Advanced concepts of electron beam pumped excimer lasers F. K. Tittel, P. Canarelli, C. B. Dane, Th. Hofmann, R. Sauerbrey, T. E. Sharp, G. SzabO, W. L. Wilson, P. J. Wisoff, and S. Yamaguchi Department of Electrical and Computer Engineering, Rice University, Houston, TX 77251-1892 ABSTRACT The development of scalable high power lasers in the UV-visible range and ultrashort high brightness laser sources will have significant impact in a number of key technologies. Experiments of scaling the e-beam pumped XeF(C—,A) laser system to the 1 Joule/pulse output level at a 1 Hz repetition rate are described. Recent progress in the amplification of tunable ultrashort laser pulses in the visible spectrum, utilizing the broadband XeF(C—A) excimer transition, is also reported. 1. SCALING CHARACTERISTICS OF THE XeF(C—A) EXCIMER LASER Excimer lasers play an important role in many specific applications that utilize their unique characteristics such as high average power for material processing, and high spectral purity and broad band tunability for remote sensing, optical communication and basic physics research. There is considerable interest in the XeF(C—A) excimer laser as an efficient, tunable source of radiation in the blue-green region of the spectrum. Using an electron beam as an excitation source and a kinetically tailored five component gas mixture , 1 efficient operation of this laser system has been demonstrated for short pulse 10 ns (10 MW/cm3),2 intermediate pulse 250 ns ('-4 MW/cm3), and long pulse 700 ns (--250 kW/cm3)4 electron beam pumping durations. When the short pulse, high current density electron beam excitation technique is employed, peak values of small signal gain exceed 3% cm1, permitting efficient injection controlled operation. This results in a very effective method for wavelength tuning. Continuous tuning between 450 and 530 nm with a linewidth as narrow as 0.001 nm and good spatial beam quality (3 x diffraction limit) have been demonstrated. An output energy density of -l.7 JM with an intrinsic efficiency of 1.3% has been achieved for wavelengths between 470 and 510 nm. With its gaseous active medium, the XeF(C—A) excimer laser is readily scalable to the high energy and power required for numerous potential applications. Experiments are described here that characterize the successful scaling of an electron beam pumped XeF(C—A) laser from an active laser volume of '—0.02 6 to one of '—0.5 with a pumped length of 50 cm. An improved output energy of 1 .2 J/pulse in repetitive operation of up to 1 Hz, was achieved with a large aperture square unstable resonator geometry, using a compact, halogen compatible, closed flow loop incorporating a transverse in-line fan for gas circulation. The electron beam generator, described in detail elsewhere,2' 8 produces a 650 keV, 90 kA pulse in 10 ns (FWHM) with a current density of 250 A/cm2 The generator was specifically designed for this application and is capable of repetitive operation at up to 1 Hz. The electron beam enters the laser chamber transversely through a 25 tm titanium foil anode coated with a 5 pin layer of ion vapor deposited aluminum to prevent its interaction with the reactive fluorine in the laser gas mixtures. A 0.2 Tesla magnetic guide field provides a three-fold increase in the electron beam current density that is delivered at the optical axis of the laser chamber. A cross-sectional schematic of the flow system is depicted in Fig. 1 . The cross-sectional inner dimensions of the laser cell were 5 cm in width and 6.5 cm in height. The gas was circulated by a transverse flow fan magnetically coupled to an external induction motor. The dimensions of the flow ioop design were, to a large SPIE Vol. 1397 Eighth International Symposium on Gas F/ow and Chemical Lasers (1990) / 21 Downloaded From: http://reviews.spiedigitallibrary.org/pdfaccess.ashx?url=/data/conferences/spiep/45241/ on 07/10/2017 Terms of Use: http://spiedigitallibrary.org/ss/termsofuse.asp