The three-dimensional heat deposition of the cryogenic Yb:YAG regenerative amplifier, which is yielded by pulsed pumped laser, is derived in details based on the theory of quasi-three-level rate equations. Furthermore, the transient temperature field, stress, and strain induced by the thermal gradients in the laser crystal are analyzed by use of the finite element method. Then the thermally induced lens and depolarization in the cryogenic regenerative amplifier are theoretically studied. We find that for the pump and cooling structure which has been designed, the focal length of the thermally induced lens is about 15m and the depolarization rate could be ignored. The maximum output energy 10.2 mJ at a repetition rate of 10 Hz with nearly TEM00 mode profile is obtained using the designed pump and cooling structure.

The fractional Fourier transform (FRFT) of the flat-topped multi-Gaussian beam (FMGB) is investigated based on the three kinds of FRFT optical systems: Lohmann I, Lohmann II, and quadratic graded-index systems. The analytical expressions for the FRFT of the FMGB are derived based on the propagation of the FMGB through the three systems. By introducing a hard-edge aperture function, the analytical expressions for the FRFT of the FMGB carried out by the apertured FRFT optical systems are presented. The FRFT characteristics of the FMGB for the three kinds of FRFT optical systems with and without apertures are discussed in detail. Results show that the three types of FRFT optical systems have the same function when the apertures are ignored but that significantly different characteristics are exhibited when the apertures appear.

This paper presents a new method for measuring vibration based on interference from twospherical waves. By integrating the two interference arms into a beamsplitter cube by reflectivefilm and dividing the probe beam into two parts with discrete apertures, the interferometer candistinguish that the vibrations are from the monitored optical components or from laser interferometer systemitself. At the same time, because the two interference waves are spherical, it can realize monitoringthe three-dimensional vibrations. The measurement system has advantages of being stable andreliable with an integrated structure. Theoretical analysis and experimental demonstration are performed.The experiment results indicate that the method can monitor three-dimensional vibrationsaccurately.

A method for electrical waveform generation based on chirped pulse stacker in intensity modulation pulse shaping is provided as a means for high precision synchronization between nanosecond shaped pulse and compressible chirped short pulse in inertial confinement fusion (ICF) research. The arbitrary shaped optical pulse could be obtained, and the measured synchronization precision between ultra-short pulse and shaped optical pulse with the same or different wavelengths is better than 2.75 ps root mean square error.

A two-dimension model is presented to analyze the spatial dependence of pulse contrast in the focal plane. The parameters of the SHENGUANG (SG) II laser system are demonstrated as examples. Comparing with the degradation in the beam centroid, the pulse contrast degrades more seriously in the transverse. This spatial degradation of pulse contrast can be improved, such as by controlling the spatial spectrum clipping.

We propose and demonstrate an object–image-grating self-tiling method for doubling the effective aperture of a grating by tiling it with its image to form an object–image-grating pair. With the aid of the object–image relation, the line-density variation, angular tip, and longitudinal piston errors within a tiled grating no longer exist. The method helps achieve and maintain a near-ideal tiled grating by using a simple far-field method. Because one tiled grating requires only one beam line, a single probe laser can be used for first-installation adjustments and long-term maintenance monitoring, with no wavelength or incident angle limitations.

Based on diffraction optical theory, diffraction of a laser beam with periodic amplitude modulation and phase distortion is derived in 3ω optics system. Influence of defocus distance and focal length of a focusing lens on intensity distribution of diffraction light is investigated by numerical simulation. The results show that appropriate distance away from the focus spot and increase the focal length in final optical systems are beneficial to control the modulation of light intensity fluctuations and reduce the optical components damage caused by small-scale self-focusing effect.

Aiming at getting the general requirements of the beam combine for ignition scale laser facilities, the analytical expressions including the factors affecting the combine results are derived. The physical meanings of every part are illustrated. Based on these expressions, the effects of the factors, including the beam configuration, piston error, and tip/tilt error, are studied analytically and numerically. The results show that the beam configuration cannot affect the Strehl ratio (SR) of the combined beam, but it influences the FWHM of the main peak and the ratio of the main peak and the side peak. The beam separation should be no more than 1.24 times the individual beam width for the multibeam combine, and be close to the individual beam width for the two-beam combine as much as possible. The piston error can change the characteristics of the combine beam focus, including the peak intensity, the focal spot morphology, the fractional energy contained within a certain area, and the center of mass. For the two-beam combine, a piston error less than 2π∕5 rad is suitable, and for the multibeam combine, the standard deviation of the piston error should be no more than 2π∕10 rad. The tip/tilt error has a great influence on the combined results. It affects the superposition degree of the focal spots of the combined elements directly. A requirement of 0.5 ～ 1 μrad for the standard deviation of the tip/tilt error is adequate.

As a newly developed coherent diffraction-imaging (CDI) imaging method, the ptychographical iterative engine not only can bypass the difficulty of having high-quality optics in x-ray microscopy by a numerical reconstruction algorithm, but also has obvious advantages on traditional CDI methods in both converging speeds and view fields. However, like in the other CDI methods, the reconstruction of the image from the intensity data of a weakly diffracting specimen is still difficult because of the low signal to noise ratio. To improve this situation, a modification to the currently used algorithms is suggested to double the presence of high spatial frequencies in the diffraction pattern and accordingly to enhance the contrast and fine details of the reconstructions. The simulation and experimental results are presented, and the results can be extended to other CDI methods also.

At the Shen Guang II (SGII) Petawatt Laser Facility, measurements of large-energy, single-shot laser pulses sometimes feature asymmetric autocorrelation signals, causing uncertainty in the measurement of compressed pulses. This study presents a method for defining and describing the asymmetry of autocorrelation signals. We discuss two sources of asymmetry: the nonuniform distribution of the near field excited by a beam, and the rotation of autocorrelator arms from the cylinder lens. The pulsewidth of an asymmetric autocorrelation signal is shorter than its real width. After updating the autocorrelator, the single-shot autocorrelator for the SGII petawatt laser exhibits a measurement uncertainty of below 12.3%. Recommendations on reducing asymmetry in large-energy, single-shot autocorrelation are discussed.

A line-imaging optically recording velocity interferometer system (L-ORVIS) fitting the high-strain rate motion of solids as in shock wave experiments requires a high power single-mode laser. We have put forward a new illumination method which can increase threefold the luminosity of such a diagnostic. A modified illumination system is applied to the L-ORVIS which was implemented at ‘Shenguang-II’ laser facility. The modified L-ORVIS is applied to laser-driven shock wave experiments and platinum Hugoniots were obtained at both high pressure and low pressure.

A fiber-based precision synchronization triggering system using fiber pulse stacker combined with high- speed electronics processing technology is presented. The relative timing jitter between two laser pulses achieved with this system is 4.09 ps (rms) in 2 h. The impact of the optical pulse amplitude fluctuation on the timing jitter is effectively reduced by high-speed analog-digital conversion and the reliability of the synchronization measurement system is confirmed.

Several experiments are performed on the ShenGuang-II laser facility to investigate an x-ray source and test radiography concepts. X-ray lines emitted from laser-produced plasmas are the most practical means of generating these high intensity sources. By using a time-integrated space-resolved keV spectroscope and pinhole camera, potential helium-like titanium Kα x-ray backlighting (radiography) line source is studied as a function of laser wavelength, ratio of pre-pulse intensity to main pulse intensity, and laser intensity (from 7.25 to ~ 11.3×1015 W/cm2). One-dimensional radiography using a grid consisting of 5 μm Au wires on 16 μm period and the pinhole-assisted point projection is tested. The measurements show that the size of the helium-like titanium Kα source from a simple foil target is larger than 100 μm, and relative x-ray line emission conversion efficiency ξx from the incident laser light energy to heliumlike titanium K-shell spectrum increases significantly with pre-pulse intensity increasing, increases rapidly with laser wavelength decreasing, and increases moderately with main laser intensity increasing. It is also found that a gold gird foils can reach an imaging resolution better than 5-μm featured with high contrast. It is further demonstrated that the pinhole-assisted point projection at such a level will be a novel two-dimensional imaging diagnostic technique for inertial confinement fusion experiments.

Based on the recently developed ptychographical iterative engine (PIE), we suggest a lens assisted microscopy to realize quantitative phase imaging without using interferometry. The sample is imaged with a lens system; a pinhole on the image plane scans the image at a proper step interval; the diffraction pattern is recorded simultaneously by a CCD at Fresnel area. With a slightly changed PIE algorithm, the phase image of the sample can be accurately reconstructed from the recorded diffraction pattern. The main advantage of this suggested method lies in its capability to retrieve the phase information from the recorded intensity directly, and thus it has more flexibility over conventional interferometric techniques. The feasibility of the suggested method is verified by reconstructing the modulus and phase image of a biological sample from a set of 10 by 10 diffraction patterns, and the result matches the analysis well.

Directly driven ablative Rayleigh–Taylor (R–T) instability of modulated CH targets was studied using the faceon X-ray radiography on the Shen-Guang II device. We obtained temporal evolution images of the R–T instability perturbation. The R–T instability growth factor has been obtained by using the methods of fast Fourier transform and seeking difference of light intensity between the peak and the valley of the targets. Through comparing with the the theoretical simulation, we found that the experimental data had a good agreement with the theoretical simulation results before 1.8 ns, and was lower than the theoretical simulation results after that.

The characteristics of the alignment and misalignment multistage spatial filters are presented in this paper based on their effects on the beam quality. First, the approximate analytical expressions of the modulations of a square beam, which are induced by scatterers and an alignment spatial filter pinhole, are derived. Then, the far field analytical expression of the modulated square beam after its propagation through a nonlinear medium is presented. Subsequently, using a square super Gaussian beam, the modulations induced by an alignment and misalignment spatial filter pinhole are illustrated. The suppressing functions of the alignment and misalignment spatial filters on the hot image are investigated. The effects of the misalignment of the multistage spatial filter pinholes on the output beam quality are studied based on two evaluation factors: fluence beam contrast and fill factor. It is shown that the spatial filter pinhole misalignment has significant influences on both the far field and near field of the downstream beam, especially when nonlinear media exist. The results presented in this paper give important references and guidance for the spatial filter design, installation and alignment.

Reconnection of the self-generated magnetic fields in laser-plasma interaction was first investigated experimentally by Nilson et al. [Phys. Rev. Lett. 97, 255001 (2006)] by shining two laser pulses a distance apart on a solid target layer. An elongated current sheet (CS) was observed in the plasma between the two laser spots. In order to more closely model magnetotail reconnection, here two side-by-side thin target layers, instead of a single one, are used. It is found that at one end of the elongated CS a fanlike electron outflow region including three well-collimated electron jets appears. The (> 1 MeV) tail of the jet energy distribution exhibits a power-law scaling. The enhanced electron acceleration is attributed to the intense inductive electric field in the narrow electron dominated reconnection region, as well as additional acceleration as they are trapped inside the rapidly moving plasmoid formed in and ejected from the CS. The ejection also induces a secondary CS.

An algorithm for simulation of laser/particle interactions using normalized units related to different laser frequencies was studied. Correct and wrong conversion methods between different normalized units were investigated in simulations of vacuum laser acceleration. The dynamic characteristics obtained with different processing methods differ greatly and some good acceleration results are actually no other than errors stemming from incorrect treatments of the normalized units.

In high power laser systems, the high-frequency noise generated by nonlinear effect is effectively removed by low-pass spatial filter, and the low-frequency noise passing through pinhole is always considered as very safe to optical devices in downstream. However, in practical applications both modulation contrast ratio and spatial frequency of the low-frequency noise will be changed and possibly become dangerous components, depending on different magnification ratios of spatial filter. In this paper, the evolution of low-frequency noise is theoretically analyzed and numerical simulated depending on different magnification ratios of spatial filter. The analysis results show that both modulation contrast ratio and spatial frequency of the low-frequency noise passing through pinhole will be changed 1/M times, where M is magnification ratio of spatial filter. For M<1, the safe low-frequency noise will be extruded into high-frequency which is the fastest growing components and finally develop into the most dangerous part to the damage of optical devices again. It is significant to consider the evolution of low-frequency noise in practical applications of spatial filter for high power laser system.

In order to improve the laser-induced damage threshold (LIDT) of the ZrO2film, the effect of polyvinyl pyrrolidone (PVP) with different average molecular weight on coatings is studied. The ZrO2 sol is prepared by the hydrolysis of zirconium n-propoxide with acetylacetone as the chelating agent. The PVP (K16-18) is more suitable to obtain high LIDT coatings than other PVPs. The LIDT of the ZrO2-PVP coatings is improved with the increase of the PVP (K16-18) content. When the PVP (K16-18) content is 2.4 wt.-%, the LIDT of the ZrO2-PVP coatings is 43.5 J/cm2 (1064 nm, 12 ns). The ZrO2 sol and ZrO2-PVP (K16-18) sol have the good stability in 3 months. The refractive indices of the ZrO2-PVP coatings decrease with the increase of the PVP (K16-18) content.

We report the generation of an 8.5-nJ chirped pulse from a mode-locked all-fiber Yb-doped laser. Mode- locking is achieved through nonlinear polarization evolution (NPE) along with spectral filtering. The laser delivers 135 mW of average output power with positively chirped 10.9-ps pulses. The pulse repetition rate is 15.9 MHz, which results in an energy of 8.5 nJ per pulse. The externally dechirped pulse duration is 223 fs, and the pulse energy is 6 nJ, which corresponds to the peak power of~27 kW.

Direct-drive and indirect-drive inertial confinement fusion (ICF) targets use temporally shaped drive pulses to optimize target performance. The timing of multiple shock waves is crucial to the performance of ICF ignition targets. Velocity interferometer system for any reflector (VISAR) is the principal diagnostic tool for shock-timing experiments. We present velocity measurements from the shock waves in polystyrene targets driven by two 200-ps pulses separated by 1–2 ns. These pulses drive two shock waves that coalescence in the target. Coalescence time and transit times are observed by VISAR.

An automatic polarization compensation method for low-repetition frequency short optical pulse is proposed and successfully applied to the master oscillator room (MOR) in inertial confinement fusion (ICF) systems to maintain the MOR maximum output energy. After an average of 37 shots, the MOR output energy reaches maximum value with the sudden occurrence of polarization variation in the fibers. The peak-to-peak amplitude jitter of the MOR output is 9.52% at 4 h, which meets the requirement of the ICF system.

A high-speed 8-channel fiber Bragg grating (FBG) sensing system is designed to monitor safety of modern ships and applied to measure strain distribution of large thruster structure with 335-Hz maximum natural frequency. All the monitoring points are tested synchronously, and the data acquisition frequency is 1 000 Hz. The strain resolution of the system is 1 με with the measurement range of ±3 300 με. Results from the tests onshore and at sea are discussed together to accomplish prediction of the dynamic data. The max stress of the whole structure is more than 40 MPa. Experimental results are accordant with mechanical theories.

An all-fiber regenerative amplifier at 1053 nm is demonstrated. The input signal pulse energy is 75 pJ in a 3.5-ns pulse at a 1-Hz repetition rate. At a low level of input pump power of 110 mW, the saturated output energy is 120 nJ with fluctuation less than 2% root mean square (RMS) even the fluctuation of the input pulse be about 15% (RMS). And the signal-to-noise ratio (SNR) is 66 dB. Maximum output energy of 780 nJ with a total gain of more than 40 dB is obtained at pump power of 130 mW. Scaling to higher pulse energy is constrained by stimulated Raman scattering.

We theoretically study the temporal contrast degradation by the spectral phase distortion in chirped pulse amplification (CPA) lasers. As an example, we analyze the impact of the surface qualities of the optical elements such as mirrors and grating in the stretcher and compressor on the temporal contrast. The temporal contrast declines fast in the case of a rapidly varying random surface error of the optical elements. When the values of PV, RMS and GRMS of the surface error curve are reduced, the temporal contrast is becoming better and better. And the temporal contrast can be improved after the surface error curve is to be spatial filtering. Those results are helpful for the choice of the surface parameters of the optical elements in the stretcher and compressor.

An optically addressed liquid crystal light valve based on the photoconductive effect of the Bismuth Silicate (BSO) layer is presented. The transmittance of read beam (1 053 nm) through the light valve changes with the intensity of address beam (470 nm) projected onto the BSO layer. Beam shaping for 1 053-nm coherent light by using this device is reported. The device has the advantage of high transmittance and it can overcome the problem of black-matrix effect compared with the traditional thin film transistor (TFT) liquid crystal modulator.

The forced convective heat transfer coefficients during the period of thermal recovery for laser slab on the multi-segment amplifies of SG II is analyzed. We simulate the parameters including coolant gas and the geometry of amplifier with computational fluids dynamics (CFD) method. Based on the simulated results, we attain the optimized parameters such as the flow rate, the temperature and the type of gas, the diameter of inlet jet, the quantity of inlet jet, the distance between the inlet jet and the laser slab, and the spray angle of inlet.

A diode-pumped cryogenic-cooled Yb:YAG regenerative amplifier based on the thin disk concept, producing 14.2-mJ, 10-ns pulses with optical-to-optical conversion efficiency of ～7% at a repetition rate of 10 Hz at 163 K, is presented.

A master-oscillator power amplifier (MOPA) system based on Nd glass laser with output intensity of 5 GW/cm2 is described. The laser operates at 1 Hz with pulse energy up to more than 4 mJ. The spatial profile is near top hat and the diameter is 1 mm, the temporal pulse shape is Gaussain and pulse width is about hundred picosecond. Frequency doubling efficiency is 37.5% with 3-mm-long BBO crystal, the pulse of microjoule output energy and 527-nm wavelength is achieved and used as the pump pulse in the short pulse optical parametric amplification, decreasing the parametric fluorescence influence to contrast of optical parametric chirped pulse (OPCPA) system.

A dynamic beam propagation model of micro-vibrating spatial filters in inertial confinement fusion (ICF) facilities is built based on the additional beam in SG-II facility. The transfer matrix is then deduced, and the sensitivities of the beam positioning to the pellet in the target area to the vibrations of every spatial filter are analyzed, which indicates that the vibrations of spatial filters in the pre-amplify zone has less effects on beam positioning stability at the target. In addition, the vibrations of spatial filters in the main amplify zone dominates the beam positioning stability of the target, especially the vibration of the spatial filter SF7.

In order to avoid stimulated Brillouin scattering and smooth the final focal spot that reaches the D-T capsule, spectral broadening is essential. However, the modulation of spectral structure might result in frequency-to-amplitude modulation (FM-to-AM) conversion. The spatial filter pinhole is used to cut off the high-frequency transmission laser, and to ensure the desired pass. Improper parameter of pinhole would lead a negative impact. Using the spatial filter pinhole, we analyze the characteristic of intensity modulation using several pinholes of improper parameters. We then compare these results with the intensity modulation obtained from an experiment. Experimental diagnosis and design of an appropriate pinhole parameter would be highly beneficial to the field of high-power lasers.

A dual-source distributed optical fiber sensor system with combined Raman and Brillouin scatterings is designed for simultaneous temperature and strain measurements. The optimal Raman and Brillouin signals can be separately obtained by adjusting the powers of the two sources using an optical switch. The temperature and strain can be determined by processing the optimal Raman and Brillouin signals. The experimental result shows that 1.7 ℃ temperature resolution and 60-με" strain resolution can be achieved at a 24.7-km distance.

A high-efficiency hybrid Brillouin/ytterbium fiber laser (BYFL) is demonstrated using a 41.5-cm-long highly ytterbium-doped fiber and a 10-m-long single-mode optical fiber. The BYFL operates at 1 052.92 nm, and the difference between it and the Brillouin pump (BP) wavelength matches the expected stimulated Brillouin scattering (SBS) Stokes shift. Its output power reaches 70.1 mW, which is more than seven times higher than the seeded BP power. The BYFL has an optical signal-to-noise ratio that is greater than 65 dB and has many potential applications, such as in controllable optical delay lines, sensing, and RF photonics.

A high-precision temperature-controlled narrow band-stop fiber Bragg grating (FBG) filter and light source self-calibration technique are proposed for application in the Brillouin optical time domain reflectometer (BOTDR) sensor system. With the proposed application, the BOTDR sensor system maintains good long-term stability and temperature precision through the reduction of the center wavelength drift in the FBG filters and corresponding decrease in the changes in light intensity. The experiment result shows that temperature precision of 1°C and temperature stability of 0.7°C can be achieved in a temperature sensor over a range of 8 km.

The model of a beam propagating in a high power laser system is built based on relay imaging. The displacement sensitivity of the lens to beam positioning error is obtained using this model, which is then compared with the traditional method. Two real systems, the pre–amplifier and four–pass amplifier in SGII-U, are presented to further discuss the differences between the two methods. The limitation and application range are summarized in the end. The findings can be used to provide guidance in similar systems.