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Physical Review Letters

Superfluorescence-Stimulated Photon Echoes

Alexander I. Lvovsky, Sven R. Hartmann, Fred Moshary

Published Dec 10, 2002• 11 citations
Publisher

Abstract

Two closely spaced 778 nm, 4-ps pulses, two-photon resonant with the 5S-5D transition in Rb vapor generate a ground state grating, which later is excited by a similar third pulse, producing conical yoked superfluorescence echo on the 5S-6P, 420-nm transition. The intensity of this emission as a function of the relative delay between the leading excitation pulses is governed by the dynamics of Doppler dephasing and rephasing. This is the first observation of an echo effect induced by a spontaneous relaxation process.

DOI
10.1103/physrevlett.89.263602

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Superfluorescence photon echo in rubidium vapor

Alexander I. Lvovsky, Fred Moshary, S.R. Hartmann

Summary form only given.By applying a sequence of three pulses two photon resonant with the 5S-5D transition in Rb vapor, we generate yoked superfluorescence (YSF) pulses via the 5D-6P-5S channel that generate a stimulated superfluorescence photon echo (SSPE) on the 6P-5S transition.

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A dense sample of atomic rubidium vapor excited by a short (4 ps) transform-limited laser pulse two-photon resonant with the 5S-5D transition in a large Fresnel number geometry emits a delayed omnidirectional infrared superfluorescence pulse (coherent flash) on the 5D-6P transition. This superfluorescence emission involves a coherent population transfer to the 6P level and results in prompt directional yoked UV emission and coherent population transfer back to the ground 5S state. This emission completes the process of parametric four-wave mixing, selectively involving only those atoms on the 6P level whose 5D-6P emission satisfies the phase-matching condition. The unique feature of this four-wave mixing radiation is that it occurs after the termination of the pump pulse, as evidenced by direct measurement of emission timing. The multidirectional character of superfluorescent emission is confirmed by the observation of non-collinear parametric four-wave mixing when exciting the sample by two simultaneous overlapping pulses, for a wide range of beam angles. Also observed and investigated is superfluorescent transient diffraction that appears when the sample is excited by a sequence of three laser pulses.

•Jan 1, 1998•2 citations

Two-pulse conical yoked superfluorescence in Rb vapor

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Summary form only given.We have observed yoked superfluorescence (YSF) on the 5D-6P-5S channel in atomic rubidium after two-photon excitation of the 5D-5S transition by a short (3 ps), 778-nm pulse from a Ti:sapphire laser system. The excitation pulse is formed by a pair of spatially overlapping pulses of wave vectors k/sub 1/ and k/sub 2/ where |k/sub 1/|=|k/sub 2/|=2/spl pi///spl lambda/ and /spl lambda/ is the wavelength of the 5D-5S transition. When the atoms are excited by taking one photon from along k/sub 1/ and one from along k/sub 2/, then phase matching requires that the yoked transition consists of photon pairs along k/sub DP/ and k/sub PS/ where k/sub 1/+k/sub 2/=k/sub DP/+k/sub PS/ and k/sub DP/ and k/sub PS/ are the wave vectors of, respectively, the upper (5D-6P) and the lower (6P-5S) transition components of the YSF. The YSF pulses are emitted in a cone determined by Brownell et al. (1995). This conical emission of YSF was observed on the 420 nm lower transition. The measured behavior of the conical apex angle /spl beta/ as a function of the angle between the excitation pulses /spl alpha/ is given as a series of points and shows good agreement with the solid line based on Brownell et al.

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We study the superfluorescence (SF) from a gas of rubidium atoms. The atoms of a dense vapor are excited to the $5D$ state from the $5S$ state by a two-photon process driven by 100-fs laser pulses. The atoms decay to the $6P$ state and then to the $5S$ state. The SF emission at 420 nm on the $6P$--$5S$ transition is recorded by a streak camera with picosecond time resolution. The time duration of the generated SF is tens of picoseconds, which is much shorter than the time scale of the usual relaxation processes, including spontaneous emission and atomic coherence dephasing. The dependence of the time delay between the reference input pulse and SF is measured as a function of laser power. The experimental data are described quantitatively by a simulation based on the semiclassical atom-field interaction theory. The observed change in scaling laws for the peak intensity and delay time can be elucidated by an SF theory in which the sample length is larger than the cooperation length.

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A dense sample of atomic Rb vapor excited by a 4 ps laser pulse two-photon resonant with the $5S\ensuremath{-}5D$ transition in a large Fresnel number geometry emits a delayed coherent omnidirectional ir pulse on the $5D\ensuremath{-}6P$ transition. This superfluorescence emission involves a coherent population transfer to the $6P$ level and results in simultaneous directional uv emission and coherent population transfer back to the ground $5S$ state. This uv emission is a manifestation of parametric time-delayed four-wave mixing. For a composite noncollinear, $|{\stackrel{\ensuremath{\rightarrow}}{k}}_{1}|\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}|{\stackrel{\ensuremath{\rightarrow}}{k}}_{2}|$, excitation, the uv radiation pattern is conical and the cone angle depends on the angle between the excitation pulses.

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Yoked Superfluorescence

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A laser pulse two-photon resonant with the ${6S}_{1/2}\ensuremath{-}{6D}_{3/2}$ 442 nm transition in Cs vapor generates delayed superfluorescence (SF) on the upper ${6D}_{3/2}\ensuremath{-}{6P}_{1/2}$ 876 nm and lower ${6P}_{1/2}\ensuremath{-}{6S}_{1/2}$ 894 nm transitions. Yoked SF is observed in the forward (along the laser) direction as evidenced by the simultaneous appearance of SF on both transitions. Cascade SF is observed in the backward direction, where SF on the lower transition only evolves after it has terminated on the upper. The four SF signals exhibit quantum beats associated with the ${6P}_{1/2}$ hyperfine splitting.

Physical Review Letters•Oct 30, 1995•65 citations
Two closely spaced 778 nm, 4-ps pulses, two-photon resonant with the 5S-5D transition in Rb vapor generate a ground state grating, which later is excited by a similar third pulse, producing conical yoked superfluorescence echo on the 5S-6P, 420-nm transition. The intensity of this emission as a function of the relative delay between the leading excitation pulses is governed by the dynamics of Doppler dephasing and rephasing. This is the first observation of an echo effect induced by a spontaneous relaxation process.
A dense sample of atomic rubidium vapor excited by a short (4 ps) transform-limited laser pulse two-photon resonant with the 5S-5D transition in a large Fresnel number geometry emits a delayed omnidirectional infrared superfluorescence pulse (coherent flash) on the 5D-6P transition. This superfluorescence emission involves a coherent population transfer to the 6P level and results in prompt directional yoked UV emission and coherent population transfer back to the ground 5S state. This emission completes the process of parametric four-wave mixing, selectively involving only those atoms on the 6P level whose 5D-6P emission satisfies the phase-matching condition. The unique feature of this four-wave mixing radiation is that it occurs after the termination of the pump pulse, as evidenced by direct measurement of emission timing. The multidirectional character of superfluorescent emission is confirmed by the observation of non-collinear parametric four-wave mixing when exciting the sample by two simultaneous overlapping pulses, for a wide range of beam angles. Also observed and investigated is superfluorescent transient diffraction that appears when the sample is excited by a sequence of three laser pulses.
Summary form only given.We have observed yoked superfluorescence (YSF) on the 5D-6P-5S channel in atomic rubidium after two-photon excitation of the 5D-5S transition by a short (3 ps), 778-nm pulse from a Ti:sapphire laser system. The excitation pulse is formed by a pair of spatially overlapping pulses of wave vectors k/sub 1/ and k/sub 2/ where |k/sub 1/|=|k/sub 2/|=2/spl pi///spl lambda/ and /spl lambda/ is the wavelength of the 5D-5S transition. When the atoms are excited by taking one photon from along k/sub 1/ and one from along k/sub 2/, then phase matching requires that the yoked transition consists of photon pairs along k/sub DP/ and k/sub PS/ where k/sub 1/+k/sub 2/=k/sub DP/+k/sub PS/ and k/sub DP/ and k/sub PS/ are the wave vectors of, respectively, the upper (5D-6P) and the lower (6P-5S) transition components of the YSF. The YSF pulses are emitted in a cone determined by Brownell et al. (1995). This conical emission of YSF was observed on the 420 nm lower transition. The measured behavior of the conical apex angle /spl beta/ as a function of the angle between the excitation pulses /spl alpha/ is given as a series of points and shows good agreement with the solid line based on Brownell et al.
We study the superfluorescence (SF) from a gas of rubidium atoms. The atoms of a dense vapor are excited to the 5D5D5D state from the 5S5S5S state by a two-photon process driven by 100-fs laser pulses. The atoms decay to the 6P6P6P state and then to the 5S5S5S state. The SF emission at 420 nm on the 6P6P6P--5S5S5S transition is recorded by a streak camera with picosecond time resolution. The time duration of the generated SF is tens of picoseconds, which is much shorter than the time scale of the usual relaxation processes, including spontaneous emission and atomic coherence dephasing. The dependence of the time delay between the reference input pulse and SF is measured as a function of laser power. The experimental data are described quantitatively by a simulation based on the semiclassical atom-field interaction theory. The observed change in scaling laws for the peak intensity and delay time can be elucidated by an SF theory in which the sample length is larger than the cooperation length.
A dense sample of atomic Rb vapor excited by a 4 ps laser pulse two-photon resonant with the $5S\ensuremath{-}5D$ transition in a large Fresnel number geometry emits a delayed coherent omnidirectional ir pulse on the $5D\ensuremath{-}6P$ transition. This superfluorescence emission involves a coherent population transfer to the 6P6P6P level and results in simultaneous directional uv emission and coherent population transfer back to the ground 5S5S5S state. This uv emission is a manifestation of parametric time-delayed four-wave mixing. For a composite noncollinear, $|{\stackrel{\ensuremath{\rightarrow}}{k}}_{1}|\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}|{\stackrel{\ensuremath{\rightarrow}}{k}}_{2}|$, excitation, the uv radiation pattern is conical and the cone angle depends on the angle between the excitation pulses.
A laser pulse two-photon resonant with the ${6S}_{1/2}\ensuremath{-}{6D}_{3/2}$ 442 nm transition in Cs vapor generates delayed superfluorescence (SF) on the upper ${6D}_{3/2}\ensuremath{-}{6P}_{1/2}$ 876 nm and lower ${6P}_{1/2}\ensuremath{-}{6S}_{1/2}$ 894 nm transitions. Yoked SF is observed in the forward (along the laser) direction as evidenced by the simultaneous appearance of SF on both transitions. Cascade SF is observed in the backward direction, where SF on the lower transition only evolves after it has terminated on the upper. The four SF signals exhibit quantum beats associated with the 6P1/2{6P}_{1/2}6P1/2​ hyperfine splitting.