Saturated high-repetition-rate 189-nm tabletop laser in nickellike molybdenum

Abstract

We report saturated operation of an 18.9-nm laser at 5-Hz repetition rate. An amplification with a gain -length product GL of 15.5 is obtained in the 4d 1 S 0 4p 1 P 1 laser line of Ni-like Mo in plasmas heated at grazing incidence with ϳ1-J pulses of 8.1-ps duration from a tabletop laser system. Lasing is obtained over a broad range of time delays and pumping conditions. We also measure a GL of 13.5 in the 22.6-nm transition of the same ion. The results are of interest for numerous applications requiring high-repetition-rate lasers at wavelengths below 20 nm. There is great interest in the development of compact saturated high-repetition-rate lasers capable of producing significant average output powers at soft-x-ray wavelengths for applications. Ne-like Ar capillary-discharge-pumped lasers operating at repetition rates of up to 10 Hz have been demonstrated to produce milliwatt average powers at 46.9 nm. 1,2More recently, saturated optical f ield ionization lasers operating in Pd-like Xe at 41.8 nm and in Ni-like Kr at 32.8 nm were obtained by use of 0.33-and 0.76-J pulses, respectively, from a femtosecond 10-Hz pump laser. 3,4 Longitudinal pumping of Mo plasma with short pulses from 10-Hz lasers produced nonsaturated amplification at 18.9 nm in Ni-like Mo, 5,6 a laser line first observed in a small-scale pump system using 80-ps pump pulses. 7Transient collisional electron excitation of targets at normal incidence with 3-10 J of pump energy has produced several saturated lasers in the 12-33-nm range at repetition rates of one shot every several minutes. 8,9 Excitation of a Mo target with 150-fs, 300-mJ pulses impinging at 60 ± from normal incidence resulted in the appearance of the 18.9-and 22.6-nm laser lines of Ni-like Mo. 10 Recently, it was shown that the pumping energy necessary for lasing could be significantly reduced by directing the short pulse onto the target at grazing incidence. 11,12This inherently traveling-wave pumping geometry takes advantage of the refraction of the pump beam to increase the path length of the rays in the gain region of the plasma, thereby increasing the fraction of the pump energy absorbed in that region. A gain -length product of ϳ15 was reported in the 18.9-nm line of Ni-like Mo with 150 mJ of total pumping energy from a 10-Hz laser. 13A normal-incidence 200-ps prepulse was focused into a 15-mm-wide line focus and followed by a 1.5-ps short pulse impinging at a grazing-incidence angle of 14 ± . Lasing was observed to occur over only an extremely narrow ϳ50-ps range of prepulse-to-short-pulse time delays.Herein, we report saturated laser operation in the 18.9-nm line of Ni-like Mo and strong amplif ication at 22.6 nm by use of a 5 -10-Hz tabletop pump laser.Lasing was obtained over a very broad range of time delays. The gain medium was created by the combination of laser pulses generated by an 800-nm tabletop Ti:sapphire laser system with three stages of amplification. A beam splitter directed 20% of the third-stage output to the prepulse arm (120 ps FWHM, 350 mJ), and the re...

High-Brightness Injection-Seeded Soft-X-Ray-Laser Amplifier Using a Solid Target

“…The plasma is formed by a 0.3 J prepulse, which arrives 5 ns after a 10 mJ pulse. The plasma is allowed to expand to reduce the density gradient and is subsequently rapidly heated by a 800 mJ, 6.7 ps duration pulse impinging at a grazing incidence angle of 23 onto the target for efficient plasma heating [13][14][15][16]. The prepulse beam is focused into a 30 m wide, 4.1 mm FWHM line focus.…”

Optimization toward a high-average-brightness soft-x-ray laser pumped at grazing incidence

“…This focusing configuration induced an intrinsic traveling wave with a velocity close to the speed of light (within less than 5% deviation). The superposition of the LP and SP at the target plane was controlled with an imaging microscope device, with a resolution of about 3 m. In contrast with previous work, 2 we vary the GRIP angle ⌽ by tilting and translating the SP beam mirrors, instead of the target. This condition was found to be important to get a constant line focus quality and to allow the implementation of highspatial-resolution diagnostics of the SXRL plasma.…”

Grazing incidence pumping for high efficiency x-ray lasers

“…For example, in our first experimental investigation on the 18.9 nm Ni-like Mo laser using the 10 Hz LLNL Callisto Ti:Sapphire laser a maximum density of ne0 = 1 × 10 20 cm -3 for the gain region and the critical density for the 800 nm optical pump of nec =1.74 × 10 21 cm -3 dictated the GRIP angle of incidence φr= 13.7 o [9,15]. Strong lasing has been observed by the Colorado State University group on Ni-like Mo with this grazing angle [16]. The turning point limits the direct heating of the plasma to densities well below the critical density.…”