Short-pulse high-intensity excimer lasers — A powerful tool for the generation of coherent VUV and XUV radiation

Abstract

Abstract. Different approaches for the generation of coherent VUV and XUV radiation with a 400 fs KrF excimer-laser system are studied. In nonlinear optical experiments it is shown that four-wave difference-frequency mixing in Xe, using a near two-photon resonance with the KrF laser radiation, is well suited for the generation of tunable VUV radiation in the range 130-200 nm. Conversion efficiencies of 2% and output energies up to 260 I.tJ have been demonstrated. Further prospects to achieve mJ energies are discussed. Using this VUV source and the KrF laser, powerful XUV radiation can be generated by different low-order frequency mixing processes. In first experiments on this subject, direct frequency tripling of the KrF laser pulse has resulted in 14 gJ XUV radiation at 83 nm.For the realization of soft-X-ray lasers, specific advantages of short-pulse KrF drivers are discussed. Novel scenarios based on a hybrid KrF/Ti: sapphire laser system and multiphoton resonant excitation are considered. PACS: 42.65.Ky; 52.40.DbThe development of practical coherent radiation sources operating at short wavelengths, in the VUV (below 200 nm), XUV (below 100 nm) and especially in the X-ray region (below 30 nm), is among the most important and long-standing problems in laser physics. For example, speculations and proposals on the possibility of X-ray lasing have begun immediately after the invention of lasers, but the first successful demonstrations of X-ray lasers (at about 20 nm) have only been reported in 1985 [1,2]. On the other hand, using methods of nonlinear optics, the generation of coherent radiation at 38 nm has already been observed in 1977, by successive frequency up-conversion of 1.06 gm Nd:YAG laser radiation in Dedicated to Prof. F. P. Sch/ifer on the occasion of his 65th birthday. nonlinear crystals and gases [3]. In these experiments ns laser pulses with energies of the order of kJ (X-ray lasers) and 30 ps, 60 mJ laser pulses (nonlinear optics) have been used.A key parameter for the efficient generation of shortwavelength coherent radiation is the laser intensity. For high-order nonlinear processes and for the creation of highly ionized non-equilibrium plasmas, very high laser intensities, above 1015 W/cm 2, are necessary. Due to the recent progress in laser technology, such and higher intensities can be easily realized with modern compact shortpulse laser systems. In these high-power laser systems, low-intensity short pulses are generated by a suitable oscillator and then amplified in one or more amplification stages. Design of the oscillator and amplifier systems depends on the laser material. Short-pulse high-power laser systems may be realized with solid and gaseous laser materials. In commercial systems, Ti:sapphire and the KrF excimer are most frequently used. Some properties of these laser materials for short-pulse high-power laser applications are summarized in Table 1.With Ti:sapphire crystals, both the generation of short pulses (typically by Kerr lens mode locking of cw argon ion-laser-pumped systems...

Control of the properties and diagnostics of a dense femtosecond plasma formed from modified targets

“…The high optical homogeneity of the amplifying gaseous medium, in combination with an offaxial amplification scheme [18^21], makes it possible to gen-erate high-contrast radiation with a divergence close to the diffraction limit. The short wavelength (248 nm for KrF and 308 nm for XeCl amplifiers, compared with 800 nm for Ti : sapphire and 1060 nm for Nd glass) means that the laser radiation can be focused down to a spot of diameter 460 nm and that an intensity of 10 19 W cm À2 can be reached when the energy per pulse is only 20 mJ [19]. In some cases an equally important feature is the higher critical density of the plasma electrons generated by UV pulses and the higher efficiency of multiphoton processes.…”

“…When a condensed target interacts with an optical photon flux of 10 16^1 0 19 photons atom À1 s À1 on the surface for an interval shorter than 100 fs, the result is a thin layer of a hot nonequilibrium plasma in which the electron temperature exceeds 100 eV and which is characterised by a high degree of ionisation of atoms and a density of the order of the density of the original target. We shall refer to this layer as a femtosecond laser plasma (FLP).…”

Solar blind chemically vapor deposited diamond detectors for vacuum ultraviolet pulsed light-source characterization

“…[1][2][3][4][5][6][7] In order to fully characterise these VUV sources, the development of solar blind, high sensitivity, and fast UV and VUV detectors is in progress. [8][9][10][11] The development of laser spectroscopy in this area is reliant upon the fabrication of VUV-specific radiation detectors.…”