum (SC) generation in photonic crystal fibers (PCFs) is researched carefully in experiment. Using an acoustic-optics programmable dispersive filter (AOPDF), the 1-4 order dispersions of the pulses from femtosecond oscillator can be accurately controlled. The experimental results show the SC generation in PCF is sensitive to the chirp of incident pulse, and the output spectrum and conversion efficiency can be tuned by changing the initial dispersion state. With different group delay dispersion (GDD) brought to the incident pulse, we find that positive chirp can enhance the energy conversion to long wavelength, and negative chirp can enhance the conversion to short wavelength. Specially, an optimal negative chirp can maximize the conversion to the shortest one at about 625 nm. The effect of the third-order dispersion (TOD) also has been investigated, and we find that the same value of the positive and negative TOD has the similar effect on the SC.

The near-field scanning optical microscope, which is integrated with scanning probe microscope technology, has been investigated as a tool for material science, biology, photolithography, and high-density optical recording. In near-field scanning optical microscope, a sub-wavelength sized probe is used to pick up the optical properties of a sample with a resolution limited primarily by the probe size. The configuration of the tip in the application is of utmost importance to the performance of the system. The spatial resolution of near-field scanning optical microscope system is mainly determined by the aperture size of the fiber tip, and the optical transmission properties of the system are highly influenced by the cone angle of the tip as well as the tip surface quality. However, the poor reproducibility in tip fabrication and the low optical throughput are still the major technical difficulties. In this paper, a design of etching automatism for fabricating the tip of near-field scanning optical microscope is proposed. The configuration of the design is very simple and can be actualized easily. The design that considers the main factors that may affect the configuration of fiber tip, makes the experimental condition of fiber tip the same in any condition, and also allows the changes of the experimental condition for fabricating different configuration tips. Static and dynamic etchings and their combinations are studied. The etching process is optimized, and the tips with short tapers, small apertures (about 50 nm) and large aperture cone angles (40 deg.) are successfully obtained. Multiple-tapered tips are also fabricated by using different dynamic regimes. The experimental results show that the design can not only fabricate sharp fiber tips, but also fabricate different configuration fiber tips. The design makes the etching of fiber tips controllable and can satisfy different requirements.

In the last two decades we have studied and developed two types of laser speckle flowgraphy (LSFG) systems to visualize blood flow distribution in skin tissue, human retina, etc.. The system based on analyses of the laser scattering phenomena consists of a diode laser, illuminating and imaging optical systems, an image sensor, a frame capture board, and a personal computer. By evaluating the time variation of the image speckles at each pixel point in the image sensor, and displaying the results in a two-dimensional (2D) color coded map, the blood flow distribution in the target tissue appears on the personal computer monitor. Currently LSFG systems are divided into two types. One type uses a charge coupled device (CCD) camera and is capable of visualizing the fast blood flow change with a rate of 30 maps/s and useful for ophthalmologic research. The other one consists of a line sensor and a stepping motor which is suitable for measuring the blood flow in a wide area of skin tissue. Various types of LSFG instruments used in clinical studies are demonstrated.

Gauge block measurement by using optical interferometry in Korea Research Institute of Standards and Science (KRISS) is described. A partially modified commercial Twyman-Green type gauge block interferometer equipped with three frequency stabilized lasers which are coupled into one single mode optical fiber, is used for the measurement of gauge blocks of nominal length up to 250 mm. Fringe scanning Fourier transform method is used to obtain the excess fraction value from the interference fringes. The temperature inside the interferometer is stabilized within +-4 mK for three hours. The standard uncertainty (k=1) of measurement is 29 nm for a 250-mm gauge block.

The McCumber relation can be deduced without assuming that all active centers have the same structure of sublevels. The range of validity of the McCumber relation is the same as that of the effective emission cross-section.

Laser materials for eyesafe wavelength generation and Q-switching crystals for short pulse operation were studied. Er,Yb:phosphate glass as a laser crystal and Co2+:MgAl2O4 as a saturable absorber were found to be an effective pair for a compact, light-weight passively Q-switched eyesafe laser operation. Laser diode (LD) pumped microchip laser was built and tested.

The problem of the intense femtosecond pulse with elliptical transverse distribution propagating in air is reduced to an analogous problem of a particle moving in a two-dimensional potential well using variational method. Different types of initial conditions are considered to provide direct physical insight of how the self-focusing and defocusing mechanisms can lead to long distance propagation and refocusing phenomenon. The difference between elliptical and circular transverse distribution beams is compared and discussed. The results are coincident with direct numerical simulations.

Light-emitting silicon nanocrystals are prepared by the pyrolysis of silane and subsequent controlled size-reduction by chemical etching. These nanocrystals show luminescence tunable through the full visible spectral region. The luminescence rate increases by two orders of magnitude when shortening wavelength from red to blue side of the spectrum, which is interpreted as relaxation of the indirect band-gap energy structure. In addition we demonstrate a novel method to prepare regular arrays of nanospikes via deposition of suitable materials through the mask formed by a self-assembled monolayer of polystyrene beads. These structures could be used to improve light-emitting silicon devices and enable advancement on the way to true integrated silicon laser.

In this article, we present some new progress in the tiled-grating field which mainly includes the theoretical description of all the errors existing in the tiled-grating system and the experimental setup used to eliminate the errors.

Single pulse laser-induced damage threshold (LIDT) was investigated for electron beam evaporated optical coatings, including ZrO2 and HfO2 single layers, ZrO2/SiO2 and HfO2/SiO2 high-reflective (HR) coatings, using a 50-fs, 800-nm Ti:sapphire laser. The experimental results showed that the damage thresholds of HfO2 single layer and HfO2/SiO2 HR coating were higher than those of ZrO2 single layer and ZrO2/SiO2 coating, respectively. Namely, the wider the band gap was, the higher the LIDT would be. Meanwhile, single layer showed higher LIDT than corresponding HR coating. A theoretical model based on conduction band electrons produced by photoionization and impact ionization was applied to discuss the damage mechanism. According to the model, the damage thresholds were also calculated and accorded with experimental results. In addition, the surface morphologies of the samples after laser irradiation were observed by Leica optical microscopy to get precise evaluations of damage characteristics.

Lidar is an efficient tool for remote monitoring, but the effective range is often limited by signal-to-noise ratio (SNR). The reason is that noises or fluctuations always strongly affect the measured results. So the weak signal detection is a basic and important problem in the lidar systems. Through the power spectral estimation, we find that digital filters are not suitable for processing lidar signal buried in noise. We present a new method of the lidar signal acquisition based on discrete wavelet transform for the improvement of SNR to increase the effective range of lidar measurements. Performance of the method is investigated by detecting the simulating and real signals in white noise. The results of Butterworth filter, which is a kind of finite impulse response filter, are also demonstrated for comparison. The experiment results show that the approach is superior to the traditional methods.

Estimating formula of the smallest power of illuminating laser of tracking, acquisition and pointing system in space is founded, and the smallest value that the illuminating laser sends when the receiving system can detect the return signal is obtained. The radiant intensity and the radiant quantity reflected by the diffuse reflection target of secondary planet are researched in theory and simulation. It is concluded that the distributing area of radiant emittance and the radiant intensity are the same as the figure of surface of projection in section of laser beam. The factor which affects radiant quantity of secondary planet is the effective area of projection, which includes the reflecting area of secondary planet and the angle between surface of projection and reflecting surface. The factors which affect the radiant intensity are the area of projection in section of laser beam and the angle between the direction of laser beam and normal of reflecting surface. The radiant intensity and quantity of secondary planet affect laser power of receiving system directly.

We propose two schemes of atom localization based on the interference of double-dark resonances in a tripod and a 'Lambda'-type four-level system. It is demonstrated that the localization is significantly improved owing to the interference of double-dark resonances. In the tripod scheme, the localization can be manipulated by the parameters of an additional control field. Via adjusting the Rabi frequency of the field, one can double the probability of detecting the atom within subwavelength domain. By decreasing the detuning of the field, higher spatial resolution can be achieved. In the 'Lambda'-type four-level system, via adjusting the probe field detuning, we can not only make the atom localized at the nodes of the standing-wave field with high precision, but also increase the detecting probability of the atom at a particular position by a factor of 2.

The effect of thickness ratio of two materials on the residual stress was studied in HfO2/SiO2 multilayers deposited by electron beam evaporation on BK7 glass substrates. An optical interferometer was used to analyze the residual stress, and X-ray diffraction (XRD) was applied to characterize the structural properties. The results showed that the residual stress of multilayers was compressive when the optical thickness ratio of HfO2 to SiO2 was 1:3. Then the value of residual stress decreased with the increase of optical thickness ratio, the residual stress became tensile when the thickness ratio increased to 3:1. HfO2 was monoclinic and SiO2 was amorphous in all the multilayers. The microstructures of 1:3, 6:13 and 1:1 multilayers were similar. For crystal plane m(020), the interplanar distance decreased and the crystallite size increased when the optical thickness ratio increased to 3:1. In addition, the evolutions of residual stress were corresponding with the variations of microstructure to some extent.

A one-dimensional (1D) pressure sensor based on defect layer has been studied by means of transfer matrix method, and the factors influencing the photonic crystal (PC) pressure sensor are analyzed. The effect of different doping ways and periodicity on transmitted light wavelength is simulated and researched by choosing small elastic modulus material as defect layer. The relation between the defect layer location and transmitted light is investigated by numeric analysis, and the calculations show that the intensity of transmitted light is greatest when the defect mode is located in the middle of the PC. The effects of periodical number of PC on the transmission are studied, and the results show that the transmission band becomes narrower with the increase of periodicity of PC, which is useful to the sensor. At the same time, when the periodicity increases to a certain number, if the periodicity is raised again, the transmission band does not almost change with the increase of periodicity of PC. On the other hand, if the transmission band becomes too narrow, the transmitted light intensity will be too weak to detect, which can affect the measurement of sensor. The relation between the thickness of defect layer and central wavelength is also studied. The change range of central wavelength will become larger with the increase of the thickness of defect layer, and the central wavelength of transmitted light will shift to long wave. When the width of defect mode is too large, the central wavelength of transmitted light can be together with cutoff wavelength, which can result in the transmitted light cutoff.

The experimental realization of partially coherent bottle beams is reported in this paper. It is shown that by controlling the coherence of the incident light we can generate the adjustable partially coherent bottle beams. The generated bottle beams may have applications in atom optics, and optical tweezers, etc..