A scheme using a lens array and the technique of spectral dispersion is presented to improve target illumination uniformity in laser produced plasmas. Detailed two-dimensional simulation shows that a quasi-near-field target pattern, of steeper edges and without side lobes, is achieved with a lens array, while interference stripes inside the pattern are smoothed out by the use of the spectral dispersion technique. Moving the target slightly from the exact focal plane of the principal focusing lens can eliminate middle-scale-length intensity fluctuation further. Numerical results indicate that a well-irradiated laser spot with small nonuniformity and great energy efficiency can be obtained in this scheme.
A high-efficiency, ultrabroadband dielectric internal reflection grating with rhombus-shaped grooves is designed by a rigorous coupled-wave analysis, and an effective method for predicting spectral bandwidths of gratings from their efficiency maps is presented. The grating can be fabricated from a single dielectric material, and its reflection diffraction efficiency of the −1st order can reach more than 0.99. More importantly, an ultrabroadband top-hat diffraction spectrum with efficiency exceeding 0.98 over 170 nm wavelength wide is achieved, which makes the gratings suitable for applications associated with broadband illumination, such as ultrashort pulses.
A numerical model of optical parametric amplification (OPA) is introduced to investigate the impact of wavefront phase distortion of pump on the beam quality of signal.Numerical results show that the unidentical walk-off directions of the pump and the idler waves are the main factors leading to the transfer of wavefront phase distortions of the pump to the signal, and by reducing the angle between the two directions, the beam quality factor (M 2 ) can be greatly decreased and hence the good beam quality of the signal can be maintained.
Estimation of the far-field centre is carried out in beam auto-alignment. In this paper, the features of the far-field of a square beam are presented. Based on these features, a phase-only matched filter is designed, and the algorithm of centre estimation is developed. Using the simulated images with different kinds of noise and the 40 test images that are taken in sequence, the accuracy of this algorithm is estimated. Results show that the error is no more than one pixel for simulated noise images with a 99% probability, and the stability is restricted within one pixel for test images. Using the improved algorithm, the consumed time is reduced to 0.049 s.
A new spectrum shaping method, based on electro-optic modulation, to alleviate gain narrowing in chirped pulse amplification (CPA) system, is described and numerically simulated.Near-Fourier transform-limited seed laser pulse is chirped linearly through optical stretcher.Then the chirped laser pulse is coupled into integrated waveguide electro-optic modulator driven by an aperture-coupled-stripline (ACSL) electricalwaveform generator, and the pulse shape and amplitude are shaped in time domain.Because of the direct relationship between frequency interval and time interval of the linearly chirped pulse, the laser pulse spectrum is shaped correspondingly.Spectrum-shaping examples are modeled numerically to determine the spectral resolution of this technique.The phase error introduced in this method is also discussed.
Abstract 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 dark-field 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 $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}1.10 \pm 0.31$ and $0.60 \pm 0.09$ , respectively.
The generalized analytical expression for the propagation of flat-topped multi-Gaussian beams through a misaligned apertured ABCD optical system is derived. Using this analytical expression, the propagation characteristics of flat-topped multi-Gaussian beams through a spatial filter are investigated. The analytical formula of the electric field distribution in the focal plane is also derived for revealing the effects of the misalignment parameters clearly. It is found that different misalignment parameters have different influences on the electric field distributions of the beam focus spot and the output beam characteristics. The intensity distribution of the beam is mainly determined by the misalignment matrix element E, and the phase distribution is affected by the misalignment matrix elements G and E.
A new high power laser facility with 8 beams and maximum output energy of one beam 5kJ/3.4ns/3ω has been performed and operated since 2015. Combined together the existing facilities have constructed a multifunction experimental platform including multi-pulse width of ns, ps and fs and active probing beam, which is an effective tool for Inertial Confinement Fusion (ICF) and High Energy Density (HED) researches. In addition another peculiar high power laser prototype pushes 1ω maximum output energy to 16kJ in 5ns and 17.5kJ in 20ns in flat-in-time pulse, this system is based on large aperture four-pass main amplifier architecture with 310mm×310mm output beam aperture. Meanwhile the near field and far field have good quality spanning large energy scope by use of a wide range of technologies, such as reasonable overall design technique, the integrated front end, cleanness class control, nonlinear laser propagation control, wave-front adaptive optics and precision measurement. Based on this excellent backup, 3ω damage research project is planning to be implemented. To realize the above aims, the beam expanding scheme in final transport spatial filter could be adopted considering tradeoff between the efficient utilization of 1ω output and 3ω damage threshold. Besides for deeply dissecting conversion process for beam characteristic influence of 1ω beam, WCI (Wave-front Code Image) instrument with refined structure would be used to measure optical field with simultaneous high precision amplitude and phase information, and what's more WCI can measure the 1ω, 2ω and 3ω optical field in the same time at same position, so we can analyze the 3ω beam quality evolution systematically, and ultimately to improve the 3ω limited output. In a word, we need pay attention to some aspects contents with emphasis for future huger laser facility development. The first is to focus the new technology application. The second is to solve the matching problem between 1ω beam and the 3ω beam. The last is to build the whole effective design in order to improve efficiency and cost performance.
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