With the development of semiconductor lasers, tunable diode laser absorption spectroscopy (TDLAS) technology has achieved great development and rapid expansion of application fields. There have been more than 1000 kinds of TDLAS instruments, which are applied to continuous emission monitoring and industrial process control fields. According to the statistics, 5%-10% of all infrared gas sensors based on TDLAS technology are sold in the world every year. Dozens of gases are measured on-line with high sensitivity and precision by the TDLAS technology, and gas parameters, including concentration, temperature, velocity and pressure, are also determined, which provide important technical support for the development of various fields. This article reviews the principle and recent research of TDLAS technology, with introduction from six application fields, such as atmospheric environmental monitoring, industrial process monitoring, deep sea dissolved gases detection, breath analysis, flow field diagnosis, and liquid water measurement.

Spectral parameters of molecular absorption lines, including positions, intensities, pressure-induced shift and broadening coefficients, are basic data for various applications, such as greenhouse effect and the atmospheric environment, and gas detection in the interstellar space. Along with the fast development of laser techniques, the cavity ring-down spectroscopy (CRDS) becomes a widely applied technique used for molecular spectroscopy, owing to its high sensitivity and high precision. Combined with the application of precise line profile models, CRDS has been used to retrieve numerous reliable and precise spectral data. These results have been integrated in spectral databases, and even used in testing fundamental physical laws and constants. Here a review of the CRDS method and its application in precision spectroscopy of molecules is given, in particular, using frequency-locked lasers. The studies of the high overtones of carbon monoxide and hydrogen are presented as examples of such applications.

Cavity enhanced absorption spectroscopy (CEAS) technology is an important part of high sensitive spectroscopy, which has the advanced characteristics of relatively simple apparatus, high sensitivity, and strong environmental adaptability. With the development of semiconductor materials and packaging technology, CEAS has been greatly improved in the light path structure, light source selection, and combined application with other spectral technologies. It has been widely used in the fields of environmental monitoring, medical diagnosis, national defense construction, industrial production, and other fields. The research status, development trend, and application fields of CEAS are discussed in detail. Starting from the CEAS basic physical principles, we describe the common experimental configurations based on different light sources, and analyze the improvement of system performance by improving the geometrical structure of the optical path. In addition, the present combined application of CEAS with other technologies in different fields is summarized. Finally, the future developments of each CEAS device are prospected.

This review focuses on discussing the latest progress in Quartz-enhanced photoacoustic spectroscopy (QEPAS) based trace gas sensing and the trend in the next few years. Fundamentals of QEPAS are described in the beginning and the different QEPAS configurations employing a standard 32.7 kHz quartz tuning fork (QTF) are introduced. Variant methods aiming to improve detection sensitivity and suppress sensor noise level are reported. Moreover, a review regarding developments of customized QTFs for trace gas sensing is present. Novel spectrophone configurations, with which the detection sensitivity is improved by two orders of magnitude, are reviewed. The customized QTFs operating in overtone modes significantly decrease the length of acoustic micro-resonators and realize dual gas simultaneous detection. Finally, the development direction of the QEPAS technique is discussed.

Tunable diode laser absorption spectroscopy (TDLAS), as an advanced spectral detection method, has been widely used in the process diagnosis of combustion flow field and wind tunnel environment. It can realize multiple parameters accurate online measurement, such as flow field temperature, species concentration, and airflow velocity. This review introduces the basic principle of TDLAS and its development history in the field of flow field parameter measurement, summarizes the TDLAS flow field application examples in recent years such as scramjet engines, aviation turbine engines and supersonic wind tunnels, mainly focusing on high-precision measurement of flow velocity, continuous monitoring of combustion temperature and species, accurate inversion of field distribution in laboratory and outfield. The development level of laser absorption spectroscopy flow field diagnostic technology, and the latest research progress and related problems that still exist are summarized at the same time. Finally, the application prospect and future trend of TDLAS technology in flow field diagnosis area are anticipated.

Interband cascade lasers (ICL) are recently developed MIR-infrared (MIR) light sources with high-performance. They cover the MIR spectral region of 3-6 μm band, and boast the advantages of high efficiency of electro-optic conversion, low-threshold current, and continuous wave operation at room-temperature. ICLs are one of the most promising MIR lasers for trace gas detection. In this paper, we firstly analyzed the characteristics of the MIR fingerprint absorption spectra, and then briefly described the development, working principle and characteristics of ICLs. We also reviewed the sensitive and selective detection technology for trace gas with the MIR absorption spectrum. In the last parts, the future development of ICL based sensors was prospected.

Noise immune cavity enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) can provide the highest detection sensitivity in the field of laser absorption spectroscopy by combining two techniques of frequency modulation spectroscopy and cavity enhanced absorption spectroscopy. The principle and implementation process of NICE-OHMS are introduced. Then, the historical development of NICE-OHMS is overviewed, which mainly focuses on the key parameters, such as the applied laser source and the cavity finesse used by each research group and their obtained detection sensitivity. Finally, the limitation factors of the detection sensitivity of NICE-OHMS are analyzed, and the related solutions are provided.

Photoacoutic spectroscopy (PAS) plays an important role in trace gas sensing. Researchers are focusing on improving the performance of PAS-based gas sensors to satisfy different applications. As a promising way to promote the detection sensitivity, power-enhanced PAS has attracted increasing attention in this field with many breakthroughs. This article aims to discuss the status of this important research field, starts from classifying the most used and different technologies to summarizing the fundamental, technical characteristics and current achievements, towards a reasonable development tendency analysis.

A differential absorption lidar (DIAL) system has been developed for background atmospheric SO2 and NO2 measurements. Second harmonic and third harmonic (532 nm/355 nm) of two Nd∶YAG lasers are used to pump four dye lasers, respectively. Two pairs of laser beams 300.05 nm/301.5 nm and 446.6 nm/448.1 nm are obtained for profiling atmospheric SO2 and NO2. Observation results show that accuracies of atmospheric SO2 and NO2 measurements under clear weather condition can be within ±2.0×10-9 and ±5.0×10-9, respectively, when spatial resolution is set to 15 m and integration time is seted to 30 minutes. Averaged atmospheric SO2 and NO2 concentrations observed through SO2/NO2 DIAL conform with the results of meteorological department at the same time. It shows that DIAL technique has the ability to measure the space-time distribution of low concentration of SO2 and NO2.

The measurement of combustion components is significant for diagnosis of combustion. The study on measurement of carbon monoxide (CO) concentration in combustion field is realized with mid-infrared inter-band cascade lasers (ICL) at 2060 cm-1 (v=1←0,P20) to cover CO absorption line based on tunable laser absorption spectroscopy (TLAS) technology. In the experiment, the spectral line strength ratio between a pair of absorptions of water vapor (7154.35 cm-1 and 7467.77 cm-1), for H2O is the product of combustion process, is used to calculate the combustion temperature, that is used to correct spectral line strength of CO to achieve accurate measurement of CO concentration. Firstly, the TLAS temperature verification test is introduced, and the results show that the fluctuation of the test temperature is less than 45 K at each set temperature step, which indicates temperature measurement is reliable. Secondly, the calibration experiment of CO concentration measurement is carried out, and measurement error of CO concentration is under 3% compared with standard gas concentration. Finally, the experiment achieves the CO concentration at the range of 0.35‰-4.5% on methane /air flat flame furnace under different combustion conditions, with a detection limit of 0.035‰. The experiment proves the feasibility and reliability of mid-infrared absorption spectroscopy technology to measure the concentration components of combustion field, which is helpful to the study of combustion diagnosis and has great application value.

The deep-sea region has great economic potential due to its rich mineral, energy, and biological resources. Dissolved deep-sea minerals are important markers that reflect the activity and evolution of seafloor hydrothermal fluids. Herein, a novel in situ measurement method is proposed to estimate deep-sea sulfur ion concentration. The all-optical fiber transmission mode is adopted as a design concept, with a high-power mini light-emitting diode (LED) used as the excitation light source. The chemical display method, which is based on the Lambert-Beer law, is combined with the full spectrum detection method to measure the concentrations of deep-sea ionic minerals. The self-established adaptive Savitzky-Golay filtering algorithm is employed to achieve a threefold to sevenfold improvement in the spectral signal-to-noise ratio for data processing. The results reveal that the proposed system can achieve a detection sensitivity below 0.1 μmol/L under the conditions of 1 s time resolution and a 20 mm effective optical path. Furthermore, a good linear response characteristic ［relativity (R2)>0.99］ is obtained in the 0-32 μmol/L concentration range.

H2S is one of characteristic components for discharge faults diagnosis in the SF6 gas insulated device. Due to the small absorption coefficient of H2S gas in the near-infrared band, the detection sensitivity is difficult to improve with traditional optical detection methods. To solve this problem, we propose an enhanced laser photoacoustic detection method, which combines the technologies of high-power fiber laser amplifying, resonant laser photoacoustic spectroscopy, wavelength modulation spectroscopy, and second-harmonic detection, for high sensitive detection of H2S decomposed by SF6. By cascading a near-infrared tunable narrow linewidth distributed feedback laser diode with a high saturation output power erbium doped fiber amplifier as the photoacoustic excitation light source, we develop a high-sensitivity laser photoacoustic spectroscopic system for trace H2S gas detection. The results show that the detection limit in the background of SF6 is achieved to be 1.5×10-8 with the measurement time of 100 s.

The laser with a wavelength of 1570 nm is used to analyze the hydrogen sulfide gas in the background of natural gas. The gas mixture containing the hydrogen sulfide with a volume fraction of 0-10-4 is produced in an automatic gas mixing station, and 92 groups of the spectral data with a stable state are obtained. The regression model of extreme learning machine (ELM) is adopted for the inversion calculation of the concentration of hydrogen sulfide. The nonlinear iteration partial least square (NIPALS) algorithm is introduced into the spectral pretreatment. The ELM regression model is established by using the spectral feature vector and the concentration vector, and is evaluated by the five-fold cross validation method. The test results show that, the regression predicating accuracy of the spectral data obtained by feature extraction is improved by 25% than that by direct ELM, and the model operation time is reduced from 0.12 s to less than 10 ms. The spectral pretreatment by the feature extraction can reduce the training time of ELM model and can also improve the analysis accuracy and the real-time capability of the analyzers.

For tunable diode laser absorption spectroscopy, we propose a method of extracting the second harmonic (2f) signal by cutting off the absorption signal for segmental fast Fourier transformation, and the proposed method is compared with the harmonic signal processing method of traditional orthogonal lock-in amplifier. C2H2 absorption signal is generated based on MATLAB software, and functions of orthogonal lock-in amplifier and segmental fast Fourier transformation are verified, respectively. A sensing signal processing platform is realized for orthogonal lock-in amplifier and segmental fast Fourier transformation based on LabVIEW software. A near-infrared C2H2 sensor system is established by combining the 1.533 μm distributed feedback near-infrared laser and a developed Herriot gas cell. The sensor calibration and Allan standard deviation measurements are carried out with the prepared C2H2 gas samples. The results show that both methods possess a good goodness of linear fitting and reveal a similar stability.

Compared with the widely used emission wavelength of 532 nm, the atmospheric temperature observation using the emission wavelength of 355 nm requires higher precision of the spectroscopic spectrometer, and the line dispersion rate of the spectroscopic spectrometer should reach 0.1 nm/mm. A new high linear dispersion pure rotational Raman laser lidar spectrophotometer is proposed, which uses the double grating structure to achieve the purpose of laser lidar pure rotational Raman echo signal separation. Zemax software is used to design, simulation results show that the interval of 0.1 nm in two adjacent spectrum spectral optical system focus lens focal plane in the center of two adjacent line can be separated from 1 mm, which satisfies the requirement of line dispersion rate of temperature measuring pure rotational Raman spectroscopic spectrometer to reach 0.1 nm/mm. Comparing the experimental Stokes echo signal strength with theoretical calculation, the feasibility of the double grating spectrometer in the pure rotational Raman lidar is verified.

In this paper, a new method based on stimulated Brillouin scattering (SBS) combined with UV-visible absorption spectra for authenticating the quality class of olive oils is investigated. UV-visible absorption spectra of different classes of olive oils are measured. According to the number and location of measured absorption peaks, the quality class of different olive oils can be preliminary authenticated. On the basis of measured absorption spectra, the SBS spectra of olive oils at the different temperature conditions are collected, and then the variation of SBS frequency shifts with temperature is analyzed. The experimental results indicate that different classes of olive oils present the same variation tendency in SBS spectra: frequency shift decreases with the increase of temperature, but each class of olive oil has its own unique curve. By employing the method of SBS combined with UV-visible absorption spectrum, the quality class of olive oils can be authenticated efficiently and quickly.

Based on 3D particle-in-cell (PIC) numerical simulation method, the high quality, high energy proton beam is transmitted and focused on the far end via a pulse current solenoid. Simulation results show that proton beam with peak energy of 250 MeV, energy spread of 10% and a spatial divergence angle less than 15 mrad can be focused on a spot 2.5 m away from the proton source, after transported in a 760-mm pulse power solenoid under magnetic field strength of 10.87 T. The focal spot cross section diameter is 1.2 mm, less than the initial proton beam spot size; meanwhile, the number loss of proton beam is less than 3%. We conclude that it is feasible to use a powered solenoid to transmit and regulate a high energy proton beam. This scheme can be used to optimize the proton beam quality and promote the laser-driven proton acceleration to be applied early in the fields such as cancer treatment, where high proton beam unipotency and small divergence angle are required.

Based on the influence functions of the deformable mirrors (DMs), the wavefront correction process is simulated by the finite element method and the influence of the fatigue characteristics of piezoelectric ceramics (PZT) actuators on the correction ability of DMs is analyzed. The research results show that the correction ability of DMs decreases when the phenomenon of the fatigue occurs in PZT actuators. The larger the peak-valley value of the distorted wavefront to be corrected or the higher the proportion of the spatial high-frequency components is, the more obvious of the decrease of the correction ability of DMs after the occurrence of fatigue is. In addition, the influence from the former is relatively larger.

In order to realize the decoupling control for the Woofer-Tweeter adaptive optics system, we propose a decoupling control algorithm based on Laplacian eigenfunction. By solving Laplacian eigen equations under different homogeneous Neumann boundary conditions, we can obtain Laplacian eigenfunctions which are orthogonal to themselves and whose first-order partial derivatives are orthogonal under different pupil regions. Using the Laplacian eigenfunctions under different pupil regions, we achieve the decoupling control for the Woofer-Tweeter adaptive optics system in different pupil regions. In addition, the first-order partial derivatives of the Laplacian eigenfunction is orthogonality, so that it is not necessary to measure the response function surface shape of Tweeter actuator to construct a constraint matrix for Tweeter. A Woofer-Tweeter adaptive optics system is used to verify the validity of this algorithm. The experimental results show that the decoupling control algorithm based on Laplacian eigenfunctions can synchronously control Woofer and Tweeter, and effectively suppress the coupling error between Woofer and Tweeter.

Limited-projection fluorescence molecular tomography (FMT) allows rapid reconstruction of three-dimensional distribution of fluorescent targets in animals through shorter data acquisition times. However, due to less projection data, the limited-projection FMT undergoes severe ill condition. In order to reduce the ill condition of FMT reconstruction and improve the reconstruction speed, we propose a reconstruction method for limited-projection FMT. Considering the characteristics of the sparse distribution of the target of FMT, this method combines with smoothed l0 norm and feasible region of prior information. A continuous function approximates the smoothed l0 norm, which improved the calculation speed. And the feasible region of the prior information improves the precision of the recovered results. The reconstruction results of digital mouse model show that the position error of the reconstructed image is less than 1 mm at 3, 6 and 9 excitation points and the reconstruction time is shortened, and the reconstruction time under the 3 excitation points is 8 s. The reconstruction result of physical phantom further verifies the feasibility of this method in practical FMT applications.

A high power fiber cladding optical filter with phase change material is designed and developed for the thermal managements of high power fiber laser in the space and other special environments. The phase change material of 18-alkanes is applied to absorbing cladding light heat. The Fluent module of Ansys is used to simulate the phase change process of phase change material and the temperature variation of the stripper at 200 W. 18-alkanes with the mass of 0.246 kg and the mass fraction of 99% is used as the phase change material. The experiment verifies that the stripper can work stably for 360 s at the room temperature of 25.6 ℃ and the light power of 206 W. The simulation results are basically coincident with the experiment.

A synchronized method of photon detection array signal slot based on measurement of photon arrival time is proposed. Firstly, to obtain the offset of the arrival time of each photon relative to the position of the pulse position modulation slot, we measure the arrival time of different photons in each branch, and finally the photon distribution at different offsets is obtained statistically. In the presence of frequency offset, the photon distribution becomes much flatter. When the initial phase shift exists, the peak of the photon distribution can deviate from the center position. Then the mean square error or second moment is used as the standard of the synchronization under different frequency offsets and initial phase offsets, and the searching method is used to achieve the slot synchronization. The simulation results show that the proposed method can achieve the slot synchronization when the counting clock frequency is twice or more than the slot clock frequency.

Based on the channel response of time-interleaved photonic analog to digital conversion (TIPADC) system, the relationship between photodetection response and channel mismatches, as well as its effects on correction of mismatches is analyzed. The simulation is also performed. The results show that the influence of channel mismatches is irrelevant to the frequency when the photondetection response do not induce the crosstalk. In this case, the mismatch correction can be achieved with mismatch parameters obtained at a single frequency. In comparison, in the situation that the photondetection response can cause the crosstalk, the channel response under different gains has the same proportion change, while the channel response at different time mismatches changes in different proportions. Thus, the gain mismatches can only be corrected through mismatch parameters obtained at a single frequency.

The ultra-stable laser is a key component in optical lattice clock, whose frequency stability is limited by the thermal noise and affected by the temperature fluctuation of ultra-stable cavity. Thus the temperature fluctuation is a serious obstacle in pursuing thermal-noise-limit of ultra-stable laser. In this paper, we analyze the requirement of the temperature stability to reach the thermal-noise-limit in frequency domain and time domain, and design the thermal-isolation vacuum system (with one passive thermal shield layer and two active temperature stabilized layers) and the corresponding temperature controller. Having developed the ultra-stable cavity system, we measure the zero-expansion work temperature of the ultra-stable cavity, the temperature transferring time constant of the thermal shield (3.6 d), and the temperature fluctuation of the temperature stabilized layer in vacuum in 11 d (<1 mK). With these data, we calculate the temperature fluctuation of the ultra-stable cavity, and evaluate that the frequency noise induced from the temperature fluctuation which is all below the thermal-noise-limit in 1000 s integration time. Moreover, we also use the clock transition spectrum of the 199Hg cold atoms in magneto-optical trap to measure the long-term drift rate of the ultra-stable cavity (4.2 kHz/d). This frequency drift rate of ultra-stable cavity is competent to mercury optical lattice clock.

We propose a novel tunable multiwavelength random fiber laser based on Brillouin scattering with half-open cavity, and it′s formed by total reflection of a connected 3 dB coupler and randomly distributed Rayleigh scattering in single mode fiber. When the Brillouin pump power amplified by the erbium-doped fiber amplifier is high enough, it is possible to generate cascaded high-order stimulated Brillouin scattering in the long single-mode fiber and achieve multiwavelength Brillouin random laser output. The results show that when Brillouin pump wavelength is 1530 nm, at best seven multiwavelength Stokes have been obtained from the Brillouin random fiber laser. We study the influence of the pump power on the output of multiwavelength random lasers by changing the Brillouin pump power and erbium-doped fiber pumped laser power. Additionally, by changing the wavelength of Brillouin pump, we find that the output wavelength of the Brillouin random laser can be tunable in wavelength range from 1515 nm to 1565 nm.

We investigate the room-temperature Raman spectrum of monoclinic monazite-type LaVO4 (m-LaVO4) crystal and report a diode end-pumped intracavity actively Q-switched m-LaVO4 Raman laser. In this experiment, a fiber-coupled diode laser (LD) with a wavelength of 808 nm is used as a pumping excitation source, a Nd∶YAG crystal is used as a gain medium for generating a fundamental-frequency laser, and a quartz-acoustic-acoustic Q-switch is used as an active Q-switched component. A compact Fabry-Perot cavity composed by two Fabry-Perot mirrors produces a first-order Stokes pulsed laser with a wavelength of 1170.9 nm. When the input pump power is 6.51 W and the pulse repetition frequency is 30 kHz, the experiment produces the first-order Stokes laser with a maximum average power of 767 mW, the corresponding pulse width of 13.8 ns, the single pulse energy of 25.6 μJ and the peak power of 1.85 kW.

The damage proceeding of charge coupled device(CCD)detector irradiated by 1.06 μm continuous laser and the weakening of the imaging capability at different damage stages are studied. Combined with damage mechanism analyzed by scanning electron microscopy (SEM) and the CCD output images at the damage stages, the reasons of the imaging quality change at different damage stages are explained. Results show that during the point damage, the microlens melts, vaporizes and loses the ability of focusing beam, which cause the incoming laser to reduce and the image gray to decrease. Besides, the vaporized microlens is adhered to the surface of encapsulated glass after cooling. These are the main reasons for the image quality reduction. During the linear damage, the deeper damage of multilayer structure by laser causes part of pixels to lose imaging capability, while the encapsulation glass is damaged due to the irradiation. So the CCD imaging ability becomes weak gradually. Combining the image clarity with morphologic detection, we built the damage assessment model to evaluate the CCD imaging capability and imaging quality at different damage stages based on existing evaluation method. By this way, the corresponding relations between damage time, damage morphology, the damage stages and the CCD imaging capability are obtained.

The coated laser with a high performance is fabricated based on the InGaSb/AlGaAsSb material system, and simultaneously the laser without facet coating is also fabricated for a performance comparison. The laser without facet coating working in the continuous-wave (CW) mode and under room temperature (RT) shows an output power of up to 300 mW at the injection current of 3.0 A and the maximum wall plug efficiency (WPE) is 8.3%. The laser with facet coating working in the CW mode and also under RT exhibits an output power of up to 380 mW at the injection current of 2.6 A and the maximum WPE is 15.6%. The WPE of the coated laser is always above 10.0% and the emission wavelength is around 2.0 μm at the injection current range of 0.3-2.4 A.

Recent studies have revealed that space beam interferenced in the gain medium would result in space burning hole phenomenon and form the gain grating. The gain grating formed by the four-wave mixing function after multiple oscillations in the resonator has self-adaptive, self-Q-switched and spatial filtering capabilities, and can obtain holographic conjugate output. Based on the above characteristics of the gain gratings in a non-reciprocal laser cavity with a grazing incidence structure, we analyze the factors which affect the output single-frequency stability and output energy with diode-pumped monolithic Nd∶YVO4 crystal, and achieve a single-longitudinal-mode Q-switched output with a single pulse energy of 0.9 mJ, a pulse width of 7.5 ns, and a line width of 0.95 pm by optimizing the extinction ratio of the non-reciprocal element, the gain area, the size of self-intersecting angle and other conditions. As far as reviewed, this is the maximum energy achieved by the current monolithic gain media, which can provide references for analyzing and optimizing the single-longitudinal mode oscillations to achieve stable non-reciprocal gain grating lasers.

The T91 heat resistant steels are welded by the laser-arc hybrid welding technique. The high temperature aging treatments of welded joints for different time at 750 ℃ are conducted and the microstructure evolutions of weld, heat affected zone and base metal are investigated. The corresponding precipitation is also analyzed. The results show that, with the increase of high temperature aging time, the grain size in the weld gradually increases, the width of the martensite lath increases and the martensite laths are gradually broken into subgrain structures. Simultaneously, the precipitation gradually coarsens and gathers to the grain or subgrain boundary and the micro-hardness gradually decreases. After the treatments for different aging time, the fractured positions of all welded joints are within the base metals.

The surface treatment of AM50 Mg alloys is conducted by the laser shock peening (LSP) technique. The resistance to tensile stress corrosion and the fracture morphologies of specimens in NaCl solution are investigated. The compositions of the fracture are also analyzed. The effects of laser shock layer number and Cl- concentration on the anticorrosion behavior of AM50 Mg alloys are researched. The results show that the large area LSP treatment to AM50 Mg alloys can induce the compressive residual stress and make the refinement of surface grains, and thus the resistance to tensile stress corrosion of AM50 Mg alloys is significantly improved. The resistance to tensile stress corrosion of AM50 Mg alloys is enhanced with the increase of laser shock layer number, but is weakened with the increase of Cl- concentration.

A three-dimensional (3D) spring-like flow sensor is integrated inside the microfluidic chip by using the femtosecond laser two-photon direct writing technique. The fabricated spring-like flow sensor can be stretched repeatedly for several times, and the deformation is reversible. In addition, different laser exposure powers can be adopted to fabricate the spring-like flow sensors with different thicknesses, and thus flow rates within different ranges can be monitored and the minimum flow rate which can be monitored is at 10-12 level. This flow sensor can be used in many kinds of microfluidic devices, especially in situations where the flow rate detection is required to be combined with other microfluidic devices and in the ultralow flow rate detection.

The Bi3.95Er0.05Ti3O12 (BErT) thin films are prepared on the indium-tin-oxide (ITO)-coated glass substrates at room temperature by the pulsed laser deposition technique. The research results show that, the BErT thin film prepared under a low deposition oxygen pressure possesses a dense and uniform surface without cracks, and an amorphous structure. Under a 3 Pa deposition oxygen pressure, the BErT thin film has a thickness of about 180 nm and shows outstanding dielectric characteristics, such as a dielectric constant of 52 at room temperature and a dielectric loss of 0.025 at the test frequency of 1 kHz. Meanwhile, the dielectric properties of the BErT thin film show a relative stability when the frequency, the voltage and the temperature change and also has a relatively high optical transmissivity in the visible light regime.

The optical recording properties and parameters of dithienylethene are investigated by the fluorescence spectrum conversed by ring-opening two-photon absorption and the fluorescence-quenching spectrum. Its nonlinear absorption coefficient is 3.46×10-13 m·W-1, the power density threshold of the two-photon absorption conversion is 107.36 GW·cm-2, and the power density threshold of the fluorescence quenching is 2.89 GW·cm-2. Based on these measurement parameters, a resolution of 60.0 nm in super-resolution optical storage is theoretically calculated and obtained, and a kind of recording and reading method for the information of the two-photon-dual-beam super-resolution optical storage based on diarylethene is designed. The results indicate that, the dithienylethene possesses the characteristics such as photo-induction-photo-inhibition, nonlinear absorption and fluorescence-quenching, and is an excellent optional material for the super-resolution optical storage.

The samples of the Tm3+/Dy3+ co-doped bismuth glasses are successfully prepared by the conventional high temperature melt-quenching method. By means of the differential scanning calorimetry curves, Raman spectra, absorption spectra, infrared transmittance spectra, fluorescence spectra and fluorescence decay curves of the samples, the 1.47 μm broadband emission properties of the samples pumped by 800 nm laser diode (LD) are investigated. The results show that, the prepared bismuth glasses have a good thermal stability, a low phonon energy and a high infrared transmissivity. When the mole fraction of Dy3+ is 0.3%, the sensitivity enhancement of the 1.47 μm emission of Tm3+ is achieved and the full-width at half-maximum of the fluorescence spectrum is 118 nm. The calculated maximum stimulated emission cross section of 1.47 μm emission is 4.37×10-21 cm2 and the figure of merit for the fiber amplification is 5.31×10-26 cm3.

Diffraction grating is widely used in a variety of applications, which requires the grating to have good quality. Among various methods of making large-sized gratings, laser direct writing has obvious advantages. We use the parallel direct laser writing technology to produce a sinusoidal grating with size of 100 mm×100 mm and line number of 1780 line/mm. Firstly, the grating is analyzed theoretically to find a groove depth where the sinusoidal grating can reach its highest efficiency, then the grating is produced by laser direct writing and finally coated with a layer of gold. We introduce the diffraction efficiency measurement of the grating, and estimate the uniformity of the grating. The result shows that the diffraction efficiencies of the grating are around 90%, which is close to the theoretical calculation. Meanwhile, the efficiency distribution is uniform. Experimental results demonstrate that the developed parallel direct laser writing technology is feasible for producing high quality and large-sized gratings.

A transport of intensity equation (TIE) based technique is proposed to measure the stress generated by the laser induced damage on the optical elements. By recording three intensity images around the focal plane in damage point area, we directly calculate the stress birefringence phase distribution generated by the damage point, and realize the quantitative detection of stress generated by laser induced damage. Compared to other phase measurement techniques, the proposed TIE based technique doesn′t suffer the disadvantage of the amplitude of π sudden change in the retrieval phase, and can be realized with incoherent light beam illumination. It has the advantages of simple optical path structure, easy operation and rapid measurement, thus it′s an ideal technique for the fast measurement of residual stress generated by laser induced damage on the optical elements. We detect a series of damage points produced by quartz glass under the action of CO2 laser, and the results are completely consistent with theoretical expectations.

To deal with the detection of the internal defect in the thick steel plate, we adopt the synthetic aperture focusing technique (SAFT) to locate and image the internal defect of the thick steel plate. The moving pulse laser line source is used to generate the longitudinal ultrasonic waves in the steel sample. The laser vibrometer is applied to obtain the time-domain ultrasound B-scan signals at the fixed point. The longitudinal echo-waves reflected by the defect are extracted from the time-domain signal. And the imaging of the internal defect of the sample is realized. This imaging process is simulated numerically by the finite element method (FEM) and verified in the experiment. The experimental results coincide well with the numerical calculation results. The proposed defect imaging method can realize the defect detection under the circumstance where the defect echo-waves have a low signal-to-noise ratio (SNR). The process of this method is simple and convenient, and the method has practical value in the laser-ultrasonic detection field.

With the introduction of an automatically scanning grating monochromator, the rapid measurement of dispersion is realized, which greatly reduces the influence of the slow drift of carrier envelope offset frequency on the measurement accuracy, reduces the experimental complexity, and improves the dispersion measurement accuracy. In the experiment, the 815 nm Ti∶sapphire mode-locked laser is used as the light source and a home-made eight-mirror ring cavity is taken as a reference, the group delay dispersion (GDD) of a piece of 6.35 mm-thick fused silica plate is measured and the difference between the results and that from the theoretical value derived from the equation of Sellmeier is 1.2 fs2 with an only uncertainty of 0.5%. The GDD of the eight-mirror ring cavity under normal temperature and pressure condition is 28.8 fs2, smaller by 12 fs2 than the theoretical value, which is attributed to the coating inhomogeneity of the eight cavity mirrors.