This PDF file contains the front matter associated with SPIE Proceedings Volume 12459, including the Title Page, Copyright information, Table of Contents, and Conference Committee lists.

D-shaped fiber manufacturing by mechanical grinding or chemical acid will inevitably introduce subsurface damages or impurity during processing. Laser ablation has been proven to be a high-efficiency non-contact technique that can achieve a low-defect surface. However, the process of laser processing fiber involves the phase change of the material, which leads to a very complicated evolution process of the surface topography of the fiber. In order to predict the surface topography of fiber during irradiation by pulse laser. Herein, a 3D model has been established to assist the understanding of the thermal mechanism of pulsed CO₂ laser ablation and phase change of evaporation during ablation. Furthermore, the temperature characteristics of the fiber surface during the laser irradiation are also analyzed. The simulation results show that from the second pulse, the ablation depth is basically stable, and the texture formed on the fiber surface is related to the processing parameters.

Carrier evolution equation (continuity equation) of semi-conductor plays an essential role in simulation of laser interference and electrical damage induced by laser irradiation on charge coupled device (CCD). Solving the Poisson equation, which is coupled with the carrier evolution equation, is a necessary step to obtain the stable electronic field caused by doped atoms and the dynamic one caused by free carriers. In terms of carrier evolution simulation in high resolution-CCD, it is important to solve the Poisson equation promptly and efficiently. For this purpose, we adopt a boundary element method with convolution core combined with Gauss integral algorithm. In this method, we propose the pixel element model in which fast Fourier transform (FFT) is introduced so that the amount of calculation is greatly decreased compared with the finite difference method. In this approach, it is possible to simulate carrier evolution in high-resolution-CCD even on a common personal computer.

Square array CCD detector is widely used in image acquisition, photoelectric measurement and other fields. However, its inherent dynamic range is affected by noise and saturation crosstalk effect, which can not meet the application requirements of laser jamming effect measrement. In this paper, an image date fusion method based on linear compensation and orthogonal compensation is proposed. By controlling the jamming laser power, collecting multi-frame laser jamming effect images, and making full use of the effective measurement information in the image for compensation, the target laser energy distribution data with lager dynamic range can be obtained. In the experiment, the laser energy distribution on the target surface diffracted by circular aperture and rectangular aperture is inversed respectively, and the dynamic range is expanded by 40dB.

A method of double-sided laser irradiation is presented for temperature control in high temperature mechanical properties test of composite materials. Based on the finite element method (FEM), a numerical model of temperature distribution of materials was established. The effects of specification, laser heating area and laser intensity，laser heating time on temperature uniformity during heating were analyzed. The results show that the laser heating area, thickness of the specimen, laser intensity and laser heating time have a decisive effect on the temperature uniformity. The limit temperature control precision reaches 2% for carbon fiber reinforced polymer(CFRP), and the heating time can be controlled in minutes. The method is especially suitable for composite materials that cannot be heated by electric induction in the traditional heating experiment of high heating rate. Furthermore, an experimental scheme of double-sided irradiation heating using a single laser beam was designed. Experiment results illustrated that the temperature control precision was high before the material appears obvious flame. This method has the advantages of rapid heating rate, high testing efficiency and high testing temperature. It can make a reference for mechanical properties test of composite materials at elevated temperature with rapid heating rate

Silicon is an indispensable raw material in the manufacture of electronic devices, and it is widely used in aerospace field. We study the motion morphology and velocity of LSW induced by millisecond-nanosecond combined-pulse laser with different pulse delay and laser energy density irradiating silicon based on the method of laser shadowgraphy. Experimental results show that when the pulse delay is 2.4 ms, the millisecond(ms) and nanosecond(ns) laser energy density is 301 J cm⁻² and 12 J cm⁻², respectively, the velocity of shock wave is 1.1 times faster than that induced by single ns pulse laser. It is inferred that the shock wave propagates in the plasma is faster than that in air. The results of this research can provide a reference for the field of optimized laser propulsion.

The incidence angle of the pulsed laser has a significant influence on the performance of laser propulsion. To further reveal the impulse coupling mechanism when the pulsed laser is obliquely incident irradiated, a plume observation system with high spatial and temporal resolution and a plasma plume emission spectrometry system were designed and built. In this paper, time-resolved images and the plasma emission spectrum were investigated for pulsed laser irradiation of aluminum targets at 0°, 15°, 30°, 45°, 60°, and 75° in a vacuum environment. The results of the study show that the plasma plume is always ejected along with the normal phase of the target surface. Additionally, the electron number density, the plume radiation intensity, and the plasma temperature weaken as the angle of incidence increases. Besides, a high-precision three-dimensional spectral collection platform was built to finely study the two-dimensional spatial distribution of the plasma parameters in the flow field. The results show that the electron number density decreases rapidly with increasing distance from the target surface. In conclusion, the foundation is established for the analysis of the impulse coupling mechanism of pulsed laser oblique incidence.

As located in the focal plane of the imaging system, the image sensor will be easily influenced by the huge optical gain, which is brought in the image sensor by the external optical system and microlens on the surface of the device. Laser has a great influence on the image sensor, which is a sensitive link of the anti-laser reinforcement of the imaging system. Improving the performance in extreme light conditions in order to study the vulnerability of image has an important significance of reinforcement. As a typical visible light image sensor, which has advantages of sensitivity, high dynamic, small, light and so on, IT-CCD has been widely used in the fields of reconnaissance, detection and military. An 800nm femtosecond pulse laser was used to carry out experimental research on the laser irradiation effect of IT-CCD. The results shown that the local pixel of IT-CCD was in a state between undamaged and the white point damaged after irradiating by the laser, which was named by gray point. It was shown that the influenced pixels of IT CCD were changed by the laser, but no obvious deformation occurred. Through microscopic detection and analysis, the damage mechanism was expounded, further analysis was done. With focus ion beam (FIB) technique, it was found that there was photosensitive potential well, micro-structure of SiNx filling layer under microlens of the IT-CCD. When the gray point damage occurred, neither the photosensitive potential well at the bottom of the device was damaged, nor was the microlens structure on the surface. It turned out that the SiNx filling layer was influenced by the laser. Through elucidating the mechanism of this damage of the gray point, it lays a foundation for damage mechanism research.

Laser ablation propulsion performance, especially the improvement of ablation efficiency, has been the focus of technological development in the field. Drawing on the principle of plasma acceleration advancement of pulse plasma thrust, using electromagnetic field enhances laser induced plasma, forming better advancement performance, is a new method of electromagnetic enhanced laser propulsion performance. In this paper, the combination of laser propulsion and electromagnetic enhancement field is used to improve the propulsion performance. Firstly, the plasma is generated by laser ablation, and then the plasma is further accelerated by electromagnetic field, so that the plasma generated by laser ablation can obtain higher speed under the interaction of electromagnetic field, so as to improve the specific impulse and efficiency. The theoretical method of laser-ablated plasma electromagnetic acceleration is discussed, and an experimental platform for laser-ablated plasma electromagnetic acceleration is constructed. The enhancement effects of impulse, specific impulse and efficiency are studied experimentally. The results show that with the increase of laser energy, the optimization trend of propulsion performance parameters first increases and then decreases. When the electromagnetic enhancement field is coupled, the propulsion performance of laser electromagnetic enhancement is significantly enhanced compared with that of laser ablative propulsion. At the optimal working point, the efficiency is increased by 5.1%.

Nuclear aerosol simulant generated in laboratory plays a unique role for the development of in-situ monitoring technology of nuclear facility emission. To simulate the emission of the trace uranium aerosol, an aerosol generator based on laser ablation was set up and tested experimentally. It is shown that the concentration of aerosol particles has a linear relationship in the range of 36.28 μg/m3 to 277.13 μg/m3 while the laser intensity keeps above 7.6×106 W/cm2 . The aerosol particle size distribution is stable, while the most particles are inhalable particles based on the measurement of an aerosol spectrometer. The composition is verified with a laser induced plasma spectroscopy. Several spectral lines of uranium have been clearly identified. It is demonstrated that aerosols generated based on laser ablation can simulate nuclear facilities emission effectively. The method will be used in further work to develop direct radioactive aerosol monitoring technology.

Silicon-based photodetector have become an important part in various laser applications. The influence in the process of laser interacted with a silicon-based quadrant detector include not only laser parameters, but also external circuit parameters. Using 1064nm millisecond pulsed laser to interact on one quadrant of a silicon-based quadrant detector, the output current of each quadrant of the silicon-based quadrant detector under different bias voltage is compared and studied. The research shows that, in the process of laser irradiation on a silicon-based quadrant detector, the change of output current in the quadrant where the laser beam is located can be divided into three stages: initial stage, maintenance stage and recovery stage. The output current in the maintenance stage decreases as time, and the output current in the recovery stage fluctuates. Combined with the change trend of output current in each quadrant, it is found that the phenomenon is related to the interaction between the quadrants. It is also found that the law between the output current and the bias voltage changes obviously in the maintenance stage and recovery stage with the increase of the bias voltage. The reason is that, the internal electric field increases with the bias voltage, and the influence on the output current increases.

In order to study the disturbing effect of pulsed laser irradiation on array CCD camera, experiment of CCD camera disturbed by single pulse laser was carried out at short-distance. A 1064nm laser was chosen as the irradiation source, which was attenuated by attenuation pieces before entering the CCD lens. An aperture was set before CCD lens to limit spot size to radius of 2.5mm. 50% laser was split for monitoring the laser stability and the other 50% entered CCD camera. The entering laser energy was started with 2.48 nano Joule, and CCD camera was in normal work condition; along with the increase of laser pulse energy, saturated pixels came out in the image plane, and saturated zone increased at the same time. With the laser pulse energy increasing to 47.1 nano Joule, a short crosstalk line appeared above the main spot, and there was a certain distance between them. With increasing of laser pulse energy, distance between crosstalk line and main spot reduced and the crosstalk line became lighter and thicker, a shorter horizontal crosstalk in the middle of longitudinal crosstalk line became obvious at the same time. The experimental results has some differences between the gap on crosstalk line and unilateral crosstalk line, which provides some new experimental data for analysing disturbing effect of laser irradiation on array CCD.

Laser as a high energy density light source and silicon cell as a widely used photoelectric conversion element, the interaction between the two has become a research hotspot in wireless energy transmission and semiconductor material damage. At present, the experimental and theoretical research mainly focuses on the damage threshold and morphology, electrical output characteristics and action mechanism. The resistance of the silicon cell affecting electrical output was mainly qualitative analysis, but few quantitative studies. Different degrees of damage were simulated though pulsed laser irradiation in different positions of the silicon cell. The parallel resistance and series resistance of the silicon cell were estimated by linear fitting at V0 and I0 of IV curve, and the variation of the resistances was quantitatively obtained under different degrees damage. The results show that the damage induced by pulsed laser irradiation is obvious melting ablation and the damage is irreversible when the optical power density is 3.3×108W / cm2 , one pulse irradiation damage is equivalent to the resistances of 67 in parallel and 189 m in series for silicon cell, the output voltage decreases approximately linearly with the increase of irradiation times and the output voltage is about half of the initial voltage after 6 times irradiation. In addition, the output voltage was rapidly increased to a peak with the loading of pulsed laser, which is almost independent of the damage of the silicon cell.

In the high power laser system, because of the high power of the laser, it is likely to cause damage to the laser devices, making the laser system paralyzed. When a certain high-intensity laser passes through an optical device, part of the energy is absorbed by the device to form physical processes such as ablation, melting and gasification of the material surface. The vaporized target vapor continuously absorbs the laser energy to form an absorption wave maintained by the laser. According to different mechanisms and characteristics, it can be divided into detonation wave and combustion wave. The research on the generation process, mechanism and characteristics of laser supported absorption wave is helpful to the design optimization of laser devices and increase the understanding of the basic physical process of absorption wave. In this paper, the physical process and characteristics of combustion wave induced by long pulse millisecond laser in two transparent materials quartz are studied. In this paper, the process of combustion wave generation is described from a more complete theoretical point of view. First, the process of laser incident on the target to generate combustion wave is described in a more complete theoretical way. Then, the physical characteristics of combustion wave under different parameters, such as the size distribution of expansion velocity, the size distribution of expansion velocity, the generation of combustion wave induced by laser, are obtained through the establishment and Simulation of the combustion wave model Fluid fraction evolution state, etc.

The experiments of combined laser are carried out for the aluminum alloy and glass fiber reinforced polymer composites. The effects of continuous wave laser and long pulse laser combination, continuous wave laser and short pulse laser combination and timing schemes on the breakdown behavior of aluminum alloy and glass fiber reinforced polymer composites are compared and analyzed. The results demonstrate the plasma impact effect caused by short pulse laser shortens the penetration time of aluminum alloy and dramatically decreases the laser energy required for breakdown based on the thermal softening effect of aluminum alloy caused by continuous wave laser. Nevertheless, for glass fiber reinforced polymer composites, the ablative behavior caused by long pulse laser can further accelerate the breakdown process of composites on the basis of continuous wave laser

The far-field diffraction pattern of laser beam through negatively polarized nano-suspension is studied. Based on the Fresnel-Kirchhoff diffraction integral formula, the relationship between the nanoparticle suspension sample’s placement location, different incident light intensity, different sample length and the far-field diffraction pattern change are compared and analyzed through numerical simulation. The simulation results prove that a perfect hollow beam is obtained by changing the wavefront curvature of the incident light beam. Different from the past, increasing the incident light intensity can not increase the number of far-field diffraction rings. The wavefront curvature is no longer the only factor that affects the far-field intensity distribution of a laser beam passing through a nonlinear medium. With the increase of incident light intensity, the far-field diffraction light intensity distribution tends to be uniform. Increasing transmission distance in nano-suspensions leads to the increase of the number of far-field diffraction rings. The research results of this paper provide a new phenomenon for the study of the nonlinear characteristics of nano-suspensions, which has many critical practical applications and significance in the self-converging waveguide of nano-suspensions, micro-optical field regulator, atom capture, generation of hollow beams, nonlinear control of light field and so on.

The precision machining of hard and brittle materials has always been a research frontier and difficult problem in the industry. In this paper, it is verified theoretically and experimentally that 46.9nm soft X-ray laser can produce regular microcrack arrays on the surface of hard and brittle materials. Taking BaF2 and SiO2 materials as examples, based on the multiphysical field coupling numerical simulation method, the evolution process of temperature and stress, as well as the results of maximum stress section and strain are obtained, which can be used to predict the damage of hard and brittle materials processed by laser thermal cracking. The simulation results show that the maximum stress and strain of BaF2 have exceeded the strength limit, while the maximum stress and strain of SiO2 are less than the strength limit. The experiment shows the same result, that is, BaF2 has fracture failure while SiO2 has no fracture failure. The simulation and experimental results are the same, showing that the 46.9nm soft X-ray laser can be used for precision thermal cracking of hard and brittle materials.

Germanium is widely used as lens or windows in infrared optical systems, however, germanium optical elements may be damaged by melting under high energy laser irradiation. Therefore, it is necessary to carry out theoretical and experiment research on laser damage threshold of the germanium optical material. In this paper, the effect of laser beam diameter on the damage threshold of germanium was analyzed by numerical calculation. Besides, the difference of damage threshold represented using line power density and area power density was compared. It was found that when the diameter ratio of beam spot to sample was 0.02 to 0.09, the damage threshold decreased by 27.9% and 85.6%, respectively, when using W/cm and W/cm2 as the unit correspondingly. Considering the difference between the size of the beam and the element in optical system, the line power density is more suitable for extrapolation and comparison. In addition, the numerical results were verified by damage threshold experiment under the continuous laser of 1080 nm, which indicates the damage threshold of germanium is 263W/cm, 280W/cm and 290W/cm respectively, and the beam diameter is 0.5mm, 1mm and 2mm correspondingly. It was found that when the diameter ratio of beam spot to sample was 0.021 to 0.083, the damage threshold increased by 10.3% and decreased by 85.6%, respectively, when using W/cm and W/cm2 as the unit correspondingly. These results provide data support for the design and application of germanium optical elements to ensure the reliability of the high energy laser system.

Experimental research was conducted on the relationship between the graphitic crystallite in the ablation glass fiber reinforced epoxy composite and the microwave transmission decay at a frequency of 10GHz. Ablation samples were prepared by intense laser irradiation of 100W •cm^-2 for different time. The microstructure and component of the ablation samples were characterized by means of X-ray diffraction and Raman spectra. The electromagnetic characteristics were investigated by vector network analyzer at 10GHz. When laser of 100W•cm^-2 irradiated the samples shorter than8seconds, the microwave transmission decay remained small. When the laser irradiated the samples 8 seconds, the graphitic crystallites were detected and the microwave transmission decay escalated. With increasing irradiation time, the size and quantity of graphitic crystallites , as well as the microwave transmission decay increased. In brief, we concluded that the generation of graphitic microcrystallites induced by laser irradiation attributed to the microwave transmission decay.

Relativistic high-order harmonics from a few-cycle laser driven plasma surface is a very promising source of an intense and isolated attosecond light pulse. The laser to harmonics conversion efficiency and the “purity” of an isolated attosecond light pulse are generally determined by a combination of interaction parameters, such as laser intensities, incidence angles, pulse durations, carrier-envelope phases and plasma scale lengths. We had already previously investigated the effect of a three-parameter combination of the laser pulse duration, the carrier-envelope phase and the plasma scale length. To complement our previous work, the parametric dependence of the other two three-parameter combinations: the carrier-envelope phase, the plasma scale length, either combined with the laser intensity or the incidence angle, were systematically investigated through one dimensional particle-in-cell simulations. We found that, although the impact of parameter combinations on attosecond pulse generations is generally complicated, there exist however an optimal plasma scale length and an optimal incidence angle to efficiently generate high-order harmonics and intense attosecond light pulses. When other parameters are fixed, a moderately intense relativistic laser is more advantageous to realize an isolated attosecond light pulse in a broad controlling parameters range. And a larger incidence angle favors a higher isolation degree as well as a broader range of controlling parameters towards the generation of intense isolated attosecond light pulses. In order to interpret these simulation results, we have modeled the corresponding relativistic electron dynamics, using which the underlying physics are discussed.

Rayleigh Taylor instability (RTI), a fundamental physical phenomenon in fluid and plasma, plays an essential role in astrophysics, space physics, and engineering. In this paper, the two-dimensional numerical simulation of RTI produced by laser-driven multi-mode disturbance modulated target is carried out using the open source radiation magnetohydrodynamic simulation code (FLASH). The evolution of RTI under the condition of no magnetic field and different applied magnetic fields along the vertical flow direction is systematically investigated and compared. The simulation results show that the applied magnetic field in the vertical direction will be compressed and amplified by the plasma behind the target by 20 times to 200 Tesla. The amplified magnetic field has a stabilizing effect on the RTI and Kelvin-Helmholtz vortex at the tail of the RTI spike. The results provide a reference for the follow-up research on target physics related to ICF and help deepen the understanding of the fluid mixing process.

The X-ray properties of Al plasmas were studied experimentally by using the excimer laser facility in the State Key Laboratory of Laser Interaction with Matte. Radiated fluxes were recorded within two X-ray diodes, and the relative spectral distributions were recorded within an X-ray flat-field grating spectrograph, respectively. Experimental results indicated that the major X-ray photons were between 60 eV and 360 eV. By employing the spectral integration method, the measured data were appropriately processed to obtain absolute energies of the X-ray that radiated from Al plasmas.

In the high-power laser device, through precisely positioning the target and pointing multiple laser beams at a very small area on the target surface, the laser power density coupled with the target can be greatly improved and is conducive to the research of laser-induced plasma experiments. This paper proposes a set of target positioning and laser beam pointing system, which has advantages of high experiment efficiency, high target positioning and laser pointing accuracy. This system can automatically correct the attitude and position of targets, and make all laser converge together by adjusting their incident directions. It was verified that the target positioning error is 14.83 µm and the beam guidance accuracy is 9.70 µm.

With the continuous development of optoelectronics science, the widespread and intensive application of transparent optical elements has become an indispensable condition for the development of information technology in society. Transparent optical elements under the action of strong laser light are prone to produce plasma and even then cause damage to the elements. Therefore, it is important to study the process of interaction between transparent optical elements and strong laser light and its results. In this paper, a theoretical research and simulation study is conducted to investigate the characteristics of 1064 nm millisecond pulsed laser induced plasma generation in transparent optical elements represented by fused silica. It is demonstrated that the plasma propagation velocity and the temperature of each part increase with the increase of laser energy density during the interaction between the millisecond pulsed laser and the transparent optical elements; the plasma propagation velocity tends to increase and then decrease with the increasing of laser action time, and the temperature continues to increase near the threshold value；The plasma propagation velocity increases with the increasing of laser pulse width, and the velocity variation pattern is similar in all pulse widths; the temperature increases with the increasing of laser pulse width and approaches the temperature threshold that can be reached by the combustion wave generated by the interaction between the millisecond pulsed laser and fused silica. Finally, the kinetic characteristics and temperature rise phenomenon of the plasma propagation generated during the interaction between the millisecond pulsed laser and the transparent optical element are explained.

This work reports a novel image denoising and reconstruction algorithm based on unsupervised learning for removing Mie scattering interference in Rayleigh images. We first superimposed numerically simulated Rayleigh images and noise images acquired in experiment to generate noisy Rayleigh images as training data. The proposed unsupervised model was then trained based on unpaired datasets. Finally, extensive evaluations were conducted to demonstrate a convincing denoising result, which displayed an excellent reconstruction quality with a peak-signal-to-noise of ~41dB and an overall reconstruction error of ~0.5%. The results showed that our algorithm was able to provide an alternative method for noise reduction in two dimensional Rayleigh measurement of combustion.

In order to improve extraction ability of the two-dimensional HTV grid experiment data and achieve rich flow field velocimetry data. In this paper, a two-dimensional grid extraction method combining cross ponits and grid lines is proposed. A template indirect correlation method was used to extract the position of cross ponits. Based on the vector position information of cross ponits, two-dimensional inversion of convective field velocity is achieved by using the method of skeleton extraction with directional template. This method not only can extend the inversion data, but also can be used in the scramjet combustion flow field, that the relative uncertainty of calculation speed is optimized from 0.8% to 0.17%.

A technique that expands the OH-LIF thermometry range is developed. The PLIF of OH from dissociation of water in gas phase is used for temperature measurement both in flame and room air. The thermometry results from photo fragmentation laser induced fluorescence (PF-PLIF) at time delay from 200ns to 1ms after dissociation agree well with results from PLIF of OH from burning which are calibrated by CARS thermometry. And the results in room air agree with environment temperature at time delay from 50ns to 0.2ms. These two results validate the PF-PLIF thermometry method both in flame and room temperature, which allowing thermometry at low temperature or non-reaction region. At last the PF-PLIF was applied in a jet flow, and the temperature results from PF-PLIF, PLIF and CARS at different height of jet were compared.

In view of the surface temperature distribution and temperature rise measurement demand of metal target irradiated by high power laser, the thermosensitive phosphor surface temperature measurement technology was studied. The principle of two-color temperature measurement was introduced. After solving the key technologies of optical system optimization design, temperature distribution inversion calculation and high precision calibration, a compact thermosensitive phosphor surface temperature measuring system was developed. The temperature measurement range from room temperature to 1500 K, the space measurement range was greater than that of diameter 50mm, and the spatial resolution was better than 0.5mm. The thermosensitive phosphor surface temperature measurement technique was used to measure the surface temperature distribution and temperature rise of stainless steel targets irradiated by high power laser, and the results were compared with the results of thermocouple and numerical simulation. It is proved that the surface temperature measurement system can realize the measurement of surface temperature field distribution of high power laser irradiated target, and has high temperature measurement precision.

The time-resolved measurement of gas components in the impact vibration environment such as combustion and explosion is of great significance for understanding the internal state and reaction process. In order to realize simultaneous detection of various gas components under impact vibration conditions, a method based on shock-resistant multi-reflection cavity is proposed to enhance spontaneous Raman scattering. The measurement system is divided into two parts: host subsystem and detection subsystem, which are connected by optical fiber. The host subsystem is far away from the impact site, while the detection subsystem is located at the measuring point, which can effectively improve the impact resistance by curing components and increasing shock absorption. At the same time, by means of signal enhancement, the measurement system can realize second-order time resolution and reliable measurement of gas components in strong impact vibration environment such as explosion. At the same time, by means of signal enhancement, the measurement system can realize second-order time resolution and reliable measurement of gas components in strong impact vibration environment such as explosion.

Laser induced plasma spectroscopy (LIPS, also LIBS) is a promising technique for the challenging issues associated with the real-time and in-situ monitoring the major elements of aerosol particulate matters. A prototype of Aero-LIPS had been set up with the techniques of aerosol beam focusing, enhanced plasma emission collector and conditional data filter to demonstrate the potential application of air pollution composition monitoring. The prototype can identify more than 40 elements from aerosols and continuously monitor 20 elements with the time resolution of 10 minutes. In the field test of an Asian dust event, the major elements, such as Ca, Mg, Al, Si, Cl, P, S, etc. have been real-time monitored, which took 77.9% part of the total particulate matter mass. The evolutions of temporal elemental concentrations went well along with the particle matter concentration. It is interesting that several persist lines of U and Th have been detected from Asian dust aerosol while their concentration in local air should range in the level of nano-grams per cubic-meter. It might indicate that the enhanced-LIPS has a potential to monitor the nuclear facility emission for Nuclear Security and Safeguards.

High-precision flame spatial positioning technology has become a research hotspot in the field of on-board fire fighting protection for special vehicles. This paper proposed a high precision fiber-optic sensing spatial localization method based on Raman spectroscopy. By using the Field Programmable Gate Array (FPGA) to dynamically adjust the phase shift of the sampling clock^1-2, the Stokes signal and the anti-Stokes signal are spatially dynamically oversampled to achieve a 250MHz ADC which can hit an equivalent sampling rate of 2GHz after sample data recombination, and the flame spatial positioning accuracy can be up to 5cm. This method is based on the premise of guaranteeing the original index of fiber optic fire extinguishing device. It can effectively identify small flames. In the detection of fire events can also accurately give the specific location of the fire. This effectively solves the technical difficulties in detecting blind areas of special vehicle optical fiber fire extinguishing devices and greatly improves the flame positioning accuracy of fire extinguishing devices, which lays a foundation for accurate regional spraying of vehicle fire extinguishing devices.

Since the growing needs of broadband optical frequency combs (OFCs) in many applications, in this paper, a carrier suppressed dual-sideband modulation recirculating frequency shift loop (RFSL) with an additional piece of highly nonlinear fiber (HNLF) is numerically investigated. The numerical results indicate that, thanking to the RFSL scheme, the frequency spacing of OFC can be both widely and precisely tuned over the range of 0.5 - 40 GHz. Moreover, the comb lines generated from RFSL can be then efficiently increased, using four wave mixing effect of HNLF in the simulation, thus the spectrum is further broadened. This work contributes to an effective and compact RFSL scheme for a frequency tunable OFC generation with broadband spectrum.

Internal temperature monitoring of high speed propulsion system is of great significance for engine performance evaluation and life prediction. As a passive optical measurement method without external light source and flow field interference, emission spectrum measurement technology has a good application prospect in harsh measurement environment. As the main combustion product, high temperature water vapor has a high emission intensity in the near infrared band, which is very suitable for temperature measurement applications. The frequency band integral ratio is proposed to eliminate the high resolution measurement requirement of spectrum acquisition system, and the temperature distribution of swirl flame is measured successfully.

With the deepening of globalization, security inspection has gradually become a necessary means in many occasions. Therefore, rapid and accurate identification of components in the opaque shielding material, without destroying the outer packaging, has become a necessary detection method. Spatially offset Raman spectroscopy (SORS) , as a new Raman spectroscopy technology, can meet such demands. In this paper, the SORS of NaNO3 aqueous solution contained in opaque PTFE vessel has been obtained, using a self-built SORS detection system. In addition, some important parameters such as offset distance and detection concentration has been also studied experimentally.

In complex environments, the measurement of trace gases is inevitably greatly affected by broadband absorption (such as water absorption in combustion exhaust). Based on the study of high-order harmonics in linear wavelength modulation spectroscopy, a method for detecting target gases (trace, weak absorption) in the presence of broadband absorption interference is proposed. Theoretical analysis and numerical simulation work give the applicable conditions of this method. The effectiveness of this method is verified by NO2 measurement of combustion exhaust gas. This study proves the application potential of this method for the measurement of trace gases under broadband absorption interference.

Further development of hybrid propulsion systems requires a deeper understanding of the complex physicochemical mechanisms governing its combustion performance. A tunable diode laser absorption tomography (TDLAT) method was developed for investigating the thermochemical processes at the nozzle exit of an oxygen/Poly Methyl MethAcrylate (PMMA) hybrid rocket motor. Firing tests were conducted for different oxidizer mass fluxes ranging from 2.73 to 3.51 g/ (cm2·s). A distributed feedback (DFB) laser was tuned to cover three H₂O absorption lines near 2.5 μm, using scanned-wavelength direct absorption (DA) mode with 2.0 kHz repetition rate. Under an assumption of cylindrical symmetry, a Radon transformation was applied to yield radially- and time- resolved absorption coefficient, from which the radial distribution of temperature and H₂O partial pressure were reconstructed. Based on the Taylor series method (TSM), measurement uncertainty was analyzed in detail considering line-strength uncertainty, Voigt fitting residuals and Radon transformation. Finally, the radial distribution and dynamic variations of both temperature and H₂O partial pressure were obtained in all firing tests, both the constructed results show measurement sensitivity to chemical kinetic progress and oxidizer mass flux changes. Our experimental results highlight the capability of TDLAT to characterize combustion processes of hybrid rocket motors.

Accurate measurement of the kerosene pyrolysis content is of great significance to study the supersonic combustion and active cooling of supersonic engine scramjet. Methane (CH₄) and ethylene (C₂H₄) are two main gas products of the kerosene pyrolysis. In this paper, TDLAS technology is used to study the synchronous measurement methods of these two gas products in near infrared region. A kerosene pyrolysis gas simulation system was constructed with pure CH₄, C₂H₄, nitrogen (N₂) cylinders and gas mass flowmeters. A set of measurement system was built by distributed feedback laser (DFB) and Herriott gas cell with an optical path of 10.5m. The absorption spectrums are selected as 1.653μm for CH₄ and 1.626μm for C₂H₄. Five groups of mixed gas with different CH₄ and C₂H₄ concentrations between 0.5% to 3% was measured in the Herriott gas cell. The experimental results show that all the relative errors of the measured CH₄ and C₂H₄ concentrations are within 3.3%, which illustrated the measurement equipment and method used in this paper have high accuracy and reliability. This study provides effective experience for further on-line measurement of kerosene pyrolysis gas using off-axis integral cavity output spectroscopy (OA-ICOS).

The shape of OHp tagging signal line is complicated and changeable under the interaction of turbulence and combustion in HTV velocity measurement of scramjet combustion flow field. The light intensity distribution on the OHp tagging line is modulated, and the broadening degree is not consistent with the Gaussian distribution, so an optimal extraction method based on Hessian matrix is presented. Using the Hessian matrix, the gray distribution function on the cross-section of the tagging line is expanded in the normal direction by the second-order Taylor, and the precise position of the center line is obtained. Compared with line-by-line Gaussian fitting method, this method has better anti-distortion and anti-noise performance. The accurate extraction method of OHp molecular information is applied to the HTV velocity measurement technology in the scramjet combustion flow field, which improves the precision of the extraction and the accuracy of the HTV velocity measurement. It lays a foundation for the development and application of HTV.

Vector mode properties in a 3×1 conventional photonic lantern (CPL) are theoretically investigated. Analytical solutions of vector modes in fiber cores at the weak tapering region of a 3×1 CPL are derived based on coupled mode theory and linear combination method. While at the strong tapering region of a 3×1 CPL where core modes cut off, vector modes in cladding can be derived by ignoring the impact of original fiber cores. These analytical solutions are verified by numerical calculations by a fully vectorial finite element mode solver. Further investigation shows that although there is no linear polarization selection mechanism in the tapering region of a CPL, linear polarization (LP) modes are still suitable for CPLs only if fiber modes finally evolve into LP modes in the output fiber. This conclusion can be very useful for simplifying the mode analysis of CPLs.

Carbon fiber composite has been widely used in structural engineering applications, and research on the mechanical properties under various conditions is attractive. The study experimentally investigated the damage effect of CW laser ( λ=1064nm ) on carbon fiber composite strip under preloading. The effects of laser power and preloading on fracture morphology, temperature of the center of the irradiation area and fracture time were investigated. The experimental results show that when the preloading was lower than the fracture threshold, the laser irradiating could cause matrix damaging, fracturing with fluffy wire drawing and burning through for laser power density of 236.17W/cm², 407.39W/cm², 634.39W/cm², respectively. The maximum temperature of the spot center increased with the increase of laser power, with rising and falling edges varying in a stepwise way. Under the laser irradiation with the same power density, the higher value of preloading corresponded to the less fracture time. However, when the preloading was 20% over the fracture threshold, the influence of the laser power density was significantly reduced. Similarly, when the laser power density was 634.39W/cm², the fracture time was less influenced by the value of

Nanosecond (ns) pulsed laser with high average power and high pulse repetition rate above 50 kHz is a potential solution for laser cutting, laser welding, laser cleaning and many other industry processing scenarios. Although Nd:YAG is a widely used solid-state gain medium, it is difficult to obtain ns pulsed laser with repetition rate above 50 kHz due to its limited stimulated emission cross section and thermal distortion under high pump intensity. In this paper, a kilowatt-level 100 kHz high repetition rate ns Nd:YAG master oscillator power amplifier (MOPA) laser system is reported, and a general optimization method was used to obtain a 205 W seed laser with a high repetition rate of 100 kHz. After beam shaping elements, the seed laser was amplified to 1008 W by a two-rod Nd:YAG preamplifier and a two-rod Nd:YAG main amplifier. The pulse-to-pulse stability factor of the pulsed laser was 0.961 and the pulse width was measured as 142.8 ns. The beam parameter product in the horizontal axis and vertical axis were measured as BPPx = 2.81 mm∙mrad and BPPy = 2.78 mm∙mrad respectively. This is the first time to obtain a kilowatt-level average power ns pulsed laser with repetition rate above 50 kHz using Nd:YAG, and the compact MOPA system is also suitable for power scaling and other practical use.

Excimer lasers driven by linear transform driver (LTD) are expected to be used in inertial confinement fusion (ICF). The main problem of LTD in excimer lasers is synchronous triggering on multiple circuits, gas spark switches are important for synchronous triggering, which are required to be fired with low prefire probability and jitter. Multi-gap switch, as a kind of the gas spark switches, is always used in LTD. In this paper, a comparison study of corona discharge current of a multi-gap switch for LTD from the aspects of self-breakdown voltage and jitter is presented. The length of equalizing voltage needle was optimized by the electrical strength simulation. Using the optimized needle, the corona currents of the two gaps were measured, then it was found that the corona currents differ when the lengths of the corona needles were equal. To study if the difference of current in each gap affects the breakdown voltage and jitter of the switch, the length of the needle was adjusted to make the corona current the same. Then the breakdown voltage and jitter were measured under the two conditions of equal and unequal corona currents. It can be found that smaller the difference of current in each gap, higher the breakdown voltage and lower the jitter of the switch. It can be concluded that the corona needle can be adjusted to make corona current of each gap equal, which can be beneficial to increase the breakdown voltage and lower the jitter of the switch.

The square pulse output of Linear transformer driver (LTD) is of great interest for excimer lasers, where the efficiency can be greatly improved in this way. The design of square pulse output LTD within the single cavity was presented, then the influence of jitter and loop inductance on square pulse output was studied, it can be found that the higher the value of the jitter and loop inductance, the more the risetime of the voltage pulse, which hinders the shaping of the square pulse output. Then the method to change the square pulse width by varying the triggering times was presented, through the simulation, it is found that when the triggering interval is set to 15s, the square pulse characteristics of the voltage output are more obvious, the flat top is flat, and the pulse width is wider. The bricks within the single cavity can be designed by two methods, where the one is using the same sized capacitors, the other is using the different sized capacitors to synthesize a flat voltage pulse, the choice of the two methods should be based on the cost and requirements of the excimer laser, including the amplitude of the output voltage, the pulse width and the laser beam quality. The reference of designing the square pulse LTD can be provided by this paper

We demonstrated a periodically poled magnesium-oxide-doped lithium niobate (MgO:PPLN) optical parametric oscillator (OPO) pumped by a Nd-doped MOPA laser (1.064 μm) with a high peak power, tunable repetition rate, short pulse width. The OPO was designed as an extral cavity singly resonant OPO. By adopting optical pulse selection technology, the repetition rate could be adjusted in the range of 30-50 kHz without affecting the beam quality of the laser. The wavelength of output signal light was 1.57 μm when the polarization period and operating temperature of the MgO:PPLN were 30.5 μm, and 95 °C, respectively. In the range of 30-50 kHz, the pulse width of the laser was less than 4.9 ns and the average power was greater than 8.43 W. A maximum peak power of 63.9 kW was obtained at a repetition rate of 30 kHz, with a corresponding pulse width of 4.4 ns.

Ultraviolet ultra-short pulse laser has incomparable advantages in strong field physics and fast ignition of inertial confinement nuclear fusion. In addition to the short wavelength and strong focusing ability, UV laser has a larger critical density and is closer to the over-dense fuel target region, thus simplifies all the process relates to the energy transport. Based on the I-λ 2 scaling law, ultraviolet laser is enough to produce hot electrons with the temperature required for fast ignition. Meanwhile, excimer laser has unique advantages in amplifying ultra-short pulses. In order to increase the laser energy irradiating on the target, the amplifier with larger energy cross section and higher energy extraction capacity are required. In this paper, a method of beam combination amplification of ultraviolet ultrashort pulse laser in a discharge-pumped excimer laser amplifier has been explored by conjugated polarization, and the feasibility of applying this technique to excimer laser is verified.

Experimental researches of the near-infrared laser with 1085nm wavelength and the mid-infrared laser with 3.8 microns wavelength irradiate on the transparent polyethylene film with a thickness of about 25 microns are carried out. Results show that the burn through time approximate exponentially decreases from 5.76s to 0.85s, for the average power density of the mid-infrared laser increases from 2.9W/cm2 to 37.2W/cm², and the damage energy density is about 22.2J/cm². The polyethylene film can be burned through by near-infrared laser irradiation with an average power density of 338.8W/cm2 for 18.6s, and the corresponding damage energy density is up to 6301.7J/cm². The failure time exponentially decreases from 18.6s to 0.75s with the incident laser density increases from 338.8W/cm2 to 428.5W/cm², and the corresponding damage energy density approximate exponentially decreases from 6301.7J/cm² to 321.4J/cm². The damage of near-infrared laser has obvious threshold effect. The polyethylene film would not be burned through until the laser power density reaches a certain high value, so the damage threshold of polyethylene film by near-infrared laser is 1 ~ 2 orders of magnitude higher than that by mid-wavelength infrared laser. The results are in good agreement with the absorption ratio of polyethylene film at wavelength of 3800 nm and 1085 nm measured under weak light.

A diode pumped alkali laser (DPAL) provides a significant potential for construction of high-powered lasers. To realize the scaling of a DPAL, heat management should be optimized. In this paper, a new kind of gas-flowing DPAL was proposed, in which a small cross-flow fan with diameter of 80 mm was set in the center of a cylindrical vapor cell whose diameter is 125 mm. The gain medium of cesium and the buffer gas of ethane were filled in the vapor cell with the total pressure is about 1 atmosphere. A mathematical model was constructed to systematically study the influence of the rotate speed, the heating temperature on the internal temperature distribution, and the output features of the laser.

To obtain low jitter and high energy ultraviolet laser pulse, the XeCl excimer laser pumped by electron-beam was reported. The construction and the principle of the XeCl excimer laser with electron-beam pump source were described. Experimental study on laser output characteristic of the XeCl excimer laser was carried out, and effects on pressure of mix gas in laser chamber and charge voltage on jitter of laser pulse were showed. When the charge voltage of the laser is 81kV, the output energy of XeCl excimer laser was about 100J, its electric efficiency was about 0.58%, and the laser pulse jitter was less than 20ns.

For the high power laser system, the power of laser to the target, the power of the bucket and the beam quality are important parameters, which have important value of identification and evaluation. However, the power density of high power laser are too high to affect the test system. And the high precision attenuation method of Fresnel reflection method can effectively solve this problem. The laser incidents on Front surface of uncoated dielectric material at near normal products different reflectivity of components in s-direction and p-direction. The effect of the difference of reflectivity can be effectively solved by placing a pair of wedge off the axis and changing the polarization state of the reflected light, the reflectivity of the S-direction is as same as p-direction components at every two stages by two normal vertical reflectors. The accurate reflectivity can be obtained according to the refractive index coefficient of dielectric materials. Under the condition of low-power near-infrared power incident light, the calculated results are consistent with the measured results. And under the condition of high power density, we study the thermal deformation of fused silica mirror. A mirror thermodynamics model based on the software was built. And experimental measurements for thermal deformation were performed with laser intensity as high as 44 kW/cm². The thermal deformation mainly depends on the absorption of the film layer. Therefore, shape variables can be significantly reduced by using a non-coated lens or reducing the absorption of the film.

A new scheme for Stimulated Brillouin Scattering (SBS) suppression is proposed based on multi-point pump technique. The pump power is coupled into the double-clad fiber by several pump points instead of one fiber combiner, which will rearrange the pump power distribution along the active fiber and influence the amplifier process of SBS light. The numerical simulation indicates that SBS is effectively suppressed in a fiber amplifier with an output up to 700W and a 1kHz line-width by virtue of the configuration. Besides, the SBS threshold demonstrates a 3.7 times increase compared with an strain allied scheme.

In order to obtain more information of far-field beam profile from limited measured data, a novel super-resolution reconstruction method for far-field beam profile based on deep learning is proposed. In this paper, the high/low resolution spot image sample is obtained by simulation, the EDSR neural network training model is used to study the mapping relationship between high/ low resolution spot images, and the super-resolution reconstruction method based on deep learning is realized. The experimental results show that the super-resolution reconstruction based on deep learning is superior to the conventional algorithms in PSNR and SSIM.