We report 2-Hz operation of a single-pass 109-nm laser with a small-signal gain of exp 33 and a saturated output energy of 1 ,J. The laser is based on an oblique-incidence, laser-produced-plasma pumping geometry and requires only 500 mJ of 1064-nm energy in a O.5-nsec pump pulse. We use the laser to produce a two-slit interference pattern and demonstrate a focusable intensity of greater than 10 9 W/cm 2 .
We report the use of a photoionization electron source to pump a 116-nm laser in the Werner band (C l n u -• X 's/) of molecular hydrogen. The laser is pumped by free electrons which are created by photoionizing molecular hydrogen with soft x rays from a traveling-wave laser plasma. We show that even though the free electrons have an average temperature of -10 eV, the lasing hydrogen molecules retain an ambient temperature of -0.01 eV. This allows an extrapolated small-signal gain of exp(43), with a 1064-nm pumping energy of 580 mJ in 200 psec. PACS numbers: 52.50.Jm, 34.50.Gb, 42.55.Em We describe the use of a traveling-wave photoionization electron source 1 (PES) to pump a 116-nm laser in the Werner band of H2. The PES is constructed by using a grazing-incidence, traveling-wave laser plasma 2 to make soft x rays which in turn photoionize ambient hydrogen molecules (Fig. 1). The electrons have an average energy which corresponds to the difference in energy of the pumping x rays and the ionization potential of H2, and at sufficient pumping intensity may have a density which corresponds to a discharge current in excess of MA/cm 2 . The rise time of the electron density is equal to that of the x-ray source, and may be picoseconds or shorter in duration, making PES an ideal source for pumping short-wavelength lasers. 3 In this Letter we quantitatively demonstrate the advantages of PES over conventional electron pumping sources by generating saturated laser emission at 116 nm in the Werner band of H 2 . We emphasize a special feature of this type of excitation, which is its ability to produce hot electrons while at the same time retaining an ambient (lasing medium) temperature which is comparatively cold. This is confirmed by measurements of the 116-nm gain as a function of the ambient H2 temperature. In this work the free electrons have an average temperature of 10 eV while the lasing hydrogen molecules retain an ambient temperature of -0.01 eV. This allows very high gain at modest pumping energy; here we obtain an extrapolated small-signal gain of exp(43), with a 1064-nm pumping energy of 580 mJ in a pulse width of 200 psec.Before proceeding we note that previous short-wavelength lasers have operated in the focus of the incident laser and under conditions where the exciting electrons and target ions are relatively thermalized. 4 H2 lasers have been constructed by using a Blumlein discharge (Waynant) 5 and by using a field-emission diode (Hodgson and Dreyfus). 6 In this work we obtain a gain coefficient which is over an order of magnitude larger than that previously obtained, demonstrating quantitatively one of the advantages of PES over conventional electron pumping sources. Using a simple model for the PES excitation mechanism we will verify that in the present experiment the H2 laser is pumped by electrons and is not directly photopumped. We will then proceed to describe the experimental setup and results. The calculation of the gain for the 116-nm laser pumped by a PES proceeds as follows:The 580-mJ, 200-psec...
We have demonstrated the use of a low energy prepulse to enhance the soft-x-ray emission of laser produced plasmas in a parameter range which has been used to pump photoionization lasers. We present data on conversion efficiency and output pulse duration as a function of input intensity, pulselength, and prepulse conditions. Our goal in these studies is to allow the design of more efficient short-wavelength photoionization lasers, and to achieve high repetition rate operation of these lasers in the near future.
The recently reported saturation1 of the 109-nm Auger laser in xenon III2 utilized a newly developed, oblique incidence, traveling-wave laser-produced plasma geometry. This geometry allows excitation of a variable gain length while maintaining constant pump laser intensity on target and soft x-ray conversion efficiency. Distribution of the soft x-ray pump flux over an increased length is desirable in photoionization-pumped lasers because of the pump flux, density, and gain limitations imposed by the free electrons created in the pumping process. The assumption that the gain will be highest at some optimum pump flux leads to simple scaling laws for the total small signal gain and transverse dimensions of the laser as its length is changed. The gain per unit pump energy, the brightness of the output beam, and the Fresnel number of the laser should all improve with increased length. We discuss experiments to verify these scaling laws, where we increase the length of the laser simply by increasing the angle of incidence of the pump beam. In addition, we expect to discuss the effects of varying intensity, wave-length, pulse length, and a prepulse on soft x-ray conversion efficiency and laser operation. These studies lead to a better understanding of the factors important in the design of useful photoionization lasers.
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