Using a plane–plane resonator composed of silicon carbide mirrors, we achieve for the first time multi-pass amplification of a 46.9 nm laser pumped by capillary discharge. In terms of the temporal characteristics, for an initial argon pressure of 17 Pa, triple-pass amplification of the laser is obtained at a delay time between the pre-pulse and the main pulse currents of 40 µs, and quadruple-pass amplification is obtained at a delay time of 50 µs. The experimental results show that the gain duration of the plasma column is more than 6 ns. In terms of spatial characteristics, the spot of the output laser has a reduced full width at half maximum divergence compared with that from a laser without a resonator.

In this paper, the influence of the delay time between the pre-pulse and the main pulse on the double-pass amplified 46.9 nm laser was studied for the first time, to the best of our knowledge, by using a high-precision polished SiC slice as a rear mirror. The temporal and spatial characteristics of the output laser were measured separately to investigate the effect of the delay time on the laser characteristics. The energy of the double-pass amplified laser was between 510 µJ and 890 µJ. In addition, a theoretical model of double-pass amplification was established to analyze the effect of the delay time on the double-pass amplified 46.9 nm laser.

In this Letter, we firstly, to the best of our knowledge, demonstrated the influence of pre-pulse current and delay time on the intensity of a discharge pumped Ne-like Ar soft X-ray laser operating at 46.9 nm by employing an alumina capillary having an inner diameter of 4.8 mm. Specifically, the delay time was changed from 8 to 520 μs in small intervals. The pre-discharge current was increased from 25 A to 250 A through small steps, while keeping the main discharge current constant. Usually, a small pre-discharge current is applied to an Ar-filled capillary to attain a plasma column having sufficient pre-ionization before the injection of the main current. The pre-discharge current of 140 A was declared the best current to obtain lasing with a 4.8 mm diameter capillary. The laser spots were captured at best time delays for the pre-discharge currents of 25, 45, 80, 140, and 250 A, which support the experimental results. We observed that by applying the pre-discharge current of 140 A, the laser spot exhibits small divergence, higher symmetry, and uniformity, which is clear evidence of strong amplification. The laser spot obtained at 140 A is cylindrically symmetric and has a better structure than those reported by all other groups in the literature. Hence, the laser spot indicates that the laser beam is highly focusable and beneficial for the applications of the 46.9 nm laser. Results of this Letter might open a new way to enhance applications of a 46.9 nm capillary discharge soft X-ray laser.