Based on the theory of semi-analytical thermal analysis, the thermal effects of the diode-end-pumped Nd:YAG microchip crystal with back surface cooling were investigated. A thermal model that matches actual working state of the laser crystal is established by analyzing the working characteristics of the Nd:YAG microchip crystal. Through using a new method to solve the heat conduction equation of isotropic material, a general expression of temperature field, thermal distortion field and additional optical path differences (OPD) within Nd:YAG microchip crystal was obtained respectively. Calculation expression of thermal focal length of the Nd:YAG microchip crystal was obtained by analyzing the additional OPD caused by heat. Research results show that a maximum temperature rise is 70.36 ℃, a maximum thermal distortion is 0.465 μm and a maximum additional OPD is 0.836 μm when the LD pump light is fourth rank of super-Gaussian distribution, the total power is 24.2 kW,and the duty cycle is 10%.

A passively mode-locked all-fiber ring soliton laser is constructed based on all-solid Yb-doped photonic bandgap fibers (AS-Yb-PBGF), which provide the laser gain and anomalous dispersion simultaneously. Without using any bulk dispersion compensators, the laser cavity is simple, compact, environmentally stable, and easy to achieve all-fiber configuration. By means of the nonlinear Schrdinger equation, the dynamics of single-soliton operation in the laser is numerically simulated and the optimal parameter is obtained with the split-step Fourier method. In the calculation, when the length of the AS-Yb-PBGF was chosen as 0.4 m and the length of single mode fiber (SMF) as 0.4 m, the single-soliton operation with the pulse duration of 244 fs, the pulse energy up to 14 pJ, in which the time-bandwidth product is 0.32 as nearly the transform-limited pulse, has been shown.

An all-fiber Q-switched Yb3+-doped fiber ring laser pumped with a 976 nm laser diode (LD), which uses a fiber-pigtailed acousto-optic modulator (AOM) as the active Q-switching element, was reported. The stable pulse can be obtained when the modulation frequency was adjusted from 200 Hz to 60.9 kHz. The laser pulse with maximum peak power of 2.7 W, pulse width of 53.2 ns and pulse energy of 145.5 nJ is obtained, when the pumping power is 183 mW and the modulation frequency is 500.2 Hz. The alternate ouptut of high and low energy pulse is observed with the shorter Q-switched turnoff time, and it is explained by the principle of the Q-switched laser. The characteristics of pulse versus modulation frequency and pump power are investigated, and the theoretical calculation is in good agreement with the experimental result.

Picosecond-scale, 1064 nm central wavelength, 0.4 nm 3 dB spectrum width, 17.3 MHz steady continuous wave (CW) passive mode-locked fiber laser is realized using semiconductor saturable absorber mirror (SESAM), highly-doped Yb fiber and fiber Bragg grating (FBG). In the process of increasing pump power, the pump power threshold of mode-locking start-up is 50 mW, while in the process of decreasing pump power, the minimum pump power of steady mode-locking is 37 mW. Q-switched pulse, CW passive mode-locked pulse with Q-switch fluctuation of little amplitude, double-pulse modulation, tri-pulse modulation and more pulse modulation appearing successively as the pump power are escalated. The modulation becomes unsteady in the process of splitting. The number and peak value of split pulses present uncertainty when the pump energy is high enough. The higher pump power and stronger mode-locking, the wider the spectra are. It is demonstrated that more split pulses mean narrower autocorrelation trace and shorter pulse width. The environmental disturbance may have some effect on the multi-pulse modulation.

A cylindrical microcavity was made by immersing a silica optical fiber in a dye solution. The pumping threshold energy of the whispering-gallery-mode (WGM) laser strongly related to the spatial overlapping between the evanescent field of the pumping laser and the WGMs, and it also was influenced by the losses of the WGMs of low and high order. The distribution of evanescent field of the WGM can be changed through changing the refractive index of dye solution and the diameter of fiber. Then the spatial overlapping and the losses of WGM are changed. The results show that there is a lowest pumping threshold value of the first order WGM laser when one of the refractive index of the solution and the diameter of fiber is changed but the other is invariable.

The output wavelength would change according to the change of the temperature of the gas mixture in a pulsed TEA CO2 laser, which is called the wavelength-temperature shift. A theoretical model based on the six-temperature mode rate equations is suggested to interpret such a phenomenon, which is used to calculate the wavelength-temperature shift relation of a TEA CO2 laser with plano-concave stable resonator. The numerical results indicate that the laser simultaneously generates several transition lines at one laser pulse, and the wavelength keeps positive change with the change of the ambient temperature. In addition, the laser′s wavelength-temperature shift occurs merely within the 10P branch no matter what ranges the temperature varies. So a grating resonator can easily eliminate the shift and keep the laser output spectra stable.

Theoretical and experimental study is presented on grating period-tuned single-resonated quasi-phase-matched optical parametric oscillator (QPM-OPO) in multi-grating periodically poled lithium niobate (PPMgLN) pumped by 1064 nm laser. Theoretical analysis includes grating period tuning, pump threshold and converting efficiency. When pump power is 6.5 times of the pump threshold with Gauss beam pumping, a converting efficiency of 71% is obtained, however a converting efficiency of 100% may be obtained when pump power is (π/2)2 times of the pump threshold with plane wave pumping and phase matching. The pump beam polarization matches the e→e+e interaction in PPMgLN, thus maximal nonlinear coefficient d33 (27.4 pm/V) is effective. Widely mid-infrared wavelength tunable output from 2.7 μm to 4.8 μm has been obtained by grating period tuning. When pump power is 23 W with repetition rate of 7 kHz, an average output power of more than 3.2 W at 3.7 μm is obtained with slope efficiency of more than 18%, and 8 W at the corresponding idler wavelength of 1.49 μm and a corresponding converting efficiency of 63% are obtained. The experimental data are in agreement with numerical analysis results.

The transfer matrix of the series-coupled microring resonators is derived in detail based on the coupled mode theory of waveguides. The influence of the coupling coefficients, the number of the rings and loss on the transmission spectrum of the resonators are analyzed. Numerical simulation indicates that the bandwidth of the pass band will increase with the coupling coefficient, and at the same time, the number of the resonant wavelength in the pass band will also increase with the number of the rings. The microring resonator can act as filters or wavelength division multiplexer (WDM) in appropriate condition. Additionally, we find that the structure has the performance of optical delay when we launch a 50 ps (full-width at half maximum, FWHM) long Gaussian-shaped pulse into the structure. The larger the number of the rings, the more group delay we can achieve when the coupling coefficients is rather small, however, no delay effect can be observed when the coupling coefficient between the rings is strong.

The adaptive optics (AO) technique without a wave-front sensor can optimize the system performance directly, while being independent of wave-front sensor. Based on stochastic parallel gradient descent (SPGD) control algorithm, an adaptive optics test-bed without a wave-front sensor was built with a 32-element deformable mirror and a CCD. Experimental results show the test-bed can correct distorted wave-front successfully when parameters of the SPGD algorithm are appropriate for distorted wave-front. The test-bed only can correct static or slowly varied aberrations due to the slow sample frequency of CCD. Several implemental methods in atmospheric laser communications were discussed. SPGD control algorithm can be used to correct aberrations in atmospheric laser communication if being combined with high speed photodetector, high speed data processing and high response frequency wave-front corrector.

This paper proposes a new method for analyzing and characterizing green teas. The excitation-emission fluorescence matrixs (EEMs) of twenty-six types of green teas were measured with FS920 fluorescence spectrometer. The three-dimensional (3D) spectra and contour maps were obtained by measuring the emission spectra in the range from 310 nm to 750 nm, and excitation wavelengths from 300 nm to 550 nm. The excitation and emission profiles of three factors were plotted from parallel factor analysis (PARAFAC) model. The spectra characters of three main components (tea polyphenols, flavonol, chlorophyll) in green teas were ascertained. Different green teas can be characterized and distinguished with the sample projection plots of the PARAFAC model. The results demonstrate the capability of the combination of 3D fluorescence spectra technology and three-factor PARAFAC model for characterizing, differentiating and analyzing green teas.

As one of the main detection schemes, phase generated carrier (PGC) technology has been implied in many fiber optic hydrophone array systems. The scheme requires a narrow bandwidth, tunable and low noise laser source. In practice, the relative intensity noise (RIN) of the laser has affected the system performance greatly. By analyzing the impact of RIN on fiber optic hydrophone’s PGC scheme theoretically, it has been found that if the RIN peak frequency can be controlled to odd multiple of one-half of PGC modulation frequency by changing the pump power, the impact of RIN on the system can be greatly reduced. Experiment results have proved that this scheme can lower the PGC noise from -86.7 dB to -106 dB. Furthermore, by using optical-electronic feedback, the RIN has been well suppressed and the relaxation oscillation peak is reduced about 25 dB. The laser noise has become -100 dB and the PGC output noise turned out to be -110 dB. This result has met the need of the fiber optic hydrophone systems.

A method to analyze the resonant wavelength and damping decrement of the transmission spectrum of long period fiber grating (LPFG) with bending curvature was reported. Based on coupled mode theory and perturbation approximation, the general expression of transmission spectrum of LPFG according to bend curvature is deduced. Furthermore, the transmission spectrum of the bended LPFG is found to be splitting when the bending curvature is 2.56 m-1. The resonant wavelength and decrement of the split peaks change nonlinearly with the bending curvature, but the distance between split peaks changes linearly with the bending curvature. The LPFG written on the B-Ge co-doping single mode fiber proves the theory.

A fiber sensor based on all polarization-maintaining fiber Mach-Zehnder interferometer is presented, in which the single-frequency polarization-maintaining optical fiber laser is used as a light source. An active feedback loop for laser source and a balanced-mixer receiver are adopted to suppress the noise of the sensor system. This system makes the intensity noise reduce about 15 dB, and the signal-to-noise ratio of the system is up to 60 dB.

Based on a compact two-dimensional finite difference frequency domain (2D-FDFD) method with anisotropic perfectly matched layer absorbing boundary conditions, an octagonal photonic crystal fiber (O-PCF) is analyzed and investigated. Through computing the first twenty modes of octagonal photonic crystal fiber, we find that the circular field distribution of the octagonal photonic crystal fiber is better than that of hexagonal photonic crystal fiber (H-PCF). The phase diagrams of cut-off, single mode and multi-mode for the two fibers are obtained through analyzing the cut-off properties of fundamental mode and second mode by effective area method. Numerical simulation results show that under the same pitch and air filling fraction (AFF), the octagonal photonic crystal fiber has wider single mode operation region and has advantage in designing dispersion-compensating fiber in comparison to hexagonal photonic crystal fiber.

Forward amplified spontaneous emission (ASE) in Er3+/Yb3+ co-doped double clad fiber amplifiers is studied by use of rate equations and transmission equations model, Stark energy level splitting theory containing 1060 nm wave band radiation, Er3+-Yb3+ absorption and emission cross sections, and Runge-Kutta 4th-order method. A multi-theoretical model is founded to analyze the ASE spectrum generally by changing the pumping power and signal power. When the signal is strong enough, it only can change the output power by changing pump power without changing the spectrum figure. When the signal is small enough, two local peaks appear at the 1535 nm and 1543 nm at the ASE spectrum. The theory is validated by experiment.

For studying the character of Hermite-sine-Gaussian (HSiG) beam in non-paraxial case, based on the theory of the second intensity moment and a series of complex calculations, the results of the far-filed divergence angle, waist width and M2 factor of non-paraxial Hermite-sine-Gaussian beams are derived, and the relationship of them versus the acentric parameters are studied by calculation and plot. The result indicates that the relationship of non-paraxial HSiG beam characters versus the acentric parameter is different from paraxial case. As the parameter w0/λ decrease, α→0, the far-filed divergence angle with even and odd orders approach 73.898° and 63.435°, respectively. With increasing the parameter, the waist width and M2 factor show large changes. Because of the effect of parameters, non-paraxial M2 factor can be less than 1 as well as approaching 0, which is different from paraxial case.

The finite-sized light beam reflected from a weakly absorbing dielectric slab would experience a longitudinal displacement. The longitudinal displacement of a linear-polarized light beam reflected from the single metal layer is theoretically investigated. It is shown that, in the region of absorbed frequency, the longitudinal displacement of TE polarized light beam is not only positive and very small but also grows slowly. The displacement is saturated to maximum when the incidence angle is very large. The longitudinal displacement of TM polarized light beam is negative and has a peak near 80°. The peak value is about one wavelength. It is also shown that the longitudinal displacement of TE polarized light beam keeps a similar action and its maximum is smaller in the region of reflected frequency. The negative displacement of TM polarized light beam is several wavelengths near 90°.

The effects of optical properties of myocardium tissue due to heating in the visible and near-infrared spectral range were investigated. A spectrophotometer was used to measure the diffuse reflectance and total transmittance of the tissue samples, and the inverse adding-doubling (IAD) method was applied to assess the absorption coefficients, the reduced scattering coefficients and the optical penetration depth of tissue from the measurements. The results of measurement show that the absorption and reduced scattering coefficients and optical penetration depths of myocardium tissues vary with the change of irradiation wavelength. There are a positive peaks at 550 nm for the absorption coefficients of both native and thermocoagulated (treated with 80 ℃) myocardium, and the peak values for native and thermocoagulated myocardium are 0.74 mm-1 and 1.16 mm-1, respectively. There is a positive peak at 550 nm for the reduced scattering coefficients of native myocardium and the peak value is 0.25 mm-1, whereas the peak disappears after myocardium tissue treated with high temperature. Further more a new increase appears at the wavelength range of 590～625 nm. The absorption coefficient of myocardium tissue is not significantly changed by treating with lower temperature but increases slightly with higher temperature. The reduced scattering coefficient of myocardium tissue is significantly increasing with the increase of treating temperature. And the optical penetration depth of myocardium tissue is significantly decreasing with the descrease of treating temperature.

The low luminescence of serum is tested with the low luminescences detection system. In the experiment the low luminescence of serum of the hyperglycemia, hyperlipoidemia, and normal man are tested respectively, and the laws of serum radiation intensity with variation of blood sugar and triglyceride concentration are studied. And the image of the low luminescence of serum is analyzed quantitatively with self-programmed software. The experimental result shows that the serum radiation intensity increase synchronously with blood sugar concentration linearly. The gray threshold of triglyceride luminescence image also increases with triglyceride concentration, but it is not obviously as the former one. So the blood sugar concentration can be estimated by the serum luminescence intensity, and it is effective. It provides experimental foundation for the medical diagnose.

Microbump structures were formed on the sample surface after micromachining the Cr films by polarized femtosecond double pulses with nanojoule energy and high repetition rate. Although the widths of the microbumps have no obvious variation among the 0～400 ps double pulses delay, the heights of them exhibit an obvious drop among the 1～10 ps double pulses delay and have no obvious variation beyond this delay. It is helpful to understand the electron–phonon coupling process in metal film during femtosecond laser micromaching. Furthermore, better micromachining quality was acquired with double pulses method for both linearly and circularly polarized light according to the scanning electronic microscope (SEM) images. Contrast to nearly circular microbumps fabricated by circularly polarized light, the microbumps fabricated by linearly polarized light is narrow and stretched in the direction of polarization of the incident beam. Namely, the micromachining feature is related to the polarized state of the incident beam with low pulse energy and high repetition rate.

Based on slip line and stacking fault appeared on the silicon surface, the dislocation theory is used to analyze the reasons of causing dislocation and stacking fault during the bending process and study their influence on the laser bending, according to the experiment of thin silicon laser bending. The analyzed results indicate that the slip line is caused by the dislocation accumulation, and the stacking fault is the results of piled dislocation. Meanwhile influence of the dislocation density and dislocation moving velocity on the process of laser bending is analyzed. The changing process of dislocation density and the deceased dislocation moving velocity are considered to form maximal angle.

In order to investigate the tribological performance of laser clad coating on die steel, laser cladding techniques were adopted with Fe-based alloy powders. The tests were carried out by using laser clad layers as upper samples and GCr15 steel as low samples with HT-500 wear tester. The morphologies of wear scars were observed with optical microscopy, and the width and the depth of the wear samples were measured. In the meantime, the wear rate was calculated theoretically. Under dry sliding condition, As the tests shown, friction coefficient decreases with the load increasement gradually, and then increases. And the wear performance of 300 g load is better than that of 500 g load under dry sliding condition. Under lubricant condition, with the increasement of load, the friction coefficient decreases gradually. And the friction coefficient, wear rate and wear width under lubricant are smaller than those under dry friction with the same load.

The quantitative analysis about a laser scanning imaging system for rotating polygon is theoretically described. The polygon scanner is located in front of the scan lens in order to guarantce the scanning image point in a flat field. It is important in system designing to determine the positional relationships between the incident beam at mirror, the rotation axis of the polygonal and the optical axis of the optical system when the angle of incident laser beam is 2α relative to the optical axis of the system. the calculation formulas of the scanning angle, scanning efficiency and the entrance pupil drift of the system are derived and the relationships between scanning angle, entrance pupil drift of system and many important factors (such as the width of the incident beam, incident angle and the geometrical size of the polygon, etc.) are discussed in details. The results show, in order to increase the scanning efficiency of the system, the incident angle of laser beam should be small. And the range of scanning efficiency from 0.4 to 0.7 is more reasonable in the system designing.

Nep detection system used in carding machine is a kind of new on-line detection system based on machine vision. The function of light source is illumination. Light source is an important factor for cleaning rate. The light source system should be optimized and designed to satisfy the broad surface, high speed and high sensitivity for on-line nep detection system. By experiments, we could know that the neps in cotton web would have the highest reflectivity illuminated by which kind of light source. Synchronously, we could know that the neps and surrounding structure how to get the best contrast. Compared with the spectral curve of traditional fluorescence lamp, high pressure mercury lamp and LED, the scheme of combination in He-Ne laser and optical system was adopted in this paper. Experimental results show that this light source, for the circumstance of nep detection in carding machine, is better than other light sources because of the high brightness and straightness of laser.

Stimulated Brillouin scattering (SBS) can be utilized in laser systems to improve alignment stability. The stability of SBS is a key factor of limiting the system stability. Combining with the theory of hydrodynamics, vibrating string and transient SBS, a new SBS model with longitudinal vibrating of media is established. The eigenvalue of vibrating is obtained by solving the model. Basing on the model, the influence of longitudinal eigenvibrating and harmonic vibrating of tetrachloride with different intensities on the Stokes beams is investigated theoretically. The result shows that the influence of vibration on SBS has a certain threshold. When the intensity of vibration is less than some value, the stability of SBS is not affected. Another numerical simulation is carried out to research the dependence of stability on the configuration of SBS. It shows that the stability is enhanced when choosing lenses with shorter focus and shorter media cell.

The characteristic of the photovoltaic spatial solitons in two-photon photorefractive media is influenced by the temperature of the media. The bright and dark spatial soliton solutions of the evolution equation of spatial solitions are related to the temperature. The intensity profile and the full-width at half maximum (FWHM) of photovoltaic spatial solitons in two-photon photorefractive media are dependent on the temperature of the media in the room temperature range. With the raising of the temperature of the two-photon photorefractive media, the photovoltaic spatial solitons with small intensity can be supported, moreover, the photovoltaic spatial solitons with small FWHM can be established under the large intensity case, and the photovoltaic spatial solitons with wider FWHM can be formed under the small intensity case. That is to say that the profiles of the photovoltaic spatial solitons can be controlled by the temperature, so as to form the steady photovoltaic spatial solitons in the two-photon photorefractive media.

Dependence of the position and light intensity of nonlinear hot image in high power laser system on the thickness of Kerr medium has been investigated theoretically and numerically. Based on the propagation of angular spectrum and Bespalov-Talanov small-scale self-focusing theory, the expression for hot image intensity is obtained without thin medium approximation, and verified by numerical simulation. It is shown that, for a given obscuration, the hot image intensity increases monotonously with the medium thickness for a given input laser power, while it firstly increases to reach a maximum value, then decreases as the medium thickness increases for a given B integral. In addition, it is shown that the thin medium approximation is applicable to hot image analysis when the Fresnel number of an obscuration with respect to the length of the Kerr medium is much more than 1. The analytic results are in good agreement with numerical simulations.

Terahertz (THz) radiation can penetrate many materials that are opaque to visible light, such as non-metal and non-polar materials, and these materials′ X-ray imaging are relative lower. Thus, THz imaging for security and quality control application has been paid great attention. Actual measurement on the THz characteristics is an important part of THz imaging technology. In this paper, THz laser pumped by a CO2 laser was used to measure polytetrafluoroethylene absorption characteristics and transmission beam profile. The absorption coefficients of polytetrafluoroethylene were achieved experimentally at wavelength of 70.51 μm, 96.5 μm, 118.83 μm, 122.4 μm, 158.51 μm, 184.31 μm and 214.58 μm.

It is very important to obtain the accurate optical constants of thin films for the design and the manufacture of high-quality optical coatings, especially for those optical characteristics very sensitive to the variation of refractive index. SiO2 as a common low refractive index material is difficult in accurately fitting the optical constants which are close to those of the substrates. In this paper, single layer SiO2 film is prepared by ion beam sputtering. Considering the error in measurement and the influence of the substrate refractive index, the refractive index of SiO2 is obtained by the transmission envelop and the reflection envelop methods. The accuracies of these two methods are compared by inverting the obtained refractive index. The analysis shows that the refractive index of SiO2 with 10-2 precision can be well obtained by directly using the residual reflection of substrate and films because of the few errors in actual measurement of residual reflection.

The delamination characteristic of optical thin films induced by laser pulse at 1064 nm and its restraining method were studied. The process of delamination was analyzed and the relationship between the area of delamination and the energy of irradiating pulse was deduced theoretically and proved experimentally. Some theories probes to control delamination were done and it was found that irradiation with low energy density pulse could enhance the delaminating threshold and reduce the area of delamination. The effect was found more evident with higher pulse energy density in some range and the mechanism was presented.

Raman-differential absorption method was introduced for monitoring ozone concentration in the bottom of troposphere. The intensity of the Raman spectra of N2 and O2 was analyzed and calculated. The retrieving equation of ozone’s concentration was presented based on the different absorption of ozone to the Raman spectra of N2 and O2 in ultraviolet (UV). A Raman-differential absorption lidar system was designed. The system collected Raman scattering signals of N2 and O2 by two channels, and concentration of ozone can be retrieved by these pairs of signals. The specifications of interference filters in two channels were presented by analyzing the sources of noises. The influences and relative errors of monitoring ozone in this method were analyzed, because SO2 and NO2 also absorb Raman scattering signals of N2, O2 in UV. Finally, vibrational Raman signals of N2 and O2 were simulated by the ozone data which monitored by AML-2 differential absorption lidar (made in Anhui Institute of Optics and Fine Mechanics, Chinese Academy of Sciences). The simulation results indicate that Raman-differential absorption method is feasible for monitoring ozone concentration in low atmosphere.

Laser scattering by bubbles over a range of scattering angles from 5° to 175° is achieved using the bistatic optical geometry. In the meantime, laser scattering by water is measured. The scattering angle is changed by moving the receiving system on the condition that the transmitting system is fixed. The compress of the large dynamic range for the bubble scattering signal is solved and the change of the scattering volume with scattering angles in the receiver’s field of view is discussed. Then, the characteristics of the bubble scattering signal are analyzed and the power spectral density estimation method is put forward to process this signal. The experimentally measured and theoretically calculated results are compared, which show that both results are agreed and bubble scattering is about one order of magnitude higher than water scattering without bubbles. Results indicate that bubble scattering can be distinguished from water scattering, and thus bubbles can be detected by laser.

For a large aperture ground-based telescope with segmented primary mirrors, in order to guarantee the continuity of the figure of the total mirrors, a new interferometric detection method was put forward to detect the phase errors between the segmented mirrors, and correct the misaligned segments correspondingly. This method could make the telescope achieve optical image with diffraction limit. The segment misalignment errors between the segments include tip/tilt error and piston error, the segment piston error between the individual segments must be reduced to less than 100 nm. We have considered an interferometric piston error measurement system based on a Michelson interferometer layout for accomplishing such object. The innovation introduced in the optical design of the interferometer is the simultaneous use of both monochromatic and white-light source that allowing the system to measure the piston error with an uncertainty of 8～10 nm in the range of 45～60 μm. Simultaneously a detailed description about the optical system layout and the theoretic interferograms was gotten.

A high-resolution flight time measurement system based on a single field programmable gate array (FPGA) in laser altimeter is designed. The time resolution of 300 ps is obtained, because the differential delay lines are used to perform interpolation and to realize the fine time measurement, and high frequency counter is designed to perform the coarse time measurement. The time splitting circuit, pulse width counter and data transmitter module are integrated in the same chip. At an ambient temperature of 20 ℃, we achieve a standard deviation of 94.68 ps which equals to 1.42 cm in distance. Furthermore, detection on the ground verifies the feasibility of measuring distance with ±50 cm resolution over 500 km ranges under general conditions.