No 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...

We demonstrate the generation of an intense soft-x-ray-laser beam by saturated amplification of high harmonic seed pulses in a dense transient collisional soft-x-ray-laser plasma amplifier created by heating a titanium target. Amplification in the 32.6 nm line of Ne-like Ti generates laser pulses of subpicosecond duration that are measured to approach full spatial coherence. The peak spectral brightness is estimated to be 2 10 26 photons= s mm 2 mrad 2 0:01% bandwidth . The scheme is scalable to produce extremely bright lasers at very short wavelengths with full temporal and spatial coherence.