A modified extended-ptychographical-iterative-engine (ePIE) algorithm is proposed to overcome the disadvantages of ePIE technique and reduce the influence of stage hysteresis or backlash error. The exit wave of a rotatable “screen” illuminated by plane wave is used as the illumination on the specimen, and the complex transmission functions of the rotatable object and specimen can be simultaneously reconstructed. Compared with the standard x-y scanning PIE algorithm, the proposed algorithm can completely avoid the influence of stage hysteresis (or backlash error). The proposed algorithm also has higher convergence speed and better accuracy than the standard PIE algorithm.

A mathematical model of the mirror misalignment of a four-equal-sided nonplanar ring cavity is established in this letter. The variations in the optical axis are discussed through an augmented 6 × 6 ray matrix formulation. Numerical analysis shows that the self-consistence of the optical axis can always be obtained because of the thermal effects in any case of mirror misalignment. For a fabricated design, optical axis variations always appear. The influence of thermal effects (i.e., pump power) on optical axis variations are studied. The tilt of the optical axis remains constant, whereas its decentration varies with pump power. Further analysis shows that the actual closing point of the optical axis moves close to the ideal point as the pump power increases. The theoretical analysis proposed is proven and validated by the experimental results.

Focusing performance is an important parameter to improve peak power intensity of a laser facility. This paper provides a diagnostic method of focusing performance in order to realize a function of online diagnosing for focusing performance in petawatt laser. A high preciseness and low tolerance far-field diagnostics unit is designed in this method. Then measurement data is testified by a focal spot measurement unit in target room. At last the far-field diagnostics unit can be used to prove online diagnosing for focusing performance in petawatt laser. Experimental result shows that similarity between the far-field diagnostics unit and the focal spot measurement unit is about 1. So measurement data of far-field diagnostics unit can be used to diagnose peak power intensity with energy data and pulse width data when online diagnosing of peak power intensity in physics experiments is realized.

The fabrication of metal film steps used in equation of state experiment targets was investigated. The metal film step of hundreds of microns width was cut by picosecond laser processing technology. The factors of generating heat effect in the processing were analyzed. The processing parameters were as follows: power 0.5 W, pulse width 10 ps, wavelength 355 nm, and scanning speed 100 mm/s. Two metal films of 400 and 120 microns width were obtained in the experiment. The measurement results show that the width of metal film can be precisely controlled and the quality of metal film surface before and after cutting was the same.

The characteristics of the induced voltage of the high power disk amplifier, which is not grounding (suspended), is researched experimentally. Results show that the peak value of the induced voltage is dominated by the capacitance between the flash lamp and the cavity and the number of flash lamps in the amplifier, and the independent cavities don′t affect each other directly. Exprimental study on induction properties of the amplifier under a variety of grounding methods is conducted, and a grounding plan of wholly grounding the amplifier with the internal and external cavities electrically integrated is demonstrated, which is successfully applied to the 350 mm disk amplifier of the ninth beam of SGⅡ. The possibility of electrical breakdown inside the amplifier is eliminated radically, and the induced voltage of the amplifier is reduced to 18% of that when the amplifier is suspended. As a result, the reliability and safety of the disk amplifier are improved obviously, the compactness and cleanliness of the amplifier are also improved simultaneously. Since this grounding plan is adopted, the 350 mm amplifiers have operated reliably and safely for more than 400 shots without any electrical breakdown and interference.

A second harmonic generation system with two type II KDP crystals in quadrature is optimized for the nanosecond chirp pulse. The acceptance bandwidth of this optimizing scheme is close to 10 nm by using two crystals with slightly opposite angular detuning from phase matching and the conversion efficiency can reach 70% for top-hat chirp pulse at ～2 GW/cm2 in theory. The preliminary experimental results are obtained on the 9th beam of Shen Guang II SGII laser system, and the performance of optimization is partially verified.

We report high-power, dual-wavelength tunable operation of an Er:Yb co-doped fiber laser using two volume Bragg gratings arranged in parallel. The wavelength separation for the two operating wavelengths was continuously tuned from 0.3 to 29.2nm (0.04 to 3.7 THz) with a total output power of >13Wfor a wavelength splitting range of <20 nm. A maximum output power of 17.9W was obtained at a wavelength separation of 0.3nm for a launched pump power of 65.3W, which corresponds to a slope efficiency of 28.6% with respect to the launched pump power.

In this letter, we report a multifunctional high-performance Nd:glass laser system. Laser pulses from an all-fiber front end are first amplified by a regenerative amplifier to 10 mJ level, and then further amplified in a four-pass amplifier. The laser system can provide 10.3-J, 3-ns laser pulses at 1053-nm wavelength. The shot-to-shot energy stability is better than 1.5% (RMS). The output laser beam is near diffraction limit. Binary amplitude masks are used to maintain a flat top near-field profile with a 71% fill factor. After the frequency conversion process, 7 and 5.5 J pulses at 526.5 and 351 nm are obtained, respectively.

Temporal and spatial optical field distributions of a stepped pulse on the hohlraum wall are numerically analyzed using fast-Fourier-transform method combined with chromatographic theory. Changes in the rising edge of the stepped pulse caused by spatio-temporal effect are systematically studied. Results demonstrate that a certain time difference exists for the laser to reach the hohlraum wall because of oblique incidence, which causes distortion to the stepped pulse, especially to the rising edge. Influences of the incident angle, focal length, and width of the input rising edge on distortion degree of the stepped pulse are also discussed. This letter provides some guidance for targeting pulse shaping and synchronization.

Ultrafast reflection and secondary ablation have been theoretically investigated with a Fresnel-Drude model in laser processing of transparent dielectrics with picosecond pulsed laser. The time-dependent refractive index has a crucial effect on the cascade ionization rate and, thereby, on the plasma generation. The relative roles of the plasma gas and the incident angle in the reflection are discussed in the case of the oblique incidence. The angular dependence of the reflectivity on the laser-excited surface for s- and p-polarization is significantly different from the usual Fresnel reflectivity curve in the low-fluence limit. A road map to the secondary ablation induced by the reflected pulse is obtained on the angles of the first and second incidence. It indicates that the laser-induced plasma plays a major role in the secondary ablation, which could overcome the saturation of the ablation crater depth or generate microcracks underneath the crater wall.

The prompt pump-induced wavefront characteristic of high power laser facility is undertaken to address an important aspect of the wavefront control system for the high power laser facility. Based on the ShenGuang Ⅱ four-pass amplification high power laser facility (SG-Ⅱ-FAF), numerical simulation is conducted on the prompt pump-induced wavefront distortion through ANSYS and Matlab. In order to obtain the space-time characteristics and variation features, the Hartmann wavefront analyzer is employed to conduct experiments on prompt pump-induced wavefront distortion and thermal wavefront recovery aberration after xenon lamp pumping. The numerical simulation results agree well with experimental results. The prompt pump-induced wavefront distortion of single-slab-amplifier is about 0.12λ (wavelength λ=1053 nm) of peak-to-valley (PV), and the whole optical wavefront of the SG-Ⅱ-FAF is about 5λ of PV with different laser beams, whose shape looks like a “saddle”. Simulations and experiments provide important data for the wavefront control system of SG-Ⅱ-FAF, emission laser passing through the space filters sucessfully and pumping uniformity of slab Ndglass amplifier. As a result, the far-field focus spot energy concentration of the laser beam is improved, meanwhile the success rate and the working efficiency of the SG-Ⅱ-FAF operational experiment are increased.

Target and beam alignment unit is one of the core parts of high power laser drivers and plays a crucial role in the adjustment of target position and pose, the laser pointing and so on. Combined the alignment accuracy requirements of the laser driver with the physics experiment implement, basic functions of the target and beam alignment unit can be acquired to meet the requirements of physics experiments using the design and adjustment of the optical-mechanical-electronic systems. However, with the increasing number of the main lasers, slewing of multi-beams and positioning with high accuracy have become the goal of developing target and beam alignment unit. Present studies on the target and beam alignment unit of both domestic and international high power laser drivers are reviewed, a universal method for the alignment unit design is investigated and main issues in the development of the target and beam alignment unit are also analyzed.

A picosecond pump laser is demonstrated for short pulse optical parametric amplification. An all fiber mode-lock laser pulse with 6 nm bandwidth, 12.4 ps duration and nJ energy is amplified by a solid state amplifier. Amplified laser pulses with 6.2 mJ single pulse energy, 8.6 ps pulse width, 1053 nm wavelength are obtained. After frequency doubling, laser pulses with 3.0 mJ energy and 4.94 GW/cm2 intensity are achieved. A high gain Nd3+YLF regenerative amplifier is used as the first stage amplifier to generate narrow-band high power laser by taking advantage of the gain narrowing effect, and a bandwidth of 0.3 nm is obtained in theory. The output laser beam shows a top flat profile with excellent beam shaping. 1% (RMS) fluctuation is achieved by the stable regenerative amplifier which employs a three-steel-rod structure to mount the cavity.

A method to accurately evaluate optical thin-film damage threshold is presented. The poor coherences in time and space of amplified spontaneous emission (ASE) result in a very smooth beam profile in the near-field region and uniform intensity distribution of the focused beamlet in the far-field region. In order to increase the uniformity of the irradiation source and test the damage threshold with a greater precision, ASE beam is used to test the damage threshold. ASE is generated by a rod amplifier of the Ndglass in SG-II high power laser system. The pulse duration is 9 ns after an electro-optical switch with the output energy changing from a few millijoules to tens of joules. The spectral full width at half maximum (FWHM) is 1 nm. According to ISO-11254, the damage threshold of the TiO2 high reflection film using ASE is 15.1 J/cm2, which is higher than that of 7.4 J/cm2 tested by laser with pulse duration of 9 ns. So a more accurate evaluation of the samples damage thresholds can be obtained using ASE as the irradiation source.

In this paper, we systematically study preheating in laser-direct-drive shocks by using a velocity interferometer system for any reflector (VISAR). Using the VISAR, we measured free surface velocity histories of Al samples over time, 10–70 lm thick, driven directly by a laser at different frequencies (2x, 3x). Analyzing our experimental results, we concluded that the dominant preheating source was X-ray radiation. We also discussed how preheating affected the material initial density and the measurement of Hugoniot data for high-Z materials (such as Au) using impedance matching. To reduce preheating, we proposed and tested three kinds of targets.

A new laser amplifier structure based on Ndglass regenerative amplifier and off-axis four-pass amplifier is designed for high power laser facilities. The parasitic oscillation and pencil beam of the four pass amplifier are studied and a method is introduced to suppress them. By injecting a 1053 nm single longitudinal mode laser pulse with pulse duration of 3 ns and pulse energy of 1 nJ, a 10.3 J amplified pulse with a 2% shot-to-shot energy stability is obtained. The total gain of the amplifier system is over 1010. The output laser beam is a flat top profile with a 71% near field fill factor and modulation of 1.4 and 91% pulse energy can be focused into 2 times of diffraction limits. The experimental results and output performance of the amplifier system fully meet the requirements of the pre-amplifier of high power laser facilities, which shows that multi-pass amplifier can be used in high power laser facilities.

A method to broaden the spectrum by direct phase modulation is proposed. The effects on the spectrum of modulation depth,modulation signal width, synchronization precision and different signal forms are investigated by numerical simulations. The results show that deeper modulation and more narrow modulation signal width lead to a more obvious effect and a broader spectrum of single modulation; different modulation signal widths require different synchronization precisions, and the narrow signals need a high-precision synchronization; compared to the parabolic signal, sinusoidal signal can lead to an obvious frequency modulation to amplitude modulation, which can bring down the compressibility and the signal to noise ratio. The experiment results of the central wavelength match well the simulation results.

Antireflective coatings prepared by sol gel method are importantly used in high power laser devices, the stability of colloidal, laser induced damage thresholds (LIDTs) and antireflective efficiencies of coatings resulted from different particle sizes silica colloidal suspensions and silica antireflective coatings are studied by controlling different molar ratios of water and tetraethoxysilane (TEOS). The results show that the transmittance of porous silica antireflective films is higher than 99.5% and LIDTs are greater than 62 J/cm2 (1064 nm, 15 ns), the transmittance and LIDTs of smaller particle size silica antireflective film reaches 99.75% and 77.42 J/cm2 (1064 nm, 15 ns), respectively. The average particle sizes of colloidal suspensions increase with the mol ratio of H2OTEOS, the particle size quickly increases when the molar ratio of water and ester is greater than 3.5. The solution with particle size below 10 nm has excellent stability, and the particle size and viscosity of the solution is almost not unchanged. The stability of films with different particle sizes in different humidities is researched, all the films′ transmittance in high humidity drops and the film with larger particle size has more obvious decrease in transmittance, and therefore the chemical films are more suitable for the use in low humidity environment.

Curved illumination is used to improve the performance of ptychographical iterative engine (PIE). Influence of illumination with different curvatures on PIE is studied. Results show that curved illumination can make the algorithm more robust to random noise and quantization error, and enhance the resolution of PIE more than three times. Thus a good reference to the choice of illumination in the PIE experiment is given.

The coupling efficiency of short-pulse ignition laser energy to hot-spot internal energy directly affects the feasibility of fast ignition. Experimental characterization of the hot spot has attracted much attention. Among temperature, density and neutron yield of fast ignition experiments, the temperature of the hot spot has few available diagnostic methods. Multispectral X-ray imaging of hot-spot continuum emission is expected to give the time evolution of the electron temperature distribution. This article describes electron temperature determination from multispectral imaging, a dual-channel X-ray Kirkpatrick-Baez (KB) microscope designed for two-spectral imaging, and the experimental results of hot-core multispectral imaging of an imploded cone-shell target at the SG-II laser facility.

Laser diode pumped solid-state lasers (DPSSL) has become an important way to realize the next generation of laser-driven device for energy conversion efficiency and repetition rate requirements. High repetition frequency leads to heat accumulation on the memory medium, which will cause thermo-optical effect, elasto-optical effect and bulk displacement, then resuls in the generation of wavefront distortion and affects the beam quality. Aimed at 100 J output energy and 10 Hz repetition frequency amplifier module, the extraction efficiency and gain performance storage are analyzed, and the sheet laser diode pumped amplifier module structure is designed using gas cooling technology. Thermal analysis models of single slice amplifier are established using the finite element analysis. The influence of signal slice thickness and convective heat transfer coefficient to the wavefront distortion are researched, in consideration of the limitation of the total wavefront distortion, we obtain the optimal value of single slice thickness. Using super-Gaussian beam on behalf of pump source and considering the distribution of helium gas flow, we analysis the thermal designed data and simulate the temperature, bulk displacement and stress distribution to get the related wavefront distortions.

Understanding of the spatial distribution of ultrashort pulse temporal signal-to-noise ratio (SNR) characteristics at the focal spot in large aperture off-axis parabolic mirror focusing optical system is helpful for more accurate understanding of ultrafast laser pulse temporal and spatial characteristics in the ultrafast laser physics experiments. With wave-front error of optical system under consideration, the two-step focusing fast Fourier transform (FFT) algorithm with the coordinate transform based on Fresnel approximation in space domain and Fourier integral transform method in time domain are used to simulate the focusing process spatially and temporally. SNR degradation by wave-front error in large aperture optical system is explained, SNR ratio characteristics influenced by the parameters of the random wave-front error such as error magnitude and space scale are calculated and analyzed, and control requirements for different spectra of optical wave-front error of optical system are put forward. Explicating the relationship between SNR and random wave-front error in large diameter optical system is theoretical basis of designing large aperture ultrashort pulse system and wave-front error control.

The recently developed Light Field Moment Imaging (LMI) is adopted to show the stereoscopic structure of the sample studied in Coherent Diffractive Imaging (CDI), where 3D image were always generated with complicated experimental procedure such as the rotation of the sample and time-consuming computation. The animation of large view angle can be generated with LMI very quickly, and the 3D structure of sample can be shown vividly. This method can find many applications for the coherent diffraction imaging with x-ray and electron beams, where a glimpse of the hierarchical structure required and the quick and simple 3D view of object is sufficient. The feasibility of this method is demonstrated theoretically and experimentally with a recently developed CDI method called Ptychographic Iterative Engine. C 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.

The X-ray spectrometer used in high-energy-density plasma experiments generally requires both broad X-ray energy coverage and high temporal, spatial, and spectral resolutions for overcoming the difficulties imposed by the X-ray background, debris, and mechanical shocks. By using an elliptical crystal together with a streak camera, we resolve this issue at the SG-II laser facility. The carefully designed elliptical crystal has a broad spectral coverage with high resolution, strong rejection of the diffuse and/or fluorescent background radiation, and negligible source broadening for extended sources. The spectra that are Bragg reflected (23°<θ<38°) from the crystal are focused onto a streak camera slit 18 mm long and about 80 μm wide, to obtain a time-resolved spectrum. With experimental measurements, we demonstrate that the quartz(1011) elliptical analyzer at the SG-II laser facility has a single-shot spectral range of (4.64–6.45) keV, a typical spectral resolution of E/DE = 560, and an enhanced focusing power in the spectral dimension. For titanium (Ti) data, the lines of interest show a distribution as a function of time and the temporal variations of the He-a and Li-like Ti satellite lines and their spatial profiles show intensity peak red shifts. The spectrometer sensitivity is illustrated with a temporal resolution of better than 25 ps, which satisfies the near-term requirements of high-energy-density physics experiments.

In order to investigate the intense laser propagation and channel formation in dense plasma, we conducted an experiment with proton deflectometry on the OMEGA EP Laser facility. The proton image was analyzed by tracing the trajectory of mono-energetic protons, which provides understanding the electric and magnetic fields that were generated around the channel. The estimated field strengths (E ~ 1011 V/m and B~ 108 G) agree with the predictions from 2D-Particle-in-cell (PIC) simulations, indicating the feasibility of the proton deflectometry technique for over-critical density plasma.

High accuracy of target aiming and positioning is required in the study of the inertial confinement fusion (ICF). A system based on the chamber center reference system, the target positing system and the target alignment sensor is designed. The finite element method is used for analyzing the static deformation and transient stability of this system, and it proposes a calibration method of the high resolution parallel light pipe to achieve the system coupling precision. It achieves target aiming and positioning precision better than 12 μm of the SG-II updated laser facility. Through the SG-II updated laser facility single laser beam across the Φ 800 μm hole target, the perforation efficiency is 97.5%. This provides a solid foundation for high accuracy targeting of the follow-up physical experiment′s requirement.

The diagnoses of laser-produced plasma electron density have important significance for inertial confinement fusion, plasma physics, high energy density physics and other relevant fields, especially for measuring electron density distribution information of medium and high-Z material plasma near the critical density surface. With 13.9 nm Ni-like Ag X-ray laser serving as a probe, using double frequency grating shearing interference technique, the electron density distribution of plasma produced by laser irradiating a gold planar target is measured. Clear interference fringe image is obtained. Preliminary deduction of the fringe shows that the maximum density measured is about 1.4 times the critical density. It is found that there are some discrepancies between experimental results and simulation results, which provides a useful reference to the further optimization of the simulation program. The experimental results fully demonstrate that the soft X-ray double frequency grating shearing interference technique is practical to diagnose near-critical-density plasma of medium and high-Z materials, which will have a good application value.

Based on the optical transmission theory, the reason why front-surface particle contamination may induce the original damage of thin optical components is considered, and a damage mechanism is put forward: The localized thermal deformation of an optical element induced by the thermal effect of particle contamination together with the shading effect of it can disturb the laser beams. Simulated results show that for a high power laser, the localized thermal deformation of thin optical components, which disturbs the laser beam, is an important cause to produce strong light intensity modulations. The surface shape, phase delay, and thermal diffusion length of a localized thermal deformation are constantly changing with the increase of laser pulse shot number, so the highest light intensity modulation will be produced at different positions in the thickness direction or the xy direction on the rear-surface of an optical element. This not only can easily induce some damages on the rear-surface of the optical element, but also cause the interior damages scattered in the thickness direction.

The capability of chirped-pulse compression and beam focusing of an object-image-grating self-tiling grating compressor is demonstrated in an optical parametric chirped-pulse amplification laser for the first time. Probe lasers for tiling error adjustments, which are generally required by the traditional tiled-grating compressor, are not needed in our demonstration any more. With the aid of the double-sized effective optical aperture of the second grating in the compressor, a 490 fs near-transform-limit pulse duration and a 90 μm near-diffraction-limit focal spot are obtained, synchronously, which are very close to the ones achieved by a non-tiled grating compressor with equal-sized individual gratings.

A simple model is presented to analyze the spectral shape and bandwidth dependence of the pulsecontrast and compressed pulse width in the chirped pulse amplification. The parameters of the 30 fslaser system are demonstrated as examples. Comparing with Top hat, Lorentzian, Sech2, Gaussian, 2ndSuper Gaussian and 10th Super Gaussian spectral pulse shape, the 2nd Super Gaussian spectral pulseshape can obtain better contrast in the case of less spectral bottom width. Those results are helpful tofind an optimized spectral shape in the chirped pulse amplification.

This paper explores the parameter measurement in laser produced plasma by X-ray line profile spectrscopy. The experiment was conducted on the SG-II laser facility. A 0.35 μm laser beam was focused on a solid chlorine (Cl) target in a vacuum chamber to produce a laser chlorine plasma and the high resolution X-ray elliptical bent crystal spectrograph was used to obtain the X-ray fine structure energy spectrum of the chlorine plasma radiation. The line integrated intensity ratio between H-like Cl (1s-3p) (Lyman-) and He-like Cl (1s2-1s3p) (He-) transitions was used for calculation of the electron temperature. By assuming optically thin, the Lyman-stark broadened profile was utilized to measure the electron density. Obtained experimental results show that the volume averaged electron temperature of Te is about 450 eV and the electron density of Ne is approximately 7.5×1022 cm-3. In addition, the line Full Width at Half Maximum (FWHM) was analyzed. The uncertainty in Ne due to uncertainties in the temperature and the assumed background level was also simply discussed and it is estimated to be within 25%. As a result, the experimental spectroscopic method may become a reference for diagnosing future higher-compression implosions.

It is important to diagnose electron density of a plasma irradiated by lasers for inertial confinement fusion, in high energy density physics and related fields, especially for measuring high-Z plasma near the interface. Use of soft X-ray laser as a probe is an important method in diagnosis of plasma electron density distribution. However, it is difficult to carry out the research in high-Z laser plasma, because of the problem of excessive plasma spontaneous radiation. In view of the characteristics of soft X-ray laser, several specific experimental techniques have been developed. By using these techniques, which can greatly suppress effects of spontaneous radiation, diagnosis of high-Z plasma with soft X-ray laser probe method becomes possible. As a typical example, an experiment of diagnosing gold plasma is performed and clear images are obtained, indicating that the techniques are effective and feasible.

Wavefront control is a significant parameter in inertial confinement fusion (ICF). The complex transmittance of large optical elements which are often used in ICF is obtained by computing the phase difference of the illuminating and transmitting fields using Ptychographical Iterative Engine (PIE). This can accurately and effectively measure the transmittance of large optical elements with irregular surface profiles, which are otherwise not measurable using commonly used interferometric techniques due to a lack of standard reference plate. Experiments are done with a Continue Phase Plate (CPP) to illustrate the feasibility of this method.

A polystyrene (CH)/aluminum (Al) dual-layer perturbation target for hydrodynamic instability experi-ments in inertial confinement fusion (ICF) was designed and fabricated. The target was composed of aperturbed 40 m Al foil and a CH layer. The detailed fabrication method consisted of four steps. The 40 mAl foil was first prepared by roll and polish process; the perturbation patterns were then introduced onthe surface of the Al foil by the single-point diamond turning (SPDT) technology; the CH layer was pre-pared via a simple method which called spin-coating process; finally, the CH layer was directly coatedon the perturbation surface of Al foil by a hot-press process to avoid the use of a sticker and to eliminatethe gaps between the CH layer and the Al foil. The parameters of the target, such as the perturbationwavelength (T) and perturbation amplitude (A), were characterized by a QC-5000 tool microscope, analpha-step 500 surface profiler and a NT1100 white light interferometer. The results showed that T and Aof the target were about 52 μm and 7.34 μm, respectively. Thickness of the Al foil (H1), thickness of theCH layer (H2), and cross-section of the dual-layer target were characterized by a QC-5000 tool micro-scope and a scanning electron microscope (SEM). H1 and H2 were about 40 μm and 15 μm, respectively,the cross-sectional photographs of the target showed that the CH layer and the Al foil adhered perfectlywith each other.

Highly efficient and high-power operation of Raman fiber lasers in fixed-wavelength and wavelength-tunable cavity configurations based on a graded-index multimode fiber is reported. Fixed-wavelength and wavelength tunable operating regimes are achieved using volume Bragg gratings (VBGs) with center wavelengths of 1658 nm and 1750 nm, respectively. The fixed-wavelength laser yielded a maximum output power of 10.5 W at 1658.3 nm with a FWHM linewidth of ~0.1 nm for the launched pump power of 23.4 W, corresponding to a slope efficiency of 82.7% with respect to the launched pump power. The measured beam quality in the form of M2 factor is ~1.35, corresponding to the fundamental mode of the fiber. For the wavelength-tunable Raman fiber laser, a wavelength tuning range of 37 nm from 1638.5 to 1675.1 nm is obtained with a maximum output power of 3.6 W at 1658.5 nm for the launched pump power of 13.0 W.

A new technique is presented for obtaining a large broadband nanosecond-laser pulse. This technique is based on multipass phase modulation of a single-frequency nanosecond-laser pulse from the integrated front-end source, and it is able to shape the temporal profile of the pulse arbitrarily, making this approach attractive for high-energy-density physical experiments in current laser fusion facilities. Two kinds of cavity configuration for multipass modulation are proposed, and the performances of both of them are discussed theoretically in detail for the first time to our knowledge. Simulation results show that the bandwidth of the generated laser pulse by this approach can achieve more than 100 nm in principle if adjustment accuracy of the time interval between contiguous passes is controlled within 0.1% of a microwave period. In our preliminary experiment, a 2 ns laser pulse with 1.35-nm bandwidth in 1053 nm is produced via this technique, which agrees well with the theoretical result. Owing to an all-solid-state structure, the energy of the pulse achieves 25 μJ. In the future, with energy compensation and spectrum filtering, this technique is expected to generate a nanosecond-laser pulse of 3 nm or above bandwidth with energy of about 100 μJ.

A high-power and narrow-linewidth Er, Yb co-doped fiber laser is demonstrated by using two serially-paired volume Bragg gratings. A maximum output power of 19.4 W at 1545.3 nm with a full-width at half-maximum linewidth of <～38 pm is obtained for 65.3 W of launched pump power, corresponding to a slope efficiency of 30.1% with respect to launched pump power.

In order to improve laser damage resistance of the Final Optics Assembly (FOA), simulation analysis have been done for 1ω, 2ω and 3ω laser beam considering ghost images to the 4th order. The panels of ground glass scatter ghost laser around the FOA walls and the panels of architectural glass absorb the 1th order energy. The appearance of smoothing fused silica surface defect and the effect of wiping off etching contamination are researched on HF-based etching processes under ultrasonic. Now, 18 shots were executed using 310×310mm laser with 3ns pulse width. During the experiment, the third harmonic laser terminal output energy is 1500J~3500J, and the maximum laser energy flux is about 4J/cm2. This presentation addresses the optical configuration of the FOA, the simulation analysis of ghost, the way of ground glasses absorbing energy and the result of laser damage resistance of fused silica on HF-based etching processes under ultrasonic.

Laser-induced damage (LID) to optical glass has become a growing problem in high-power laser systems. It is well known that the main reason of glass being damaged is due to defects and impurities in the material. Damage caused by subsurface defects (SSDs) is especially common in actual system running. Accordingly, in the presence of SSDs, a simple and alternative calculation method is developed to evaluate the enhancement of light field around the incident and exit surface. This ray tracing approach, based on the classical optics theory, is very direct and clear to show the optical phenomena of light intensity enhancement. Some basic SSD shapes have been studied and investigated here, which reveals the importance and boundary condition of controlling the size and density of SSDs in grinding and polishing process. Finally, to achieve optimal breadth depth ratio, the least etching amounts by hydrofluoric (HF) acid is investigated. The theoretical analysis and simulation results provide an appropriate range of removal amounts, which is very important in the HF etching process.

Beam alignment depends on CCD real-time image analysis and processing. In order to improve the quality of the alignment, multiple filters are used in far-field and near-field image processings. These multiple filters are constituted of an average filter and a median filter in different connection sequences, so that they can deal with different kinds of noise. To reduce the effect of the unknown nonlinear relationship between motor running steps and deviation pixels, a feasible methodology is offered to improve this phenomenon and a fuzzy algorithm is applied to the motor feedback control process. Because of the fuzzy control it is not necessary to establish an accurate mathematical model, so the impact of the nonlinear relationship will be reduced.

The physical meaning and essence of Fresnel numbers are discussed, and two definitions of these numbers for offaxis optical systems are proposed. The universal Fresnel number is found to be N=(a2/λz)*C1+C2. The Rayleigh–Sommerfeld nonparaxial diffraction formula states that a simple analytical formula for the nonparaxial intensity distribution after a circular aperture can be obtained. Theoretical derivations and numerical calculations reveal that the first correction factor C1 is equal to cosθ and the second factor C2 is a function of the incident wavefront and the shape of the diffractive aperture. Finally, some diffraction phenomena in off-axis optical systems are explained by the off-axis Fresnel number.

An effective damage test method based on a marker-based watershed algorithm with gray control (MWGC) is proposed to study the properties of damage induced by near-field laser irradiation for large-aperture laser facilities. Damage tests were performed on fused silica samples and information on the size of damage sites was obtained by this new algorithm, which can effectively suppress the issue of over-segmentation of images resulting from non-uniform illumination in darkfield imaging. Experimental analysis and results show that the lateral damage growth on the exit surface is exponential, and the number of damage sites decreases sharply with damage site size in the damage site distribution statistics. The average damage growth coefficients fitted according to the experimental results for Corning-7980 and Heraeus-Suprasil 312 samples at 351 nm are 1:10+(-)0:31 and 0:60+(-)0:09, respectively.

Flat-topped beam theoretical model and unified theory of coherence and polarization of light are used as the bases in examining aberrated, partially coherent, electromagnetic, square, flat-topped pulsed beams focused by a thin lens. This study demonstrates that Astigmatism is not necessarily undesirable in certain circumstances, and a certain amount of astigmatism can be guaranteed a similar spatial envelope of the beams in the geometric focal plane as the source of aberrated, partially coherent, electromagnetic, square, flat-topped pulsed beams. This feature may be useful in determining the fidelity of high-power laser-beam transmission areas.

The flow field of thermal recovery system in the rod amplifier has significant influence on the laser beam quality. The flow field of the thermal recovery system depends on the inlet and outlet angles of water. Based on the flow field distribution of the direct-flow type for the thermal recovery system, we develop the optimum inlet and outlet angles of the thermal recovery system to the rod amplifier, which enhances the uniformity of the flow field and heat exchange efficiency of the thermal recovery system.