Beam positioning stability in a laser-driven inertial confinement fusion (ICF) facility is a vital problem that needs to be fixed. Each laser beam in the facility is transmitted in lots of optics for hundreds of meters, and then targeted in a micro-sized pellet to realize controllable fusion. Any turbulence in the environment in such long-distance propagation would affect the displacement of optics and further result in beam focusing and positioning errors. This study concluded that the errors on each of the optics contributed to the target, and it presents an efficient method of enhancing the beam stability by eliminating errors on error-sensitive optics. Optimizations of the optical system and mechanical supporting structures are also presented.

Considering the time delay in different hohlraum wall positions caused by oblique incidence, the spatio-temporal optical field distribution characteristics of a hohlraum wall, especially during the rising edge of a flat-topped pulse, is simulated by a fast Fourier transform method together with chromatography. Results demonstrate that beam propagation along the hohlraum wall is a push-broom process with complex dynamic spatial–temporal evolution. In the first few picoseconds, the optical intensity of the front position increases rapidly, while that of the rear position is relatively weak. The ratio R of the optical intensity during the rising edge is smaller than that of the steady state. R gradually increases and finally tends to the value of the steady state with time. Calculation also shows that, with shorter total width of the rising edge, R of the optical field decreases and the difference compared to the steady state becomes larger. The evolution is more severe with smaller angle of inclination.

Damage experiments are conducted by irradiating fused silica with the multiple wavelength laser near field. The multiple wavelength laser consists of 1053、 527、 351 nm laser. It designs a definition of damage threshold based on laser near-field irradiation and extracts damage areas from damage images by the marker-based watershed algorithm with gray control. The initial damage threshold is defined as the fluence of critical site between damage region and no damage region, which is calculated by comparing the damage image with the multiple wavelength laser near field. The research shows that the damage of fused silica is induced by the three wavelength lasers. The 351 nm laser plays a leading role. The initial damage threshold is 8.22 J/cm2. With multiple irradiation of fused silica in multiple wavelength laser, the damage growth of exit surface is exponential, and the coefficient of damage growth is 0.59.

A 527nm pump laser generating 1.7mJ energy with peak power of more than 0.12GW is demonstrated. The theoretical simulation result shows that it has 10⁶ gain in the picosecond-pump optical parametric chirped pulse amplification when the pump laser peak power is 0.1GW and the intensity is more than 5GW/cm², and that it can limit the parametric fluorescence in the picosecond time scale of pump duration. The pump laser system adopts a master-oscillator power amplifier, which integrates a more than 30 pJ fiber-based oscillator with a 150 μJ regenerative amplifier and a relay-imaged four-pass diode-pump Nd glass amplifier to generate a 1 Hz top hat spatial beam and about 14 ps temporal Guassian pulse with <2% pulse-to-pulse energy stability. The output energy of the power amplifier is limited to 4mJ for B-integral concern, and the frequency doubling efficiency can reach 65% with input intensity 10GW/cm².

Optimized convective heat transfer is applied to accelerate the thermal recovery of a large aperture multi-segment amplifier. The paper proposes a novel project of changing the structural parameters of the inlet jet to the Nd:glass slab in the multi-segment amplifier at the same flow rate. The convective heat transfer coefficient depends on the diameter of the inlet jet, as well as on the number of inlet jets. The simulation calculations indicate that at the same flow rate, different numbers of inlet jet lead to different temperature gradient contours and flow field distributions on the Nd:glass slab surface in the multi-segment amplifier. In addition, the convective heat transfer coefficient increases with the decrease of inlet diameter. This work analyzes the path of the coolant air over the slab surface to lessen the eddy and to achieve better convective heat transfer, as well as to determine the optimized number of inlet jets (5) and the optimized diameter (5 mm)

Coherent diffraction imaging (CDI) and ptychography techniques bypass the difficulty of having highquality optics in X-ray microscopy by using a numerical reconstruction of the image that is obtained by inverting the diffracted intensity recorded by a charge-coupled device array. However, the reconstruction of the image from the intensity data obtained from a weakly diffracting specimen is known to be difficult because of the obvious reduction in signal-to-noise ratio (SNR). In this case, the specimen only slightly modifies the probe diffraction pattern, resulting in difficulty in the identification of the detailed structure of the specimen from the reconstructed image because of the poor contrast and sharpness of the image. To address this situation, a modification in the image retrieval algorithms used in the iterative reconstruction of the image is suggested. This modification should double the presence of high spatial frequencies in the diffraction pattern to enhance the contrast and edge detection in existing imaging techniques.

An in situ multi-beam optical sensor system was used to monitor and analyze the force per unit width (F/w) and stress evolution during several stages in magnetron-sputtered SiO₂ and SiN_x films. Stress was observed to relieve quickly after interrupt and recover rapidly after growth resumption in both films. Stress relief was reversible in SiO₂ film but partial reversible in SiN_x film. Stress relief results from both physical and chemical adsorption. Stress recovery is caused by physical desorption. And chemical adsorption results in an irreversible stress relief component. No chemical adsorption occurs in SiO₂ film because of the stable chemical structure. The relationship between adsorption kinetics and films’ mechanical behavior is revealed.

A diode-pumped cryogenic-cooled nanosecond Yb:YAG regenerative amplifier based on the disk concept has been developed and used in a joule-class MOPA laser system. The output pulse energy is more than 11 mJ at a 10 Hz repetition rate at 163 K. An excellent energy stability of 1.8% fluctuations is achieved.

Damage experiments are conducted by irradiating 351 nm laser near-filed to fused silica based on the damage threshold definition of near-filed irradiating. Damage areas are extracted from damage images by the marker-based watershed algorithm with gray control. The initial damage threshold is defined as the fluence of critical site between damage region and no damage region, which is calculated by comparing the damage image with 351nm laser near-field. This damage testing method is sample, quick, which can effectively decrease the effect of beam diameter for damage threshold due to the bigger aperture. The algorithm of image segmentation effectively removes the noise and suppresses the over-segmentation, and improves the accuracy of initial damage and damage growth. The research shows that the damage of fused silica is induced by 351 nm laser near-field with pulse width of 3.13 ns. The initial damage threshold is 2.94 J/cm2. With multiple irradiation of fused silica, the damage growth of exit surface is exponential, and the coefficient of damage growth is 0.32.

This paper describes the development of a novel infrared point-diffraction interferometer (IPDI), which can be readily applied to real-time quantitative phase measurement. We generate reference wave with the help of Michelson-like unit combined with a low-pass spatial filter, and extract the phase information using windowed Fourier transform algorithm from single off-axis fringes. The arrangement of the proposed setup offers a quasi-common-path geometry, which could significantly minimize the systematic errors. The proposed method of IPDI is effective and sufficient for the dynamic process measurement of small deformation with higher spatial resolution compared with the conventional off-axis scheme. The feasibility of the proposed setup is demonstrated, followed by methods of reconstruction and system calibration. The nanoscale repeatability is achieved in our experiment.

A special-velocity-matched electro-optic (EO) phase modulator employing a microwave resonant design in lithium niobate is presented. Both the microwave property and phase-modulation performances of the 3.25-GHz modulator agree well with the numerical simulations. Using this modulator in a single-pass configuration with 1-kW microwave drive power, the spectral bandwidth of a 1 053-nm, 3-ns pulse-length laser is broadened to 0.13 nm. With a clear aperture of 5×5 (mm), the modulator is suited for two- dimensional smoothing by spectral dispersion in high power laser systems.

An experiment with thin titanium foils irradiated by two pulses delayed in time is conducted on the Shenguang-II laser facility. A prepulse induces an underdense plasma, 2-ns later a main pulse (λ_L = 0.35 μm, E_L = 120 J, τ_L = 100 ps) is injected into the underdense plasma and produces strong line emission from the titanium K shell (i.e., He_α at 4.7 keV). Data show that the intensity of 4.7-keV X-ray emission with the prepulse is approximately twice more than without the prepulse, and can be used as a backlighting source satisfying the diagnostic requirements for dense plasma probing. Highquality plasma images are obtained with the backlighting 4.7-keV X-rays in a Rayleigh–Taylor hydrodynamic instability experiment.

An all-fiber optical laser pulse multi-pass stretcher using a chirped fiber Bragg grating (CFBG) is demon- strated. Pulses from a 1 053-nm mode-locked fiber seed oscillator are stretched by multiple passing through a chirped fiber grating set in a fiber regenerative amplifier structure. We stretch the pulse from 16 ps to 1.855 ns after it transmits seven loops in the stretcher. The main factors that affect the stretching results are discussed.

Object image grating self-tiling reduces difficulties of obtaining an ideal grating tiling condition by eliminating three tiling errors in six within a tiled grating. However, this may bring two potential problems: higher requirements of adjustment accuracy and maintaining stability. To examine the application values of this grating tiling configuration, the performance of object image grating self-tiling and traditional grating tiling configurations on accuracy and stability are compared theoretically and experimentally. Adjustment accuracy requirements of two grating tiling configurations are calculated, a comparative experiment of long-term stabilities is demonstrated, and relevant theoretical simulation analyses are developed to explain the experiment results.

We report an optically addressed liquid crystal light valve, a home-made device that has solved the problem of low transmittance caused by opaque electrodes in present transmissive spatial light modulators. The operating characteristic of the light valve is analyzed. The optimum driving voltage of this device is 27 V at 300 Hz, as deduced from the equivalent electric model. Its transmittance reaches 80% and its contrast is approximately 40:1. Its dynamic performance, especially its ability to obscure laser light at programmed locations, is demonstrated. The results are in good agreement with the desired shape, which indicates that our light valve performs very well.

The experimental performance of beam smoothing by combined one-dimensional (1D) spectral dispersion and lens array (LA) technology is presented, as applied in the ninth beam of SG-II. Using 3! spectral dispersion with a bandwidth of 270 GHz and a line dispersion that is 24.9 times the beam’s diffraction- limited width decreases the focal spot non-uniformity of 80% energy concentration from 46% to 17%. The multiple-beam interference properties of the LA are theoretically and experimentally validated by spatial power spectral density analysis. Peak–spectra suppression ratios of 20 and 10 dB are achieved in the dispersion and orthogonal directions, respectively.

A polycrystalline ceramic Tm³⁺-doped yttrium aluminum garnet (Tm:Y₃A_l5O₁₂, Tm:YAG) laser based on the novel fiber-bulk hybrid configuration is demonstrated using a high-power and tunable Er,Yb co-doped fiber laser as the pump source. Lasing characteristics of a 4.0 at.% Tm:YAG ceramic are investigated at different pump wavelengths from 1617 to 1625 nm. With an output coupler of 10% transmission, a maximum output power of 3.9W is obtained at 2013.2nm under an 8.8W incident pump power at the Tm:YAG absorption peak of 1620.4 nm, corresponding to a slope efficiency of 50.1% with respect to the incident pump power.

We investigate bulk ion heating in solid buried layer targets irradiated by ultra-short laser pulses of relativistic intensities using particle-in-cell simulations. Our study focuses on a CD₂-Al-CD₂ sandwich target geometry. We find enhanced deuteron ion heating in a layer compressed by the expanding aluminium layer. A pressure gradient created at the Al-CD₂ interface pushes this layer of deuteron ions towards the outer regions of the target. During its passage through the target, deuteron ions are constantly injected into this layer. Our simulations suggest that the directed collective outward motion of the layer is converted into thermal motion inside the layer, leading to deuteron temperatures higher than those found in the rest of the target. This enhanced heating can already be observed at laser pulse durations as low as 100 fs. Thus, detailed experimental surveys at repetition rates of several ten laser shots per minute are in reach at current high-power laser systems, which would allow for probing and optimizing the heating dynamics.

High power and widely wavelength tunable operation of cladding-pumped Er,Yb fiber lasers are demonstrated with operating wavelength covering the whole C- and L-band and spectral linewidth FWHM of less than ～0.3 nm over the whole tuning range. Wavelength tuning is realized by the use of an external cavity containing a volume Bragg grating with peak reflectivity >99% at 1650 nm. A tuning range of 45.5 nm from 1533.5 to 1579 nm is obtained for a 7 m Er,Yb fiber. Output power up to 23.8 W is generated at 1565.7 nm for 142.4 W of launched pump power. Using a longer gain fiber of 17 m, the operating wavelength shifted toward the long wavelength side, covering a tuning range of over 67 nm from 1556.7 to 1624.4 nm. A maximum output power of 24.9 W at 1567.5 nm is achieved for the launched pump power of 126.5 W.

An optical alignment and a corresponding reconstruction algorithm are proposed to realize a single shot Ptychographical Iterative Engine (PIE). Multiple light beams generated by a cross grating are used to illuminate the specimen, and the resulting diffraction patterns formed on the detector plane by each beam are recorded simultaneously. The modulus and phase images are properly reconstructed with standard PIE algorithm. The proposed single shot method omits the needs for a mechanical x-y scanning of standard PIE algorithm and hence dramatically reduces the data acquisition time.

We study the roles of thermal ionization and electronic damage in the internal modification of bulk borosilicate glass by high repetition rate picosecond laser pulses. Laser-induced plasma generation, nonlinear energy deposition and steady temperature distribution are numerically analyzed. The simulated modified regions show good agreement with the experimental results, thereby revealing the roles of thermal damage and electronic damage in the internal modification. While the elliptical outer structure is recognized as the molten region, we found that the teardropshaped inner structure is the damaged zone caused by high-density freeelectrons. In the formation of the inner structure, cascade ionization is seeded by thermal ionization instead of multi-photon ionization and dramatically increases the free-electron density to the damage threshold. The contour of the inner structure is found to be corresponding to a characteristic isotherm of around 3000 ~4000 °C.

A joint diagnostic system was established for the diagnosis of laser-driven shock wave experiments. The system has high temporal resolution (time resolution ～12 ps) and high spatial resolution (spatial resolution ～7 μm) and fits for diagnostics of the experiment with small sample size and short time physical process. The joint diagnostic system was applied for shock wave measurement on the Shenguang-II laser facility. The passive shock breakout signal and active diagnostic signal were simultaneously obtained. The temporal measurement reliability of the system was verified using a multi-layered target. The experimental results show that the two measurement results were consistent.

A special optical alignment is adopted and corresponding reconstruction algorithm is developed to reduce the reconstruction error induced by the hysteresis or backlash error of the translation stage in Ptychographical Iterative Engine (PIE) imaging with weak scattering specimen. In this suggested method, the positions of the scanning probe are determined directly from the recorded diffraction patterns rather than from the readout of the stage meter. This method not only remarkably improves the reconstruction quality, but also completely lowers the dependency of PIE on the device accuracy and accordingly enhances its feasibility for many applications with weak scattering specimen.

This study presents a novel numerical model for laser ablation and laser damage in glass including beam propagation and nonlinear absorption of multiple incident ultrashort laser pulses. The laser ablation and damage in the glass cutting process with a picosecond pulsed laser was studied. The numerical results were in good agreement with our experimental observations, thereby revealing the damage mechanism induced by laser ablation. Beam propagation effects such as interference, diffraction and refraction, play a major role in the evolution of the crater structure and the damage region. There are three different damage regions, a thin layer and two different kinds of spikes. Moreover, the electronic damage mechanism was verified and distinguished from heat modification using the experimental results with different pulse spatial overlaps.

The adaptive optics system for the second-generation VLT-interferometer (VLTI) instrument GRAVITY consists of a novel cryogenic near-infrared wavefront sensor to be installed at each of the four unit telescopes of the Very Large Telescope (VLT). Feeding the GRAVITY wavefront sensor with light in the 1.4 to 2.4 micrometer band, while suppressing laser light originating from the GRAVITY metrology system, custom-built optical components are required. In this paper, we present the development of a quantitative near-infrared point diffraction interferometric characterization technique, which allows measuring the transmitted wavefront error of the silicon entrance windows of the wavefront sensor cryostat. The technique can be readily applied to quantitative phase measurements in the near-infrared regime. Moreover, by employing a slightly off-axis optical setup, the proposed method can optimize the required spatial resolution and enable real time measurement capabilities. The feasibility of the proposed setup is demonstrated, followed by theoretical analysis and experimental results. Our experimental results show that the phase error repeatability in the nanometer regime can be achieved.

Self-pulsation effects of cladding-pumped Erbium-Ytterbium co-doped fiber laser (EYDFL) at around the lasing threshold are investigated. It is demonstrated that laser output of the Erbium-Ytterbium co-doped fiber under the bi-directional pumping regime is more stable than that under the unidirectional pumping one due to the relatively uniform pumping of the fiber. Mechanisms of self-pulsations in the laser system are discussed and possible techniques to avoid self-pulsing and stabilize the laser are proposed.