A continuous wave (CW) frequency-doubled and frequency-stabilized laser with red light output was designed and built. The laser resonator is in a ring configuration consisting of four mirrors, and a YVO4-Nd:YVO4 composite crystal end-pumped by a laser-diode serves as the laser material. A type-I critical phase-matched (CPM) LBO crystal and an optical diode constituted by a TGG and a λ/2 waveplate are placed inside the resonator to be used for the intracavity frequency-doubler and for forcing the laser to operate unidirectionally, respectively. The optical resonator is designed to satisfy the conditions of the thermal insensitivity and the optimum frequency-doubling. Under the pumped power of 19 W, the single-frequency second-harmonic-wave output of 610 mW at 671 nm wavelength and the fundamental laser output of 400 mW at 1342 nm are obtained, simultaneously. The intensity fluctuation of the output red laser is less than ±0.6% in 30 minutes. With and without the frequency-stabilizing servo system on, the laser frequency shifts at 1342 nm wavelength are better than ±1 MHz and ±5 MHz within 1 minute, respectively.

Means of intra-cavity frequency doubling 914 nm transition of Nd:YVO4 pumped by laser diode (LD) is an important technical scheme to get high power blue laser output, thus achieving high efficiency 914 nm laser is the key point. A high power continuous-wave (CW) end-pumped Nd:YVO4 laser operating at 914 nm by utilizing a quasi-three-level transition was demonstrated. A 0.1% Nd-doped bulk Nd:YVO4 was applied to reduce the thermal effect in the laser crystal. In order to avoid re-absorption losses further, a suitable length of the crystal was chosen based on a careful calculation. Two wavelengths of 1064 nm and 1342 nm with high gain were restrained effectively by suitable control of the parameters of the medium film on cavity mirrors. Finally, the laser was operated at a very low threshold at the pumping power of 8.5 W, and a 914 nm laser with power of 7.2 W was gotten at the pumping power of 31 W. The slope efficiency of the laser was 32%, and the optical-to-optical efficiency was 23.2%.

The thermal conduct model of laser crystal was established. Using Possion equation, the temperature and temperature distribution in laser crystal were obtained, and the optics path difference (OPD) induced by end-face deformation and total OPD were caculated. Based on the former calculation, the focal length of laser crystal with different pumping powers was obtained. The experimental result agrees with the caculated result very well. When the pumping power is 10 W and the radius of pumping beam is 320 μm, the OPD induced by end-face deformation is 45% of the total OPD for Nd:YVO4 crystal. When the pumping power is 24 W, the focal length of crystal is 65.8 mm. The end-pumped resonators with one highly reflective coating directly on the laser crystal can aggravate its thermal effect. The study shows that, for the solid-state laser with high power, the OPD induced by end-face deformation has a large influence on thermal effect of laser crystal. This study provides a theoretical direction for improving the stability of laser and studying the thermal effect of laser crystal.

Rayleigh scattering-stimulated Brillouin scattering (RS-SBS) passive Q switched Er-doped fiber (EDF) laser has the potential to achieve low repetition, short pulse duration and high peak power, which satisfy the requirement for the optical pulse source of optical time domain reflection (OTDR) system, but the repetition frequency is not stable enough for real application. So, a hybrid Q-switched Er-doped fiber laser by inserting an acousto-optic modulator (AOM) into the RS-SBS passive Q cavity was proposed and studied. For the pump level of 120～200 mW, the repetition frequency of the output pulse strain can be continuously adjusted from 30 Hz to 90 kHz. The peak power can be about 200 W and the pulse duration can be about 20 ns. The stability of the repetition frequency is better than 5% and the amplitude fluctuation is less than 10%. The peak power and pulse duration are almost independent on the pump level, but the peak power will reduce and the pulse duration will increase as the modulation frequency increases.

Q-switched technique is one of the most efficient methods to produce high-peak-power and narrow-duration pulses. An all-fiber Q-switched laser based on the modulation of coupling loss is proposed and the Q-switching principles and relative parameters are analyzed. Two fibers are used in the laser cavity. The neighbor terminals of these fibers are placed end-to-end, one of which is mounted on a piezoelectric actuator (PZT). When a changed voltage outputted from a driver is applied to the PZT, a corresponding displacement of the fiber is generated. The displacement can be a longitudinal separation, a lateral offset or an axial tilt, which can modulate the coupling loss between the two fibers and change the round-trip loss in the fiber laser cavity as a result. When the lateral-offset mode is applied, Q-switching pulses are obtained up to the repetition rate of 10 kHz by changing the coupling loss efficiently. This method is easy and low cost, and increase its stability by external control.

An actively mode-locked femtosecond pulse fiber laser with coorse wavelength division multiplexing (CWDM) as the filter was successfully achieved. When the laser was pumped at 186 mW, the mode-locked pulses centered at 1550 nm with 10.2 nm bandwidth (corresponding to 247 fs pulse width) was obtained at the repetition rate of 2.5 GHz. The average output power of the laser was 1.3 mW.

The influence of combining errors in the system for coherent combining of fiber lasers on the far field of output is studied numerically. Influences of the duty ratio, position errors and parallel errors on the distribution of far field are researched. The results show that the increase of duty ratio of output elements will raise the energy of the central lobe rather than change the central lobe′s average intensity; and position errors will decrease the energy of side lobes and the energy transfer efficiency of the system. It is found that the influence of position errors can be offset by increasing the output element′s duty ratio. Finally, the influence of parallel errors on far field is discussed and relative suggestion is provided.

A rapidly tunable TEA CO2 laser is reported. The main electrodes of the laser take the form of Ernst with the spark array preionization. With the method of a two-dimensional (2D) scanning system and a diffraction grating, rapidly tuned TEA CO2 laser output is realized. Laser with 75 emission lines of the CO2 molecule rotational transition is obtained, and there are 55 lines, whose pulse energy of laser radiation exceeds 1 J. The pulse energy of 10P(20) line is over 300 mJ in single-transverse mode at a repetition rate of 100 Hz, and the width of the light pulse is 70 ns. The system can be tuned between two different rotation lines spanning the wavelength range from 9.2 to 10.8 μm within 10 ms.

The impact of the sensitive parameter of the delay time between pre- and main-current pulse on emission of Ne-like Ar 46.9 nm soft-X-ray laser in capillary discharge at low Ar pressure was investigated. The results indicate that, for ceramic capillary channel with 20 cm in length (4 cm long electrode) and 3 mm in diameter, when the main current pulse spike and Ar pressure were stabilized at 20～21 kA and 38 Pa respectively, the delay time τ of lasing locates in the range of 2.5～12.5 μs which included the optimal smaller range of 3.5～8.5 μs with relatively larger emissions. And at delay time of 5.8 μs there is the biggest laser output. Furthermore, the delay time with the maximum laser output increases gradually with Ar pressure. More detailed experiment afterwards proves that a definite Ar pressure gives out its own delay time range which generates neglectable difference with nearby delay time ranges.

To improve the convergence speed of adaptive optics (AO) system controlled by genetic algorithm (GA), a new 19-element AO system model based on GA is set up. The system chooses the first 10-order Zernike mode coefficients on the deformable mirror (DM) as the optimization function, rather than the 19 voltages on the DM. The transform matrix between the 19 voltages and the first 10-order Zernike mode coefficients was deduced and comparative mathematic simulations were done. The simulation shows that the correction ability of the proposed AO system is much better than that optimizing the 19 voltages. Moreover, compared with the GA optimizing DM voltages, the convergence speed of GA optimizing Zernike mode coefficients is improved by more than five times.

Based on the optical characteristics of lead lanthanum zirconate titanate (PLZT) electro-optic ceramic, an optical phased-array beam deflector with up-down electrode structure′s transverse electro-optic effect was proposed. The electro-optic deflection characteristic and mechanism of the deflector were analyzed theoretically. And the phase modulation and electro-induced loss characteristics were measured experimentally. A systematic experiment of related optical phase-array devices and measuring system was also designed to verify the theoretical results. The results show that the beam obtains a relative large angle deflection by using different applied voltages.

A novel approach of a phase shifted all-optical analog-to-digital converter with double parallel intensity modulator is proposed and demonstrated. The phase shift of quantization curve is simply realized by optical attenuation. The proposed scheme can solve the problem of pulse walk-off, and low precision of phase shift in the present phase shifting quantization schemes as well as the influence of environment and temperature. In this scheme, the outputs of two parallel LiNbO3 intensity modulators are split into 4 channels with an optical attenuator inserted in each channel. By appropriately adjusting the optical attenuators, the phase shift between two adjacent channels is achieved, thus 8-channel optical quantizer is realized with resolution of 4 bits. In the experiment, a 10 GHz sinusoidal input signal is quantized using this scheme with an effective number of 3.7 bits. The deviation from the ideal case is only 0.3 bits. This result donates that the proposed approach is feasible, and has a relatively high effective number of bits compared with the present schemes.

The length and lifetime of the plasma channel induced by nanosecond laser in air is investigated. The energy of Nd:YAG laser (pulse energy about 2.1 J) was averaged to a straight line through beam shaping and a 1 m long plasma channel was formed by laser breakdown. The lifetime of this channel was detected with intensified charge coupled device (ICCD) and the electric continuity was studied by electrical detecting method. The experimental results indicate that the continual electric conduction spatial length of nanosecond laser-induced air plasma channel can reach near 80 cm, with the survival life above 500 ns. The channel total resistance is mainly constituted of the coupling resistance. These results are helpful for researching the femtosecond laser induced plasma channel, and also provide experimental evidences for prolonging the decay time and length of laser-induced air plasma channel in technical applications.

It not only needs space match but also needs timing match of pumping laser and dye laser seed in pulsed dye laser master-oscillator power-amplifier (MOPA) chain which employs more than one diode-pumped-solid-state lasers (DPSSL). So a laser pulse timing control method is reported to realize the timing match of pumping laser pulse and the seed laser pulse. The computer data acquisition of fast laser pulses is realized through fiber, fiber switch and random repetitive sampling technologies. When the pumping pulse and seed pulse are timing match, their peaks are almost superposition. So the laser pulse delay time is measured at its peak point to eliminate the influence of pulse-width change. The noise at laser pulse peak point is eliminated using binominal curve fitting in data process. This control system realizes the laser pulse timing measurement and close-loop control in nanosecond rank. The single step control error and measurement error are less than ±0.2 ns. The close loop control precision is ±1 ns.

The terahertz (THz) radiation properties of low-temperature-grown GaAs photoconductive antenna (LT-GaAs PCA) are studied in order to improve the THz radiation efficiency. The emission spectra of the photoconductive antenna are obtained by THz time domain spectroscopy (TDS) technology. The corresponding frequency domain spectra are obtained by fast Fourier transform (FFT). The results show that the THz signal generated by LT-GaAs PCA is more efficient than that generated by femtosecond electromagnetic pulse from semiconductor surface. The peak of THz electric field increases linearly as bias voltage increasing, and tends to saturation as pump power increasing.

The light field expressions of cylindrically polarized Bessel-Gaussian (CPBG) beams focused by a high numerical-aperture lens are derived using Richards-Wolf vectorial diffraction method. Numerical calculations are taken to analyze the influences of varying values of the parameters on the light intensity distribution at the focal plane and in the vicinity of focus. The research results show that both the intensity at the focal plane and its profile shape depend on the values of parameter β corresponding to Bessel function, polarization rotation angle φ0, beam waist width w0 and the maximal angle α determined by the numerical-aperture. By adjusting the values of corresponding parameters, the bottle beams and the flat-topped beams which possess the characteristics of vortex are obtained and will have many significant applications.

Based on Hugens-Fresnel diffraction integral theory, the propagation formula of an optical bottle beam generated by an axicon-lens system was deduced. The three-dimensional (3D) and cross-section optical intensity distribution were simulated. Using the diffraction integral theory and geometry method, the influence of the focal length of the lens on the sizes of the bottle beam was analyzed in detail. The results show that the sizes of the bottle beam (including the bottle radius and bottle length) increase with the increase of the focal length of the lens under the same condition. In the experiment, the bottle radii of 200 μm, 300 μm and 430 μm are obtained with the focal length of 50 mm, 70 mm and 100 mm respectively. The result fits well with theoretical calculation and numerical simulation.

optical communication; waveguide modulator; mapping transform; velocity matching; back slot structure

All optical wavelength conversion of the 10-GHz clock signal is demonstrated based on cross-phase modulation of optical pulses in an 80 m long microstructure fiber (MSF), and the conversion bandwidth is over 30 nm. The experimental microstructure fiber with a nonlinear coefficient of ～11 W-1·km-1 has small normal dispersion and flat dispersion curve from 1530 nm to 1570 nm. The experimental results show that a compact wavelength converter can be realized by utilizing this microstructure fiber.

There are three key modules in coherent optical code division multiple access (OCDMA) system: ultra-short optical pulse source, en/decoder and receiver. Equivalent phase shift super structured fiber Bragg grating (EPS-SSFBG) OCDMA en/decoders were experimentally demonstrated. 2.5 Gbit/s OCDMA experiment is shown to achieve 60 km error free transmission using gain switch laser diode, 63-chip EPS-SSFBG phase en/decoder and threshold adjustable receiver. The receiver sensitivity is -22.5 dBm at 10-9 bit error rate (BER). The experimental results prove that EPS-SSFBG en/decoder could be used in practical OCDMA system due to its high performance and realizability. It is a very important method to improve system performance by using optical and electrical processing to restrict noise and side lobe.

The power distribution of the tapered fiber has been investigated based on Maxwell’s equation and the Taylor series expansion method. Following rigorous analytical approach, the general expressions for power in the core are derived, and a study is presented for the power distribution along the propagation direction in respect of different lower order modes. It is observed that the variation of the taper length, taper ratio, and refractive index can influence the power distribution of different fiber modes dramatically. The leakage loss, the taper length, taper ratio should be decreased. And refractive index difference should be increased if the light is launched from the smaller core-size end. And the taper length, taper ratio and refractive index difference should be increased if the light is launched from the larger core-size end to confine the power efficiently. When the fiber has long length and large taper ratio, the influence of refractive index on the power distribution is small compared with those of taper length and taper ratio.

The large mode area in conventional fiber is achieved generally by design fiber structure, which leads to limited mode area about several hundreds square microns. Gain guiding plus index guiding is a new method to realize single mode fiber with large mode area. By analyzing the effect of gain coefficient on refractive index and the complex-valued normalized frequency, the relationship between index-difference, gain-coefficient and cutoff conditions of different modes is obtained. Finally taking a Nd doped phosphate fiber with a 100 μm diameter core for an example, where the refractive index of 10% (atomic fraction) Nd-doped core is 1.5689 and 1.5734 in the cladding, through simulation computation, the mode-diameter is lager than 90 μm at 1.064 μm. To achieve large-mode-area single-mode fiber, it is a good method of applying gain guiding and index guiding for conventional fiber.

The rotation rate drift induced by optical Kerr effect in passive ring-resonator optical fiber gyroscope (PROG) using hollow-core photonic band-gap (HCPBG) fiber is different from that in the conventional single mode passive ring-resonator optical fiber gyroscope. To study the rotation rate drift induced by Kerr effect in the PROG system above, optical Kerr effect in the passive ring-resonator optical fiber gyroscope made from hollow-core photonic band-gap fiber is analyzed theoretically using a simple optical field overlap method, meanwhile, the numerical calculation is developed to study the system drift caused by Kerr effect. And it is compared with the Kerr effect of the passive ring-resonator optical fiber gyroscope made from conventional fiber. The theoretical evidence shows that optical Kerr effect induced by rotation rate shift in PROG made from hollow-core PBG fiber is reduced by 1～2 orders at different fiber loop lengths than that caused by ring-resonator optical fiber gyroscope made from conventional fiber when the spectral width optical source is fixed.

A newly developed single-mode fiber-designed optical coherence tomography (OCT) system is built based on low coherence interferometry and optical heterodyne detection. A broadband infrared optical source centered at 840 nm with a bandwidth of 50 nm is used as the system source. A stable high carrier is generated by Fourier-domain rapid scanning optical delay line (RSOD) as phase modulator. With this developed system, two-dimensional (2D) cross sectional images of tissues in vivo are reconstructed. The experiment results indicate that the system has an axial resolution of 6.7 μm, approaching the ideal resolution, and transversal resolution of 4.7 μm in air. The depth imaging range is above 3 mm in air. Although less than 300 μW optical power is incident on the sample, the system sensitivity is above 88 dB. With the same incident power on the sample, an image of the same sample (fresh orange) with a 1310 nm OCT system is also provided. The qualitative comparisons between the two system at different central wavelengths demonstrate the impressive potential of 840 nm OCT system to perform eye posterior structure imaging. The image of the animal retina in vivo is presented.

A new method of detecting body fluid is brought forward by studying the laser-induced spectroscopy (LIBS). The sample solution, which is comprised of 10% glucose and 0.9% NaCl, is broken-down by focusing the 1. 064 μm Nd:YAG laser beam (energy ～300 mJ, frequency 10 Hz, pulse width ～10 ns). And the plasmas spectra are collected by an experimental setup including echelle spectrograph and ICCD. The experimental results show that the organic matter ( as glucose) and metal elements can be synchronously analyzed by LIBS and the metal elements are more sensitive than the organic matter. The results also indicate that there is the exponential relation between the intensities of characteristic spectra and concentration. These results provide some experimental evidences for extending this mothed to be a new way of accurately detecting trace element in body fluid.

A method of etching micro-grating structures (MGSs) on the surface of glazed stainless-steel directly was investigated, and a 532 nm diode-pumped solid-state laser (DPSSL) was used. The influences of the experimental parameters such as laser power, source beam diameter and period of grating, on the depth of grooves and duty cycle of MGSs were analyzed. The results were concluded and analyzed with conventional optical microscopy and atomic force microscopy (AFM). When the laser power and cross angle are 45 mW and 20° respectively, the best MGSs are obtained with 1.34 μm in period and 300 nm depth. Meanwhile, either increasing the grating period or the source beam diameter can enhance the depth of grooves.

A numerical model of velocity distribution of shielding gas-metal powder two phases flow field output from the nozzle in laser cladding is established, and it is calculated by FLUENT software. In this model, the influences of momentum and mass transmission on the two phases flow are taken into consideration. The metal powder flow field velocity distribution on horizontal and center line is analyzed, as well as the velocity vector distribution of powder flow inside or outside the nozzle. The results show that powder velocity magnitude on center line increases first, then decreases, finally it keeps linearly increasing from the stand-off distance 100 mm below the nozzle; powder velocity magnitude on horizontal line reaches its maximum near the center line, then linearly decreases to 0 from the radial distance 6 mm to 11 mm. Under the same process parameters, the same flow field is measured with digital particle image velocity (DPIV) technique. The calculated result agrees well with the measured result, which indicates that the established model is reliable. The model can be used to obtain flow field parameters and further design the nozzle size.

CO2 laser beam was used to weld 2519-T87 high strength aluminum alloy, and the microstructure and mechanical properties of the welds were studied and compared with the melting electrode inert gas (MIG) welds. Results indicate that the grains in laser welds are very fine, and the eutectic phase distributes more uniformly. After aging treatment, there are lots of finer θ′ phase in laser welds. And there is no equiaxed grain zone along the laser weld fusion line. Whereas the grains in MIG welds are coarser. The eutectic phase is strip morphology and network distributes along the grain boundary. After aging treatment, the size of θ′ phase is big and number of θ′ phase is small, and it does not distribute uniformly in the grains. There is a wide equaixed grain zone along the fusion line. The tensile strength of the laser weld after aging treatment can reach 74% of that of the base metal, whereas the tensile strength of MIG weld is only 61% of that of the base metal. And there is no softened zone in the heat affected zone (HAZ) of laser welds.

One-dimensional dynamic semiconductor model was presented. The model has been used to investigate the influence of different laser power density on the laser ablation and the expansion of plume. The laser ablation is greatly influenced by laser power density. The more intensive the laser power density is, the higher surface temperature it would have. In this case, the depth of evaporation, the temperature of vapor, and the expansion velocity and spatial scale of ablated plume will also increase with the rising of laser power density. Meanwhile the more intensive the laser power density is, the earlier the plasma shielding would appear. For the given conditions, the threshold of plasma shielding value is between 1×108 W/cm2 and 1.5×108 W/cm2.

The influence of laser transmission welding parameters for polypropylene (PP) plastics on welding quality is investigated by orthogonal design method. Tensile and section tests are conducted for experimental samples, and the influence of welding factors on tensile strength and welding seam size is analyzed, which indicates subsequence of the influence of welding parmeters on PP plastics is welding velocity→laser frequency→cooling time→fixture pressure→beam diameter on the material→laser power. And high laser power density can cause resulting from coking on samples′ faces black welding line and fake fracture appears when welding seam is not even. The optimized welding parameters are determined by using range method.

Hydrogenated amorphous silicon (a-Si:H) thin films have been prepared by direct current (DC) magnetron sputtering. The effects of the hydrogen flow rate, sputtering power influencing on deposition rate and the optical characteristics of a-Si:H thin films have been investigated. The hydrogen content (CH) of the films is calculated by Fourier transform infrared (FTIR) spectroscopy method, and the maximum CH is obtained at 11% (atom percent). The refractive index (n) and extinction coefficient (k) are measured by spectroscopic ellipsometer. It is found that the n and k of the prepared film decrease with the increase of CH. The optimizing parameters are applied to the preparation of high reflection mirror of diode lasers, and the n and k at 808 nm wavelength are 3.2 and 8×10-3 respectively with a satisfactory laser output characteristics.

The two-layer ZrO2/SiO2 and SiO2/ZrO2 thin films were deposited on K9 glass by sol-gel dip coating method, and the infiltrating between this two types of films was explored. X-ray photoelectron spectroscopy (XPS) was used to measure the variation of composition in different thickness of film, and ellipometry was used to fit the experimental result of the XPS. According to the experimental results of the XPS, the ellipsometric model was coustructed. The results showed that the ellipsometric curve of simulated results accorded with that measured by ellipsometry very well. The infiltrating between the two-layer ZrO2/SiO2 film was not serious and the variation of film composition in interface was very obvious; at a given thickness, the film′s composition no longer changed; On the contrary ,the infiltrating between two-layer SiO2/ZrO2 film was very serious and infiltrative layer is very thick, and the complete infiltrating almost happened in the bottom layer.