The beam quality and far-field beam profile of broad-area diode laser (BAL) are investigated. In accord with the theory of self-consistency, the wave propagation of the output laser of external cavity BAL is calculated. In Fourier optic methods, the external cavity can be interpreted as a spatial filter in the Fourier plane of the laser diode. The transverse mode can be selected by changing the position of the filter. The relative external cavity BAL experiment is completed, and a single-lobed output beam of the external cavity BAL is achieved. The output laser with divergence angle of 0.074° (full-width of half-maximum (FWHM)) and corresponding M2 factor of 1.16 is obtained when external cavity feedback at I=1.18Ith, which agrees well with the theoretical result.

With the development of micro-electro-mechanical system (MEMS) based on silicon micromaching technology, it becomes possible to develop a low-cost adaptive optics system to compensate the aberration of laser beams. The effect of thermally induced aberration on laser beam quality is analyzed based on mode coupling theory. The relation between coupling amplitude of ideal and aberrated fundamental mode and Zernike aberration is numerically simulated. An adaptive optics system is presented based on a MEMS deformable micro-mirror to compensate the thermally induced aberration. From the test result, it is explicit that the adaptive system can correct the thermally induced aberration of high power lasers and increase the Strehl ratio to about 80% averagely.

To satisfy the stringent requirements for measuring accuracies of charge coupled device (CCD) laser autocollimators in the fields, such as high accuracy metrology system, and azimuth aiming and tracing system, an anti-noise and precise circle target center location method based on orthogonal Fourier-Mellin moments (OFMMs) is proposed. The specific characteristics of the circle target edge of CCD laser autocollimators can be fully extracted, the noises in images can be efficiently diminished by using the rotation invariance and lower radial orders of the orthogonal Fourier-Mellin moments, edge location can be accomplished by setting the edge in vertical direction and analyzing the relationships among these moments of the edge, and the center position of the circle target can be accurately acquired by using the least square fitting method.

There have been controversial reports on photobiomodulation on cartilage healing so that the research on the potential effect of low intensity He-Ne laser irradiation (HNI) on the proliferation and variation of rabbit cartilage cells in vitro was systematically done in this paper. The chondrocytes isolated from the cartilage sample of 3-week-old New Zealand white rabbits were cultured with newborn calf serum (NCS) at 0%, 2.5%, 5%, and 10%, irradiated by HNI at 5.74 mW/cm2 for 2, 8, 16, 30 and 45 min per day for 6 days, and then incubated till the 13th day. The proliferation and collagen synthesis were assessed by XTT assay and hydroxyproline (Hrp) content measurement, respectively. The DNA expression was observed by acridine orange stain and confocal laser scanning microscope. The chondrocyte morphology and ultrastructure have been observed on the 9th and 13th day after the first HNI by scan electron microscope. There is no significant photobiomodulation (PBM) on the proliferation of the chondrocytes (PPC) cultured with NCS at 10%. There is PPC cultured with NCS at 2.5% or 5%, and the effects are significant when the cells were irradiated by HNI for 16, 30 and 45 min, respectively, among which the radiation time 30 min corresponds the optimum dose 9.42 J/cm2. Hrp secretion increased steadily with days in NHI group. When the photobiomodulation is significant, the chondrocyte DNA expression was significant, and its morphological characteristics have no significant differences from the one cultured with NCS at 10%. There might be photobiomodulation on the proliferation of the chondrocytes cultured in nutritional deficit condition and irradiated by HNI at limited dosage, which is of clinic importance.

In order to explore the possibility of photodisruption in rabbit sclera by femtosecond laser and to seek the appropriate ways of incision and relevant parameters, femtosecond laser (800 nm/50 fs) with different pulse energies was applied to irritate rabbit sclera in vitro. By moving a three-axis, computer-controlled translation stage to which the sample was attached, femtosecond laser could achieve three types of incisions, including transscleral channel, snake pattern and linear cutting. The irritated sclera was observed by light microscopy and scanning electron microscopy (SEM). In comparison with femtosecond laser, Nd:YAG laser was used as control. It was shown that through a 0.2 numerical aperture (NA) objective lens, femtosecond laser with the power intensity larger than 9.55×1014 W/cm2 and the pulse energies ranging from 37.5 to 125 μJ could achieve cuttings with the depth from 30 to 70 μm after linearly scanning on the sclera at the speed of 0.1 mm/s. Whereas, it failed to make any photodisruption if laser power intensity was below 7.96×1014 W/cm2 or the pulse energy was less than 31.25 μJ under the same condition. Comparing with Nd:YAG laser, the inner wall of channel was smoother and the damage to surrounding tissues was slighter by femtosecond laser. The high precision and minimal damage to surrounding tissues with femtosecond laser predicted its potential use in the treatment of glaucoma.

The wave-front conversion between cylindrical and plane waves by photorefractive local volume holograms recorded at 632.8 nm and reconstructed at 800 nm is investigated in this paper. Based on two-dimensional coupled-wave theory, the coupled wave differential equations of the cylindrical lenses on double-doped LiNbO3 crystal are derived, and the analytical integral solutions for the amplitudes of the space harmonics of the field inside the transmission geometry are presented. The values of off-Bragg parameter at the reconstructed process are analyzed. Furthermore, the dependences of diffraction efficiency on recording cylindrical wave and on the geometric size of the gratings are discussed, and the amplitude distribution of the diffracted beam at the output boundary is also analyzed. It is found that: 1) the diffraction efficiency increases as the focal length of the volume holographic cylindrical lenses increases; 2) the diffraction efficiency increases with increasing the grating thickness, but the diffraction efficiency decreases with increasing the width of the diffraction surface at vertical direction; 3) diffracted amplitude distribution derivates much from the desired uniform amplitude as the initial recording cylindrical, and the diffracted intensity mainly concentrates at the line B-B′ of the gratings. At last, the effect of selectivity of different on-Bragg reference points for recording hologram on the diffraction efficiency of the grating is discussed, the results show that reference points have no influence on diffraction efficiency.

The readout characteristics for the hologram recorded in the novel LiNbO3:Fe:Ru crystal have been investigated in order to resolve the problem of hologram data erasure during readout. Grating readout characteristics for two-center and single-center recording are analyzed, and the simulating calculation is performed through jointly solving the two-center material equations and coupled-wave equations. The results show that the readout time constant for a saturated grating recorded by two-center method is much shorter than that in LiNbO3:Fe:Mn; an efficient hologram can be realized with one-color recording, the readout time constant is much larger than the recording time constant, and the quasi-nonvolatile readout can be observed. The analysis shows that Ru perhaps is much easier to be excited than Mn by red light, so the grating persistence would decrease; red light can act as recording light and sensitizing light in one-color scheme, and the grating recorded in Fe can be transferred to Ru, which is weakly sensitizing to red light.

A 100 J TEA CO2 laser was employed to study the effects of variety of pulse energy from 13 J to 80 J on the momentum coefficient for air-breathing mode. The results indicated that the momentum coupling coefficient (Cm) had no obvious change when the pulse energy decreased from 80 J to 24 J. While the energy was under 22 J, the Cm declined 52%. A preliminary analysis of theory was given, and an experiment of changing the air pressure in the vacuum chamber was carried to verify that.

The new material “black silicon” formed by arrays of sharp conical spikes on the silicon surface is fabricated under the cumulative ultra-short laser pulses irradiation in different ambient atmospheres. The physical mechanisms of conical spikes evolutions impacting silicon surface under picosecond (ps) and femtosecond (fs) laser irradiations are different. The formation of spikes arrays depends on the pulse duration and ambient atmosphere. Especially, in SF6 ambient atmosphere, silicon surface micro-structuring evolutions under ps and fs laser irradiations are analyzed in detail. Under the ps laser irradiation, silicon surface is melted before the spike arrays formed; while under the fs laser irradiation, the formation of spike array does not go through the liquid phase. The preliminary experiment shows that the infrared radiation absorptance is more than 80% at the wavelength range of 1.5～16 μm.

A single axial and transverse mode Q-switched pulsed laser system is demonstrated based on injection seeding and fast resonance detection technique combined with self filtering unstable resonator. 600 mJ energy at 1064 nm and 300 mJ energy when frequency-doubled, are achieved at Fourier-transform limit and with a beam divergence near diffraction-limit. The system is also characterized by the long-term stability in high vibration environments. The influence of injection-seeding on giant pulse setup time, beam-spot mode, and energy is observed experimentally. The perfect laser radiation is desirable in the area such as nonlinear optics, optical synthesized aperture and high-resolution spectroscopy.

A compact and efficient 213 nm deep-ultraviolet all solid state laser based on Q-switched laser diode (LD)-pumped Nd:YVO4 laser is presented. In the experiment, KTP crystal (KTiOPO4) and BBO crystal (beta-BaB2O4) are used for the 532 nm second-harmonic generation and the 266 nm fourth-harmonic generation respectively. Subsequent sum-frequency mixing is performed in a second BBO crystal to mix the fourth-harmonic at 266 nm and the residual fundamental at 1064 nm. At 10.3 W of incident pump power, the average power of 3.1 mW at 213 nm with the pulse width of 7.5 ns is obtained.

Generation of compact and efficient self-stimulated Raman pulses by a laser diode (LD) pumped actively Q-switched c-cut Nd:GdVO4 laser is demonstrated. At 1.8 W incident pump power, the self-stimulated Raman laser produces stable 19 ns pulses at a Stokes wavelength of 1176 nm with 10 μJ pulse energy at 10 kHz repetition rate. The threshold of the self-stimulated Raman laser is 510 mW, the conversion efficiency from the diode pump to the Stokes is 5.6%. Experimental results reveal that efficient self-stimulated Raman conversion frequency can be achieved with a c-cut Nd:GdVO4 crystal and actively Q-switched.

A simple wavelength tunable erbium doped fiber laser, with a fiber polarization controller and a polarization dependent isolator (PDI) as wavelength selective devices, is theoretically and experimentally demonstrated, which consists of gain flattened erbium doped fiber amplifier (EDFA), polarization dependent isolator, fiber polarization controller, and output coupler. The polarization induced losses of different wavelengths were analyzed with Jones matrix; theoretical result showed that wavelength-tunability and dual-wavelength operation of the fiber laser could be obtained by adjusting the polarization controller. A tunable range from 1542 nm to 1564 nm, the side-mode suppression ratio above 35 dB and average output power over 2.6 mW were achieved for this fiber laser. Dual-wavelength operation at 1549 nm and 1564 nm of the fiber laser was also obtained.

To establish the reconstruction method of incidence laser energy based on measuring the temperature rise at back-surface of detector cell, an analytical expression of temperature distribution is derived in detector cell. In terms of the analytical expression of temperature distribution in detector cell, the characteristic factors are confirmed for incidence laser energy reconstruction. By introducing a calibrated-coefficient, the formulae are obtained for laser energy reconstruction and calibrated-coefficient calculation. The calibrated-coefficient is analyzed by numerical simulation that is depended on detector-cell dimensions, laser characteristics, and circumstance conditions. In virtue of modification of convection-irradiation heat loss and laser reflectivity in reconstructed laser energy, the calibrated-coefficients are seasoned with circumstance conditions and different laser parameters. The precision of laser energy measured with calorimetric array is improved effectively.

An iterative phase retrieval algorithm is put forward, which makes use of intensity distributions on the input plane and several fractional Fourier transform planes. The intensity distributions on the input plane and other two fractional Fourier transform planes with relatively high orders are utilized to retrieve the phase profile, then the phase detail is retrieved by using other two fractional Fourier transform planes with relatively low orders. Good retrieval performances are obtained for two-dimensional slowly varying phase distribution and random phase distribution. Finally, the influences of the measurement noise and the fractional order error to the stability of this algorithm are analyzed in one-dimensional case, respectively.

Suppression condition of stimulated Brillouin scattering (SBS) in high-power single-frequency fiber amplifier is analyzed and simulated in this paper. The set of differential equations for an fiber amplifier with pump, signal and the first-order Stokes, taking into account effects of thermal gradients caused by heat generation, is presented.The influence of pump powers, convective coefficient, fiber lengths, and detuning of the Stokes frequency from exact SBS resonance on SBS gain (G) is studied under unidirectional and bi-directional end pumps. Compared to forward pump and bi-directional pump schemes, backward pump scheme offers the least gain (G), which can be further reduced through decreasing convective coefficient and fiber lengths. When total pump power is 1 kW, gain (G) of three-segment distributed pumping scheme is higher than the SBS gain threshold value. The results show that the backward pump scheme has advantage over other pump schemes in suppression of SBS, and the SBS is not a limiting factor to single-frequency power extraction from fiber amplifiers for a properly temperature variation and sufficiently short amplifier length.

Optical properties and adhesion of Ag films with Cr interlayer of different thickness on glass substrates were investigated by using spectrophotometer and X-ray diffraction (XRD). The spectra results showed that the reflectivity of Ag films increased with the thickness of Cr interlayer increasing from 8 to 17 nm and then decreased with increasing Cr film thickness to 24 nm. Compared with pure Ag films on glass substrates, the reflectivity of Ag films with 17～21 nm Cr interlayer was higher and that of Ag films with 8～14 nm and 24 nm Cr interlayer was lower. Thus, the reflectivity of Ag film can be promoted by introducing a certain thickness of Cr interlayer. The XRD analysis showed that with a certain thickness of Cr interlayer, the crystalline grains increased, intergranular defects and scattering decreased, and so the strain decreased. The adhesion was also improved by using the tape test method.

A novel method for exciting and detecting vibration of silicon microresonator sensors is presented. A single laser diode is used for excitation and detection, and an all-fiber Fizeau interferometer is applied. The displacement signal of microresonator is demodulated from the interference signal, which is modified with the intensity change of the laser diode. The Bessel function ratio method is used to enlarge the measurement range. And some working parameters need not be measured. Using this method the resonance frequency about 8.81 kHz and the tested cantilever amplitude at resonance about 135 nm were obtained. The experimental results are consistent with those of other method, so practicability of the new method is proved.

Projection data obtained through optical techniques for tomographic measurement are often with noise. The reconstruction accuracy is deteriorated by the Gauss- or Poisson-distributed noise. Corresponding to the major steps of tomographic technique, a two-stage denoise technique has been developed. The deflectometric data are denoised by wavelet-based procedure after projection data reduction. Deflection-angle averaging revision algorithm is applied to suppress the noise in iteration. The Moire tomographic reconstruction technique with eight-neighbor derivative algorithm and denoise method is tested using numerically generated data from a known temperature distribution and noise source. The results show that the denoise processing is able to improve the reconstruction accuracy significantly, which reduces the reconstruction errors of 45%. The temperature field of butane flame is then measured by the Moire tomographic technique and the experimental reconstruction is compared with the thermocouple temperature measurement.

Based on lasing wavelength red-shift of semiconductor lasers due to junction temperature rising in pulsed operations, time-resolved spectra were measured by adjusting Boxcar gate position related to the current pulse. The thermal relaxation times of TO-can and cm-Bar array AlGaAs laser were obtained to be 66 μs and 96 μs, respectively. The measured dynamic thermal characteristics are of significance for pumping solid-state lasers.

The reflectivity of optical mirrors can be obtained by measuring linewidth of transmission spectrum of optical cavity and the fineness of Fabry-Perot (F-P) cavity. It is difficult for a spectrometer to measure the linewidth accurately due to its limited resolution. In this paper, laser phase modulation is introduced on the basis of fineness of F-P cavity, and laser phase modulation and fineness of F-P are proposed for measuring the reflectivity of optical mirrors. The frequency interval between the carrier and one sideband generated by electro-optical modulation is used as a radio frequency ruler to precisely measure the linewidth. Thus the reflectivity of mirrors is obtained with uncertainty reaching the level of 10-4 by the relation of fineness of cavity, spectral linewidth and reflectivity of mirrors.

Banyan optical networks play an important role in free-spatial photonic networks. The characteristics and structures of two-dimensional (2D) banyan network are analyzed. A new 2D banyan network architecture, which consists of polarizing beam-splitters, 4×4 micro blazed-grating arrays, half silvered mirrors, 4×4 spatial light modulators and mirrors, is proposed to accomplish optical signal switching, multicasting, broadcasting and matrix conversion through the 4×4 2D planes. The 4×4 micro blazed-grating arrays fulfill vertical connection and horizontal connection switching in 2D banyan networks, while the mirrors perform straight connections. The theoretical analysis shows that the architecture has the advantages of transparent switching, high speed, and high space-bandwidth product, therefore it can be implemented in free spatial optical interconnection widely.

Tunable differential phase-shift keying (DPSK) demodulator based on fiber Mach-Zehnder interferometer (MZI) is investigated, which has advantages of low insertion loss, high isolation, good stability, and tunable phase. Operation principle for DPSK demodulation is analyzed. Temperature of the fiber arm is set by the temperature control system, in which the tuning range is 20 ℃ and the resolution is 0.1 ℃. In the experiment, 40 Gb/s DPSK signal was demodulated successfully, and the extinction of the demodulated signal is 14.5 dB. With the help of temperature control, the experimental results have a long-time stability and can be switched between constructive interference and destructive one.