Cheng Yuan-Li

Laser output and multiple pinches of plasma in capillary discharge

The pinch process of plasma columns generated by capillary discharge is studied theoretically with a snow-plow model. The multiple pinch evolution of plasma is obtained from the theoretical results. The effects of pressure and current amplitude on multiple pinches are calculated, and the results show that the pinch time decreases nonlinearly with decreasing pressure or increasing current. In the experiment, the laser spike of Ne-like Ar at 46.9 nm is obtained with an X-ray diode (XRD). The pressure filling in the capillary is changed to observe the variation of lasing onset time. According to real current waveforms, the pinch process is simulated. The results show that the laser spike occurs around the third pinching time. In addition, the experimental results indicate that there is an optimum pressure for the laser output.

X-Ray and Extreme Ultraviolet Emission from Small-Sized Kr Clusters Irradiated by 150-fs Laser Pulses

x-ray and extreme ultraviolet (EUV) emission from Kr clusters irradiated by 150-fs laser pulses at the peak laser intensity of 5?1015W/cm2 was experimentally investigated. Strong transitions (10?nm-13?nm) from Kr X and Kr IX were observed and some spectral lines from Kr XIII and Kr XIV, which have been predicted to be not produced by optical-field-ionization at the laser intensity used, also appeared. The laser energy absorption and the intensity of x-ray emission started to grow remarkably above the backing pressure of 0.5?MPa and to decrease at the backing pressure of 3?MPa. It is suggested that an optimum backing pressure may exist for Kr clusters heated by 150?fs laser pulses at a certain laser intensity to produce x-ray emission.

A New Discharge Scheme of a Prepulse Plus Two Main Pulses for Capillary-Discharge Soft-X-Ray Laser

Reducing the capillary-discharge current is one way of possibly decreasing the pumping power requirement. We examine the influence of various discharge currents on laser intensity and determine the suitable pre-discharge condition for a 46.9-nm discharge-pumped Ne-like Ar soft-x-ray amplifier. The experimental results show that a high additional pre-pulse current at amplitude of several kA and with a very short duration of several tens of nanosecond can effectively decrease the amplitude of the main discharge current at the lasing time. We propose a new discharge scheme of a pre-pulse plus two main pulses which appears to significantly decrease the requirement for discharge current. This in turn may decrease the pumping power requirement for the capillary discharge laser and can greatly increase laser efficiency.