Effect of counterintuitive time delays in nonlinear mixing.

The effect of varying the relative arrival time of the two laser pulses employed in doubly resonant four-wave sum mixing, enhanced by induced transparency, is studied with the aim of optimizing the efficiency of vacuum-ultraviolet generation. With atomic hydrogen as the nonlinear medium, pulsed radiation with wavelengths of 243 and 656 nm and durations of 8 and 14 ns, respectively, is mixed to generate 103-nm coherent radiation. It is shown that by delaying the arrival time of the ground-state pump beam (243 nm) by 2.

Supersonic cooling of rare-gas excimers excited in dc discharges.

Emission spectra of the homonuclear rare-gas excimers have been investigated in the wavelength region of 50 to 200 nm by using continuous discharges with supersonic jet expansion. The well-known dimer bands were readily observed in the emission spectra of He, Ar, Kr, and Xe along with an extremely weak band of Ne. A detailed examination of the Ar(2) band at 128 nm was carried out, and its envelope and bandwidth (8.

Second-harmonic generation at Lyman-alpha in atomic hydrogen.

Second-harmonic generation in atomic hydrogen is investigated with and without an applied electric field, by tuning laser radiation at 243.1 nm through the 2 (2)S((1/2))-1(2)S((1/2)) two-photon resonance. Even at zero applied field, secondharmonic radiation at 121.

Efficient population inversion in excimer states by supersonic expansion of discharge plasmas.

Laser emission at 126 nm has been obtained from excimers of Ar(2) excited electrically in a nozzle discharge followed by supersonic expansion. The direct measurement of light amplification with a tunable VUV probe leads to a gain of >3 cm(-1). This high gain arises from efficient population inversion of low vibrational and rotational levels of the excimer state brought about by the supersonic expansion and cooling of the discharge plasma.

Endocardial photoablation by excimer laser.

A xenon-chlorine excimer laser was used to irradiate normal endocardium of fresh sheep and pig hearts as well as unfixed human endocardial scar. Forty pulses of 370 J and 35 ns each resulted in penetration of up to 12 mm in normal tissue and only 3.5 mm in scarred endocardium.

Tunable extreme-ultraviolet radiation from 105 to 87.5 nm using Hg vapor.

Tunable, coherent radiation has been generated in the region 105 to 87.5 nm by resonant four-wave frequency mixing in Hg vapor. A glass capillary array forms an efficient XUV window with 50% transmission.

Vacuum-ultraviolet laser-excited spectra of Xe(2).

Fluorescence excitation of Xe(2) at 149.0 nm has been observed using a pulsed supersonic jet for dimer formation and cooling and using tunable coherent VUV radiation from four-wave mixing in Mg vapor for excitation. The resolved vibronic structure resulting from isotopic Xe(2) molecules has yielded unambiguous vibrational numbering (upsilon'=37-46), giving the following constants for the first O(+)(u) excited state of Xe(2): T(e) = 63 796(6) cm (-1), omega'(e) = 124.

Intensity ratios of (2)D(5/2,3/2)?(2)S doublets in the two-photon absorption spectrum of Rb and Cs.

Absorption ratios of doublets arising from n(2)D(5/2,3/2)? n'(2)S transitions in Rb (n = 5-9, n' = 5) and Cs (n = 7-13, n' = 6) were measured by Doppler-free two-photon spectroscopy using a thermionic ion detector. The observed ratios agree with calculated values for transitions to the higher levels but differ significantly for levels n = 5 in Rb and n =7, 8 in Cs. These experiments also provide new lower bounds for the ionization potentials of Rb(2) (3.

Generation of continuously tunable coherent vacuum-ultraviolet radiation (140 to 106 nm) in zinc vapor.

It is shown that resonantly enhanced, four-wave frequency mixing in Zn vapor provides coherent vacuum-ultraviolet radiation that is continuously tunable over the range 140.4 to 106.3 nm (or ~23000 cm(-1)).

Resonantly enhanced second-harmonic generation in zinc vapor.

Coherent second-harmonic radiation has been generated in atomic zinc vapor at 1792.5 and 1601 A from the 5(1)S(0)and 4(1)D(2) states, respectively, by two-photon resonance enhancement. Measurements of the ratio of second-to third-harmonic generation suggest the occurrence of static electric fields of ~5 kV/cm.

Radiative lifetimes of the B' (2)Delta state (v' = 0, . . . ,8) of NO obtained by vacuum-ultraviolet laser excitation.

Radiative lifetimes of rovibronic levels of the B', (2)Delta state of NO (from u' = 0,. . .

Tunable, coherent radiation in the Lyman-alpha region (1210-1290 A) using magnesium vapor.

Tunable, coherent vacuum-ultraviolet (VUV) radiation has been produced in the 1210-1290-A region by four-wave sum mixing in magnesium vapor. This important extension of the wavelength range of tunable radiation was achieved using KrF-laser-pumped uv dye lasers, whose sum frequency then directly overlapped the first odd-parity autoionizing state in magnesium. With powers of 10 kW in the fundamental dye-laser beams, a flux >/=10(8) photons per pulse was produced at Lyman-alpha, with higher intensities at the longer wavelengths.