This paper describes the application of an improved synthetic aperture technique based on phase compensation. This technique corrects the phase distortion of the echoes caused by ultrasound degradation to enhance the resolution of endoscopic ultrasonography. The degradation of the echoes in lateral and axial directions is investigated to obtain the impact of center frequency and lateral resolution caused by ultrasound degradation. Two different cross correlations are implemented to compensate the phase distortion in both lateral and axial directions. One is achieved in the form of segmented cross correlation in axial direction to evaluate the instantaneous change of phase. The other one is used to compensate the remnant phase distortion after range curve correction to enhance the performance of lateral pulse compression. The results of simulation indicate that phase compensation can improve the resolution and signal-to-noise ratio (SNR) of ultrasound images. The increases are 0.2 mm and 1.6 dB in resolution and SNR, respectively, compared with the uncompensated images. It can be concluded that phase compensation has the potential to enhance the resolution and SNR.

Two type degeneration processes: dehydration and proteolysis are studied, and the description based on polarization sensitive optical coherence tomograph (PS-OCT) measurement is presented respectively. Birefringent changes due to dehydration or proteolysis process are different. For the former case, the average birefringence increases with dehydration, caused by the size and index changes of muscle fibers. However, the hydrolysis process shows an opposite tendency. The average birefringence decreases with proteolysis, which can be explained by the damage of fibrous microstructures and the appearance of isotropic scattering elements. The above experimental results reveal different optical and microstructural changes in these two degeneration processes, and can be used to evaluate the muscle quality.

An improved Linnik interferometer for phase-shifting digital holographic microscopy in reflection configuration is demonstrated. Some phase-shifting configurations which have been used are analyzed and compared. Higher phase-shifting precision can be achieved in this improved Linnik interferometer, so the microscopic imaging quality can be improved. In experiment, to prove its feasibility, the 3D microscopic imaging of the USAF-1951 target surface structure has been realized, the amplitude and phase distributions of object wave are reconstructed.

In order to study the influence of laser shot peening (LSP) on the corrosion resistance of Mg alloy, some AM50 samples are processed with Ndglass pulsed laser. The experimental results show that plastic deformation occurred in the surface layer, density and hardness are improved, great compressive residual stress is formed, and the residual stress on the surface reaches 146 MPa with laser power density of 3 GW/cm2. The electrochemical polarization results show that the corrosion potential and pitting potential of the LSP sample increase by 64 mV and 92 mV as compared to the untreated sample, respectively, while the corrosion current density decreases about 88.6%. After 20 hours continuous spraying in the salt spray environment, more and larger pits appear on the surface of untreated sample, and the corrosion area is reduced by 84.7% after laser shot peening. The corrosion resistance of AM50 Mg alloy is improved markedly by laser shot peening.

In order to research laser welding of dissimilar magnesium alloys NZ30K and AZ31, the microstructure and property of the joint of AZ31 and NZ30K welded with a CO2 laser is analyzed. A sound weld is formed with the laser power of 4~5 kW and the welding speed of 4 m/min. The joint microstructure, the precipitated phase and weld element distribution are analyzed, the hardness and tensile strength of the joint are also measured. The optical microscope (OM) observation shows that the weld metal is a fusion of the two different alloys, which presents an incomplete mixture and the alloys interweave in wave-form with each other. By X-ray diffraction (XRD) analysis, α-Mg, Mg17Al12 and Mg12Nd phases are identified in the joint. The scanning electron microscope (SEM) shows further fine structure and regions of different chemical compositions in the weld. An obvious concentration gradient of alloying elements crossing the joint is observed too. The hardness of the joint is not lower than that of the base metal. The tensile strength of the joint is 169 MPa, which is lower than those of the base metals.

According to the developing direction of laser remanufacturing technique with automation, flexibility and intelligence. An integrated high-power flexible laser remanufacturing system for industry application is studied, which is developed by means of the existing interface of the robot, the laser and the design of hardware and software for system integration. Coaxial powder feeding system and temperature vision system are developed to three-dimensional cladding and temperature measurement in laser molten pool. Some samples are built by the flexible laser remanufacturing system. It is showed that the system is efficient.

Influence of heat treatment on microstructures and properties of 17-PH alloy by laser solid forming (LSF) process is investigated. Results of optic microscope (OM) and scanning electron microscope (SEM) show that main microstructure of LSF 17-4PH includes quenched martensite, tempered martensite and second precipitated phase. As aging temperature increases, martensite becomes smaller and more uniform. Rate of transformation from quenched martensite to tempered martensite is accelerated. Precipitated phases begin to coarsen, grain boundary becomes distinct. After heat-treatment, alloy plasticity is highly improved, and the strength and hardness reach maximum when aging temperature is 480 ℃. With the aging temperature increasing, strength property and hardness get worse, while plastic property gets better. Analysis on fractography shows fracture of all tensile samples results from ductile fracture. In addition, fiber area and shear lip of fracture become bigger, and size and depth of dimples increase gradually with the aging temperature increasing.

By using femtosecond laser pulses with two different wavelengths separately interacted with the silicon sample, it′s experimentally demonstrated that under the same laser fluence, the fabricated surface microstructure of silicon is determined by the relation between laser power and pulse number. During the fabrication process, pulse number represents the interaction time between laser pulses and sample, which determines the depth of energy transferred into the inner part of material; while the laser power represents the ability of laser to ablate and volatilize the material. The optimal selection of the laser power and pulse number can produce the microstructured silicon with a high spike height, which can realize the effective absorption of micro/nano silicon-based PV material in a wide wave band. These results are important for the efficient fabrication, surface morphology control, and the corresponding photoelectrical properties of surface-microstructured materials.

We have developed a novel process: nano powder implanting via laser shock peening process, by which the nano powders are squeezed into the surface layer of light metal alloys by the very high pressure (up to giga pascals) induced by the laser shock peening process. Laser shock peening hardens the material surface by the laser-induced shock wave and the residual compressive stress, it is typically a cold process, which is capable of avoiding the defects like the melting loss of the lower-melting-point elements, porosity, cracking and surface deterioration associated with a conventional thermal hardening approaches of aluminum alloys. This also eliminates the problem when hardening a material with nanoparticles, that is, the easy melting of nano particles in a melt pool and then solidified a microstructure without nano characteristics. This paper reports the work on nano WC powder implanting onto aluminium alloy surface by laser shock peening, focusing on the process development, parameter influence, microstructure, hardness, residual stress and wear resistance. The research approves that after implanting of WC nano particles by laser shock peening, the surface hardness of aluminum alloy is enhanced by 20%, wear resistance increases 5 times than that of original aluminum and 1.5 times than that of the only laser shock peened surface. The surface tensile state of aluminum alloy is changed to be beneficial compressive state at the same time.

The design of unstable resonator has carried out by Nd:GGG. Coupling system is optimistically designed to get the uniform of gain distribution to 94%. Thermal simulation module is established and temperature-distribution of laser medium is calculated. The simulation module is attested by the experimental results. Then the design parameters of unstable resonator are optimized by theoretically analytical module of unstable resonator. The experimental results show that the output power is more than 10 kW and the average beam quality is 5.84 times diffraction limit.

An all fiber high peak power nanosecond pulsed source based on large mode area (LMA) fiber cascade amplification configuration is presented. 10 ns/100 nJ arbitrarily shaped pulses generated from a single mode fiber (SMF) front end are injected into a LMA fiber cascade amplifier. The amplifier is composed of LMA Yb doped fibers with core diameters of 15, 30 and 140 μm. By cascade amplification, shaped nanosecond pulse with 3.2 mJ pulse energy and 0.3 MW peak-power is obtained. The maximum output capacity of the fiber system is further studied. By injecting Gaussian pulse into the fiber amplifier, high energy of 10 ns/7.2 mJ/0.7 MW output and high-peak-power of 1.16 ns/3.7 mJ/3.2 MW output are obtained.

A picosecond mid-infrared optical parametric oscillator (OPO) synchronously pumped by an Yb-doped fiber laser is reported. The OPO is pumped by an all fiber master oscillator power amplifier (MOPA) centered at 1064 nm picosecond pulses with duration of 20 ps at a repetition rate of 52 MHz. A 50 mm periodically poled MgO-doped LiNbO3 (PPMgLN) with a poled grating period of 30.5 μm is used as the nonlinear crystal and a single resonant cavity is adopted. At room temperature, 0.67 W average idler is obtained at pump power of 5.2 W with the conversion efficiency from pump to idler being 12.9% and the slope efficiency being 14.5%. By controlling the temperature of PPMgLN crystal, the wavelength tuning range can cover 1.544~1.608 μm (singal) and 3.15~3.43 μm (idler). Additionally, the stability of this OPO system is discussed.

Nondiffracting Bessel beam is less disturbanced when propagating in the atmosphere. It′s very suitable for alignment and measurement on large scale. To overcome the limited nondiffracting distance generated by the traditional axicon, two kinds of combined axicons based on the transmission properties of conventional axicons, are proposed for generating long-distance nondiffracting Bessel beam. Transmission properties of combined axicons are analyzed and simulated by optical ray tracing and diffraction theory. The results show that two kinds of combined axicons are equivalent to conventional positive axicon on transmission properties, but both of them can generate high quality and long-distance nondiffracting Bessel beam. Meanwhile, they also reduce the difficulties of element processing.

The spatially induced group velocity dispersion (SIGVD) of ultrashort pulsed Airy light beam propagating in free space is theoretically studied with wave equations. The factors influencing SIGVD are also analyzed. Moreover, the numerical simulation results confirm that the second-order SIGVD broadens the pulsed Airy beam in temporal domain; and the third-order SIGVD brings the unsymmetrical temporal trailing oscillatory structure of beam, which is just the Airy beam in temporal domain. As a result, it can bring the Airy-Airy-Airy beam in free space, which is Airy distribution both in spatial and in temporal domain, by utilizing the third-order SIGVD on the condition of compensating the second-order SIGVD.

Based on the coherence theory of non-stationary fields, the closed-form expression for the cross-spectral density matrix of spatially and spectrally partially coherent electromagnetic cosh-Gaussian pulsed beams propagating in free space is derived. It is shown that the spectral density, the spectral degree of polarization and the spectral degree of coherence of electromagnetic cosh-Gaussian pulsed beams depend on the position of the field point and the beam parameters, such as the decentered parameter, spatial correlation length and temporal coherence length. Spatially and spectrally partially coherent electromagnetic Gaussian-Schell-model pulsed beams, spectrally fully coherent electromagnetic pulsed Gaussian beams and spatially fully coherent electromagnetic Gaussian pulsed beams can be treated as special cases of our results.

The resonator is optimally designed for the construction of four disks in series, using the method of ABCD transmission matrix. With four Nd:YAG disks in the concave-concave symmetrical resonator, the output power of 2.15 kW is obtained, which proves that the laser diode-pumped disk laser has the ability of output scaling and amplification.

Certain irradiance profile of laser output is needed to increase the entire efficiency of laser system. Beam shaping with adaptive optics based on stochastic parallel gradient descent (SPGD) algorithm is developing rapidly because of its outstanding applicability, however, shaping effect of this method largely depends on the target beam size. A new method of far field irradiance profile control is presented. The input beam is shaped in the near field with SPGD algorithm, and then imaged by a 4f system. The effect of far field irradiance profile control is studied for the input beams with and without wavefront aberration. Size control of the far field irradiance profile is analyzed. The result reveals that the new system could realize beam shaping whether the input beam has wavefront aberration or not. And it could realize size control of the far field irradiance profile. The new system has better applicability and utility than traditional ones.

Boltzmann equation is numerically solved for the plasmas generated in the process of discharging of O2, O2/He and O2/Ar in the gas phase. Thereafter, electron energy distribution function, mean electron energy and power efficiency are obtained. The results indicate that electron energy distribution functions are typically non-Maxwellian. For the same reduced electric field (E/N), the mean electron energy for pure oxygen discharge is lower than O2/He and O2/Ar mixtures. For the same oxygen content, the electron energy distribution function curves versus E/N for O2/He and O2/Ar mixtures cross together. The O2/Ar mixture discharge plasma has higher mean electron energy at lower E/N, while the O2/He mixture has higher mean electron energy at higher E/N. The influence of NO additive gas on the breakdown electric field can be negligible. Therefore, the improvement of O2(a1Δ) yield in the presence of NO gas may be not due to the slight decrease of E/N. An addition of 15% (volume fraction) O2(a1Δ) into O2 causes an increment of the mean electron energy which is not significant. In order to obtain the maximum yield of O2(a1Δ), the optimum E/N value of pure oxygen discharge plasma is about 10 Td. And the optimum E/N value decreases with the oxygen content. The mean electron energy as a function of the discharge frequency has a long steady baseline before its decrease. The power efficiency for excitation of O2(a1Δ) as a function of discharge frequency has two type curves. It decreases all the while at 10 Td. However, it rises and then goes down when the E/N is 50 Td. The optimum discharge frequency is 10 GHz for the conditions of 300 K and 1333.22 Pa.

Average output power more than 50 W, 1064 nm picosecond laser with three power amplifier systems (LD double-pass amplifier, LD double end-pumped amplifier and LD single end-pumped amplifier) is reported. When input 6.67 W picosecond seed pulse, power amplifier′s average power achieves to 53.7 W with optical-optical conversion efficiency of 30.07%, a pulse duration of 10.45 ps. By using of nonlinear crystal LBO for second harmonic generation (SHG) with high average power of 27.16 W, a repetition rate of 80 MHz, a pulse duration less than 10 ps, SHG efficiency higher than 50.58% are obtained. At premise of high SHG efficiency, the system guarantees against damaging SHG crystal, keeps uninterrupted running with stable power more than 8 h.

La2CaB10O19 (LCB) is a favourable nonlinear optical crystal. Dy3+ doped La2CaB10O19 crystal of good quality with a size of 40 mm×25 mm×15 mm has been grown by the top-seeded solution growth method. The 4F9/2-6H13/2 transition of Dy3+ ion can emit 575 nm yellow laser, which may be applied in the medicine and biological detection. The rocking curve measurement showed that the full width at half maximum is 16.2″ in the b plane. The absorption spectra of Dy3+LCB were measured at room temperature. The sample was excited at the 452 nm radiations and the fluorescence spectrum was obtained, in which the strongest peak was at 575 nm. The fluorescence lifetime was 636 μs at the 575 nm emission. The Judd-Ofelt (J-O) theory was applied to the evaluation of the spectral properties. The J-O parameters, absorption oscillator strength, the absorption and emission cross section and radiative lifetime were calculated which show Dy3+LCB crystal is a promised yellow laser material.

The surface spike microstructures are fabricated by irradiating the surface of mono-crystal silicon with femtosecond laser in the atmosphere of SF6 and then coated with aluminium-doped zinc oxide (AZO) thin film by magnetron sputter method. The surface microstructures and optical absorption of coated and uncoated sample are observed and studied. The results indicate that laser energy density has effect on the size and spacing of the spikes on the surface. The main reason for microstructured silicon exhibiting good optical absorption in the wavelength region of 200~1000 nm is multiple-reflection of incident light between the spikes. The rough surface of microstructured silicon and anti-reflection effect of AZO thin film enhance the visible light (400~800 nm) absorption of coated sample and high infrared light reflection of AZO thin film causes a red-shift of reflection peak.

Design and manufacture of ultraviolet imaging filters which meet the needs of imaging and realize accepting and detecting imaging of sun spectrum blind area in ultraviolet alarm detection systems are focused on. Hafnium oxide (HfO2), magnesium fluoride (MgF2), ultraviolet silicon dioxide (UV-SiO2) are deposited on the fused silica substrates (JGS1) with electron beam (EB) heating method and ion assisted deposition (IAD) method to coat ultraviolet filters. Quartz crystal oscillation method and photoelectric extremum method are utilized to monitor thickness of the filter. The filters could meet the demand of high transmittance range from 240~280 nm at an angle of incidence from 0°~25°. At wavelength from 300~620 nm, the filter can act as suppression filter. Through optimization of the coating design and investigation of the process parameters, the problem of film stripping, accuracy controlling of thickness, absorption of material and other issues are solved. The filter basically meets the demand of warning system through performance test.

The ZrO2/SiO2 multilayer thin films deposited by electron beam are studied by high-low temperature alternating experiment under different environmental conditions. The results of scanning electron microscope (SEM) and X-ray diffraction (XRD) show that there is no crystal forming and no change in layer structure before and after temperature test. The transmission spectrum, surface morphology and laser induced damage threshold (LIDT) are acquired by measurement before and after the high-low temperature environmental test and then are analyzed. The results show that after high-low temperature experiment, the spectral transmissivity of thin film components at the center of wavelengths declines, as well as LIDT, and surface deformation develops sag direction.

In order to improve the absorption of oxide thin films in wavelength of deep ultraviolet (DUV), Al2O3 and SiO2 thin films for DUV are fabricated by ion beam sputtering (IBS). The refractive index n and extinction coefficient k of the thin films are obtained using spectrophotometry and ellipsometry in the 190~800 nm. High reflectance (HR) Al2O3/SiO2 coatings are designed and produced at 193 nm. After annealing, the optical loss of the coating becomes smaller. The scattering loss is much lower than the absorption loss which occupies the main role of the total loss. Oxide coatings deposit according to optimized process can have more suitable optical properties at DUV. The optical loss reduces so considerable that the reflectance of HR coatings reach more than 96% at 193 nm.

Ultraviolet communication as a new means of communication receives extensive attention increasingly with its high secrecy, strong anti-interference ability, and other advantages in terms of military. To meet the requirement of ultraviolet communication system, the coatings on a diameter of 210 mm quartz substrates are made to meet the following characteristics: the reflectance at 254 nm is greater than 95% while the average transmittance in 280~600 nm is greater than 98%, which can also applies to angle range from 12° to 30° meanwhile. Through the comparative study on several kinds of the common materials used in ultraviolet areas, HfO2 and MgF2 are selected as the high and low refractive index materials. The film stack is got through the film pile being stacked based on the theory of the design, combining with the needle optimization, and designing the filter of the film. In the preparation of the film, the absorption is reduced by optimizing the parameters, and also the quality improved with ion-assisted deposition used, the film thickness control accuracy is improved by means of the repeatability of parameters accurately control. The results show that the preparation of filter meets the requirements well.

A one-dimensional photothermal model of multilayer media is established based on thermal-wave impedance method, and the particle swarm optimization (PSO) method and total variation (TV) regularization are employed to reconstruct the depth profile of thermal properties of the multilayer media by the analysis of the surface photothermal signals. In the proposed method, the multilayer media is discretized into a series of virtual layers with the same thickness, the depth profiles of thermal properties of the multilayer media are represented in the form of particle, and the optimized thermal parameters are obtained by the particles′ searching in the solution space. The numerical results demonstrate that the algorithm presented in this paper is very effective, and suited to reconstructing thermal conductivity or thermal diffusivity profiles of a multilayer media with unknown number of layers. It is also proved that the algorithm is stable even with noise disturbance. Moreover, the simulation results also show simultaneous profile reconstruction of thermal conductivity and thermal diffusivity is feasible by using the inversion method.

A mechanical chopper is designed based on the programmable logic controller, servo motor amplifier, servo motor and encoder. The interaction potential measurement system is constructed by the mechanical chopper and dual optical tweezers. The characteristic of the system such as the design of the chopper, the switching time of the blinking optical tweezers, the tuning range, the origin position return feature, the compatibility and the usability of the system are discussed. The system is used to measure the interaction potential of a pair polystyrene spheres. The result is consistent with the Darjaguin-Landau-Verwey-Overbeek theory, which demonstrates the reliability of the apparatus. In addition, the apparatus provides an effective technique for measuring the interaction potential between two micro colloidal particles.

In order to ameliorate the performance in vibration measurement, sinusoidal phase modulating technique is introduced into a conventional laser self-mixing interferometer. An electro-optic modulator is placed in the external cavity of the light source to yield sinusoidal phase modulation. The self-mixing interference signal is processed in frequency-domain to retrieve a vibration waveform. The dynamic range of the system is analyzed by proposing the stop-order theory and a relationship between the lowest modulating frequency of the electro-optic modulator, and the parameters of a vibration are obtained to guarantee the validity of a measurement result. Experimental vibration measurement results of a commercial piezoelectric transducer are compared with simultaneous measurement results from Agilent 5529A dynamic calibrator, and an accuracy of 20 nm is achieved. It is shown that the phase-modulated laser self-mixing interferometer is suitable for real-time continuous vibration measurement.

Aspheric surface test is one of the priority research areas for high precision optical surface measurement. Computer-generated holography (CGH) is an important method to test aspheric surface, but its measurement accuracy is restricted by lots of influent factors. This paper focuses on the error analysis of paraboliod surface test with a corresponding CGH. Measurement errors are calculated by Zemax software. A paraboliod is practically tested by a corresponding CGH, and the mainly measurement errors, such as the CGH substrate′s transmitted wavefront error, coma and sphere a berration are analyzed. The measurement results are compared with confocal ball method. Analytical and experimental results indicate that CGH design and fabrication can achieve very high accuracy. After the calibration of CGH substrate′s transmitted wavefront, the root mean square (RMS) value of theoretic test accuracy is better than 4.2 nm. Defocus of CGH and decentration of paraboloid result in the major measurement error. After fine adjustment, the RMS value of practical measurement error will be better than 4.5 nm.

A novel and universal mathematical description of the phase-to-height mapping relationship under divergent illumination is presented, which meets the condition of the imaging system axes being not perpendicular to the reference plane and the link of system′s two pupils being not parallel to the reference plane. In the proposed method, the undetermined coefficients are separated from the coordinate system, which are independence to the coordinate system, so the amount of sampling points for calibration is reduced greatly, and only two calibration planes are required. The experiment has verified the feasibility and validity of the proposed method.

A wavelength demodulated method of fiber Bragg grating (FBG) is proposed to measuring human temperature and heart sound, which can achieve distributed static wavelength demodulation of multi-FBGs and dynamic wavelength demodulation for single FBG. The relation between control voltage of Fabry-Perot (F-P) filter and its output wavelength is rectified by pectinate filter, so the precision of static demodulation is improved. By adding dithering signal the center wavelength of F-P filter could be remained on work point so that it could demodulate dynamic wavelength for a long time. The experiment results indicate that the precision of static wavelength demodulation is ±5 pm and the repeated error is about 5 pm. The theoretical dynamic demodulated range is 225 pm and the actual range is about 203 pm. The theory bandwidth of 3 dB of system frequency response is 1 kHz and the measured value is about 950 Hz. In the heart sound concentrated band of 20~200 Hz, frequency response are basically the same.

An improved method to control the incident light power distribution ratio in each core of a multi-core optical fiber is proposed. This method is realized by tapering the multi-core fiber to be a bi-tapered shape after fusing the multi-core fiber with a normal single mode fiber on the condition of core alignment. Based on a coupling theoretical model and analysis, the controlling method is introduced, and the results are demonstrated by both theory and experiment. This incident power distribution controlling method may provide a helpful and potential application prospect for multi-core optical fibers devices and sensors.

All-solid hybrid photonic crystal fiber with micro-structured core is proposed. The micro-structured core is consisted of pure silica and a high refractive index germanium-doped rod. Using the full-vector finite-element method, the fiber′s guiding mechanism, mode field, confinement loss and dispersion are investigated. Simulation results demonstrate that with the increment of central high refractive index rod′s diameter from 0 μm to less than cladding high-index rod, the fundamental model′s effective index moves up from closing to the bandgap′s lower boundary. Furthermore, the guiding mechanism is transformed from bandgap effect into hybrid mechanism and the confinement loss is reduced. In the short wavelength, the guiding mechanism is dominated by the totally international reflection mechanism, the bandgap edge′s influence on loss reduces and the loss decreases monotonically with the decrement of wavelength. But in the long wavelength, light is guided by the bandgap effect and the loss curve moves down integrally. By adjusting the radius of the central high refractive index rod, zero dispersion wavelength of the fiber can be tailored flexibly. When the radius of the central rod is set to 0.5 μm, the zero dispersion wavelength shifts to shorter wavelength, about 30 nm away from the original value. When the radius is 1.2 μm, the zero dispersion wavelength can be shifted to longer wavelength, about 230 nm away. The tunable band-width is up to 260 nm.

Grin fiber lens is used in achieving the effective coupling between laser diode (LD) and single mode fibers (SMFs). The ABCD matrix theory of the all-fiber coupling of LDs is also consummated. During the experiment, the optimized length of the Grin fiber is precisely accomplished through a home-made fiber-progressing system to achieve a high coupling efficiency according to the focusing characteristic of Grin fiber, and the maximum efficiency of 80.5% is ultimately realized. This all-fiber coupling configuration has several advantages including the small-sized, easy-made and low cost, which is important for the realization of the low-cost, pigtailed LDs.

A Pd/Ag metal-coated optical fiber sensor with high sensitivity to hydrogen concentrations change which is achieved by exciting surface plasmon resonance (SPR) is presented. Simulation results show that with the increase of the refractive index of sensing area, effective refractive index of the SPR mode of metal-coated side-polished "D" shape fiber increases; while with the increase of the thickness of metal coating, the effective refractive index of the SPR decreases. Experimental results show that when the hydrogen concentration is 4% , transmission power changes as high as 130 nW. The fiber optic SPR sensor improve the stability and sensitivity of the the hydrogen sensor. This sensor would be of great interest to produce novel and enhanced devices for chemical and biological sensing.

To simulate the periodic and weak vibration in the fiber sensor application, a loop-cavity fiber laser of the periodic frequency sweeping is constructed by tuning the fiber Bragg grating (FBG). To measure the sweeping frequency, the optical frequency multiplication is applied with the help of fiber Bragg grating Fabry-Perot cavity. This fiber laser has experimentally radiated a 7.2 Hz frequency-swept laser and 14.39 Hz electric signal is obtained by the frequency multiplication method. The experimental results show that this system can efficiently simulate the periodic frequency-swept light wave and exactly measure the sweeping frequency.

Based on a long-period grating (LPG) formed in a index guiding photonic crystal fiber (PCF) that is filled with a liquid of temperature-sensitive refractive index, a novel temperature sensor is proposed. Using a full-vector finite element method, the modal profiles and the dispersion curves of the core mode and the cladding mode of a large mode area photonic crystal fiber (LMA-PCF) are calculated with their hexagonally arrayed air-holes filled and unfilled with liquid ethanol, respectively. By means of the coupled-mode theory, the temperature dependence of the transmission spectrum of the PCF-LPG is studied. The result shows that in the temperature range from -20 ℃ to 80 ℃ the PCF-LPG resonance wavelength varies almost linearly with the temperature when the PCF is filled with liquid ethanol and the temperature sensitivity is 1.766 nm/℃.

The main components of vehicle exhaust as carbon monoxide (CO) and nitric oxide (NO) not only pollute the environment, but also do great harm to human body. Since CO and NO have fundamental absorption in mid-infrared wave band, it is suitable to detect them with infrared absorption spectroscopy. A set of apparatus for the measurement of CO and NO with room-temperature pulsed quantum cascade lasers (QCLs) is introduced. This system utilizes long pulsed QCL which produces a complete scan of molecular absorption lines of gases to satisfy the need for sensitivity and rapid response, with a time resolution beyond 1 Hz. It is employed to measure CO and NO from moving vehicles exhausts. The results show its capability of investigating individual plumes. Different characteristics of CO and NO emissions for gasoline and diesel vehicles are also presented. An explanation to the difference is given.

Lens array is always used to improve the uniformity of far field spatial intensity distribution on a high power laser system. This article introduces the simulated annealing algorithm into an optimal design of lens array, which changes the size and lens attributes of array elements, and finally reduces the ununiformity of the focal speckle from 0.2268 which is measured with a classical design to 0.1202 under the condition that the energy efficiency is satisfied, this shows that the optimal design greatly improves the uniformity. The curves of power spectral density of two speckle are also contrasted to research the impact of different design structures on it.

The inner refractive index distribution and absolute thickness of sample can be accurately measured by transmitted laser heterodyne interferometer. The combined optical scanning configuration composed of micro-electro-mechanical system (MEMS) mirror and f-θ lens is proposed, which is applied for the transmitted laser heterodyne interferometer system. The f-θ lens set is composed of three lenses with different materials, and has an approximately 40% transmission coefficient and a scanning area of 300 mm2. The f-θ lens model is optimized from the aspects of diffraction spot, distortion coefficient and beam divergence angle. The optimization results show that the series beam out of f-θ lens is perpendicular to the sample surface, and the system has a focal length of 434 mm and a distortion coefficient of 0.5%. The configuration for f-θ lens is presented. The result of optical scanning on the first surface of f-θ lens is introduced by He-Ne laser, which meets the requrements of the design target.

Lidar is a powerful tool for atmospheric detection, and its estimation of error is an important content for data processing. In the inversion formula of aerosol backscatter coefficient, it is difficult to calculate the partial derivative of aerosol backscatter coefficient for direct measuring variables, and the conventional error transfer formula can not be applied. To solve the above problem, a direct error formula is proposed, and its reasonability and reliability are tested by comparison calculation. This method can be applied in estimation of aerosol backscatter coefficient total error from molecular extinction coefficient error, aerosol backscatter coefficient error at reference point, lidar ratio error and measuring signal error in lidar data processing.

Pre-ablation double-pulse (DP) is applied to induce Fe plasmas, and the emission spectrum is investigated. Spectra intensities are compared using single-pulse laser-induced breakdown spectroscopy (SP-LIBS) and pre-ablation double-pulse laser-induced breakdown spectroscopy (DP-LIBS). The signal intensity is enhanced largely by pre-ablation DP-LIBS excitation compared to SP-LIBS. Signal enhancement acts as object of study. The influence of the delay between the two laser pulses (-102~0 μs) is investigated, and enhancement reaches maximum at -9 μs, and 6.5 times enhanced signal is observed in atomic line. Electron density is reflected by spectral line of full width at half maximum (FWHM). FWHM is studied with the delay between the two laser pulses and the gate delay time. A correlation between the increases in emission lines intensities and the gate delay time is established in pre-ablation DP approach. Difference of the delay between the two laser pulses, intensity enhancement versus the gate delay time is different.

Accurate and real-time diagnostics of combustion process is critical to understand combustion mechanism, improve combustion efficiency and reduce the production of pollutants. The thermometry of tunable diode laser absorption spectroscopy (TDLAS) technique is briefly introduced. Two adjacent water lines near 1397.75 nm are selected, and the TDLAS measurement system is established by using a multifunctional data acquisition (DAQ) card for signal processing and diode laser control. The measurements are performed on the instantaneous supersonic flow, the measure repetition frequency is 1 kHz, and the temperature of the evolution of supersonic flow is acquired.