A comprehensive finite element physics model is constructed to analyze the thermal effects of a thin disk medium. Based on this physical model, the temperature and stress distribution inside the medium are obtained. According to the corresponding theory, the internal optical path difference (OPD) and thermal focal length of the medium can be calculated when subjected to thermal load. According to the numerical model of the thermal effect, which has been verified by experiments conducted on commercial thin disk purchased from Dausinger + Giesen GmbH (DG), the study investigated the influence of various factors on the thermal effect of the thin disk medium. Additionally, a thin disk medium based on photoadhesion technology has been developed. The thermal focal length of the thin disk medium has been compensated by adjusting the surface shape in advance to match the desired focal length, which is significantly higher than that of the uncompensated medium. Below a pump density of 1.27 kW/cm2, the thermal focal length of the self-developed thin disk medium is comparable to that of the DG's thin disk medium.
To achieve high-precision dispersion measurement of optical components, a new method based on spectral shaping and frequency-to-time mapping was proposed, which was experimentally demonstrated and verified. In this research, a modelocked laser and a home-made spectral shaper were used to realize the spectral shaping of laser pulse with fingerprint-like characteristic. After transmitted through a dispersive medium, the temporal profile of the laser pulse became a scaled replica profile of the spectrum owing to the frequency-to-time mapping of chirped pulse. A Taylor-expanded chromatic dispersion model and least-square method were adopted for data analysis, which realized a measurement of 1-km fiber to the second-order dispersion with an error of 0.43%. The precision of the dispersion measurement was greatly enhanced by constructing a fingerprint-like characteristic spectrum. The experimental results showed that this method has better robustness and fidelity for different types of optical fiber, as well as various dispersive components in high-power laser system.
The frequency domain optical parametric amplification technology, as a new technology reserve for ultra-strong ultrashort pulses of 10 PW or even EW-level OPCPA systems, has many advantages in achieving high-energy ultra-wideband OPCPA. It can take the large gain bandwidth into consideration while enlarging the energy of ultra-short pulses, does not need stretcher and compressor, and is not restricted by materials such as crystal growth and grating damage threshold. In this thesis, the theoretical analysis and numerical simulation of frequency-domain chirped-pulse parametric amplification (FOPA) are mainly performed to complete the entire system design and experimental verification. Based on the picosecond laser system in the laboratory, the experimental verification of the frequency-domain optical parametric chirped-pulse amplification technology with a center wavelength of 800 nm and a gain bandwidth of nearly 100 nm has been completed.
The issue of laser-induced damage on critical components emerges as a bottleneck that limits the high-power or high-energy laser systems, especially for the fused silica optics used in ultraviolet light. Sub-surface defects such as microcracks and impurities on fused silica optics have been discovered as damage precursors and determine the laser-induced damage threshold (LIDT) of the optics. Under the state-of-the-art advanced mitigation processes (AMP) and laser conditioning, only a few destructive damage sites that grow rapidly with successive shots still exist on a large-aperture fused silica optic. Therefore, we propose a method of selectively eliminating the destructive damage sites on fused silica optics by laser micromachining and consequently lead to a significant enhancement of LIDT in this paper. The removal of a damage site is implemented by precisely shaping the destructive damage site into an optically benign cone of special design using a femtosecond laser, with a subsequent CO2-laser-polishing process to reduce the roughness. Compared with previous methods, the thermal effect on the processed region is dramatically reduced because of the nonthermal ablation by a femtosecond laser. Through optimizing the parameters of laser micromachining, a typical damage site is eliminated and replaced with a designed cone of excellent quality. The manufactured cone typically has a smooth wall with a slope angle of 12°, a diameter of 800 μm, and a negligible raised rim with a height of 14.5 nm (∼ λ/25 @ 355 nm). By employing the raster scan LIDT test procedure, several fused silica optics processed by laser micromachining are investigated and a laser-induced damage threshold (@ 355 nm, 1.6 ns) higher than 14 J/cm2 and 10 J/cm2 on the input surface and output surface are discovered, respectively. Furthermore, the downstream light intensification is proven to be trivial in the absence of a detrimental high-intensity central spot, owing to the ultra-low raised rim. These results demonstrate that rapid laser micromachining is an effective way to improve laser-induced damage resistance of fused silica optics and eventually enhance the performance of high-power or high-energy laser systems.
Laser ablation of aluminum alloy and stainless steel were investigated experimentally with a picosecond laser (1053 nm, 8.6 ps, 1Hz). We analyzed and compared the damage threshold and morphology of stainless steel and aluminum alloy. The single-pulse ablation threshold of stainless steel is higher than that of aluminum alloy. The ablation morphology are quite different under multi-pulse irradiation, and the micro-scale periodic surface structures are formed on the stainless steel surface but not on the aluminum alloy sample. The influence of metal thermodynamic properties on laser ablation characteristics is analyzed.
Many literatures have focused on the design, fabrication and intrinsic damage of multilayer dielectric gratings (MLDGs). However, contamination may be a key factor of the MLDGs lifetime. In this paper, we compare the laser damages of the clean and contaminated MLDGs, and damage threshold of clean MLDGs is 3.12J/cm2 . We obtain the curve of the critical particle size at various laser fluences, above which the MLDGs will be damaged. Intrinsic LIDT of clean MLDGs is larger than that of contaminated ones, so the cleanness control is a crucial problem for the MLDGs. The scanning electron microscope (SEM) morphologies of intrinsic and contaminant induced damages are different. The intrinsic damage is cold ablation, while contaminant induced damage is thermal ablation.
In order to broaden the spectrum of laser pulse and reduce the gain narrowing effect in Nd:glass regenerative amplifier to
realize the ambition of inhibiting amplitude and frequency modulation, proper quartz birefringence crystal plate is inserted
into the cavity. The influence factors of central wavelength, depth of modulation and range of modulation are obtained
theoretically. The width of the spectrum is broadened by controlling all the factors. Two kinds of thickness, 5mm and
6mm, are inserted into the regenerative amplifier cavity. The results of theoretical calculation and experiment both show
that the effect of spectrum widening is evident, which reduces the gain narrowing effect to some extent. The amplitude and
frequency modulation resulted from gain narrowing effect is inhibited when the central wavelength deflects. The simulated
results show that inhibited effect of amplitude and frequency modulation is remarkable. And the method is a potential
effective technique for amplitude and frequency modulation inhibition.
Pre-amplifier between the frontend and main power amplifier is the key unit of high power laser divers. The recent
progresses on the off-axis quadruple pass amplifier are presented, which include the beam path design, parasitic
oscillation research and experimental results. A single longitudinal mode, temporally shaped laser pulse with 5ns pulse
duration at 1053nm is injected into a Nd: Glass regenerative amplifier, which can provide a 12mJ energy output with
0.5% long term energy stability. The quadruple pass amplifier is designed as an off-axis pattern. With 1.3mJ energy
injection, amplified pulse with 16.5J can be achieved, and the measured output energy stability of the amplifier is 7.3%
(PV) at this output energy level, corresponding to a 21 shot result. The total gain of the amplifier is more than 10,000.
The parasitic oscillation was analyzed and discussed, and the parasitic mode and pencil beam are neither observed in the
experiment.
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