Successful cleaning procedures for gradient-doping GaN surface have been investigated and achieved. The chemical cleaning of the gradient-doping GaN photocathode surface is carried out. The analysis of the surface after the chemical cleaning with X-ray photoelectron spectroscopy (XPS) shows that the chemical cleaning can effectively remove the organic attachments, residues in the process on the surface. Subsequent annealing of the surface under ultra-high vacuum at temperature of 710 ℃ leads to a decrease in the residual carbon, so the photocathode can obtain the ideal atom clean surface for high-performance negative electron affinity (NEA) photocathode. Finally, the photocathode active experimental results confirm that thermal annealing after chemical treatment method can effectively clean the gradient-doping GaN photocathode surface.

A novel fiber Bragg grating with micro-structured defect is proposed and demonstrated. Its temperature characteristics are studied experimentally. It was obtained by wet chemical etching part of fiber Bragg grating in different concentrations of hydrofluoric acid solutions. The change of the local effective refractive index in the etched area induces two resonant peaks. Experimental results show that the two resonant peaks have different temperature sensitive coefficients. The wavelengths of the two resonant peaks become 0.8127 nm and 0.7329 nm longer while the temperature increases from 20 ℃ to 90 ℃, and the temperature sensitive coefficients are 0.01161 nm/℃ and 0.01047 nm/℃ respectively. The fitting linearity is 0.991 and 0.998 respectively. So the two resonant peaks of novel fiber grating present good linear relationship with temperature.

Skin welding with a combination of 1064 nm and 980 nm diode lasers, which′s the first-time discuss in the literature, was performed in this study. The long-time effect of laser skin welding was investigated through macroscopic and microscopic examinations as well as tensile strength tests at different time after the welding, comparing with that of conventional suturing. At the same time, the temperature of rat skin tissue during laser-welding was measured in vivo with a thermo-couple temperature measurement in order to analysis the relation between the effect of tissue welding and tissue temperature. Using a power density of 15.92 W/cm2 with power of 0.5 W in continuous wave mode and exposure time of 5 seconds per spot for both 980 nm and 1064 nm lasers, it′s found that laser tissue welding yielded more effective closure and healing than conventional suturing technique that with faster recovery, better apposition of tissue, less tissue interaction and tighter closure. As a result, tissue welding with a combination of two near-infrared lasers is an effective method for wound closure, and further investigations are in progress for clinical use.

Vortex optical trap is generated by projecting computer-generated phase patterns to liquid crystal spatial light modulator. Because vortex beam itself owns orbital angular momentum, it can be utilized to trap and rotate yeast cell. The angular rotation rate of yeast cell is measured by Fourier transforming of rotation time-sequencial signal. Besides, how laser power, topological charge and height of the vortex trap from bottom affect the angular rate of rotation is discussed in detail. The experimental results indicate that the rotation rate is proportional to laser power, but inversely proportional to the square of the topological charge. The rotation rate reaches maximum when the height of trap is about 14 μm. The sign of topological charge determines the direction of rotation of yeast cell. When the sign of topological charge is positive, the yeast cell rotates counter-clockwise, and it rotates clockwise when the sign is negative. The results may find their potential applications in the measurement of the torque of bacterial flagella motor.

In order to explore optical transmission characteristics between meridian tissue and non-meridian tissue before and after moxibustion, a self-made device is used to detect optical transmission characteristics with high sensitivity. The optical transport characteristic of pericardium meridian before and after moxibustion neiguan acupoint is reserched, optical transport characteristic of the non-meridian tissue before and after couterizing non-acupoint point is also researched which is 1 cm far away from neiguan acupoint. The optical transmission efficiency in pericardium meridian and non-meridian tissue both decrease after moxibustion, but there is a much more significant decrease in pericardium meridian than non-meridian tissue(P<0.05). These findings suggest that the optical transmission characteristics of pericardium meridian and non-meridian tissue are different, and pericardium meridian appears more sensitive to moxibustion. The results herein can offer beneficial reference in meridian studies and clinical application of moxibustion.

The main residual aberrations of Rowland circle mounts are astigmatism and sagittal coma, which seriously deteriorates the throughput and spectral resolution. An analytic study on the aberration property of a Rowland circle mount which is recorded with the off-Rowland recording geometry is presented. It is found that the astigmatism and sagittal coma can be simultaneously eliminated for two wavelengths, between which the aberrations are both greatly reduced. The Rowland-circle mounts used for broad-band spectrographs can be optimized by properly choosing the using geometry and correction wavelength. A grating working in the wavelength range of 160~600 nm is designed and compared with a conventional grating. The result indicates that significant reduction of the astigmatism and improvement of resolution are both achieved over a wide wavelength range.

Zero time delay can be achieved by using dither stripping method for the readout signal processing of mechanical dithered ring laser gyro (MDRLG). An external dither pickoff reference signal is needed for all existing dither stripping apparatuses. The obtaining of the dither reference will make the application system more complex, and the system will be less stable. A new dither stripping method is developed, in which external reference signal is needed no more; instead the reference signal is generated by the gyro itself. The circuit is simplified by using this method; meanwhile experimental results show that this method can achieve better output results than those of the method using external reference. This method makes the MDRLG easier to be used in the applications of fast control and tracking.

A probe capable of two dimensional scanning for endoscopic optical coherence tomography based on the asymmetry fiber cantilever driven by single piezo bender actuator is developed. However, Lissajous pattern realized by driving signal of sine form is hard to balance between uniformity, coverage and frame frequency, which hinders the optimization of scanning pattern. Based on response characteristic of the asymmetry fiber cantilever, the paper presents an amplitude modulated sine function as the driving signal for optimization of the scanning pattern. Simulations on scanning patterns under the same frame rate based on different driving signals are conducted, and evaluations in terms of uniformity and coverage are given. The comparative experiment is conducted too, and the results demonstrate the feasibility of this method.

0.7 mm thickness invar alloy sheet is welded at 2.2 m/min laser scanning speed by using butt and lap joint. Microstructure analysis is conducted by optical microscope and scanning electric microscope. Hot tearing mechanism and susceptibility of butt and lap joint are discussed, respectively. Results show that the weld metal is composed of as-cast single phase dendrite austenite. Some hot tearing is in the weld center of butt joint, but none is in the lap joint. At the last solidifying stage of impinging dendrite, generally, dendrite grain boundary energy γgb is always two times larger than liquid/solid interfacial energy γsl of liquid film. The liquid film coalescence will not occur until adequate undercooling ΔTb, which results in hot tearing of butt joint under welding residual tensile stress. However, the remained liquid of upper weld pool can flow down and fill into torn liquid film, then lap joint has a lower hot tearing susceptibility.

Aiming at the deficiency which traditional micropump structures are complex, and difficult to fabricate, a novel actuating approach is proposed basing on mechanical effect of laser-induced shock waves, micropump designed by this approach has the characteristics of simple structure, ease to manufacture, low cost and the benefit of miniaturization and integration with micro electro mechanical system (MEMS) system. The modal of surface pressure produced by laser induced shock waves is investigated. The valve-less micropump is designed, and its coupling modal is calculated. The feasibility of this actuated approach is validated. The influence of laser parameters (frequency, duty cycle, intensity, spot diameter) on flow rate is analyzed by the fluid-structure interaction simulation and the stability of flow rate is also investigated. The result reveals that laser intensity and spot diameter are the main influencing factors on the flow rate, flow rate maximizes when duty cycle is 0.6, the difference of flow rate at each single pulse is less than 5% at steady operation.

A novel high-power wide-band laser beam shaping method using a fan-shaped quasi-parabolic mirror is exploringly proposed. The design principle and preliminary experimental results of the wide-band beam shaping system based on a fan-shaped quasi-parabolic mirror are presented. According to the geometrical optics, the focusing characteristics of a real beam passing through the beam wide-band shaping system are investigated by ray tracing. It is demonstrated that, after transformed by the wide-band beam shaping system, the original high-power circular laser beam can be shaped into an arc-shaped scanning strip of uniform intensity distribution and large size (20~500 mm). By using a transverse flow CO2 laser, the optical transformation characteristics of the actual wide-band beam shaping system are invested. The experimental and theoretical results are in good agreement.

The laser gas nitriding is carried out on the surface of TA2 titanium alloy by use of the DL-HL-T 5kW continuous wave CO2 laser equipment. The stereo microscope，scanning electron microscopy, X-ray diffraction and energy spectrum analysis are adopted to analyze the surface morphology, microstructure and phase composition. The microhardness and uniformity of the hardness of the nitrided layers are measured by the microhardness tester and the nano indenter. The corrosion resistance of nitrided layers is analyzed by M283 potentiostat and M352 analyse software. The result shows that TiN is formed on the surface of TA2 which serves as a reinforcing phase. It is made up of nitrided layer, heat affected zone and the base metal after the laser gas nitriding treatment. The nitrided layer mainly consists of TiN and α′-Ti which has a uniform hardness with a thickness of 30 μm. The heat affected zone is mainly composed of needle α′-Ti. TA2 laser gas nitriding improves the uniform and localized corrosive resistance of the base metal.

Temperature and stress distribution of Nd∶YVO4 crystal are simulated according to the difference of optical absorption properties of Nd∶YVO4 crystals pumped by 808 nm and 888 nm, respectively. The changes of crystal temperature distribution and thermal focal length are also simulated when the pumping beam polarization components in a-axis and c-axis are changed. From simulation results, the crystal temperature gradient with 888 nm pump-wavelength is one sixth than that of 808 nm and the crystal temperature stress value is much less than that of 808 nm pump-wavelength. The resonator and output power are not affected by the change of pumping beam’s polarization because the light absorption coefficients on a-axis and c-axis of Nd∶YVO4 are the same when pump wavelength is 888 nm. This is one of the effective ways to reduce Nd∶YVO4 crystals thermal effect and increase Nd∶YVO4 laser power with 888 nm pump-wavelength.

Beam quality (BQ) of the coherent beam combination system of lasers in two-dimensional distribution is studied with BQ as the evaluation factor for beam quality of the output laser. By using passive phase locking technology with optical feedback in a ring cavity, the experimental setup of coherent beam combination of four lasers in two dimensions is built, and the combination of four fiber lasers is realized. When the diameter of ideal beam is selected as the circumscribed circle diameter of sub-beams in near-field, circular flat-topped beam or Gaussian beam is taken as the ideal beam model. Corresponding to different bucket sizes of laser spot in far-field, BQs are measured separately. The results show that, the selection of ideal beam model in the definition has little effect on BQ, but the selection of bucket size of laser spot in far-field has greater impact on BQ. The BQs of different coherent beam combination systems should be evaluated with a clear definition of BQ.

It is the most difficult point of high brightness high power semiconductor lasers to improve horizontal directional beam quality and performance characteristic of broad area laser diodes (LDs). According to diffraction losses characteristic of those different modes, lasing light propagates in the passive waveguide of broad area semiconductor laser. And AlxNy dielectric film stress is used to prepare no-absorption passive waveguide by changing base band gap of semiconductor materials. Combining both the principle and the technology, broad area semiconductor lasers with no-absorption mode filter (passive waveguide) have been designed whose average peak power output increases by 49% for new structural device, vertical divergence angle is up to 20.6°, and horizontal divergence angle is up to 3.3°. It is less than 0.085% of aging speed per thousand of the LDs after testing of 3500 h aging.

A continuous-wave (CW) Tm2O3-doped FGe glass laser is demonstrated. An uncoated one percent of mole fraction Tm2O3-doped GeO2-Ga2O3-BaF2-MO/F2 (FGe) glass is employed as the laser medium. Pumped with a Tisapphire laser at 790 nm, CW laser is realized using two kinds of output couplers (OC). Under the 3% OC, output power of 83 mW is obtained, corresponding to a slope efficiency of 13.7%, and the optical conversion efficiency is 8.8%. The measured central wavelength is 1968 nm.

A laser diode(LD) dual-end-pumped electro-optic Q-switched NdYVO4 solid-state ultraviolet laser is reported by using a U flat-concave resonator, with type I phase-matched LiB3O5(LBO) as the second harmonic generation crystal and type II phase-matched LBO as the third harmonic generation crystal. A block of La3Ga5SiO14(LGS) crystal is used as a Q-switch. The 1.29 W output power of 355 nm is obtained at the pump power of 20.4 W and repetition frequency of 10 kHz with pulse width as short as 9.6 ns. The optical-optical transformation efficiency is about 6.3%.

In order to obtain the rectangular beam required for liquid crystal display(LCD) repair technology with good beam quality and uniform energy distribution, a new beam shaping system has been proposed. In this system, related diffraction patterns can be obtained by calculating and analyzing the diffraction effects in theory at different positions through rectangular aperture, and a proper diffraction surface, which will be used to process the sample, can be extracted and transferred by using 4f image relaying system. In addition, a relevant experimental device has been designed to prove the feasibility of this system. The results show that there exit some of the complex diffraction patterns after passing through the aperture, and some diffraction planes with very good energy uniformity distribution can be selected in the 56.0~58.5 mm range of the equivalent distance. The effective delivery is achieved by the use of 4f imaging system, the fluctuation range of energy on the top of shaped beam is less than 5%, and energy efficiency is about 80%.

With repetition rate of 1000 Hz, detailed experimental investigation on single large aperture tapered fiber phase conjugation mirror (PCM) has been done. Comparison of stimulated Brillouin scattering (SBS) reflectivity between tapered fibers incised by simple ruby cutter and imported LDC-200 fiber cutter is shown, which implies that the quality of fiber′s end surface plays an important role in enhancing SBS reflectivity. For fibers incised by LDC-200 fiber cutter, comparison of SBS reflectivity with pump pulse widths of 24 ns and 15 ns is also given and maximum SBS reflectivities of 70% and 50% with pump energy about 40 mJ have been achieved respectively. Keeping the pump pulse width to 15 ns and applying the tapered fiber PCM, the double pass output energy, pulse width and beam quality are measured. 1000 Hz, 42 mJ, 1.5 ns laser output has been obtained and obvious beam quality improvement has been observed.

Bottle beams with different sizes can be used to trap particles at different scales. A new method of changing the size of bottle beam using a popular sphere lens telescope system is proposed. The analysis is based on the geometrical optics, and simulated by ray tracing with optical design software ZEMAX. The bottle beams were captured and measured before and after the telescope system. It is shown that the size conversion ratio of bottle beam corresponds to the ratio of focal length of the two lens (magnification of the telescope). The theoretic analysis and numerical stimulation agree well with the experimental results.

The model of laser beam with distorted wavefront has been given, where the root-mean-square (RMS) gradient and the random phase perturbation have been introduced to describe the low and the high frequency phase distortions, respectively. According to the known low frequency phase in near-field, the intensity distribution in near-field and the intensity distribution in far-field, the successive iteration method has been proposed to recover the high frequency phase in near-field, and the recovery effect of high frequency phase has been analyzed quantitatively in the terms of the residual error, peak-valley (PV) value, RMS and power spectral density (PSD) of the wavefront. In addition, the adaptability of the retrieval method has been convinced by recovering different distorted wavefronts. The results show that the high frequency phase of distorted wavefront can be recovered effectively by using the successive iteration method, and the wavefront distortion including the low and the high frequency phases can be readily obtained. Furthermore, the successive iteration method is valid to recover different distorted wavefronts.

A dual-wavelength fiber laser with a narrow bandwidth, based on a high finesse fiber ring filter has been proposed. Polarization-maintaining fiber Bragg grating（PM-FBG） and a high finesse fiber ring filter are introduced based on the traditional fiber laser. PM-FBG is used as the wavelength selection device to produce dual-wavelength. The fiber ring filter consists of two optical couplers and a section of weak pumped erbium-doped fiber(EDF). Because of the delay of cavity length and the gain generated by the EDF, the filter has spectral response with a high finesse. The incorporation of the fiber ring filter leads to the suppression of undesirable mode and makes the output laser narrow bandwidth. Under 980 nm LD pumped, the maximum outputs of the two wavelengths are 5.27 mW and 1.02 mW, respectively, at the room temperature. And the wavelength spaces of the two wavelengths are tunable within the range between 0.16 nm and 0.32 nm.

Laser beam pointing systems are generally affected by pointing errors. The pointing errors cause energy loss and the decline of the system performance while the center of the laser beam is not on the target. The pointing errors can be estimated from the scatter return photons back from the illuminated target. The performance of pointing error can be improved with close-loop control on the measurement of the return signals. In this paper a method to reduce pointing error based on the return signals from the illuminated target is studied. The stochastic parallel gradient descent (SPGD) algorithm is applied in this method. Some effects to influence the precision of pointing errors are analyzed. The analysis is verified by experiment.

Heterogeneous heating of the laser beam is one of the most important effects on the beam propagating through the atmosphere. For the intensity distribution of the flat-topped rectangular beam, the rotary laser beam is adopted to weaken the thermal effects induced by the heterogeneous beam intensity distribution. Based on the computational fluid dynamics(CFD) software of Fluent, thermal effects of the beam in the line pipe with axial pipe flow are modeled. The results indicate that the second order astigmatism which is one of the greater components of optical path difference(OPD) induced by the heterogeneous beam intensity distribution is almost vanished because of the rotary laser beam, while the defocus and the spherical aberration which are the other greater components of the OPD are still exist. The effect of rotary laser beam does not affect the time of the thermal effects reaching the steady state. So the rotary beam effect can improve the beam propagating property.

Basing on the dynamic model of the vertical cavity surface emitting laser with optical feedback, the parameter range for the laser being in chaos is confirmed by analyzing the bifurcation of the photon density for feedback strength. Then a chaos driving synchronization scheme for the lasers is presented. The synchronization of two driven lasers can be well realized by the scheme. The parameter ranges for two driven lasers being in the synchronization are also confirmed by analyzing their correlation coefficient. At last, the influence of parameter mismatch on synchronization is investigated. The result shows that the scheme has a good robustness.

The characteristic of the intensity noise suppression at the low frequencies of Tisapphire laser by using the optoelectronic feed-forward is theoretically analyzed. It shows that the best gain of the feedback circuit corresponds to the injecting noise. The suppression of intensity noise at low frequencies of Tisapphire laser by optoelectronic control is experimentally investigated, and the intensity noise of laser is suppressed as soon as possible by tuning the gain of the feedback circuit. The amplitude of the intensity noise reduces from 8.7 dB to 1.4 dB, and the maximum noise suppression of 7.3 dB is obtained at 1.125 MHz. It has been demonstrated that selecting the best delay time and feed-forward gain, the intensity noise can be suppressed near the quantum noise level at any sideband frequency.

Tm3+/Ho3+/Yb3+-codoped tellurite glasses are prepared by conventional melt-quenching method. The heavy metal oxide Bi2O3 with lower phonon energy is introduced into the tellurite glass with a composition of TeO2-ZnO-La2O3, and the effect of the Bi2O3 content on the Raman spectra of the matrixes and the upconversion luminescence spectra of the Tm3+/Ho3+/Yb3+-codoped samples are studied. The results show that the intense red (662 nm), green (546 nm) and blue (480 nm) emissions of the tellurite-based glasses are simultaneously observed at room temperature under 975 nm laser diode(LD) excitation. With the increase of the Bi2O3 content, the phonon energy of host glass decreases, and the three fundamental color upconversion luminescence intensities of the Tm3+/Ho3+/Yb3+-codoped glasses enhance accordingly, in which the effect of the Bi2O3 content on the enhancement of the blue luminescence intensity is greater than that of the green and red.

A rapid fabrication method for conducting poly(vinylidene fluoride) by creating active centre using KrF excimer laser direct etching technique is demonstrated. Study shows that the etching point-defects and line-defects perform active centre function for facilely controlling conducting layer when laser irradiation decreases the laser threshold. The results of laser scanning confocal microscope(LSCM) and scanning electron microscope(SEM), indicate that the 2D net-like microstructures surround the defects are the precursor of conducting layer, which significantly affect the velocity of preparation. The effect of laser thermal cross-linking reaction and laser irradiation cross-linking reaction together contributes to the rapid formation of great conducting layer.

Eu2+-doped BaYF5 nanoparticles are prepared via microemulsion method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence spectroscopy are used to characterize the samples. The results of XRD are in agreement with the PDF # 46-39 of BaYF5, and the average size is about 20 nm estimated by Scherrer formula. The SEM images show that the nanoparticles are spheric morphology, while the shape is regular and the particle size is homogeneous. The emission band of BaYF5Eu2+ nanoparticles locate in the range of 300~410 nm. The predominant peak corresponding to the 4f65d→4f7 transition of Eu2+ locates at 330 nm, which exhibites a blue shift of 48 nm compared with that of the polycrystalline materials prepared by traditional solid-state reaction that centers at 378 nm. The main excitation peak locates at 263 nm, which shows a blue shift of 59 nm compared with that of the polycrystalline materials that centers at 322 nm.

Based on the theory of Fabry-Perot cavity, the resonant characteristics of microcavity structure are studied, which is formed by reflectors composed of two slabs of the same single-negative materials. If the reflectors are composed of ε-negative (ENG) material, the omnidirectional transmission of TM mode can be realized under certain conditions; for the case of μ-negative (MNG) material, the omnidirectional transmission of TE mode can be realized. The omnidirectional transmission spectrum narrows and quality factor increases with the increase of incident angle. The increase of the refractive index of material in cavity effectively reduces the size of microcavity structure for omnidirectional transmission of TM mode, but the modulation is less obvious for that of TE mode. The existence of single-negative material loss does not break the characteristics of omnidirectional resonance of two microcavity structures, but the transmissivity of resonant mode reduces with the incident angle. Through optimized processing, the conditions are found for these two types of microcavities to realize the omnidirectional transmission, which provides useful theoretical guidance to the design of omnidirectional filters.

In hyper numerical aperture (NA) lithography imaging, the incident angle of imaging rays on pellicle varies in a wide range, so it is difficult to enhance the transmittance of oblique incidence employing the conventional pellicle optimization methods. A novel pellicle optimization method is developed based on the film optics theory, which maximizes the average transmittance within the whole incident angles range. The transmission properties and phase characteristics of pellicle are studied using Johns matrix representation. The corresponding Johns pupil is obtained to analyze the polarization aberration induced by pellicle. The results show that, compared with the conventional pellicle optimization methods, the novel method enhances the transmittance of oblique incidence and decreases the pellicle-induced polarization aberration more effectively. The novel method provides the essential theoretical basis and technical support for pellicle setting in hyper NA lithography imaging.

Zn0.99Fe0.01O thin films on Al2O3 substrates are successfully prepared by using pulsed laser deposition(PLD) technique.And the influence of annealing oxygen pressure on the crystal structure and laser-induced voltage (LIV) effect of Zn0.99Fe0.01O thin films is studied. X-ray diffraction (XRD) analysis shows that Zn0.99Fe0.01O thin films are hexagonal wurtzite structure and ［001］ orientation. Meanwhile, with annealing oxygen pressure increasing, the grain size D of Zn1-xFexO thin films first increases and then decreases. At annealing oxygen pressure of 2000 Pa, the grain size D of Zn1-xFexO thin films achieves maximum, and crystallization quality is the best. In addition, at annealing oxygen pressure of 3000 Pa, the largest LIV signal of 79.5 mV is measured in Zn0.99Fe0.01O films grown on 10° vicinal-cut Al2O3 single crystal substrates.

In order to protect the military opto-electronic instruments from laser blinding weapons, the high and low refractive index combinations of Si and YbF3, ZnS and YbF3 are selected to design and fabricate laser protective infrared antireflection coatings. On the substrate of multi-spectral ZnS, coatings with laser protective function to 532 nm and 1064 nm laser while with high transmittance in the 3~5 μm spectral band are fabricated, and electron beam and ion assisted deposition technique is used in this process. The deposition process of Si by electron beam is studied, and the deposition process of YbF3 in different materials combination is optimized. The adhesion problem between coatings and substrate is resolved. Devices of antireflection for detection and protection are both integrated into the coatings, and the structures of opto-electronic instruments for satellite and aeroplane can be simplified. Results of spectrum analysis and environmental test show that all the parameters meet the requirements.

An integrated single-frequency laser interferometer is researched based on polarized light theory. A four-subdivision configuration of the interferometer is achieved by using method of polarization states conversion which can improve the precision of the system. A four-orthogonal detection system is built up and the passive polarization modulation is accomplished which can expand the range of measurement. The integration of the interferometer is achieved by integration optical path. The vibration measurement experiments of the laser interferometer are carried out under laboratory condition. The error of the static displacement measurement is less than 0.3 nm, and the resolution of the vibration measurement reached is up to 10 pm/Hz1/2. The results show that the integrated interferometer has advantages of high accuracy, good stability, large measurement range and resistance to environment effect. Therefore, the integrated interferometer can be widely used in various fields of nano measurement.

Based on theoretical model of beat frequency using two independent lasers, beat frequency linewidths of Lorentz and Gaussian linetypes changing with different attenuation values are obtained theoretically. It is significant that smaller attenuation value should be chosen to calculate laser linewidth if laser linetype is unknown previously and larger attenuation value for known laser linetype. In the experiment of beat frequency using two external cavity diode lasers (ECDL), linewidth ratio is measured under typical attenuation values, which can be used to judge linetype of laser. Using the method above, linewidth of laser is achieved with an error about 0.23% compared with its calibration data, therefore linewidth measurement precision of laser is enhanced. The method is still applicable to other linetypes analysis.

The scanning rotation mirror is one of the most important components in laser scanning detecting system. Based on the principle of geometrical optics, an analytical expression for the scan trace of hexahedral column rotation mirror is derived. The relationship between the position of incident beam to rotation mirror and the scan trace is also analyzed. In addition, the relation curve of scan trace versus scanning angle is produced. The structural characteristics of the system are the origin of creating scanning nonlinearity and asymmetry. In order to reduce the nonlinearity of scan trace, a curved rotating mirror scanning system is proposed, and the scan trace for curved rotating mirror is computed. The numerical results for the designed rotation mirror system show that the system can solve the nonlinearity problem of plane rotating mirror effectively.

A new method based on the measurement of velocity of laser-generated ultrasound is proposed to determinate the second order elastic (SOE) constants and density of isotropic materials. A serial of ultrasonic pulses can be detected by self-made PZT transducer fixed in the detection point when scanning the line source focused from NdYAG laser with electronic control translation stage. Then the velocity of Rayleigh waves is computed by waveform cross-correlation technique; the velocities of longitudinal wave and shear wave reflected by the bottom surface of the sample are obtained by different traveling time with their propagation distance. At the end, the SOE constants and density of isotropic material are determinated according to the Christoffel theory of elasticity. Results show that the values of SOE constants and density which signed with C11, C44 and ρ agree well with the corresponding parameters reported in the existing papers. What′s more, the relative accuracy of the determinated parameters indicated from error analysis demonstrates the feasibility and reliability of this method.

A high resolution ultra low frequency phase generated carrier(PGC) demodulation technique for interferometric fiber sensors is proposed. The differential cross multiplication(DCM) algorithm and the Arctangent algorithm of PGC technique are analyzed theoretically and simulated by computer for ultra low frequency demodulation. And the results show that an unnecessary random direct current (DC) drift is induced in the recovered signal of DCM-PGC, but it doesn′t exit in that of Arctangent-PGC. To demonstrate the conclusion, an optical fiber interferometer-based ultra low frequency sensing system is set up, and the comparable experiments of DCM-PGC and Arctangent-PGC are carried out. The experimental results show that only Arctangent-PGC can be used for ultra low frequency demodulation, for it avoids the problem of DC drift as DCM-PGC. At last the ultra low frequency demodulation system is achieved by Arctangent-PGC, and the testing results show that the system has the lowest frequency of 0.01 Hz, a minimum detectable phase shift of 4×10－4 rad/Hz, a dynamic range of 110 dB @ 1 Hz and a linearity of 99.99 %.

A novel approach to generating ultrawideband(UWB) chaotic pulse is proposed and demonstrated by using optical feedback laser diode. The chaotic laser is generated through a commercial C-band laser diode (LD) with external feedback. This continous-wave chaotic laser is modulated by utilizing an electro-absorption modulator. And then, a series of chaotic pulses are generated, their radio frequency (RF) spectrum can be controlled by adjusting the bias current and feedback strength of the LD. The UWB chaotic pulses with center frequency of 4.0 GHz and fractional bandwidth of about 181% and 214% are obtained. The experimental results agree well with the numerical demonstration. The proposed method is simple, and the spectrum property can be controlled easily. It is suitable for UWB-over-fiber communication systems as photonic microwave signal source.

In order to use white LED as a lighting source and communication part, new modulation schemes such as reverse on-off keying with return-to-zero signal modulation (ROOK-RZ), reverse pulse position modulation (RPPM), reverse differential pulse position modulation (RDPPM), and reverse digital pulse interval modulation (RDPIM) are proposed for indoor visible light communications. Based on the given symbol structure, bandwidth requirement and average transmission power are analyzed and compared with on-off keying(OOK). Meanwhile, slot error rate is derived, and compared with each other. Simulation results show that OOK has the minimum bandwidth, while RPPM has the highest average transmission power and best slot error rate performance, but the maximum bandwidth.

Different from the basic sensing theory of the fiber Bragg grating (FBG) sensors based on spectral analysis, a new method utlizing the polarization dependent loss (PDL) of FBG for transversal pressure measurements is proposed. The evolution of the PDL with wavelength with respect to transversal pressure is studied theoretically and experimentally. A theoretical model for transversal pressure sensing by use of PDL is built and numerical simulation is also carried out. The theoretical analysis suggests that the PDL of FBG is more suitable for measuring transverse pressure than single spectral analysis in the low pressure region because of its greater sensitivity. Under the transverse pressure conditions of 0~180 N, the demodulation is realized by use of the centroid height and the wavelength spacing of the two peaks respectively. The resolutions of 0.06 dB/N for small pressure (0~80 N) and 2.5 pm/N for large pressure (81~180 N) are demonstrated. Good agreements between experimental results and numerical simulations verify the feasibility of the method.

The fabrication technics of fiber grating coupler(FGC) based on fused biconical taper coupler and phase mask fiber grating technics is designed through the improvement of trial-manufacture and the analysis of influencing factors in detail. The FGC which can be used as optical add-drop multiplexer(OADM) is successfully produced and the experiments of optical add multiplexer(OAM)/ optical drop multiplexer(ODM) are all carried out. The valuable reference for the design and fabrication of FGC is provided.

Simulation research helps to aid and optimize the designing of gain-modulated scannerless lidar, and helps to analyze the configuration and imaging principle. A theoretical model of the gain-modulated scannerless imaging lidar system is established. A simulation software for gain-modulated scannerless lidar is programmed according to the theoretical model. Simulation results and experimental results show that it is helpful for the designing and parameter optimizing of gain-modulated scannerless lidar.

In the area of ladar target recognition, orientation estimation is always needed to align the point cloud with models for recognition. The relationship between the target′s orientation and the point cloud projection distribution is analyzed, a feature called projection density entropy (PDE) is extracted to measure this distribution. A novel method for target orientation estimation is proposed according to the relationship between the target′s orientation and PDE. The point cloud is rotated around one coordinate axis, then the PDE of the rotated point cloud is calculated, and the rotation angle with the least PDE is taken as the orientation angle. Point clouds of five kinds of ground armored targets under different viewpoints are simulated, and the performances of PDE, rectangle fitting and principle component analysis (PCA) methods under the situations of self-occlusion and occlusion are analyzed. The strategy of parameter selection is discussed, and a fast realization method of PDE is proposed. The experimental results show that the estimation performance and robustness of PDE method outperform rectangle fitting and PCA methods greatly in the cases of self-occlusion and occlusion. PDE is very suitable for application under severe occlusion.

Nowadays, terahertz(THz) imaging is an important research focus among the development of THz techniques. And imaging systems based on array detectors which have real time imaging capability have attracted lots of research interests. It is essential to reduce power losses during the system design. Owing to the low energy losses and design convenience it brings, off-axis parabolic mirrors have been frequently used in many THz imaging systems. A 2D THz array imaging system comprised of off-axis parabolic mirrors is analyzed using an optical design software ZEMAX. The deterioration of the image quality caused by the misalignment of off-axis parabolic mirror in the receiving part is investigated. The simulation results show that the image resolution can reach 0.5 mm for the ideal case, and the grid distortion is 0.069%. The system has a tolerance of 1.1° for the misalignment angle of the off-axis parabolic mirror. The tolerance for the decenter error is 6.5 mm.

High-power nanosecond pulsed terahertz (THz)-wave radiation is achieved via a surface-emitted MgO∶LiNbO3 terahertz parametric oscillator (TPO). THz-wave radiation from 0.8 THz to 2.8 THz is obtained. The maximum THz-wave output is 173.9 nJ per pulse at 1.73 THz while the pump power density is 197.4 MW/cm2. The corresponding energy conversion efficiency is 2.2×10-6. During the experiments the first-order and the second-order Stokes waves are observed. The frequency shift of the first-order Stokes wave is equivalent to the frequency of generated THz-wave.