A femtosecond fiber laser system with high average power and short pulse duration is demonstrated,whose oscillator and amplifier are based on an Yb-doped single-polarization large-mode-area photonic crystal fiber (LMA-PCF) with low nonlinearity, high gain and nice environmentally stability. The dependence of the output pulse duration on the pulse energy, duration and chirp of seed light from oscillator and the pump power of amplifier is studied. The fiber laser amplifier generates 16 W average power, corresponding to 320 nJ pulse energy, at 40 W pump power, when the seed light is fixed at 180 mW average power, and the pulse duration is compressed to 39 fs after gratings.

To attain high efficiency, miniature and stable laser, we take Tm,Ho:YLF(Tm 6%;Ho 0.4%) microchip pumped by diode laser as the seed laser. Short resonant cavity which owns broad free spectral range is useful to select single-frequency. The microchip is 0.9 mm. Both end faces are coated. The microchip itself is the oscillate cavity. It is placed in the Dewar bottle. The bottle is filled with liquid nitrogen to keep the temperature at 77 K, which enhances the stability of output power. Self-beat of fiber delay method is used to measure the short-term frequency stability. It indicates that the short term stability is about 2.6 kHz/μs. And by using the oscilloscope, the long term stability is estimated at 35 MHz. Single-mode output laser with the wavelength of 2.067 μm is obtained, and its bandwidth is less than 40 MHz. The beam quality is about 1.082 which is measured by the knife-edge method. The maximal output power is up to 32.8 mW. The slope efficiency is 25.2%, and the optical-optical efficiency is 23.8%. The instability of the output power is less than 1%.

The experimental study on an ultrashort laser amplifier using a domestic Yb3+-doped large-mode-area fiber as gain media was presented. The seed pulse has a width of 2.3 ps and repetition rate of 95 MHz, provided by an all-solid-state mode-locking laser designed by ourselves. The pump source is a 976 nm fiber-coupled laser diode (LD). The output pulse with the average power of 2.41 W from the 1.6 m gain fiber is achieved under the input pump power of 11.2 W, while the seed pulse average power is 100 mW. The amplified energy per pulse is up to 25 nJ. The width of the pulse is broadened from 2.3 ps to 3.0 ps, synchronously.

To enhance the understanding of combustion-driven continuous wave (CW) DF chemical lasers, especially for knowing the situation of the generation of F atoms in combustion chamber and the excitation situation in the optical cavity, a series of experiments is carried out without diluent. The results show that, DF lasers will be in good condition without primary diluent, and lose a half of power and specific power without secondary diluent. The effect of diluents on lasers is discussed based on the results. DF lasers can run stably without diluent, which provides the evidence for the simplification of DF lasers.

Fiber lasers are impacted by temperature in various ways. This article studies on thermal characteristic of absorption cross section, luminescence cross section and lasing wavelength and describes the thermal impact on fiber lasers in details. As the temperature varies, the distribution of the particles in all sub energy levels changes, which makes the absorption cross section and luminescence cross section different. The relationship between temperature and absorption cross section is calculated by a fitting method. The luminescence cross section is the function of temperature and absorption cross section by which the luminescence cross section in different temperatures can be calculated. Relationships between lasing wavelength and temperature, fiber length, cavity loss, doping concentration are deducted. Furthermore, the article compares the numerical result of lasing wavelength under different temperatures with the experiment data, which match with each other well.

A femtosecond fiber laser based on Yb-doped single polarization large-mode-area photonic crystal fiber (LMA-PCF) is demonstrated. The photonic crystal fiber acts as laser gain medium. Since the single mode area of the fiber is an order higher than that of conventional fibers, the fiber nonlinearity is effectively scaled down, and much higher energy laser pulse output is achieved. The laser is based on a linear cavity design, and a piece of semiconductor saturable absorber mirror is used to initiate mode-locking operation. A pair of gratings are used as intracavity dispersion compensation, and the fiber laser operates in the stretched-pulse regime where the amount of net cavity dispersion is in the vicinity of zero. For negative net cavity dispersion, the laser generates 500 fs pulses with an average power of 400 mW at a repetition rate of 47 MHz (corresponding to a single pulse energy of 8.5 nJ), and the pulses are dechirped to 98 fs after extracavity dispersion compensation. For positive net cavity dispersion, the laser generates 1.76 ps pulses with a single pulse energy of 10.6 nJ, and the pulses are extracavity dechirped to 160 fs.

Continuous-wave fiber amplifier plays an important role in the field of manufacture and military. In order to investigate the critical factors that modify the extraction efficiency of continuous-wave ytterbium-doped fiber amplifier, this paper describes a model of a fiber amplifier incorporating amplified spontaneous emission (ASE) based on the steady-state rate equations. The relationships between extraction efficiency and the reflectivity of fiber ends, signal power, pump power are researched. The model by comparing predictions with experimental results obtained from backward pump fiber amplifier was tested. Deviation of these two results is less than 10%. The results show that how the extraction efficiency of fiber amplifier is impacted by those factors and these influences could be beneficial to the design and application of continuous-wave high power fiber amplifier.

A novel fiber-optic sensor consisting of a long-period fiber grating (LPFG) and a Fabry-Perot (F-P) interferometric sensor is proposed and demonstrated for simultaneous measurement of high-temperature and strain. The LPFG and fiber F-P sensor form the sensor in cascade. The LPFG written by high frequency CO2 laser pulses is used for high temperature measurement while the F-P sensor fabricated by 157 nm excimer laser pulses is used for strain measurement. Such combined fiber-optic sensor can stand for high temperature of 500 ℃ and achieve precise measurement of strain under high temperature environments simultaneously.

A new temperature compensation method of fiber Bragg grating was put forward and experimentally demonstrated based on side polished fiber Bragg grating overlaid with polymer with negative thermo-optic coefficient. Experimental results show that the new method provides a good temperature compensation for fiber Bragg grating. Temperature sensitivity of the fiber Bragg grating packaged by polymer with negative thermo-optic coefficient is reduced to 1/16 of that of fiber Bragg grating without compensation in the range of 63 ℃ to 79 ℃; and to 1/4 in the range of 58 ℃ to 101 ℃. The new device of fiber Bragg grating packaged for the temperature compensation has a diameter of 2mm and length of 20 mm.

This paper is focused on the peak-detection algorithms in the demodulation for the fiber Bragg grating (FBG) sensor system. 6 peak-detection algorithms have been analyzed and compared, such as the Monte-Carlo algorithm, the direct peak-located algorithm and the quadratic polynomial numerical derivative algorithm, the polynomial fitting, the polynomial-Gaussian fitting and the Gaussian nonlinear curve fitting. The theoretical and practical errors and the relative effect factors of errors were introduced, analyzed and evaluated by the combination of the simulations and the experiments. It is demonstrated that the relationship between the signal noise ratio (SNR) at the input of the algorithms and the error is linear. When the SNR is constant, the error in using Gaussian nonlinear curve fitting is the lowest. The error can be only 0.44 pm when the SNR is 40 dB in the FBG sensor experiment. Consequently SNR is the major factor which dominates the errors of the peak-detection algorithms in the demodulation and the Gaussian nonlinear curve fitting is considered as the best peak-detection algorithm.

Based on the unified theory of coherence and polarization of random electromagnetic beams and the propagation law of partially coherent light, the change in the degree of polarization of beams which is generated from a partially coherent source after passing through a series of circular apertures was investigated. Gaussian Schell-model beam was taken as an example to study the change in the degree of polarization for on-axial points. It is found that, with the increase of the number of circular apertures, the degree of polarization for on-axial points will change. It is shown that for a sufficiently long propagation distance, the degree of polarization for on-axial points will tend to a certain value. And three circular apertures are chosen as a typical multiple circular apertures system for investigating change in the degree of polarization. It is shown that, the change in the degree of polarization depends on the size of circular apertures, the distance between circular apertures, the correlation length in the source plane and the degree of polarization in the source plane.

The nonlinear scattering loss in the single-mode fiber is analyzed. It is proved theoretically and experimentally that the maximal transmitting power in an optical fiber is limited by the stimulated Brillouin scattering (SBS). Based on mode field coupling theory, a model to calculate the butt-joint coupling efficiency between a multi-mode fiber and a single-mode fiber is presented. The dependence of the coupling efficiency between the multi- and single-mode fibers on the core radius of the multi-mode fiber is investigated. A experiment is conducted with 532 nm laser, multi-mode fiber (NA=0.11, a=12.5 μm) and single-mode fiber (NA=0.11, a=1.75 μm) to measure the butt joint coupling efficiency of multi-mode fiber to single-mode fiber. Good agreement is obtained between the experimental results and the theoretical predictions. A combined multi- and single-mode fiber relay system is proposed to transport laser beams with high power and good beam quality.

Cryogen spray cooling (CSC) is an effective cooling technique used for laser treatment of port wine stain (PWS). The cooling process involves complex droplet evaporation, strong convective heat and mass transfer, therefore a deep understanding of spray characteristics is essential to optimize the nozzle design and improve the cooling efficiency of the spray. This paper presents a theoretical model to describe the equilibrium evaporation process of a single droplet in cryogen spray. The model considers mass transfer through mass transfer number method, the momentum transfer by selecting the suitable empirical correlation of drag coefficient, and heat transfer by taking into account the droplet evaporation and convective effect with ambient air. Through simulating the cooling stage of a hanging water droplet and the temperature variation of cryogen droplets in cryogen spray, the model is validated by the reasonable agreement with the experimental measurements. Then a parametric study of the influences of initial diameter and velocity on the droplet evaporation is carried out, which states that an effective analysis method can be provided by the proposed model to guide the CSC of laser therapy.

This paper studied the biophysics’ index of low power laser irradiation on human’s red blood cell (RBC) to find the primary factor that affects biophysics of RBC. The blood cells of the deformability health human deposited in 4 ℃ for 48 h are used as samples, and the effects of low power laser irradiation on these samples are investigated. These samples are divided into two groups. One group is irradiated for 30 min under the laser with the powers of 2 mW, 4 mW, and 8 mW. The RBCs in the other group are doped with PBS with the same concentration. After centrifugating, they are processed in the same way. The results show that the characteristics of the blood cell irradiated by laser are less than the whole blood. Our study indicates that the magnify effects of the human’s red cells’ membrane are important to the rheology characteristic of the blood.

Evaporative cutting front shape of PMMA by CO2 lasers is photographed through CCD camera. Effects on cutting front shape and depth by cutting parameters as defocus distance, cutting speed and laser power are discussed. An energy coupling model is built up on the front and kerf shape photographed. The results indicate that multiple reflections are favorable to the increase of depth. When the focal position is above the surface, the absorptive intensity on the front decreases, so the cutting depth decreases. When the focal position is below the surface, the position on the front with the maximum power intensity is downward. The intensity distribution is toward the deeper position, the cutting depth increases. But if the negative focal distance is extremely big, the intensity of the deeper position attenuates sharply with the increase of focal radius and light distances, so the depth deceases. With reducing the cutting speed and increasing the laser power, the curvature decreases, the length of front directly irradiated increases, and thus the cutting depth increases.

Numerical simulation is an effective way to predict the residual stress field induced by laser shock processing (LSP) and study the effects of laser shock parameters on the residual stress field .The finite element sorftware ANSYS/LS-DYNA was applied to simulate the three-dimensional (3D) residual stress field of 40Cr steel surface layer induced by LSP. The 3D finite element model of laser shock processing 40Cr steel was built. The numerical simulation of residual stress field of 40Cr steel surface layer induced by LSP was realized. The effects of laser shock parameters, intensity, pulse width and beam spot, on the residual stress field of 40Cr steel surface layer were studied by simulation. The result of numerical simulation indicates that the value of residual stress from simulation has a good consistent with that from measurment. There is an optimum laser power density for inducing a maximum surface residual compressive stress when the duration of laser pulse was fixed. The surface residual compressive stress decreases as the duration of laser pulse prolongs while the laser power density is fixed and the pulse duration is over 45 ns; The surface residual compressive stress also increases as the size of laser beam spot increases when laser power density and duration of laser pulse are fixed.

Using RS2000SM CO2 laser of 2.5 kW to irradiate the nodular cast iron (QT-450) plate, and altering the process parameters during laser forming, and analyzing test samples with the X-ray stress analysis instrument (type: X-350A), digital microhardness tester HVS-1000 and scanning electric microscope (SEM) respectively, laser forming regularity of brittle material is studied. The results show that increasing the laser power and the feed number of the beam, decreasing the scanning speed, and the thickness of the test sample eventually result in the increase of the bending angle. There are ferrite and cementite in the surface layer of the test sample after laser forming. The number of ball graphite in the surface layer decreases; The maximum tensile stress of the upper surface in test sample is about 250 MPa, the residual stress value of the lower surface in test sample is about zero. The hardness of the test sample in cross section varies between 700HV and 200HV, the hardness near the upper surface is the greatest. The microcrack inside the deforming area appears when the energy of laser beam is quite strong.

A new detecting method of infrared laser scratching is presented to estimate the bond strength of film-substrate interface. The infrared laser constinuously works on the sample film. The scratching images of the film-substrate interface are obtained by vidicon, and are prepared to be used after Matlab disposal. At the same time, the temperature apparatus system detects the temperature of sample surface in real time. The temperature of sample surface and the scratching image are detected by signal detection system in order to estimate the bond strength of film-substrate interface.

A reshaping Brillouin amplifier is suggested to combine with the main amplifier in the system of the stimulated Brillouin scattering (SBS) phase conjugate mirror (PCM). In this novel scheme, the main amplifier can coarsely tune the output pulse shapes, while the reshaping amplifier is to finely control the output pulse shapes. Effects of encounter time on pulse shapes are theoretically and experimentally researched, and pulse shapes versus the distance between the two amplifiers are achieved with various encounter time. Results show that the encounter time decides the general pulse shape and is an important parameter to control the pulse shape. The longer the encounter time, the wider the control range, and the lower the efficiency of the system.

The characteristics of the conjugate wave in Brillouin-enhanced four-wave mixing (BEFWM) with large incident signal are investigated experimentally. It is demonstrated that under the condition of large signal and deep interaction, temporal stability and correlation between the input and output pulse shapes are better than that of BEFWM with small signals, and modulation phenomena will no longer appear in this case. At the same time, the conjugation fidelity is almost 100% and constant with different signal intensities. With enlargement of the signal intensity, energy transform efficiency of BEFWM increases.

Er3+:Y0.5Gd0.5VO4 crystal has been grown by the Czochralski method. The effective separation coefficient of Er3+ in the crystal was 1.03 and the concentration of Er3+ ions in crystal is 0.83%, which was measured by the method of inductively coupled plasma (ICP) spectrum. The measured thermal expansion coefficients were αa=2.08×10- 6/℃, αc=8.87×10-6 /℃ from 30 ℃ to 1300 ℃ along its crystallographic a axis and c axis, respectively. The measured specific heat was 0.48 J/(g·K) at 25 ℃. The thermal diffusion coefficients of Er3+:Y0.5Gd0.5VO4 were measured by laser pulse method and the thermal conductivity was also calculated. The a axis and c axis thermal conductivity of Er3+:Y0.5Gd0.5VO4 was 6.1～4.9 W/(m·K), 7.7～6.2 W/(m·K) respectively in the temperature range from 25 ℃ to 200 ℃.

In order to study cross correlated properties and light scattering of optical thin films interfaces roughness, the theoretical models of optical thin films interfaces roughness light scattering were concisely presented. Furthermore, based on the expression of vectorial scattering of optical films, influence of interfaces roughness cross-correlated properties on light scattering was analyzed by total backscattering theory. Moreover, effects of TiO2 single optical films thickness, substrate roughness of K9 glass and ion beam assisted deposition (IBAD) technique on interface roughness cross correlated properties were studied by experiments, respectively. The results show that theoretical results obtained by integrating vector light scattering are agreement well with experimental results. With the increase of films thickness and substrates roughness, the interfaces roughness cross-correlated properties decrease. When ion beam assisted deposition is used, a high degree of cross-correlated properties can be observed.

The c-axis oriented thermoelectric Ca3Co4O9 thin films were prepared on sapphire (0001) substrates using pulsed laser deposition (PLD) technology. X-ray diffraction (XRD) was used to determine the micro-structure and orientation of Ca3Co4O9 thin films. The influence of substrate temperature and oxygen pressure on crystalline and orientation of thin films was investigated and the optimal conditions were determined. Optimal conditions were used to prepare Ca3Co4O9 thin films on vicinal-cut Al2O3 (0001) substrates. When the Ca3Co4O9 film was irridated by laser with wavelength of 248 nm, pulse bandwidth of 20 ns, the two ends of the film would induce thermoelectric voltages (LITV). And the peak voltage and response time at the two ends of the film can reach 4.4 V and 36 ns respectively. And the bandwidth of the voltage is 131 ns. The correlated mechanism of this phenomenon was discussed.

Based on the aperture averaging effect of the scintillation effect of light propagation, a large aperture laser scintillometer (LALS) for measuring the refractive index structure constant of atmospheric turbulence was developed. This apparatus can restraint the scintillation saturation at certain extent. This scintillometer has symmetrical structure. Meanwhile, signal modulation and demodulation method is used to increase signal-to-noise ratio dramatically and the embedded control unit is introduced to sample, dispose, display and store the data. Compared with the measuring results from traditional measurement device, the slope of linear regressions of the data in 1000 m horizontal propagating path is 1.01 and the correlation coefficient is 0.92. Further analysis reveals that the inner scale of the atmospheric turbulence which will influence the measurement of the scintillation variance may lead some degree of scattering of the measurement results of the refractive index structure constant.

Edge detection plays an important role in laser ladar image processing. Its capability has direct influence on precision and performance of ladar imaging system. Considering the features of laser radar image, this paper raises a method based on wavelet transform and mathematical morphology to process the laser radar image. Firstly, using the wavelet theory and the multi-scale wavelet decomposition strengthens the weak parts of the image edge appropriately. Then, we do edge detection from the perspective of gray morphological and get the edge information. Matlab is used to perform the experimental simulation. The results show that adding edge detection operators in laser radar image processing gets better effects than only using wavelet or morphology. The theory proposed in the paper has great effects in edge accuracy, strong and weak edge extraction and noise suppression.

The effective radiative rates for Rb (5P3/2) resonance level in the presence of Ar or N2 have been determined. Rb atoms were excited to the 5P3/2 state using a single-mode diode laser(pumping laser). The single-mode laser beam (probing laser) tuned to the 5P3/2→7S1/2 transition passes through samples paralled to the pumping laser. The excited-atom density and spatial distribution were mapped by monitoring the absorption of a counter propagating single-mode diode laser beam (probing laser). In the presence of radiation trapping, the effective radiative rate is the product of spontaneous radiation rate and transmission factor, which describes the average probability that photons emitted within the fluorescence detection region can pass through the optically thick vapor without being absorbed. The transmission factor is calculated by combining the 5P3/2 atom density and its spatial distribution and collisional broadening of 5P3/2←5S1/2 transition line. The effective radiative rates of the Rb D2 line as a function of the Ar or N2 pressure P are obtained. The fluorescence intensity I780 of the 5P3/2→5S1/2 emission is measured simultaneously. For 5P3/2-Ar system the measured fluorescence ratios determine the ratios of the effective radiative rates at different Ar densities. These ratios are in agreement with theoretical evaluation. For 5P3/2-N2 system the electronic to vibrational energy transfer has been investigated. The cross section was obtained.

The effects of Raman amplification on propagation characteristics of the optical soliton are experimentally investigated by using second-harmonic generation frequency-resolved optical gating (SHG-FROG) technology. Raman amplification can compensate the fiber loss, does not change the temporal waveform and has little influence on the linear chirp of the soliton. And it can completely compensate the fiber loss when the propagation distance is smaller than effective fiber length, and can partially compensate the fiber loss when the propagation distance is larger than the effective fiber length. The fiber loss compensation of Raman amplification increases with the increase of the Raman pumping power. Experimental results show that the soliton is not sensitive to the polarization of Raman pumping source.

An intensity channel model of wireless optical communication based space modulation is proposed and two basic condition are outlined. A vector signal space is defined by defining the two-dimensional (2D) orthonormal basis functions, and three critical measurements of performance, namely, probability of error, efficiency of spatial spectra and power efficiency are also defined as metrics for comparing candidate modulation schemes. Then three candidate modulation schemes exploiting spatial dimensions are proposed. At last, the three modulation schemes are compared by power efficiency and bandwidth efficiency. It shows that spatial quadrature amplitude modulation (QAM) scheme is appropriate for long distance wireless optical communications for its high bandwidth efficiency and spatial circular symmetry. And the spatial circular symmetry of QAM signal patterns is very suitable for realizing space synchronization in wireless optical links based spatial modulation.

Vertical bell labs layered space-time (V-BLAST) is a technology combining space multiplexing with space diversity. It has the high spectrum efficiency and the transmission speed, so the technology is applied to free space optical communication. In this paper, after researching the characteristic of atmosphere channel, a free space optical communication channel model based on V-BLAST is proposed. Code principle of V-BLAST is introduced, and channel capacity of this system is analyzed. The difference of the channel capacity and error rate of the system with and without V-BLAST structure is compared through simulation experiment. As a result, when receiving antenna number is larger than the transmitting antenna number, the channel capacity is improved directly proportional with transmitting antenna number, and the error code performance of system coded V-BLAST is improved effectively. It shows that the system has channel capacity supplied by V-BLAST structure and well error code characteristic, and the scintillation effect caused by atmosphere turbulence is effectively overcome.

A novel frequency-hop (FH) scheme is proposed for optical code division multiple access (OCDMA) system. According to the characteristics of FH-OCDMA system, an upper bound on the code size is deduced and the quadratic congruence-hop codes (QCHC) which achieves this bound is presented, with examples given. On the basis of it, a novel scheme for FH-OCDMA system with fiber Bragg grating array based encoder/decoder and QCHC is designed. Furthermore, a detailed performance analysis of the system is given. The results reveal that such a new scheme for FH-OCDMA system is not only easy to plan, but also has a large number of simultaneous users and low bit error rate.

When light field interacts with metamaterials, both the electric field and the magnetic field must be considered. The dispersive permeability of metamaterials induces many new characteristics under the nonlinear interaction between light field and metamaterials. The research progresses on the second-order nonlinear optical phenomena are briefly described, and some research results on the propagation characteristics of electromagnetic waves in the metamaterials with third-order nonlinear optical responses are specially presented, such as the establishment of the propagation model, the results for modulation instabilities, solitons, self-focusing.