We have reported the first observation of large soft-x-ray amplification in a discharge-created plasma. A gain coefficient of 0.6 cm " at 46.9 nrn was measured in a Ar-H 2 mixture, while higher laser intensities were reported in pure argon. It was later realized that the fraction of H 2 in the gas mixture experiments was, due to incomplete mixing of the gases, smaller than the 1:2 ratio reported, and amounted to less than 10%. Subsequent experiments have confirmed that larger amplification occurs in pure argon discharges, resulting in gain coefficients of up to 1.1 em -1.

We report the generation of laser pulse energies up to 30 mJ at 46.9 nm in the plasma column of a fast compressional capillary discharge. Double pass experiments using an iridium mirror achieved a gain-length product greater than 25. The results provide the first clear evidence of saturated operation of a table-top soft x-ray amplifier. [S0031-9007(96) PACS numbers: 42.55. Vc, 52.55.Ez, 52.75.Va A major goal in ultrashort wavelength laser research is the development of practical laser sources that can impact applications. Of particular interest is the demonstration of compact "table-top" amplifiers capable of generating soft x-ray pulses of substantial energy. Such development motivates the demonstration of gain media generated by compact devices that can be successfully scaled in length to reach gain saturation. At this condition, which occurs when the laser intensity reaches the saturation intensity, a large fraction of the energy stored in the laser upper level can be extracted. To date, gain saturation had only been achieved in a few soft x-ray laser transitions in plasmas generated by some of the world's largest laser facilities [1][2][3][4].While gain in soft x-ray lines has been reported in several compact systems [5][6][7][8][9][10][11][12][13] only in three cases the gain-length product was measured to be greater than 5 [5][6][7]. These include the observation of amplification at 46.9 nm in Ne-like Ar by our group in a plasma column generated by a fast capillary discharge [5,14], and the demonstration of gain at 41.8 nm in Pd-like Xe and at 32.6 nm in Ne-like Ti in plasmas generated by relatively compact terawatt class femtosecond and picosecond laser facilities, respectively [6,7]. In all cases, however, the laser energy extraction from table-top amplifiers has been small and detection of the laser lines was performed with high sensitivity detectors such as microchannel plate (MCP) intensifiers.A next major step in the development of compact ultrashort wavelength lasers consists in advancing from gain observations to the demonstration of substantial laser output energies. Depending on the specific amplifier characteristics, this amounts to overcoming barriers that are imposed by small gain volumes and short plasma lengths, by short duration of the gain, or by axial plasma inhomogeneities and limiting refraction effects.Recent optimization of the capillary discharge scheme, which has the advantages of a relatively large gain volume and long gain duration, allowed amplification at 46.9 nm to reach 14 gain-length products [15], but no demonstration of substantial laser energy extraction was realized. In this Letter we report the generation of laser pulse energies up to 30 mJ at 46.9 nm in the plasma column of a fast compressional capillary discharge and the first clear evidence of gain saturation of a table-top soft x-ray amplifier. Single pass amplification experiments yielded laser pulse energies up to 6 mJ. Greater energies were obtained by using an iridium mirror, in the first clearly successful d...

We report the demonstration of an amplitude-division soft-x-ray interferometer that can be used to generate high-contrast interferograms at the wavelength of any of the saturated soft-x-ray lasers (5.6 -46.9 nm) that are available at present. The interferometer, which utilizes grazing-incidence diffraction gratings as beam splitters in a modif ied Mach -Zehnder conf iguration, was used in combination with a tabletop 46.9-nm laser to probe a large-scale ͑ϳ2.7-mm-long͒ laser-created plasma.

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A direct measurement of the amplitude and the phase of a femtosecond light pulse is performed for the first time to our knowledge. The measurement is made in the frequency domain, and the time dependence of the field can be easily obtained by a Fourier transform. The technique relies on a pulse synthesis scheme to unravel the frequency dependence of the phase. A mask filters the spectrum, which gives rise to a pulse with a measurable temporal profile related to the frequency dependence of the phase. In particular, with a rectangular slit the time delay of the synthesized pulse is the first derivative of the phase with respect to the frequency of the original pulse at the central frequency of the filter. The amplitude of the spectrum is obtained from the power spectrum.