Tunable Short-Wavelength Laser Sources

Abstract

The availability of tunable laser radiation in the visible and infrared wavelength regions has made possible many important advances in physics, chemistry, and biology. At the present time, the ultraviolet (UV) region of the spectrum, and in particular the vacuum ultraviolet (VUV, from 200 to 100 nm) and extreme ultraviolet (XUV, from 100 to ~20 nm) regions lack tunable lasers. In fact, only a few lasers have been made to operate at these short wavelengths, in spite of considerable efforts being made in the past decade. The excimer lasers ArF (193 nm), Xe₂ (~170 nm), and Ar₂ (~120 nm), and the H₂ laser (~110 nm) have been available for some time now, but these emit at discrete wavelengths or are tunable only over their relatively narrow bandwidths. More recent efforts have resulted in stimulated VUV emission by the anti-Stokes Raman process in I and Brl and by 2-photon excitation of H ²₂ , and in the XUV region by 4-photon excitation in Kr (~93 nm)³. Other techniques being explored inclLde recombination processes⁴ and excitation of ions⁵ such as Li⁺; and as we have learned at this school, in principle, the free-electron laser could operate at these short wavelengths.