Optics Letters

Effect of counterintuitive time delays in nonlinear mixing

R. I. Thompson, L. Marmet, Boris Peter Stoicheff

Published Jan 15, 2000• 9 citations

Abstract

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 2.5-3.5 ns relative to the arrival of the upper-state coupling beam (656 nm), it is possible to enhance the generated intensity by a factor of 2 or more.

DOI: 10.1364/ol.25.000120

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Optics Letters

Effect of counterintuitive time delays in nonlinear mixing

R. I. Thompson, L. Marmet, Boris Peter Stoicheff

Published Jan 15, 2000• 9 citations

Publisher

Abstract

DOI: 10.1364/ol.25.000120

Related papers

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Quantum Optics Journal of the European Optical Society Part BAug 1, 199412 citations

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Physical Review AJul 1, 199719 citations

(n=4--8)

in atomic hydrogen. Pulsed radiation was generated by strong coupling of the

\mathrm{np}

and

2s

levels with laser radiation at Balmer wavelengths, and simultaneously (weaker) coupling of the

2s

and

1s

levels by two-photon resonance with 243-nm laser radiation. Investigations were carried out over a range of laser intensities and products of interaction length and atomic density

(\mathrm{NL}).

As the product

\mathrm{NL}

increased, the XUV intensities were greatly enhanced by EIT, and at high

\mathrm{NL}

values, the spectral distributions of some of the generated signals were found to be distorted by the presence of molecular hydrogen. Calculated profiles, modified to incorporate the effects of nearby molecular resonances, were shown to be in good agreement with the observed spectra.

{4p}^{6}{}^{1}S

ground state and the

{4p}^{5}5p[0,\frac{1}{2}]

excited state $(94093.7 {\mathrm{cm}}^{\ensuremath{-}1}).$ The second field (the coupling field) at 759 nm was in single-photon resonance with the transition between the

{4p}^{5}5p[0,\frac{1}{2}]

state and the

{4p}^{5}5s[1,\frac{1}{2}]

state at $80917.6 {\mathrm{cm}}^{\ensuremath{-}1}.$ The presence of the coupling field leads to electromagnetically induced transparency (EIT) at the wavelength of the generated field, 123.6 nm. This is predicted to enhance the four-wave-mixing efficiency by a large factor. We have studied the dependence of the four-wave mixing process on the detuning and strength of the coupling field. The efficiency for four-wave mixing was found to be enhanced by a significant factor (>5) by the EIT effect when the resonant coupling field strength exceeded about half the Doppler width $(0.1 {\mathrm{cm}}^{\ensuremath{-}1}).$ A calculation for monochromatic fields and a uniform slab of gas provided qualitative agreement with the results of experiment. The relative conversion efficiency for this resonant mixing scheme is found to be

{10}^{4}

times greater than that for a similar scheme where the coupling laser is tuned far $(1270 {\mathrm{cm}}^{\ensuremath{-}1})$ off resonance. A substantial part of this resonant enhancement can thus be attributed to the EIT effect.

The generation of tunable, nanosecond-pulsed extreme-ultraviolet (EUV) light

(84.92\mathrm{nm}

84.97\mathrm{nm}

$\ensuremath{\sim}14.6\mathrm{eV})$ using four-wave mixing in optically deep krypton gas was investigated experimentally and theoretically. The sum-frequency mixing scheme generated light from two overlapping autoionizing resonances, ${17s}^{\ensuremath{'}}$ and ${15d}^{\ensuremath{'}}$. We investigated whether the laser-induced atomic coherence effect of electromagnetically induced transparency (EIT) could enhance the intensity of the EUV light generated. The maximum EUV output was seen from the region where the ${15d}^{\ensuremath{'}}$ autoionizing resonance has a transparency window due to Fano-type quantum interference. An analytical model using appropriate atomic parameters explains how background absorption can prevent EIT enhancement of EUV generation; and shows how a background Raman-like coupling term in the nonlinear susceptibility can well describe the measured EUV generation spectrum.