Conversion efficiency of multi-keV L-shell-band X-ray emission

This study explored the influence of foil thickness, laser pulse width, and laser intensity to optimize the multi-keV X-ray conversion efficiency of a sandwiched (CH/Sn/CH) planar target under laser irradiation at the Shenguang II laser facility. The X-ray photon field values were measured using a set of elliptically bent crystal spectrometers and the conversion efficiencies (ξ_x) of photon energies were in the range of 3.7-4.3 keV. The experimental results indicate that the X-ray yields of 3.7 to 4.3 keV radiation strongly depend on the laser pulse width, target thickness, and laser intensity. The results also demonstrate that three-layer thin foils can provide an efficient multi-keV X-ray source because they can change the distribution of emitted multi-keV X-rays and target dynamics versus nanosecond laser pulses to produce large, hot, and underdense plasma. However, the underdense plasma produced as a rarefaction wave causes the overdense plasma generated by the laser pulse to expand. Therefore, the laser parameters and foil thickness must be carefully optimized to produce an efficient 3.7 to 4.3 keV X-ray source. Otherwise, the rarefaction waves from both sides of the thin foil may suppress multi-keV X-ray emission. This study represents an important advancement in the development of an efficient multi-keV L-shell-band X-ray source.

Elliptically bent crystal x-ray spectrometer for time-resolved laser plasma experiments

Measuring time-resolved spectra is crucial in inertial confinement fusion and radiation source development experiments. An elliptically bent crystal spectrometer is designed to measure X-rays in the range of 2.5-11.0 keV, which was achieved using four different lattice spacings of 0.8512, 0.6687, 0.4246, and 0.2749 nm with spectral resolution E/δE of ∼500. The X-rays emitted from a source at one focus of the ellipse undergo Bragg reflection off a crystal and pass through the second focus of the ellipse to a streak camera slit with 18-mm length and 80-μm width to generate a time-resolved spectrum. An alignment method for the time-resolved spectrometer was developed with the straight line connecting the centers of the two small holes on the fabricated substrate being the axis of the ellipse, thus allowing the spacing between the source and the elliptical crystal to be tuned to couple with the streak camera. The time-resolved spectrometer's performance was experimentally tested at the Shenguang II laser facility. The results indicate that its performance is close to that predicted theoretically.

A pinhole camera for ultrahigh-intensity laser plasma experiments

A pinhole camera is an important instrument for the detection of radiation in laser plasmas. It can monitor the laser focus directly and assist in the analysis of the experimental data. However, conventional pinhole cameras are difficult to use when the target is irradiated by an ultrahigh-power laser because of the high background of hard X-ray emission generated in the laser/target region. Therefore, an improved pinhole camera has been developed that uses a grazing-incidence mirror that enables soft X-ray imaging while avoiding the effect of hard X-ray from hot dense plasmas.

The growth mechanism for silicon oxide nanowires synthesized from an Au nanoparticle/polyimide/Si thin film stack

During pyrolysis of polyimide (PI) thin film, amorphous silicon oxide nanowires (SiO(x)NWs) were produced on a large scale through heat treatment of an Au nanoparticle/PI/Si thin film stack at 1000 °C. It was shown that carbonization of the PI film preceded the nucleation of the SiO(x)NWs. The formation of the SiO(x)NWs was sustained by the oxygen derived from carbonization of the polyimide thin film while Si was provided from the substrate. Au nanoparticles promoted the SiO(x)NW growth by inducing localized melting of the Si substrate and by catalyzing the nanowire growth.