Physical Review Letters

Two-Photon Coherent-Transient Measurement of the Nonradiative Collisionless Dephasing Rate in S F6 via Doppler-Free Degenerate Four-Wave Mixing

Duncan G. Steel, Jenny Lam

Published Nov 19, 1979• 51 citations

Abstract

This Letter reports, for the first time, an experimental measurement of the collision-less dephasing time of the ${\ensuremath{\nu}}_{3}=2$ level in S${\mathrm{F}}_{6}$ using Doppler-free two-photon degenerate four-wave mixing. The measurement is performed in the time domain by use of a short-pulse C${\mathrm{O}}_{2}$ laser to establish a molecular two-photon coherent state. The coherent state is then probed as a function of time to yield a dephasing time of 1.8 nsec which is related to intramolecular dephasing rates.

DOI: 10.1103/physrevlett.43.1588

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Physical Review Letters

Two-Photon Coherent-Transient Measurement of the Nonradiative Collisionless Dephasing Rate in S F6 via Doppler-Free Degenerate Four-Wave Mixing

Duncan G. Steel, Jenny Lam

Published Nov 19, 1979• 51 citations

Publisher

Abstract

This Letter reports, for the first time, an experimental measurement of the collision-less dephasing time of the

{\ensuremath{\nu}}_{3}=2

level in S

{\mathrm{F}}_{6}

using Doppler-free two-photon degenerate four-wave mixing. The measurement is performed in the time domain by use of a short-pulse C

{\mathrm{O}}_{2}

laser to establish a molecular two-photon coherent state. The coherent state is then probed as a function of time to yield a dephasing time of 1.8 nsec which is related to intramolecular dephasing rates.

DOI: 10.1103/physrevlett.43.1588

Related papers

Degenerate four-wave mixing in a resonant homogeneously broadened system

Duncan G. Steel, Richard C. Lind, Jenny Lam

Detailed measurements have been made of degenerate four-wave mixing (DFWM) in a resonant homogeneously broadened gas. The measurements were performed in S ${\mathrm{F}}_{6}$ using a pulsed C ${\mathrm{O}}_{2}$ laser operated on the 10.4-\ensuremath{\mu} m branch. A pulse width of 1.2 nsec was used to reduce effects of collisional relaxation. Data are also presented for pulse widths of 140 nsec. At high-energy fluences (\ensuremath{\sim}0.1 J/ ${\mathrm{cm}}^{2}$ ) pulse breakup is observed and is believed to arise from multiple-photon effects. The data obtained with the short pulse width are compared to a four-level saturable-absorber model where excellent agreement is obtained when pump absorption is included. The qualitative behavior of DFWM due to dispersion is also demonstrated in the wings of the S ${\mathrm{F}}_{6}$ absorption spectrum. Peak reflectivities of 38% were readily obtained. In addition contributions due to a coherent three-level nonlinearity are presented showing a contribution equal to the measured saturable contribution.Detailed measurements have been made of degenerate four-wave mixing (DFWM) in a resonant homogeneously broadened gas. The measurements were performed in S${\mathrm{F}}_{6}$ using a pulsed C${\mathrm{O}}_{2}$ laser operated on the 10.4-\ensuremath{\mu} m branch. A pulse width of 1.2 nsec was used to reduce effects of collisional relaxation. Data are also presented for pulse widths of 140 nsec. At high-energy fluences (\ensuremath{\sim}0.1 J/${\mathrm{cm}}^{2}$) pulse breakup is observed and is believed to arise from multiple-photon effects. The data obtained with the short pulse width are compared to a four-level saturable-absorber model where excellent agreement is obtained when pump absorption is included. The qualitative behavior of DFWM due to dispersion is also demonstrated in the wings of the S${\mathrm{F}}_{6}$ absorption spectrum. Peak reflectivities of 38% were readily obtained. In addition contributions due to a coherent three-level nonlinearity are presented showing a contribution equal to the measured saturable contribution.

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Physical Review AOct 1, 199811 citations

Studies of picosecond collisional dephasing in atomic sodium vapor using broad-bandwidth transient four-wave mixing

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Phase-conjugate four-wave mixing with partially coherent laser fields

Binh Do, Jongwhan Cha, Daniel S. Elliott +1 more

We present results of our experimental investigations of phase-conjugate four-wave mixing in a nearly Doppler-free, collisionless, two-level quantum system with a partially coherent non-Markovian laser field. The two components of the laser field---an intense pump and a weak, time-delayed probe---are derived from a single narrow-band cw laser source on which phase and frequency fluctuations conforming to the phase diffusion model are superimposed. We carry out these measurements using the ${D}_{2}$ transition in an optically pumped diffuse beam of atomic sodium. We vary the pump intensity, laser bandwidth, and temporal delay between the pump and probe, and measure the peak signal strength, the bandwidth, and the asymmetry of the four-wave-mixing spectrum. For comparison with our experimental results of the peak signal strength, we also analyze the same interaction numerically, through direct integration of the optical Bloch equations. The numerical results are in good agreement with the measurements.We present results of our experimental investigations of phase-conjugate four-wave mixing in a nearly Doppler-free, collisionless, two-level quantum system with a partially coherent non-Markovian laser field. The two components of the laser field---an intense pump and a weak, time-delayed probe---are derived from a single narrow-band cw laser source on which phase and frequency fluctuations conforming to the phase diffusion model are superimposed. We carry out these measurements using the ${D}_{2}$ transition in an optically pumped diffuse beam of atomic sodium. We vary the pump intensity, laser bandwidth, and temporal delay between the pump and probe, and measure the peak signal strength, the bandwidth, and the asymmetry of the four-wave-mixing spectrum. For comparison with our experimental results of the peak signal strength, we also analyze the same interaction numerically, through direct integration of the optical Bloch equations. The numerical results are in good agreement with the measurements.

Physical Review AJul 1, 19995 citations

Propagation of a Cavity-Dumped C O2 Laser Pulse through S F6

Peter K. Cheo, C. H. Wang

Coherent interactions between short C ${\mathrm{O}}_{2}$ laser pulses and a resonant absorbing S ${\mathrm{F}}_{6}$ gas medium have been examined carefully, using a laser cavity-dumped rectangular pulse with a width of 20 nsec and input intensities from 10 to ${10}^{4}$ W/ ${\mathrm{cm}}^{2}$ . Parameters studied included the width, shape, and delay time of the transmitted pulse after propagation through several absorption lengths of S ${\mathrm{F}}_{6}$ cell. In addition to these measurements, we have observed two new phenomena, namely, optical free induction decay and edge echo, which are induced by this short rectangular C ${\mathrm{O}}_{2}$ laser input pulse. Results indicate that although level degeneracy in S ${\mathrm{F}}_{6}$ may be involved, the simple two-level model can account qualitatively for most observed phenomena, with the exception that the observed shape of a $2\ensuremath{\pi}$ pulse deviates significantly from the symmetric hyperbolic-secant function predicted by the simple two-level theory. In the $\ensuremath{\pi}$ pulse region, we have demonstrated that the free-induction-decay tail can be valuable for studies of atomic and molecular collision processes.Coherent interactions between short C${\mathrm{O}}_{2}$ laser pulses and a resonant absorbing S${\mathrm{F}}_{6}$ gas medium have been examined carefully, using a laser cavity-dumped rectangular pulse with a width of 20 nsec and input intensities from 10 to ${10}^{4}$ W/${\mathrm{cm}}^{2}$. Parameters studied included the width, shape, and delay time of the transmitted pulse after propagation through several absorption lengths of S${\mathrm{F}}_{6}$ cell. In addition to these measurements, we have observed two new phenomena, namely, optical free induction decay and edge echo, which are induced by this short rectangular C${\mathrm{O}}_{2}$ laser input pulse. Results indicate that although level degeneracy in S${\mathrm{F}}_{6}$ may be involved, the simple two-level model can account qualitatively for most observed phenomena, with the exception that the observed shape of a $2\ensuremath{\pi}$ pulse deviates significantly from the symmetric hyperbolic-secant function predicted by the simple two-level theory. In the $\ensuremath{\pi}$ pulse region, we have demonstrated that the free-induction-decay tail can be valuable for studies of atomic and molecular collision processes.

Physical Review AFeb 1, 197021 citations

This Letter reports, for the first time, an experimental measurement of the collision-less dephasing time of the

{\ensuremath{\nu}}_{3}=2

level in S

{\mathrm{F}}_{6}

using Doppler-free two-photon degenerate four-wave mixing. The measurement is performed in the time domain by use of a short-pulse C

{\mathrm{O}}_{2}

Detailed measurements have been made of degenerate four-wave mixing (DFWM) in a resonant homogeneously broadened gas. The measurements were performed in S

{\mathrm{F}}_{6}

using a pulsed C

{\mathrm{O}}_{2}

laser operated on the 10.4-\ensuremath{\mu} m branch. A pulse width of 1.2 nsec was used to reduce effects of collisional relaxation. Data are also presented for pulse widths of 140 nsec. At high-energy fluences (\ensuremath{\sim}0.1 J/

{\mathrm{cm}}^{2}

) pulse breakup is observed and is believed to arise from multiple-photon effects. The data obtained with the short pulse width are compared to a four-level saturable-absorber model where excellent agreement is obtained when pump absorption is included. The qualitative behavior of DFWM due to dispersion is also demonstrated in the wings of the S

{\mathrm{F}}_{6}

absorption spectrum. Peak reflectivities of 38% were readily obtained. In addition contributions due to a coherent three-level nonlinearity are presented showing a contribution equal to the measured saturable contribution.

{D}_{2}

transition in an optically pumped diffuse beam of atomic sodium. We vary the pump intensity, laser bandwidth, and temporal delay between the pump and probe, and measure the peak signal strength, the bandwidth, and the asymmetry of the four-wave-mixing spectrum. For comparison with our experimental results of the peak signal strength, we also analyze the same interaction numerically, through direct integration of the optical Bloch equations. The numerical results are in good agreement with the measurements.

Coherent interactions between short C

{\mathrm{O}}_{2}

laser pulses and a resonant absorbing S

{\mathrm{F}}_{6}

gas medium have been examined carefully, using a laser cavity-dumped rectangular pulse with a width of 20 nsec and input intensities from 10 to

{10}^{4}

{\mathrm{cm}}^{2}

. Parameters studied included the width, shape, and delay time of the transmitted pulse after propagation through several absorption lengths of S

{\mathrm{F}}_{6}

cell. In addition to these measurements, we have observed two new phenomena, namely, optical free induction decay and edge echo, which are induced by this short rectangular C

{\mathrm{O}}_{2}

laser input pulse. Results indicate that although level degeneracy in S

{\mathrm{F}}_{6}

may be involved, the simple two-level model can account qualitatively for most observed phenomena, with the exception that the observed shape of a $2\ensuremath{\pi}$ pulse deviates significantly from the symmetric hyperbolic-secant function predicted by the simple two-level theory. In the $\ensuremath{\pi}$ pulse region, we have demonstrated that the free-induction-decay tail can be valuable for studies of atomic and molecular collision processes.