Laser drive ramp compression is an important way to achieve extremely high pressure but relatively low temperature material state. This article introduces our progresses in recent years. The main progresses contain theoretical researches and experimental researches. In theoretical part, an analytical model for designing driving pressure pulse was set up, and a new characteristic method based on a Murnaghan-form state equation was developed. What’s more, X-ray preheating in the target and laser pulse design in laser-indirect-driven experiments were studied. In the experimental part, laser-direct driven experiments and laser laser-indirect driven experiments were performed on aluminum and iron, results showing the experimental design methods were feasible, and the compressions were in isentropic ways.
K-shell spectra of a laser-produced carbon plasma have been measured and analyzed. A graphite plate was irradiated by a 2.1ns ultraviolet laser pulse, and the radiated X-rays were measured with a flat-field grating spectrograph. The recorded lines have been identified as hydrogenic Lyman series 1s-np and heliumlike transitions 1s2 -lsnp (n=2-4). The measured wavelength and the spectral resolution of the flat-field grating spectrograph were calibrated by utilizing those lines. Hydrodynamic simulations and calculations of charge-state distributions in the local thermodynamic equilibrium (LTE) regime were carried out to interpret the K-shell spectra.
Ultrafast phenomenon has presented widely in natural phenomenon and scientific and technological research. Therefore, study on ultrafast phenomenon is of great important in many research and technology fields. In recent years, the development and application of ultra-short laser pulse has been covered many areas. It has been developed into a powerful tool used to research ultrafast phenomena. In the implementation process of the ultra-short laser pulses, high-speed switching plays a vital role. The difficulty of high-speed switching design is to make the ultrafast electric pulse load on the both ends of the crystal with minimum distortion and delay. It is very difficult to switch electro-optic crystal at a high frequency in traditional method. In this paper, a new method is designed, which combined the electro-optic crystal and micro-strip line. The crystal is a part of the transmission path and the signal path of the micro-strip line is broadened or narrowed continuously to make the impedance matching to 50 ohm. The good match between pulse signal and the crystal make sure the high frequency switches of the crystal. The amplitude loss is less than 11%, and the delay is less than 1 nanosecond.
A large angularly multiplexed XeCl Excimer laser system is under development at the Northwest Institute of Nuclear Technology (NINT). It is designed to explore the technical issues of uniform and controllable target illumination. Short wavelength, uniform and controllable target illumination is the fundamental requirement of high energy density physics research using large laser facility. With broadband, extended light source and multi-beam overlapping techniques, rare gas halide Excimer laser facility will provide uniform target illumination theoretically. Angular multiplexing and image relay techniques are briefly reviewed and some of the limitations are examined to put it more practical. The system consists of a commercial oscillator front end, three gas discharge amplifiers, two electron beam pumped amplifiers and the optics required to relay, encode and decode the laser beam. An 18 lens array targeting optics direct and focus the laser in the vacuum target chamber. The system is operational and currently undergoing tests. The total 18 beams output energy is more than 100J and the pulse width is 7ns (FWHM), the intensities on the target will exceed 1013W/cm2. The aberration of off-axis imaging optics at main amplifier should be minimized to improve the final image quality at the target. Automatic computer controlled alignment of the whole system is vital to efficiency and stability of the laser system, an array of automatic alignment model is under test and will be incorporated in the system soon.
Excimer laser has been shown to be efficient tools in plasma physics and material science. Recent progress on techniques of beam control in excimer laser system required for energy scaling are overviewed, Configuration and initial results of a 100J/10ns, 18 beam excimer laser system are given.
In high power eximer laser system, amplified spontaneous emission (ASE) decreases the signal contrast ratio severely, leads to waveform broadening and distortion, and impacts on accurate physical experiments. In this article, based on principle of short pulse generation by electro-optical (E-O) switch, a method for ASE suppression of laser amplifiers chain was established. A series of studies on UV electro-optical switches were carried out, and electro-optical (E-O) switches with high extinction ratio were developed. In the waveform clipping experiments of the first pre-amplifier, the extinction ratio of the single and cascaded dual E-O switch reaches 103 and 104 order of magnitude, the laser pulse signal contrast ratio was promoted to 105 and 106 level, respectively. In the experiments of single channel MOPA (Master Oscillator Power Amplifier system), the cascaded dual E-O switch was adopted to suppress ASE of the whole system, and a fine narrow pulse was obtained on the target surface, which gives out one effective solution to the problem of waveform amplification of the high power eximer laser system.
A special designed long pulse XeCl MOPA laser system and its initial laser-target experiments are introduced. Laser produced plasmas of carbon, aluminum and copper are concerned. Based on measured results of plasma spectra and framing pictures of ejected plume, Plasma temperature and expanded speed of plasma flume are obtained.
A 250 J/210 ns four-stage XeCl laser system named Photons has been developed. Five lasers in MOPA chains characterized by different pumping techniques are described. Also, the main experimental results of the Photons are given.
A four-stage XeCl laser system named Photons has been developed for studying laser interaction with materials. The Photons are outlined and preliminary results characterizing the system are given. The master oscillator Photon-1 can provide “seed” light with laser energy of about 40mJ, pulse duration of about 250ns and good beam quality of nearly diffraction-limited divergence angle and narrow line width less than 1 cm-1 for whole system. The output energy of laser system of 251J has been obtained by four-stage amplification. The synchronization among five lasers is realized by the combination of low voltage timer, high voltage synchronic generators and compensated cables. The demonstration shows Photons good operation with low jitter of less than ±20ns.
Development of a long-pulse spark preionized XeCl-lasers pumped by a self-sustained discharge using a double-discharge circuit is reported. The pre-pulse is formed by novel generator with an inductive energy storage and semiconductor opening switch. The lasers produce up to 1-1.5 J in a pulse with total duration up to 500 ns and total efficiency up to 1.5-2%. Circuit for the discharge current correction is suggested for further extension of the optical pulse. The laser producing 300 ns (FWHM) was used as a master oscillator in a powerful XeCl-laser system.
A high power XeCl and KrF excimer lasers pumped by an intense relativistic electron beam have been developed. The pump power density ranges between 1.5 to 2.0 MW/cm3. The maximum output energy of 136 J with the peak power of 1.5 GW is obtained for the XeCl laser. In KrF laser case, the maximum output energy is 157 J and the peak power 2.0 GW. The UV laser interaction with some materials has been studied by this excimer laser.