Gain-saturated 69.8 nm neon-like argon laser pumped by capillary discharge at a high main-pulse current of 19 kA

Abstract

Extreme ultraviolet (EUV) lasers based on capillary discharge offer a compact and efficient short-wavelength source; yet, compared with the 46.9 nm laser well-established in practical applications, achieving high gain at 69.8 nm in neon-like argon ions (Ar8+) remains challenging. Instead of relying on capillary length extension, saturation was achieved by optimizing plasma conditions through enhanced energy injection in a 35 cm capillary. Increasing the discharge current to 19 kA yielded a record gain coefficient of 0.47 cm−1, the highest value reported to date for a 69.8 nm laser. This enabled saturation at an active length of 32 cm with a gain-length product of 15, reaching a maximum of 16.5 at 35 cm. Further increasing the current to 24 kA causes the laser intensity and gain to decrease markedly, with the gain coefficient reduced to 0.25 cm−1 and no saturation observed. In addition, by spectrally isolating the 69.8 nm laser with a self-made monochromator, this work achieves the measurement of the 69.8 nm laser pulse width under high main current. One-dimensional magnetohydrodynamic (MHD) simulations show that the higher main-pulse current produces intensified Joule heating and a faster pinch, leading to excessive electron density and overionization near the implosion point. This suppresses the Ar8+ density required for population inversion and limits the achievable gain. These combined experimental and computational results clarify the role of main-pulse current in affecting plasma state for 69.8 nm lasing and guide for optimizing discharge-waveform parameters in capillary-based EUV laser sources.