Laser induced damage in the final optics assembly is one of the bottleneck problems in high power laser systems for the inertial confinement fusion. Defects on the optical elements can cause optical intensity intensification and therefore damage the optical elements in the downstream. However, only single defect is considered for most cases. In this paper, physical models are established to study enhancement of light intensity related to distribution of defects in the final optics assembly. Results show that, when the distance of two localized defects reduces to a certain distance, there will be a stronger light intensity intensification duo to the interference effect. What’s more, it will be much more serious when the nonlinear effect is taken into consideration. Meanwhile, the interaction of two kinds of different defects are also studied, i.e., the periodic defect and the localized defect. The optical field will be enhanced to a certain extent at the overlapped area. Thus, we can see that single defect may not cause optical damage. But when there are more than one defect with a certain distribution, light field may be further enhanced, thus damaging the optical element. As a conclusion, the distribution of defects also needs strict constraints. The results could give some references to the mitigation of damage caused by defects in the final optics assembly.
Optical components are often damaged by hot images in high power laser system, especially for the final optics assembly. There are several nonlinear optical elements and a focusing lens. So both the hot images in free space propagation and in the focusing system are theoretically and numerically studied. We find that the focusing lens moves the hot images towards the lens. Through Fresnel number, the connection of hot image position in free space propagation and in the focusing system is discussed. What’s more, the nonlinear effect of the focusing lens is also considered for the hot images formation because the lens is sometimes very thick. At last, the influence of the size and modulation depth of scatter on the hot images position and intensity are also given. The hot images analysis is essential for the final optics assembly design, which can shed some light on avoiding the optical damage.
Enhancing performance status of final optics assembly on high power laser at 351nm laser is experimentally studied. We experimentally demonstrate 61 shots of 310mm × 310mm laser. The maximum laser energy flux is 5.5J/cm2. The laser energy conversion efficiency is more than 72%. And the laser perforation efficiency across 800μm at 3000J is more than 96%. These results provide valuable information to improve final optics assembly performance research of high power laser.
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.
The high fluence performance of high-power laser systems is set by optical damage, especially in the final optics assembly (FOA). The flaws on the frequency converter surface can cause optical intensity intensification and, therefore, damage the downstream optical elements, such as the beam sampling grating (BSG), which is an important component in the FOA. Mitigation of BSG damage caused by flaws is discussed. Physical models are established to simulate the optical field enhancement on BSG modulated by the upstream flaw, considering both the linear and nonlinear propagation effects. Numerical calculations suggest that it is important to place the BSG in a properly selected position to mitigate the laser-induced damage. Furthermore, strict controls of flaw size, modulation depth, distance between frequency converter and focusing lens, and the thickness of the focusing lens are also significant to mitigate the BSG damage. The results obtained could also give some suggestions for damage mitigation of optical components and the layout design of the final optics assembly.
In high-power laser facilities for the inertial confinement fusion, there are many large-radius optical elements, which
inevitably have some flaws on the surface. The flaws can cause optical intensity intensification and therefore damage the
optical elements in the downstream, especially for the beam sampling grating (BSG), which is an important element in
the final optics assembly. In this paper, several physical models are established to study the optical field enhancement in
the BSG position modulated by upstream flaw. Firstly, when only the linear transportation is considered, it is found that
there is a peak or valley of the maximum intensity after the focus lens compared with the ideal wave front. Meanwhile
the influence of flaw has an effective range. Secondly, when the nonlinear effect of the focus lens is also considered, the
peak maximum downstream is much bigger than the one for the linear consideration and the damage risk of the BSG
there is much higher too. From the simulation, we can see that it is important to place the BSG in a properly selected
position to mitigate the laser induced damage. The results could give some references to the mitigation of BSG damage
caused by upstream flaws and the layout of the final optics assembly.
Proc. SPIE. 9142, Selected Papers from Conferences of the Photoelectronic Technology Committee of the Chinese Society of Astronautics: Optical Imaging, Remote Sensing, and Laser-Matter Interaction 2013
KEYWORDS: Diffraction, Diffractive optical elements, Imaging systems, X-rays, Wave plates, Wave propagation, Picosecond phenomena, Zone plates, X-ray imaging, Hard x-rays
Zone plates and photon sieves can be used to focus soft X-rays and hard X-rays. Relative to the parallel plane wave incidence and focusing on the optical axis, we here present two different models to describe the other kinds of focusing properties. The former, the scaled zone plates or photon sieves are appropriate for the titled plane wave to image, which can alter the propagation direction. The latter, the eccentric elliptical zone plates or photon sieves are appropriate for the point-to-point off-axis focusing. Based on the above-mentioned models, the different algorithms are discussed in detail under the condition of different numerical apertures. Furthermore, the correctness of our model has been verified through the commercial software VirtualLAB. The obtained results can be used for the analysis, design, and simulation of different zone plates and photon sieves, meanwhile the non-coaxial characteristics can increase the flexibility of the optical system.
In high-power laser facilities for inertial confinement fusion, there are many large-diameter optical elements, which
inevitably have some flaws on the surface. The beam is modulated by these flaws after diffraction transmission, thereby
reducing the beam quality of the system. The optical field with high modulation may cause self-focusing in fused silica
and thus damage the optical components, which seriously affects the load capacity of the device. Therefore, for
high-power laser systems, near field beam quality also has a high demand. In this paper, the effect of flaws and nonideal
wavefront of sinusoidal modulation on the near-field quality at specific position behind the focusing lens is analyzed for
final target system of high power laser device based on the Huygens-Fresnel diffraction theory. Firstly the beam
modulation of ideal wavefront disturbed by flaws is investigated. And the modulation by phase type flaw is more serious
than amplitude type. Secondly, near field beam modulation of nonideal wavefront of sinusoidal phase disturbed by flaws
is analyzed. Results demonstrate that under some specific conditions of sinusoidal phase, modulation degree is reduced
and the beam quality is improved by the nonideal wavefront compared to the ideal wavefront. The results could give
some references to the improvement of near field beam quality and mitigation of risk of optical damage caused by