Rita Mahon

Third-harmonic generation in argon, krypton, and xenon: Bandwidth limitations in the vicinity of Lyman-α

Using experimentally determined oscillator strengths and photoionization cross-sectional data, we compute the dispersion characteristics of Ar, Kr, and Xe up to their first ionization levels and determine the spectral regions in the VUV where these gases exhibit negative dispersion and so can be efficiently used for frequency tripling. We then investigate the bandwidths over which efficient tripling can be achieved in phase-matched gas mixtures. The bandwidth is limited by the rapidly varying dispersion in the vicinity of resonance transitions in the gases. In particular, we look at the case of frequency tripling 3647 A radiation to 1215.7 A (hydrogen Lyman-α) and show, that for fundamental wavelength bandwidths as narrow as 1 A, the rapid change in refractive index with wavelength can preclude phase matching over the entire bandwidth of the radiation.

Nonlinear generation of Lyman‐alpha radiation

Tunable narrow‐band Lyman‐alpha radiation (∼1216 A) has been generated by frequency tripling in krypton. A near‐diffraction‐limited tunable 15‐nsec 10‐MW input at 3648 A was used to generate ∼3.6×1011 photons (60 W) per pulse at 1216 A. Measurements of the output as a function of gas pressure give the refractive index for krypton at 1216 A, demonstrating its negatively dispersive character.

Frequency up-conversion to the VUV in Hg vapor

The efficient generation (up to 1 percent, 10 kW) of tunable, narrow-band radiation in the spectral ranges 1219-1221 A, 1228- 1235 A, and 1247-1255 A, using two-photon resonant, four-wave sum mixing in Hg vapor, is reported, using both the planewave and the tight focusing situations. Oscillator strengths are derived from the planewave experiments for the 6s^{1}S_{0}-9P, 10p , and 11p^{1}P_{1} transitions with an accuracy of 3 percent.

High-efficiency four-wave sum and difference mixing in Hg vapor

Mercury vapor has been used as a nonlinear frequency upconverting medium to generate peak powers of 5 kW at 1251 A in a bandwidth of 0.04 cm(-1) with a 10-Hz tunable system. The energy conversion efficiency is 0.3%. Parametric oscillation at the Hg resonance wavelength of 1849 A, as well as two other tunable (2omega(1)-omega(2)) frequency-mixed signals producing radiation at 2085 and 1833 A, are reported.

Generation of Lyman-α radiation in phase-matched rare-gas mixtures

When frequency tripling to Lyman-α in Kr, we find a Kerr-induced index mismatch per atom of γKr = −5.6 × 10−36 esu, which dominates the dispersion for power densities exceeding 4 × 1012 W/cm2. Results of phase matching Kr with Ar and Xe are presented. Dielectric breakdown provides a limitation that, when combined with a requirement of a 1-A bandwidth at Lyman-α, indicates that powers of a few kilowatts are achievable in a Kr–Ar phase-matched medium.

Generation of continuously tunable narrow-band radiation from 1220 to 1174 A in Hg vapor.

Continuously tunable, narrow-band radiation is generated in Hg vapor from the 11(p) (1)P(1) transition at 1220 A, through the series limit at 1187.9 A, and on out to 1174 A. This range includes the resonance transitions of neutral atomic hydrogen, deuterium, nitrogen, and xenon, some absorption profiles of which are presented.

Optimization of a Raman shifted dye laser system for DIAL applications

We describe an efficient Raman shifted dye laser system that generates tunable radiation at 765 and 940 nm with a bandwidth of 0.03 cm(-1). Operating a Raman cell at hydrogen pressure below 14 atm, we recorded optimum first Stokes energy conversions of 45% and of 37% at 765 and 940 nm, respectively. Optical depth measurements made at the centers of twenty-five absorption lines in the P branch of the oxygen A band imply a high spectral purity for both the laser and the Raman shifted radiation, and thus indicate the feasibility of using the stimulated Raman scattered radiation for differential absorption lidar (DIAL) measurements.

Four-wave sum mixing in beryllium around hydrogen Lyman-α

Radiation was generated between 1210 and 1230 A by four-wave sum mixing in beryllium vapor where the 2s(2)(1)S-2s3d(1)D transition was two-photon resonant. Results indicate that beryllium will be an efficient nonlinear medium in this spectral region with improvements to the stability of the furnace to allow phase matching and operation at higher pressures.

Observations of shadow bands at the total solar eclipse of 16 February 1980.

Photoelectric observations of short term light variations (shadow bands) at the 16 Feb. 1980 total solar eclipse have been made using a set of spatially separated PIN diodes. Light variations in a bandpass of 1-500 Hz were detected during the half-minutes preceding and following the total phase. Fourier analysis of the noise spectrum of the variations reveals a sharp drop-off for frequencies above 50 Hz and an overall spectrum quite similar to previously reported power spectra of stellar scintillation. This is consistent with an atmospheric origin for the shadow bands. Cross-correlations between the detector outputs are low, suggesting a short persistence time for the turbulent elements causing the patterns.

Imaging through a low light level Raman amplifier

The noise characteristics and the low-light-level imaging capabilities of a stimulated Raman amplifier have been investigated. Stokes beams carrying spatial structure have been amplified using a collimated pump with a Fresnel number of 17. Both direct imaging of the Stokes signal and Fourier transform imaging of the Stokes signal through the Raman amplifier were used. Evidence of interference between the quantum noise field and the seed-Stokes field is present at the lowest seeding levels.