Measurement of gain-length product and output energy in a capillary discharge soft X-ray laser

Abstract

Summary form only given, as follows. In 1994, J.J. Rocca et al. reported that a capillary discharge could produce a laser amplification at 3p-3s level of Ne-like Ar line (J = 0-1, /spl lambda/ = 46.9 nm). This has led to a successful construction of a tabletop soft X-ray laser, which is capable to generate saturated laser energy of 1 mJ at 4 Hz, with a discharge current of 26 kA. In our laboratory, research has also been performed on capillary discharge to achieve the Ne-like Ar soft X-ray gas lasing. A ceramic capillary, which has an inner diameter of 3 mm and a length of 150 mm, has been used for soft X-ray laser amplification. Spike output signal which has a characteristics of directivity, has been observed, when operating the device with a predischarge current of 5 to 15 A, a current of 9 kA to 35 kA with a half period of 110 ns in an argon gas pressure range from 100 mTorr to 800 mTorr. Gain-length product gl = 12 (g = 0.8 cm/sup -1/) was obtained with a current amplitude of 30 kA at the optimum pressure of 400 mTorr. But, we have not yet observed the beginning of gain saturation. Compared with the result of J.J. Rocca et al., the spike output observed in our experiment is quite possibly attribute to the Ne-like Ar ion soft X-ray lasing at the same wave length of 46.9 nm. However, spectroscopic measurement is needed to be conducted to confirm this. For the current of 9 kA with optimum pressure of 150 mTorr, estimated output energy is 300 nJ. And for the current of 30 kA and the optimum pressure of 400 mTorr, the estimated output energy of laser reaches 5-6 /spl mu/J. The output energy is significantly low because the lasing in our case does not reach the saturation level. Therefore, measurement of gain-length and output energy with longer capillary is needed to reveal the saturation of soft X-ray amplification and more output energy.