Search

The laboratory generation and diagnosis of uniform near-critical-density (NCD) plasmas play critical roles in various studies and applications, such as fusion science, high energy density physics, astrophysics as well as relativistic electron beam generation. Here we successfully generated the quasistatic NCD plasma sample by heating a low-density tri-cellulose acetate (TCA) foam with the high-power-laser-driven hohlraum radiation. The temperature of the hohlraum is determined to be 20 eV by analyzing the spectra obtained with the transmission grating spectrometer. The single-order diffraction grating was employed to eliminate the high-order disturbance. The temperature of the heated foam is determined to be T = 16.8 ± 1.1 eV by analyzing the high-resolution spectra obtained with a flat-field grating spectrometer. The electron density of the heated foam is about N e = 4.0 ± 0.3 × 10 20 cm − 3 under the reasonable assumption of constant mass density.

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.

An analytical ramp compression model for condensed matter, which can provide explicit solutions for isentropic compression flow fields, is reported. A ramp compression experiment can be easily designed according to the capability of the loading source using this model. Specifically, important parameters, such as the maximum isentropic region width, material properties, profile of the pressure pulse, and the pressure pulse duration can be reasonably allocated or chosen. To demonstrate and study this model, laser-direct-driven ramp compression experiments and code simulation are performed successively, and the factors influencing the accuracy of the model are studied. The application and simulation show that this model can be used as guidance in the design of a ramp compression experiment. However, it is verified that further optimization work is required for a precise experimental design.

A proper x-ray source is crucial to extended x-ray absorption fine structure (EXAFS) measurement as parameter diagnosis for compressed materials on large laser facilities. In this article, modification of the CH capsule as an x-ray source has been done through simulations and experiments for the SGIII prototype laser facility. On the one hand, simulation results show that the radiation intensity of the CH capsule increases largely while wall thickness decreases. On the other hand, chlorine atoms whose atomic number is higher than that of carbon were brought into the capsule by doping on the inner side wall to enhance x-ray radiation intensity. CH capsules were designed, and experiments were carried out on the SGIII prototype laser facility. The x-ray source spectrum, size, radiation intensity, radiation pulse, and Ti K-edge EXAFS spectrum under ambient conditions were compared and discussed. Experimental results show that, with the doping of chlorine atoms and decreasing the wall thickness from 9 µm to 6 µm, the x-ray radiation intensity increases by about 63.5 times, energy efficiency is improved a lot, and other properties are also improved. The chlorine atom doped CH capsule with 6 µm wall thickness is proved to be the best x-ray source in the experiments in this article. Its size is 57 ± 0.5 µm, pulse width is 240 ps, and radiation intensity is about 9.1 times the undoped one with the same wall thickness. The methods can be extended to other laser facilities for the EXAFS measurement of other materials.

An analytical isentropic compression model for condensed matter is reported, which can provide explicit solutions for isentropic compression fields. To demonstrate this model, a laser-direct-driven ramp compression experiment is performed using an 8-ns, 740-J temporally shaped laser, achieving a peak pressure of 425 GPa in solid aluminum, which value exceeds all previous experimental results. The primary application suggests that this model can function as an important prototype for ramp compression experiments, and the temporally shaped laser direct-driven ramp compression technique can form a practical method to achieve isentropic compression.

How to control the photonic spin Hall effect (PSHE) at will is a very interesting and significant task. In this letter, we propose an electrically driven method for modulating the spin-dependent splitting in the PSHE. When the light transmits through a liquid crystal variable retarder, the spin-dependent spatial and angular shifts can be periodically manipulated with an applied electric field. The weak measurement technique is introduced to experimentally observe the spatial and angular displacements by choosing different postselection states. These findings may have potential applications in spin-based nanophotonic devices.

Laser drive ramp compression is an important method to achieve an extremely high-pressure but relatively low-temperature material state. In this study, we found VISAR streaks disappearing under high pressure. To solve this problem, the mechanism of probe-laser absorption in laser drive ramp compression experiments has been studied, and X-ray preheat is found to be the main factor in this mechanism. Subsequently, target configuration optimization and code simulation were performed based on previous experiments, and laser drive ramp compression experiments were performed on the SHENGGUANG prototype facility. In the experiments, the probe-laser reflectivity was above 90% at 450 GPa, which is much higher than those in previous experiments, demonstrating that the X-ray preheat was shielded well with the optimized target configuration.

Laser pulse shape design is a key work in the design of indirect-laser-driven experiments, especially for long pulse laser driven quasi-isentropic compression experiments. A method for designing such a laser pulse shape is given here. What’s more, application experiments were performed, and the results of a typical shot are presented. At last of this article, the details of the application of the method are discussed, such as the equation parameter choice, radiation ablation pressure expression, and approximations in the method. The application shows that the method can provide reliable descriptions of the energy distribution in a hohlraum target; thus, it can be used in the design of long-pulse laser driven quasi-isentropic compression experiments and even other indirect-laser-driven experiments.

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.

The characteristics of Delano diagram are especially helpful in instrumental systems type with considerably separated components. For high power excimer laser system, especially for image relay scheme, the Delano diagram method is highly advantageous for the system’s thin lens layout design. A primitive experimental image relay and it’s combination optical layout is investigated in our high power XeCl laser system, with intensity smoothed spatial incoherent source. Instead of the uniform intensity distribution on the target as expected, it is obvious shows in the final image on the target that a gauss like intensity profile and a large amount of astigmatism results. There are two possible reasons: the first one is that not keeping proper relay of pupil plane (or Fourier plane) in the final stage, simply care the collimated beam of virtual object in the final focusing stage. With the help of Delano diagram, it’s clearly shown in the diagram that the Fourier plane and the image plane come very close, indicates that a complete image relay of the object plane and Fourier plane is needed. The second reason is due to the off-axis setup in the large aperture main amplifier, which introduce significant astigmatism aberrations in the final optical path. This question can be solved using proper tilt and de-center of reflective mirror pair setup, and two possible such combination pairs are proposed.

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 10 3 and 10 4 order of magnitude, the laser pulse signal contrast ratio was promoted to 10 5 and 10 6 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 short pulse XeCl laser system is being developed for plasma physics and material science study. Partial spatial incoherence seed with short pulse is amplified by MOPA chain including three discharge pumped amplifiers and two electron beam pumped amplifiers for one beam. Final laser output of 5~10J in energy with pulse width of around 10ns has been achieved, which lays a good foundation for full scale construction.

Based on the given parabolic gas-liquid interfaces, a two-dimensional fluid flow in superhydrophobic microchannels is numerically simulated with the steady volume of fluid model in the laminar regime. The influence of several crucial parameters on drag reduction effect is discussed. The results indicate that the superhydrophobic microchannel containing rectangular cavities displays significant drag reduction effect. With increasing inlet velocity, the pressure drop reduction decreases slightly. Augments in the pressure drop reduction tend to be large with the increase of the cavity fraction or the decrease of the channel height. The results also reveal that the variation of the normalized slip length with the cavity fraction tends to be more dramatic when the channel height is smaller. As the parabolic height of the gas-liquid interface is enlarged, both the pressure drop reduction and the normalized slip length decrease linearly, while fRe increases linearly. The impact of the cavity depth on the normalized slip length, fRe, and the pressure drop reduction is minimal supposing the depth of the cavity is greater than 40% of its width. The drag reduction effect corresponding to the dovetail cavity model is the best, and the consequence of the rectangular, trapezoidal, and triangular cavity models sequentially worsens.

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.

Laser-direct-driven ramp compression experiments were performed on long temporally shaped laser pulses based on an analytical isentropic compression model. Upper pressure limits, the ablation pressure scaling law, and stress-density curves were studied. The validity of the analytical model used, the ablation pressure scaling law, and the phenomena of missing line-imaging velocity interferometer (VISAR) fringes in the experimental results are discussed.

A characteristic method has been developed using a Murnaghan-form isentropic equation and characteristics, which has been verified by example uses. General information of two ramp compression experiments was calculated, which matched experimental ones well except for some tiny distinctions. Finally, the factors influencing the precision of this model were discussed and other practical applications were presented.