This PDF file contains the front matter associated with SPIE Proceedings Volume 11562, including the Title Page, Copyright Information, and Table of Contents.

For the past years, ArF immersion has been employed as the major lithography tool in the foundry manufacturing to fabricate the patterns of minimum pitch and size. However, for semiconductor scaling beyond N7 the application of EUV lithography is considered to be crucially important to overcome the physical limitation of ArF immersion and to realize even smaller patterns. In the case of ArF photo processes, the best mask size for a specific pitch could be selected with the consideration of optical performances such as NILS, MEEF, etc. In contrast, for the EUV processes the optical and resist stochastic effect should also be taken into account as an important factor in deciding the best mask size. In this paper, we are going to discuss the dose and mask size optimization process for an DRAM contact hole layer with EUV lithography utilizing stochastic simulations; this contains also the stochastic response of the resist. In order to calibrate a predictive stochastic resist model, which is required for this application, measurements of the stochastic resist response are necessary. In addition, the systematic and stochastic errors of CD-SEM measurements have to be estimated. We will compare experimentally obtained NILS and MEEF to simulated results, which are in very good agreement. Also, we show a comparison of experimental and computational analysis of LCDU (Local CD Uniformity).

The high gain of pumping end in end-pumped all solid state lasers can easily cause self-excited oscillation, which limits the output energy of Q-switched laser. In order to obtain a 1064 nm Q-switched laser with high energy, high conversion efficiency and compact structure, the following three aspects are mainly studied to suppress the self-excited oscillation caused by the end pump: (1) the doping concentration of active particles is optimized to reduce the end gain of laser medium, (2) the wavelength of pump light is changed by adjusting temperature of laser diode to deviate from absorption peak of Nd:YAG, (3) Nd:YAG rod is processed by tapered side, which improves the difficulty of self-excited oscillation. By using the above techniques, a 1064 nm Q-switched laser with output energy of 100 mJ is obtained at a pump current of 20 Hz and 170 A, and the corresponding dynamic to static Q-switching ratio is 77%. The three technical means proposed in this study complement each other and work together, providing a practical and effective technical way for obtaining high-energy end pumped Q-switched laser.

We demonstrate passively Q-switching in a 2.1 μm Tm/Ho composite laser via developing a hybrid cavity to separate the intra-cavity Tm laser from modulated by the saturable absorber (SA). Enhancement in Ho laser efficiency was demonstrated in the proposed hybrid cavity, compared with the common two-mirror laser resonator. Using the crystalline Cr:ZnSe SA, maximum average output power of 553 mW at 2090 nm under absorbed 808 nm LD power of 6 W was obtained at pulse repetition rate of 9.5 kHz. Using layered WSe₂ SA fabricated with the CVD process, maximum Ho laser power of 141 mW with pulse width of 185 ns at a repetition rate of 33 kHz was obtained. The current gain medium could be replaced with other hosts such as YVO_4, YLF, and YAP with natural birefringence, which facilities a potential polarized pulse Ho laser. Also, the current SAs could also be replaced by other nanomaterials with controllable broadband saturable absorption such as gold nanorods,topological insulators and carbon nano tube for seeking novel pulse Ho lasers.

We present a simple method to measure the width of a focused laser beam, where we define the width as the radius of the beam at which the intensity is 1/e2 of its on-axis value. Our method is based on measuring the power of light reflected off a metallized microstructure patterned on a oxidized silicon substrate that is placed on a tri-dimensional positioner. As the boundary between the microstructure and the substrate is scanned across the beam, changes in reflected power provide a quantitative measurement of the width of the beam. Our method is a useful alternative to the knife edge technique if optical measurements in transmission are not possible.

A high-power all-fiber ytterbium-doped picosecond fiber laser was developed using the main oscillation power amplification (MOPA) structure. The seed laser source was based on a novel two-dimensional perovskite material ((CH3NH3) PbI3) as a saturable absorber, achieving a stable picosecond with the center wavelength of 1063.8nm, the repetition frequency of 18.51MHz, the linewidth of 5nm, and the average power of 10.56mW. Based on this, four-stage pre-amplification and one-stage main power amplification were used to achieve high-power picosecond pulsed all-fiber laser output. The center wavelength is 1064.7nm, the linewidth is 8nm, the pulse width is 17.2ps, and the repetition frequency is 100MHz. The average output power is 51.5W, and the optical conversion efficiency is 56%.

Street trees are important elements of urban ecological environment. Due to the complex shape of trees, there is still no effective means to identify trees from Mobile Laser Scanning (MLS) point clouds. Aims to segment single street tree from MLS point clouds, this study proposed a new method of extracting street trees by dimensional feature analysis and improved FCM method. After filtering MLS point clouds, dimensional features are introduced to detect candidate tree trunk and tree canopy points. Then, region growing method and cross-validation method are used to extract street tree points according to tree semantic rules. Thirdly, tree positions are taken as initial values for the FCM algorithm to cluster tree points, which also are used to limit the change of the cluster center during cluster process to improve the segmentation effect of trees with overlapping canopies. To evaluate the performance of the method, datasets with different size street trees are tested in the experiment and results show that the proposed method can segment single street trees from MLS point clouds effectively.

The mode-locked fibre laser technology has significantly simplified ultrashort-pulsed lasers. It introduced their design as maintenance-free systems approaching in convenience standard laboratory equipment or commercial devices, which do not require special training for their operation. These advantages find their fullest expression in all-fibre configurations where all intra-cavity laser radiation propagates within the core of the cavity fibre. This isolation of intra-cavity laser radiation has both advantages (higher stability, more compact implementation, etc.) and drawbacks: controlling generation properties of an all-fibre laser requires unusual means and methods, such as are not normally employed in non-fibre lasers. This review covers these special means and methods with an emphasis on the possibilities and advantages of electronic control over the generation parameters all-fibre mode-locked lasers.

Publisher’s Note: This paper, originally published on 5 November 2020 was withdrawn on 1 December 2020 per author request.

We propose a fiber-solid hybrid amplifier system which consists of a semiconductor saturable absorber mirror (SESAM) mode-locked fiber seed with pulse width of 10.6 ps and repetition rate of 17.6 MHz, a two-stage fiber pre-amplifier and a Nd: YAG regenerative amplifier. This structure not only endures high peak power, but also reduces the influence of fiber nonlinear effects. In the regenerative amplifier, a Pockels cell made up of BBO crystal is used as the electro-optical Q switch. It can effectively amplify the fiber seed source while keeping the beam quality constant. Besides, the pulse frequency, round trip time and thermal lens effect of the regenerative amplifier are considered and the stability of the high repetition rate regenerative cavity is further improved. The system achieves average powers of 1.5, 2.5, 3.4 W at the repetition rates of 1, 3, 5 kHz, corresponding to single pulse energies of 1.5, 0.83, 0.68 mJ respectively. And the beam quality factor M₂ reaches 1.5 at the output power of 3.4 W. This system will make significant contributions to many fields such as material micro-processing, laser ranging, and laser detection. To make it more systematizing and engineering, we design an engineering prototype of the fiber-solid hybrid amplifier system.

The Optical Parametric Oscillator (OPO) is a simple and effective method to generate desirable and specific wavelength. The OPO laser is small, portable and has high efficiency, low threshold and can be operated at room temperature. In this paper, we report an electrically controlled tunable optical parametric oscillator operating from wavelength of 3.0 to 6.7 μm. The nanosecond OPO is based on BaGa4Se7 (BGSe) crystal and pumped by a 10 ns 1.064 μm electro-optic Q-switched Nd:YAG laser. The output mid infrared idler wave can be tuned from 3.0 μm to 6.7 μ with pulse energy as high as 2.55 mJ at 3.8 μm and can be even increased with more pump power. The output idler wavelength can be tuned by turning the rotation angle of the crystal, which is controlled by an electronic motor. The motorized continuous rotation stage is compact and highly precise with minimum rotation step of 0.0025°. This enables the fine tuning of the phase-matching angel and the resulting output wavelength. The central idler wavelength is 4.6 μm (rotation angle is 0°).

In this paper, the current generated by the photoconductive antenna was calculated using the Drude-Lorentz(DL) model. Influence of the structural parameters of SI-GaAs dipole antenna on the terahertz radiation characteristics was studied using CST Microwave Studio software. The results indicate that the length and width of the antenna are appropriately smaller, which can increase the radiated power. According to the simulation results, silicon-based antennas with radius of 0.5 mm, 1 mm and 1.5mm were designed, and the influence of the radius and extended length of the lens on the antenna performance was studied. The results indicate that when the radius is small, the lens antenna has a peak gain in the high frequency band, and the radiation spectrum bandwidth of the lens antenna will increase significantly. When the ratio of extended length to radius is 0.28, the directivity of the lens antenna is better, and the peak gain of 0.5-mm lens antenna is 26.1 dBi. A 2×2 dipole antenna array was designed. The radiated power of the array element is about 10 μW, and the signal-to-noise ratio of the array element is about 50 dB. The antenna array was tested using a terahertz time-domain spectroscopy system (THz-TDS). The results indicate that the peak value of the time domain waveform of the 2×1 array is about twice the peak value of the array element, and the superposition of the time domain waveform is achieved. The peak value of the time domain waveform of the 1×2 array is lower than the peak value of the array element. The radiated power of the 2×2 antenna array has increased in this design, and the peak value of the antenna array has increased by about 3.5 times.

For reducing the self-excited oscillation of end-pumped laser, the laser properties of the end-pumped Nd:YAG Q-switched laser is investigated with different Nd³⁺ ion doping concentration. The experiment results indicate that the output energy of the end-pumped Nd:YAG Q-switched laser is saturated when the pump energy is greater than 467mJ with 0.6% Nd³⁺ ion doping concentration, and the maximum output energy of 62.9mJ is generated under the pump energy of 498mJ, corresponding to the optical conversion efficiency of 12.6%. When the Nd³⁺ ion doping concentration decreases to 0.4%, the output energy of the end-pumped Nd:YAG Q-switched laser increases continuously with increasing pumping energy, the output energy is up to 64.7mJ under the pump energy of 498mJ, corresponding to the optical conversion efficiency of 13.0%, and no saturation occurs. By optimizing the structure parameters of the pump system, a 82.1mJ 10ns 1064nm laser is obtained under the pump energy of 527mJ, corresponding to the optical conversion efficiency of 15.6%. In view of the saturation of output energy in the end-pumped Nd:YAG Q-switched laser, Nd³⁺ ion doping concentration adjustment is carried out to reduce the pump end-face gain of laser medium, the self-excited oscillation can be effectively suppressed, an effective technical means for obtaining high-energy end-pumped Q-switched laser output is provided.

Chinese traditional lacquerwares, ornamental objects decorated by multiple, composite layers of lacquers, are one of the most significant expressions of China art. Existing X-ray radiography and other detection technologies will cause irreparable damage to the lacquerware due to their high photon energy. Terahertz time-domain spectroscopic reflectometric imaging (THz-TDSRI) system being capable of highlight interfaces between layers in a stratigraphic buildup, could be a complementary technique for obtaining structural information about lacquered objects. In this study a Chinese lacquerware has been investigated by terahertz (THz) reflectometric imaging. The investigated lacquerware belongs to Palace Museum. The lacquerware is a decorative work made of a wood panel covered with several layers of lacquers to depict motifs. In order to detect lacquerware, the THz-TDSRI system was built by us. For imaging applications, the source of contrast is the optical density of materials and in reflection geometry the back-reflected THz pulse is analyzed for reflections originating from the various interfaces present between the various sample layers. The value of the electric field measured for each spatial coordinate (X, Y) of the scanned areas has been used for the bidimensional visualization of the lacquerware. The displaying method used in THz imaging application is pseudo coloring. Utilizing THz-TDSRI system, we observe non-invasively buried layers of the lacquerware, including faults in the wood layer, with the lacquerware was not injured. This shows that THz time-domain spectroscopic reflectometric imaging is a non-destructive inspection method for lacquer ware and has great potential in the future.

Aim at the shortages of the laser system simulation software EasyLaser v1.0, the function architecture and simulation ability of EasyLaser were designed and upgraded, and the EasyLaser v2.0 was developed, which can much more fulfill the requirements of the design and the analysis for the real complicated laser systems. The improvements include modeling with multi-level relative coordinate systems and importing the engineering entity models. In the end, a simulation example was given to show that the laser propagation effects in complicated systems can be simulated, and the modeling efficiency and the authenticity and intuitiveness were improved.

In this paper, we report a simpler and efficient hybrid laser amplification system, which delivers a single pulse energy of 20 mJ at 500 Hz with a pulse width of 278 ps. This hybrid amplification system mainly consists of a hundred-picosecond all-fiber structure seeder, a regenerative amplifier and a single-pass amplifier. The hundred-picosecond laser pulse from the fiber seed is first amplified to 4 mJ by a regeneration amplifier with a normally doped Nd:YAG rod. For the improvement of the laser energy, the QCW side-pumped Nd:YAG single-pass amplifier has been adopted at the second stage of solid-state amplifiers. To reduce the serious thermal effect, the bonded composite YAG-Nd:YAG-YAG rod crystal is used as the gain medium, which possesses 6 mm in diameter and 85 mm in effective pumped length, and a doping concentration of 0.8%. Finally, 20 mJ output energy and 278 ps pulse duration are obtained with a peak power of 72 MW, and its beam quality factor is 1.7. In addition, this laser amplifier is confirmed by latter theoretical simulations of laser-induced plasma in silicon-based photodiode. The high-energy amplification of the hundred-picosecond pulse is realized in this hybrid amplifier system, which will be used as laser irradiation source in laser-induced damage application.

For the asymmetric plane-plane cavity, the influence of cavity length as a variable factor on the thermal lens diopter, dynamic stable zone, and modes selection in the stable zone is discussed. The relationship between the length of the cavity and the width of the dynamic stability zone is pointed out. The influence of the ratio of the long arm to the short arm on the degree of separation of the various oscillation modes is indicated. A suitable pump operating point for modes selection is indicated. A end-pump Nd:YVO₄ cavity with different long arms is built up for modes selection experimentally, the fundamental mode and hollow beam (TEM₀₁+TEM₁₀) output are observed in the experiments, which are concordant with the theoretical predictions.

We develop a theoretical model of multimode rate equation that accurately describes mode evolution mechanism of prelase Q-switched Pr3+:YLF single longitudinal mode (SLM).The theoretical simulation process explained each part of the operation and experimental phenomenon in the pre-lase process effectively.We identify that there is an optimal parameter for the two step signal of acoustic-optic modulator which determines the stability of SLM output.Our theoretical model can be applied to most solid-state lasers, and offer theoretical references for the design and construction of experimental facilities, which is significant for future research.Up to now, there is still not a complete theory to accurate description of prelase Q-switching technology. Moreover, there have been no reported about directly emitting Q-switched SLM laser in the visible region.

In this paper, the surface temperature rise and damage morphology of biased Si avalanche photodiodes (APDs) fabricated in external capacitor circuit irradiated by 1.0ms and 1.5ms pulse width laser are studied. The effects of external capacitance on surface temperature rise and damage morphology of APD irradiated by pulsed laser under different laser energy densities were compared and analyzed. Compared with the absence of external capacitance, the existence of external capacitance reduces the surface temperature of Si-APD and has a certain impact on the damage morphology. The results show that under the same external capacitance and laser energy density, the surface temperature rise of APD treated by 1.5ms pulsed laser is lower than that of 1.0ms pulsed laser, and the surface temperature rise of APD decreases with the decrease of external capacitance.The results show that the existence of external capacitance can further improve the laser damage resistance of Si-APD.

A dual-wavelength alternately Electro-Optic (EO) Q-switched output laser operating at 1064 and 1319nm is demonstrated. The mathematical model describing the operation mechanism of alternately Q-switched output of dual-wavelength laser was put forward, and the principle of the dual-wavelength laser alternately Q-switched output was analyzed. When the full pumping current of Nd:YAG (A) crystal is 90 A and that of Nd:YAG (B) crystal is 70 A, alternating dual-wavelength pulsed lasers are achieved with a delay of 200μs at the pulse repetition frequency (PRF) of 10 Hz under the voltage on RTP crystals of 1000V. The results show that the experimental results were consistent with the theory, which proved the correctness of the theory of dual-wavelength laser alternately Q-switched laser.

As a new bottom-up processing method, femtosecond laser two-photon polymerization (TPP) technology, has the advantages of simple working environment, high resolution and flexibility, which is widely used in the fields of micro-optical devices, micro-mechanical devices and micro-fluid devices. Structures with different chemical or physical properties on either side are called Janus structures. In particular, when there is difference in expansion coefficient between the two sides of the Janus structure in different external environments, the structure as a whole will show shape changes controlled by the external environment, so processing Janus structure is an important way to achieve structural deformation. The key to prepare the Janus structure is the uniformity of the diprosopic structure itself. At first, we fabricate ordinary micropillars by focusing controllable femtosecond laser into photoresist (SZ2080). Then the vacuum evaporation technology is used to transform the ordinary micropillars into Janus micropillars by steaming metal on one side of the micropillars. These Janus micropillars will have a directional bending towards the side of coating metal. This phenomenon is analyzed theoretically and simulated numerically by COMSOL, which is verified by experiments. Since the thermal expansion coefficients of different materials on both sides of the micropillar are different, these Janus micropillars have the ability to change their shapes with the change of temperature, which have potential applications in temperature drive and temperature sensing.

The premise of the rapid establishment of Free Space Optical Communication Based on Cat's Eye Modulating Retroreflector (CEMRR FSO) link is that the CEMRR terminal can modulate incident beam and reflect it reversely to the drive end. The influence of cat’s eye effect on CEMRR FSO link gain is a crucial research content. Focusing on the influence of cat’s eye effect on CEMRR FSO, a cat’s eye effect model under defocus will be established firstly. Next, the characteristics of cat’s eye optical system under positive and negative defocus oblique incidence will be studied. Finally, the influence of cat’s eye effect on the characteristics of reverse reflection will be verified through simulation experiments, which will provide the basis for the design of the CEMRR optical system.

The ceramics is easily broken due to various reasons. These reasons include unearthed excavation, careless operation and so on. When the ceramics is broken in pieces, the antique restorers take advantage of the adhesive to stick these fragments together to exhibit the beauty of original cultural relics. Therefore, the removal of adhesives such as adhesives on the cross-section of ceramic samples is a very important link in the restoration and protection of cultural relics and has important significance. In ancient times, the way of restoring these ceramics is so inappropriate and unreasonable that the adhesive is left among the cross section of these pieces. It becomes a problem for the following antique restorers. In order to solve this problem, we select a piece of the ceramics that possess above characteristics by utilizing laser to clean the left adhesive on the cross section tentatively. To better explore the optimized cleaning parameters relatively, we have made standard samples of adhesive to get better cleaning effect. These results will provide the reference value to our following study.

Cirrus clouds are widespread in the atmosphere. The inhomogeneous distribution of ice crystals in the cirrus cloud has a serious impact on laser communication with high accuracy requirements. This study improves the traditional model and proposes inhomogeneous plane-parallel model for laser transmission in different atmospheric environments. In the model we consider the vertical variation of ice particle density. Four examples demonstrate direct transmission and first-order scattering power in four different environments (rural, city, ocean and desert) after a 1.55 μm laser transmits through inhomogeneous cirrus clouds. The results show that the closer the receiving terminal is to the ground, the greater the attenuation of the laser by atmospheric molecules and aerosols. When the visibility is 5km, the attenuation in the city is greater than in the rural. When the aircraft is in the cloud, inhomogeneous cirrus clouds cause direct transmission and firstorder scattering to be different between the cloud top and the cloud base. This study will provide a more accurate theoretical model for the application of laser communication to aircraft and serve as a guideline for further laser communication experiments and network technology research.

We firstly demonstrated an obtainable Ho:YAP laser intra-cavity pumped by a diode-pumped Tm:YAP laser. A common 792 nm AlGaAs fiber coupled laser diode was used to pump the a-cut Tm:YAP crystal. In the Tm laser experiment, a maximum output power of 1.9 W at 1958.4 nm was obtained, corresponding to a slope efficiency of 12.1 %. In the Ho laser experiment, a maximum output power of 1.1 W at 2118.2 nm was obtained with a slope efficiency of 8.9% for 21.9 W diode incident pump power on the Tm:YAP crystal. At the maximum output power of the Ho laser, beam quality factor (M²) was measured to be 1.79 and 1.72 in the horizontal and vertical directions, respectively. Further improvement in the performances of the current Ho:YAP laser is predictable via direct producing a more compact gain module by adhesive-free bonding of Ho:YAP to Tm:YAP crystals.

According to the requirement of system，an one-dimensional beam shaping system is designed for semiconductor laser. In this beam shaping system, we choose an aspheric cylindrical mirror as the shaping element. To design the aspheric cylindrical mirror, we first calculate the incipient structure and then use the software light tools to optimize and simulate. The result shows that for a semiconductor laser whose beam diverging angle is 40°, the diverging angle will smaller than 1mrad after shaping by the aspheric cylindrical mirror. Also, we test the actual beam shaping system and the result shows that it meets the requirement of system well.

Spacebornelaser communication system utilize laser to transfer information, which can realize star to star, star to earth communication. It hasthe advantage of wide bandwidth, high anti-jamming capability, good secrecy performance, small size and weight, and lower power dissipation. Laser communication telescope, which is use for laser beam alignment, is the main part of spaceborne laser communication system to realize long distance transmission. As transmit-receive integration is the mainstream form of spaceborne laser communication system in current, isolation become a kernel index which determined the signal-to-noise ratio and transmission distance. Optical telescope of coaxial two-mirrorreflective structure and off-axis three mirror reflective structure were built, and stay light analysis was done on both kind of laser communication telescope to get the isolation. The results show that the isolation of coaxial two-mirror reflective optical telescope is 62dB and the isolation of off-axis three mirror optical telescope is 70dB. Furthermore, the results show that mirror scatter is the dominant influence factor of isolation. Through comparative analysis of two forms of optical system, under the same condition, off-axis three mirror optical telescope has a better performance in isolation.

The research focuses on measuring body wave by continuous laser scanning along the surface of aluminum plate. The model of aluminum plate was established by finite element method. The temperature near the upper edge rises, and the temperature rise is small. In infinite large aluminum plates, there are transverse and longitudinal wave front, and the wave front velocity is affected by the velocity of the scanning laser source. Finally, the wave front in plate bottom is used to identify the wave front type, which is generated by scanning laser and determined by combining the relationships between wave velocity and scanning velocity and Bscan diagram.

Laser damage threshold is one of the most important parameters for optical materials used in ultrafast laser system and the related application system. We have investigated experimentally laser damage threshold on the surface of gold sample induced by femtosecond laser pulses using a so called ablation diameter regression technique. More than one ablation regime, which has logarithmic relationship between the ablated diameter and the laser fluence, has been found. Correspondently, laser damage threshold for gold sample is almost one order of magnitude in difference, from 1.55 J/cm² to 12.01 J/cm² . In our opinion, accurate calibration of the damage threshold for optical components should be done with laser fluence close to the damage threshold.

We have experimentally demonstrated the generation of DSR in normal and anomalous dispersion regimes by using a chirped fiber Bragg grating (CFBG) for dispersion management. The dispersions of our proposed laser are calculated to be around +5.34 ps² and -2.66 ps² with different directions of CFBG. By properly adjusting the polarization state and pump power, we can achieve two kinds of square pulses with different shapes at the fundamental frequency of 3.58 MHz and 3.583 MHz, respectively. The width of square pulse can be tuned from 1.65 ns to 5.43 ns in normal dispersion regime. The width of square pulse can be tuned from 1 ns to 2.7 ns in anomalous dispersion regime.

Terahertz (THz) wave has significant potential in label-free biomedical diagnosis because of its fingerprint spectrum and noninvasive and nonionizing properties to living organisms. Here, a transmission continuous-wave THz spectroscopy system was used to measure 3 groups of human cancerous and normal ovarian tissues. Fresh tissue samples were made into paraffin-embedded tissue sections with a thickness of 1-2 mm, and the THz transmittance spectra of these samples were obtained in the 0.4-1.5 THz range. These results indicate that cancerous ovarian tissues have a higher THz absorption compared with normal ones. The absorption peaks at 0.588, 0.748 and 0.812 THz of normal ovarian tissue get weaker and even disappear in the transmittance line of serous ovarian cancer tissue, while the absorption peak at 1.396 THz get enhanced. Our preliminary results demonstrate the promise of continuous-wave THz spectroscopy technology in label-free ovarian cancer detection.

This paper reports a zigzag-pump polygon amplifier and has more detailed simulation about it. Study on the pump light distribution in the gain medium with different side cut angle and doping parameters. Through the optimization of laser system parameters, a nearly uniform flat-top energy storage distribution is obtained through simulations. In addition, we have some preliminary simulations analysis of the thermal effect of the medium. This paper provides many references for the design and experiment of zigzag-pumping laser system.

Copper based alloy is widely used to manufacture shaped charge liner. Limited by conventional manufacturing technology, complex liners are hard to produce. While the additive manufacturing (AM) is capable to produce parts of almost any geometry and intricacy. In this paper, the CuSn10 bronze shaped charge liner was manufactured by AM technology and the penetration performance of the liner was analyzed. Experimental results show that the liner made by AM technology could be applied under high stress-strain conditions, the penetration depth of CuSn10 liner is 18.9 % larger than that of traditional copper liner.

In this paper, a two-stage phase control method was proposed to increase the control bandwidth of the target-in-the-loop coherent beam combining (CBC) system. Firstly, the principle of the target-in-the-loop CBC system based on two-stage phase control was introduced. In order to verify the feasibility of two-stage phase control technology, then a 7-channel fiber laser array beam combining system was established. The experimental research showed that when the phase noise in the fibers and on the transmission path from the collimators was controlled by two phase controllers respectively, the laser array coherently combined in the far field stably. The power in bucket was 11.4% in the close-loop, which was 70.1% of the theoretical value. The normalized mean voltage detected by the photoelectric detector increased from 0.107 to 0.648, with an increase of 6.1 times. This experiment initially verified the feasibility of the two-stage phase control method, which will be helpful for the control bandwidth increasing in the target-in-the-loop CBC system.

We propose a compact all fiber Yb-doped rectangular burst-mode laser with high inter-burst repetition rate (~MHz) and high intra-burst repetition rate (~GHz). In this burst-mode fiber laser, the dissipative soliton resonance (DSR) passive mode-locked laser is employed to generate tunable rectangular burst-mode pulse while combining with active modulator (Electro-Optic Modulator, EOM). Tunable burst-mode pulse is achieved includes 5-10 ns of tunable burst duration, 0.8- 1.5 GHz of adjustable intra-burst repetition rate and tunable intra-burst duty cycle. The inter-burst repetition rate is 1.58 MHz. This system combing with such parameters can be employed to generate ultra-high repetition rate microwave signal at high frequency band.

In this paper, the lateral single-mode emission from 1064nm edge-emitting (broad area) BA diode lasers with laterally coupled passive waveguide (LCPW) structures is presented. The LCPW structure is introduced to both sides of the broad active waveguide, and the high-order lateral modes can be tunneled into the LCPW, which results in an increase in higher-order lateral modes loss and an increase in the 2D optical confinement factor difference between fundamental lateral mode and higher-order lateral modes, thereby suppressing the higher-order lateral modes. The influence of LCPW structure on the suppression of higher order lateral modes in broad area lasers are investigated. The results show that for the semiconductor laser with active waveguide width of 15μm, the introduction of LCPW structure effectively eliminates the high-order lateral modes and achieves a single lateral mode output.

We carried out a comparative study on laser cutting of fiber-reinforced plastic and its honeycomb sandwich structure widely used in aeronautic industry. The influence of pulse duration (CW, ns, ps and fs), wavelength (MIR, NIR, and NUV) on cutting quality (characterized by the HAZ) and productivity was experimentally studied. It was demonstrated that for either the aramid fiber reinforced plastics/polymers (AFRPs) or high-modulus carbon fiber reinforced plastics/polymers (CFRPs) and its honeycomb sandwich structure, tradition laser cutting was unable to satisfy the requirements of the appearance qualities in the astronautic industry due to the thermal damage induced discoloration, in spite of the less extension of damage than the contact machining used currently. The pulse duration effects on HAZ, the wavelength effects on cutting quality and productivity, the differences and similarities for low-HAZ cutting of AFRPs and high-modulus CFRPs, was studied, and the possible physical origins was discussed.

In the construction period and operation period of an urban subway, due to the comprehensive impact of geology, groundwater, the construction of adjacent foundation pits and the load of its own structure, the tunnel structure of the subway may go through deformation and other changes that endanger the safety of the tunnel. With the growing scales of subways and tunnels projects, structure monitoring becomes increasingly important and a fast and accurate extraction method is critical for the monitoring of tunnel structures. In this paper, a method of extracting tunnel section based on gray map is proposed to fit the tunnel section, which is applied in a subway tunnel interval in Suzhou city. Data such as horizontal convergence value and ellipticity of a particular section in the test interval are extracted, and the results are compared with those measured by the total station measurement method at the same time. The results show that the proposed method can extract a specific section accurately and takes a short computing time. Compared to the traditional total station measurement method, the 3D laser measuring method not only improves the efficiency and data comparability of the tunnel deformation in the long-term operation monitoring, but also makes it easier for structured data to be used in the evaluation of the tunnel operation status and the development trend of the long-term deformation of a tunnel.

Agile mode switching between LP₀₁ mode and LP₁₁ mode and power amplification in specific mode can be achieved at the same time by inserting an acoustically-induced fiber grating into a Raman fiber amplifier. The maximum signal light output power of the LP₀₁ mode and LP₁₁ mode is 8.51W and 7.98 W with the characteristic frequency of 769 kHz and 763 kHz, respectively. Moreover, the ratio of the two modes can be adjusted by modulating the frequency loaded on the acoustically-induced fiber grating. This work could provide an example of realizing a mode-switchable Raman fiber amplifier for practical application.

Based on the power spectrum of the index fluctuation with the outer scale of seawater turbulence, we develop the channel capacity of oceanic turbulence links with carrier Bessel-Gaussian vortex localized wave. By this capacity model, we investigate the influences of seawater turbulence and carrier parameters on the channel capacity. The results show that higher rate of dissipation of kinetic energy per unit mass of fluid, larger inner scale, or lower dissipation rate of the meansquared temperature causes the higher channel capacity; the Bessel-Gaussian localized vortex wave with broader initial half-pulse width has stronger resistance to oceanic turbulent perturbation. This work provides a theoretical basis for realizing high capacity oceanic optical communication with carrier Bessel-Gaussian vortex localized wave.

High-volume SiC_p/Al materials were processed by Laser-induced Oxidation assisted machining technology.We obtained the laser induced oxidation process and oxidation mechanism, through the analysis of the average laser power, scanning speed, scanning distance and other factors on the oxidation effect.The results show that:1) In an oxygen-rich environment, the oxide layer will eventually exist as mullite(2 Al₂O₃·SiO₂)after sufficient reaction of the surface material. 2) When the average laser power is 6W, the laser scanning speed is 1 mm/s, and the laser scanning distance is 10 μm, the optimal combination of parameters is obtained. The results show that the thermal hardening layer and dense layer are the least and the hardness is low, which is suitable for high efficiency and precision milling; 3)The laser induced oxidation assisted milling technology can significantly improve the processing efficiency, the material removal rate is greater than 3000 mm³ /min, the surface roughness value after Precision machining is better than Ra0.4 μm.

In order to analyze the backscattering characteristics of graphite smoke in pulsed laser fuze, a pulsed laser fuze detection model in graphite smoke was established based on Mie scattering theory and Monte Carlo method. We simulated the graphite smoke backscattering echoes of pulsed laser fuze at various laser pulse widths and smoke visibilities. The results show that the normalized echo peak intensity of graphite smoke approximately exhibits an exponential growth relationship with the pulse width, while a power function decay relationship with the visibility. Compared with the emitted laser waveform, the graphite smoke echo waveform is distorted, presenting an asymmetrical feature with steep rising edge and gentle falling edge. Moreover, the narrower the laser pulse width, the greater the smoke visibility, and the more obvious the echo waveform asymmetry. This study provides a theoretical basis for exploring ways to enhance the detection performance of pulsed laser fuze in the graphite smoke environment.

Radial polarization (RP) and azimuthal polarization (AP) of vector beams differ in many applications, and thus the splitting of the two polarization modes is highly required in many scenarios. Considering that there has been no specific and commercial device for RP/AP beam splitting, this work presents a simple and compact approach for the splitting by use of a commercial-access polarization axis finder (PAF). The configuration on how to implement the approach is elaborated.

In this article, we present the first-ever mode-resolved bending loss measurement for Large-mode-aera (LMA) fiber based on S² mode measurement method. The new method can be extended to measure the bending loss of all high order modes (HOMs) of LMA fiber at different bending radii, which is more accurate than previously reported methods. What is more, it can provide guidance for the design and control of LMA fiber, and provide parameter basis for the beam quality optimization of high-power fiber laser (HPFL) system.

The acousto-optic modulator (AOMs) have great applications in the fields of laser technology, information processing and micro-processing, which is mainly applied to control and modulate the intensity of light at high frequency. The diffraction efficiency (DE) is the important parameter of AOMs. Researchers have studied many influencing factors of diffraction efficiency. However, few research on internal transducer parameter design in AOMs. In this paper, we propose an electrode optimization scheme to obtain AOMs with high diffraction efficiency. Combining the divergence angle ratio, we experimentally demonstrated the optimal size of the electrode. Furthermore, we model the sound pressure field in COMSOL Multiphysics® software, and analyze the DE of the optimized apodized transducer and the conventional transducer AOMs. The results show that comparing with rectangular transducer, optimized apodized shaped transducer can increase the DE of AOMs by 8.33% on average.

Polarization purity is an important indicator for both radial polarization (RP) and azimuthal polarization (AP) beams. This work presents a simple and compact approach to measure the RP/AP purity. It is implemented by using a polarization axis finder (PAF) and two half-wave plates. This measurement approach is easy to implement and all of the involved devices are commercialized.

Microwave photonic technology is a new technology which combines microwave technology and photonic technology. It has great advantages in many aerospace fields such as satellite navigation and space exploration. In the harsh space environment, Fresnel reflection is easy to be produced in the optical connector. In this paper, we build a RF microwave photonic transmission platform to analyse the influences of the optical echo increase and the optical phase change arising from Fresnel reflection of the optical connector on the phase noise. First of all, we present a scheme to simulate the echo of the optical signal caused by the Fresnel reflection. The results show that in our built platform the optical echo caused by the Fresnel reflection can not give rise to phase noise degradation. Secondly, the influence of optical phase change on phase noise by changing the size of air gap is experimentally analysed. As the size rises from 0.3mm to 0.7mm, the phase noise deteriorates to be - 93dBc / Hz at 1kHz.

808nm laser is widely used in solid-state laser pump source, information technology, military field, like laser weapon. The main problem of high power CW laser is the high working temperature caused by low photoelectric efficiency. There are two ideas to solve this problem: one is optimizing the package structure, to make huge energy be eliminated by water or others; the other is optimizing the structure of chip, to improve the photoelectric conversion efficiency, minimize the voltage and reduce the heat producing finally. This article mainly concentrates on how to adjust the structure of active layer, waveguide layer and gradient layer. The target of those adjustments is producing 2mm and 3mm cavity length chip which can work at 210A and emit light more than 200W.

This work lays great emphasis on studying the technique of the laser cutting the closed curve shape inside glass with laser induced thermal-crack propagation. The conventional LITP cutting is unable to complete a closed curve. The reason and the crack propagation behavior are studied by the extended finite element method (XFEM) analysis and experiments. In order to achieve the closed curve shape inside glass, the stress-release crack is proposed for the first time. The stressrelease crack-tip with 90° and 1.5mm is the suitable arrange. This paper indicates the experiment of the LITP cutting the closed outer curve shape with the stress-release crack. Optical microscope photographs of the crack surface are obtained to examine the cutting quality. This work provides a method to cut the closed curve shape inside glass with LITP successfully

Based on the radiation test of APD, the change of parameters is analyzed, and the degradation rule of performance after radiation damage is mastered. A typical IM/DD optical communication system is established. The BER and signal eye chart of the system under different dark currents and responses are obtained. The influence of APD performance parameters degradation on communication quality is further analyzed. The result shows that the increase of the dark current and the decrease of the responsivity of APD will cause the BER of the system increase. With the decrease of the responsivity, the influence of the dark current on the BER will decrease gradually, and the variation amplitude is nearly 5 orders of magnitude. With the increase of the dark current, the influence of the responsivity on the BER will change about 3 orders of magnitude. Compared with the increase of dark current, the BER is more sensitive to the decrease of responsivity.

With the rapid growth of military medium and heavy UAV(Unmanned Aerial Vehicle) equipment, the steady prolongation of training/operation time, and the gradual enrichment of operation mode, the UAV is facing many practical challenges, such as high system complexity, fast update of new technology, rapid development of anti-UAV defense technology, etc. The number of accidents of UAV equipment is increasing, and the reliability and safety problems are increasing obviously. In this paper, the latest accidents of foreign medium and heavy UAVs in the past 10 years are analyzed. Combined with the performance and technical characteristics of each equipment, the accident stages, causes and rules are classified, summarized and analyzed in detail, and the accident trend is predicted. Finally, the equipment design, use suggestions and safety countermeasures are put forward to provide reference for reducing the accident rate of domestic UAV system and forming the safety and reliability requirements of domestic UAV system.