G. C. Bjorklund

Conjugate wave‐front generation and image reconstruction by four‐wave mixing

Operation of a new nonlinear backward‐wave optical device which produces the conjugate of an arbitrary incident wave front is demonstrated. Good‐quality reconstructed images are obtained through a phase distorting media.

Detection of atomic hydrogen and deuterium by resonant three‐photon ionization

Resonantly enhanced three‐photon ionization spectroscopy is employed for the detection of ground‐state atomic hydrogen and deuterium. Concentrations as low as 4×109 atoms/cm3 in the presence of 1017 atoms/cm3 of buffer gas are detected with an implicit time resolution of less than 10 nsec. A useful dynamic range of at least 4×104 is demonstrated and saturation of the ionization in a 2×10−4‐cm3 focal volume is observed. The presence of H can easily be distinguished from that of D and the three‐dimensional spatial distribution of H or D can be determined.

Hydrogen plasma diagnostics by resonant multiphoton optogalvanic spectroscopy

Direct pulsed‐laser photoionization of neutral atomic hydrogen or deuterium in a discharge plasma is shown to result in large voltage changes across the electrodes. The ground‐ and excited‐state densities and the translational temperature of the H and D atoms within the plasma are probed by this technique.

Generation of cw VUV coherent radiation by four‐wave sum frequency mixing in Sr vapor

The production of cw VUV coherent radiation by four‐wave sum frequency generation in Sr vapor is reported. Significant enhancement of the nonlinearity at the output frequency is obtained upon application of large (∼50 kG) magnetic fields. Total power of 10−11 W (∼107 photons/sec) at 1700 A in a bandwidth of approximately 6 GHz for input powers of less than 1 W was obtained.

Enhanced production of coherent vuv radiation by four‐wave mixing in Sr vapor

Significant enhancement of the unsaturated conversion efficiencies of four‐wave sum frequency mixing processes involving autoionizing states in Sr vapor is obtained by utilizing the 5s7s 1S0 two‐photon channel and phase matching by frequency adjustment. Extrapolation to low power levels indicates that production of cw vuv radiation may be possible. A saturation effect arising from depletion of one of the fundamental beams by two‐photon absorption is observed.

Phase matching of two‐photon resonant 4‐wave mixing processes in alkali metal vapors

Many classes of two‐photon resonant 4‐wave mixing processes in alkali metal vapors are shown to be phase matchable by adjusting the frequencies of the fundamental waves. Essentially perfect phase matching of one such process in Na vapor is demonstrated experimentally and shown for plane waves to be insensitive to variations in spatial distribution of the nonlinear medium.

Distributed‐feedback color center lasers in the 2.5–3.0‐μm region

We have demonstrated pulsed distributed‐feedback laser action in KCl:Li containing FA(II) color centers with spatially modulated concentrations. Laser outputs at various wavelengths between 2.6 and 2.8 μm have been observed with linewidths narrower than 0.2 nm. The absorbed pump power at threshold was 1.5 kW, and efficiencies of up to 6.7% were measured.

Phase Matching of 2-Photon Resonant 4-Wave Mixing Processes

Recently, 4-wave sum and difference frequency mixing processes in gases and vapors have received considerable attention as possible sources of tunable, coherent radiation in new regions of the electromagnetic spectrum [1]. The efficiencies of these processes have previously been enhanced either by phasematching by addition of a buffer gas of compensating dispersion or by two-photon resonant enhancement of the nonlinear susceptibility. The buffer gas technique works well for nonresonant mixing processes, but has the disadvantages of requiring a highly uniform gas mixture and of introducing additional absorption due to pressure broadening. This pressure broadening is more serious for two-photon resonant processes since broadening of the two-photon resonance reduces the nonlinear susceptibility [2].