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Conference on Lasers and Electro-Optics

A Rapid Inspection of Atomic Interference using Superfluorescent Picosecond Pulses

Gombojav O. Ariunbold, Vladimir A. Sautenkov, Marlan O. Scully

Published Jan 1, 2010• 3 citations
Publisher

Abstract

The conventional method to measure atomic interference is usually based on incoherent processes which can be scaled by nano or microseconds. However, atomic interference may be studied in association with coherent process such as superfluorescence. Producing superfluorescent picosecond pulses in 87Rb vapor pumped by ~100 fs laser pulses, we report an observation of quantum beat due to D-lines. The relative delay of the superfluorescent pulses is measured by the streak camera with picosecond time resolution, as a function of time interval between input pulses, which also enables us to study atomic interference.

DOI
10.1364/cleo.2010.cma4

Related papers

Temporal coherent control of superfluorescent pulses

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We demonstrate that collective atomic interferences can be investigated by measuring the superfluorescence (SF) time delay. A pair of broadband (≈20 nm), ultrashort (≈80 fs), collinear pulses with a variable delay coherently excites rubidium (Rb) atoms. The generated superfluorescent pulses at 420 nm on the cascade transition are recorded by a picosecond streak camera. Both intensity and SF time delay of the 420 nm pulse are altered as the delay between input pulses varies. In particular, the SF time delay of the normalized 420 nm pulse exhibits oscillations with different periods. This can be understood in terms of atomic and quantum interferences due to two possible two-photon excitation pathways through the intermediate levels (Rb D-lines).

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Observation of picosecond superfluorescent pulses in rubidium atomic vapor pumped by 100-fs laser pulses

Gombojav O. Ariunbold, Michael M. Kash, Vladimir A. Sautenkov +4 more

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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Quantum beat observations in rubidium vapor

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Probing the interactions between a mode-locked laser pulse and saturated rubidium vapor with a pump–probe technique has resulted in observations of coherences within the atom that persist longer than 150 ps. Quantum beats due to the interference between the 7S and 5D_{5/2} energy states were observed by a four-wave mixing process. The difference frequency between the 5D–5P_{3/2} and the 5P_{3/2}–5S transitions was also observed for interpulse delays up to 180 ps. The temporal evolution of the beat amplitude indicates the existence of a superfluorescent process and a scattering process detected simultaneously with the four-wave mixing process. A model was developed to explain the processes and was used to predict the range of pulse parameters for which the scattering process and four-wave mixing could be simultaneously detected.

•Jun 27, 2012•1 citation

Ultrafast Cooperative Phenomena in Coherently Prepared Media: From Superfluorescence to Coherent Raman Scattering and Applications

Ariunbold Gombojav

Technological progress in commercializing ultrafast lasers and detectors has allowed realization of cooperative processes on an ultrashort time scale, which demand a re-evaluation of the conventional cooperative phenomena with a new insight. Ultrafast cooperative phenomena in coherently prepared media and various applications of superfluorescence and coherent Raman scattering are studied in this dissertation. In particular, a simple theoretical testimony on analogy between a cooperative emission and coherent Raman scattering is presented by offering an opportunity to perform parallel research on these two processes from a unified point of view.\n\nOn one hand, the superfluorescent pulse with a time duration of a few tens of picoseconds (ps) from alkali metal vapor is observed for the first time, even though cooperative phenomena in atomic vapor have been extensively studied for more than five decades. A dense rubidium vapor pumped by ultrashort (100 femtosecond, fs) pulses allows a realization of the ultrafast superfluorescence while a time-resolved study of superfluorescence is accomplished by using a streak camera with 2 ps time resolution. Experimental research on quantum nature of cooperative emissions has been “frozen” over the years (three decades) possibly because of the technical difficulties. Quantum fluctuations of superfluorescence development are explored experimentally by taking advantage of the ultra fast streak camera. Presumable applications of the superfluorescent pulse in e.g., a remote sensing, and an ultraviolet upconversion of the input infrared laser pulse are presented. The quantum interference due to different excitation pathways is revealed by the temporal coherent control technique while observing interferometric signals from alkali metal vapors. \n\nOn the other hand, a new spectroscopic technique based on ultrafast coherent Raman scattering is developed. The key advantage of the presented technique is to suppress the non-resonant background noise which usually obscures possible applications of the other conventional coherent Raman techniques in practice. A reduction of the background noise is achieved by shaping and delaying the third pulse which probes the coherence of the medium (i.e., an enhancement of specific vibrations of the target molecules in unison) firstly prepared by two broadband pulses. We demonstrate a robustness and superiority of signal-to-noise ratio of the developed technique by identifying as few as 10000 bacterial spores at a single laser shot level.\n\nFinally, several comparative studies between cooperative and uncooperative processes are presented. A picosecond cooperative phenomenon in a three-photon resonant medium induced by a single as well as two-color ultrashort pulses is investigated. A time-resolved study shows that a picosecond cooperative effect is crucial in the well-established fields of resonant-enhanced multiphoton ionizations and harmonic generations. We also present a quantitative analysis for spontaneous versus broadband coherent Raman scattering on pyridine molecules. The spontaneous Raman signal is enhanced by 5 orders as a result of cooperative phenomena.

•Jan 1, 2011•4 citations

Observation of picosecond UV pulses produced by coherent scattering of IR femtosecond pulses in atomic rubidium vapor

Gombojav O. Ariunbold, Michael M. Kash, Vladimir A. Sautenkov +4 more

We report the observation of coherent UV light pulses by the coherent scattering of IR pulses from atomic rubidium vapor. Rubidium atoms were first excited by a 100 fs pulse from the 5S ground state to the 5D state via a two-photon transition. The atoms were then pumped by an IR pulse resonant to the 5D–12P transition. The presence of the IR pulse triggered the instantaneous emission of a UV light pulse on the 12P–5S transition. The pulse had a time duration of tens of picoseconds, which was measured by a picosecond-resolution streak camera. The temporal shape of the generated light is explained by a simplified atom–field interaction theory.

Journal of the Optical Society of America B•Feb 25, 2011•10 citations
The conventional method to measure atomic interference is usually based on incoherent processes which can be scaled by nano or microseconds. However, atomic interference may be studied in association with coherent process such as superfluorescence. Producing superfluorescent picosecond pulses in 87Rb vapor pumped by ~100 fs laser pulses, we report an observation of quantum beat due to D-lines. The relative delay of the superfluorescent pulses is measured by the streak camera with picosecond time resolution, as a function of time interval between input pulses, which also enables us to study atomic interference.
We demonstrate that collective atomic interferences can be investigated by measuring the superfluorescence (SF) time delay. A pair of broadband (≈20 nm), ultrashort (≈80 fs), collinear pulses with a variable delay coherently excites rubidium (Rb) atoms. The generated superfluorescent pulses at 420 nm on the cascade transition are recorded by a picosecond streak camera. Both intensity and SF time delay of the 420 nm pulse are altered as the delay between input pulses varies. In particular, the SF time delay of the normalized 420 nm pulse exhibits oscillations with different periods. This can be understood in terms of atomic and quantum interferences due to two possible two-photon excitation pathways through the intermediate levels (Rb D-lines).
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 technique for producing phase-related picosecond optical pulses is described. A sequence of two phase-related pulses, well separated in time, is applied to the D1 line in Na vapor. When the phase between the two pulses is scanned, oscillations in the incoherent fluorescence are observed. This demonstrates the well-defined phase relationship between the pulses. Measuring the amplitude of the oscillations as a function of pulse separation yields the Na optical coherence decay. A beat arising from the ground-state hyperfine splitting is observed, and the results agree well with calculation.
Probing the interactions between a mode-locked laser pulse and saturated rubidium vapor with a pump–probe technique has resulted in observations of coherences within the atom that persist longer than 150 ps. Quantum beats due to the interference between the 7S and 5D_{5/2} energy states were observed by a four-wave mixing process. The difference frequency between the 5D–5P_{3/2} and the 5P_{3/2}–5S transitions was also observed for interpulse delays up to 180 ps. The temporal evolution of the beat amplitude indicates the existence of a superfluorescent process and a scattering process detected simultaneously with the four-wave mixing process. A model was developed to explain the processes and was used to predict the range of pulse parameters for which the scattering process and four-wave mixing could be simultaneously detected.
Technological progress in commercializing ultrafast lasers and detectors has allowed realization of cooperative processes on an ultrashort time scale, which demand a re-evaluation of the conventional cooperative phenomena with a new insight. Ultrafast cooperative phenomena in coherently prepared media and various applications of superfluorescence and coherent Raman scattering are studied in this dissertation. In particular, a simple theoretical testimony on analogy between a cooperative emission and coherent Raman scattering is presented by offering an opportunity to perform parallel research on these two processes from a unified point of view.\n\nOn one hand, the superfluorescent pulse with a time duration of a few tens of picoseconds (ps) from alkali metal vapor is observed for the first time, even though cooperative phenomena in atomic vapor have been extensively studied for more than five decades. A dense rubidium vapor pumped by ultrashort (100 femtosecond, fs) pulses allows a realization of the ultrafast superfluorescence while a time-resolved study of superfluorescence is accomplished by using a streak camera with 2 ps time resolution. Experimental research on quantum nature of cooperative emissions has been “frozen” over the years (three decades) possibly because of the technical difficulties. Quantum fluctuations of superfluorescence development are explored experimentally by taking advantage of the ultra fast streak camera. Presumable applications of the superfluorescent pulse in e.g., a remote sensing, and an ultraviolet upconversion of the input infrared laser pulse are presented. The quantum interference due to different excitation pathways is revealed by the temporal coherent control technique while observing interferometric signals from alkali metal vapors. \n\nOn the other hand, a new spectroscopic technique based on ultrafast coherent Raman scattering is developed. The key advantage of the presented technique is to suppress the non-resonant background noise which usually obscures possible applications of the other conventional coherent Raman techniques in practice. A reduction of the background noise is achieved by shaping and delaying the third pulse which probes the coherence of the medium (i.e., an enhancement of specific vibrations of the target molecules in unison) firstly prepared by two broadband pulses. We demonstrate a robustness and superiority of signal-to-noise ratio of the developed technique by identifying as few as 10000 bacterial spores at a single laser shot level.\n\nFinally, several comparative studies between cooperative and uncooperative processes are presented. A picosecond cooperative phenomenon in a three-photon resonant medium induced by a single as well as two-color ultrashort pulses is investigated. A time-resolved study shows that a picosecond cooperative effect is crucial in the well-established fields of resonant-enhanced multiphoton ionizations and harmonic generations. We also present a quantitative analysis for spontaneous versus broadband coherent Raman scattering on pyridine molecules. The spontaneous Raman signal is enhanced by 5 orders as a result of cooperative phenomena.
We report the observation of coherent UV light pulses by the coherent scattering of IR pulses from atomic rubidium vapor. Rubidium atoms were first excited by a 100 fs pulse from the 5S ground state to the 5D state via a two-photon transition. The atoms were then pumped by an IR pulse resonant to the 5D–12P transition. The presence of the IR pulse triggered the instantaneous emission of a UV light pulse on the 12P–5S transition. The pulse had a time duration of tens of picoseconds, which was measured by a picosecond-resolution streak camera. The temporal shape of the generated light is explained by a simplified atom–field interaction theory.