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Bulletin of the American Physical Society

An experimental investigation of superfluorescence in calcium

Anantharaman Kumarakrishnan, James F. Kelly, Xianming L. Han

Published May 1, 1993• 0 citations
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Abstract

We have studied Superfluorescence (SF) under highly unfavorable conditions of rapid collisional and radiative distribution in a Doppler broadened medium. Nanosecond SF pulses at 5.5 {mu} were generated from a 50 cm column of calcium vapor buffered with argon by optically pumping the Ca (4s{sup 2} {sup 1}S{sub 0} - 4s4p{sup 1}P{sub 1} - 3d4s{sup 1}D{sub 2}) Raman Amplifier scheme. Power broadening due to an intense 13 nsec pump pulse precludes the evolution of SF for essentially this duration. As a result, the scaling laws which govern the properties of SF in a transversely excited system are shown to apply in our situation in which the conditions resemble swept excitation.

Related papers

Superfluorescence from optically trapped calcium atoms

Anantharaman Kumarakrishnan, Xianming L. Han

We have studied superfluorescence (SF) under highly unfavorable conditions of rapid collisional and radiative distribution in a Doppler-broadened medium. Nanosecond SF pulses at 5.5 \ensuremath{\mu}m were generated on the Ca $4s4p{}^{1}{P}_{1}--3d4s{}^{1}{D}_{2}$ transition from a column of calcium vapor buffered with Ar by optically pumping the ${4s}^{2}{}^{1}{S}_{0}--4s4p{}^{1}{P}_{1}$ transition. The Rabi frequency associated with the intense pump pulse prevents the occurrence of SF while the pump laser is on. As a result, the predicted scaling laws that describe the properties of SF in a transversely excited system, such as peak heights, pulse widths, and delay times, are shown to apply in our situation in which the conditions resemble swept excitation. The delay times were found to be in agreement with a fully quantum mechanical calculation which describes the initiation of SF. Measurements of the densities of the three levels, the absolute SF photon yield, and the spatial distribution of the excited states indicate that the system has a quantum yield of unity. The SF intensity increases with an increase in Ar pressure due to collisional redistribution until the collisional dephasing rate inhibits SF. The conditions describing the transition of SF to amplified spontaneous emission allow us to measure the collisional broadening rate for the SF transition.

Physical Review A•Nov 1, 1998•29 citations

Collision-induced superfluorescence

Anantharaman Kumarakrishnan, S. Chudasama, Xianming L. Han

We have studied superfluorescence (SF) in Ca vapor evolving on the 3d4s ^3 D_J -4s4p ^3 P_J-1 transitions at 1.9 µm by exciting the 4s^21 S_0 -4s4p ^1 P_1 with a pulsed dye laser. SF is generated following population transfer by spin-changing collisions with an inert gas Ar from the 4s4p ^1 P_1 and 3d4s ^1 D_2 levels. We show for the first time to our knowledge that the time delay for SF evolution follows the 1/sqrt N dependence expected for the case of uniform excitation of the vapor column by collisional transfer. Here, N is the number of participating atoms that was measured directly from the photon yield. The measured photon yield for the signal as a function of Ar pressure was found to be consistent with rate equations that simulate the buildup of populations in the ^3 D_J levels based on known collisional rates. This suggests that collisional rates can be directly inferred on the basis of SF photon yields and the atomic level populations. The pulse shapes for SF show temporal oscillations that depend on two distinct factors. The first is the presence of a number of independently evolving regions in the gain medium, and the second is the presence of spatial modes. Temporal ringing is a well-known effect related to the exchange of energy between the atoms and the radiation field during pulse propagation. However, the temporal ringing observed in this experiment is far more pronounced than in previous SF experiments due to a particular choice of evolution parameters. This should make it feasible to compare our results with detailed numerical simulations that have been carried out previously.

Journal of the Optical Society of America B•Jul 1, 2005•14 citations

Superfluorescence polarization: Signature of collisional redistribution

Anantharaman Kumarakrishnan, S. Chudasama, Xianming L. Han

We have studied effects of magnetic sublevel degeneracy on the polarization of superfluorescent pulses generated on the Ca $4s4p{}^{1}{P}_{1}--3d4s{}^{1}{D}_{2}$ transition at $5.5\ensuremath{\mu}\mathrm{m}.$ These pulses were generated from a cell of length 50 cm by optically pumping calcium vapor on the ${4s}^{2}{}^{1}{S}_{0}--4s4p{}^{1}{P}_{1}$ transition in the presence of Ar gas. The axis of ellipticity of superfluorescence (SF) polarization is oriented parallel to the axis of the pump-laser polarization at large detunings, and undergoes an abrupt rotation through $90\ifmmode^\circ\else\textdegree\fi{}$ for detunings close to resonance. The distribution of populations in the magnetic sublevels of the ${}^{1}{P}_{1}$ state can be estimated using a simple model based on previously calculated cross sections for collisionally aided absorption in the presence of an intense (pump) field. For large detunings, these estimates are consistent with the polarized SF intensity measured in the experiment. A direct measurement of the populations of the ${}^{1}{P}_{1}$ magnetic sublevels also supports the collisional redistribution predicted by the calculated cross sections. We therefore suggest that SF polarization can be a useful signature of collisional redistribution. However, the change in ellipticity is unexpected, and probable causes for this effect are discussed.

Physical Review A•Sep 10, 2003•3 citations

Investigations of superfluorescent cascades

J. Kelly, Anantharaman Kumarakrishnan, Xianming L. Han

We report studies of SF cascades in atomic calcium which result from two-photon excitation of several levels reasonably close to the ionization limit. We have observed significant conversion efficiencies for some of these transitions which result in subnanosecond pulses particularly in the visible wavelengths. In addition, we report the discovery of a novel two-photon scattering mechanism which could prove to be a good method of determining collisional broadening rates.

Bulletin of the American Physical Society•May 1, 1993•0 citations

Laser studies of electronic excitation transfer in atomic calcium: Ca(4s5p /sup 1/P/sub 1/)+Ararrow-right-leftCa(4s5p /sup 3/P/sub 2,1,0/)+Ar

William H. Pence, S.R. Leone

Time-resolved nsec kinetic methods are used to measure state specific electronic excitation transfer for the near-resonant process: Ca(4s5p /sup 1/P/sub 1/) +Ar /sup k//sub 1/arrow-right-left/sub k//sub -/1 Ca(4s5p /sup 3/P/sub 2,1,0/)+Ar. In stimulated emission experiments it is found that the Ca(4s5p /sup 3/P/sub 2/) level is preferentially populated. The rate constant k/sub 1/ for the specific /sup 3/P/sub 2/ channel is 5.2 +- 0.5 x 10/sup -11/ cm/sup 3/ molecule/sup -1/ sec/sup -1/. These results are discussed in terms of near-resonant spin changing collision mechanisms. Radiative lifetimes for Ca(4s5p /sup 1/P/sub 1/) and Ca(4s5p /sup 3/P/sub 1/) are also determined to be 77 +- 2 nsec and 67 +- 2 nsec, respectively.

•May 15, 1981•0 citations

Collisional excitation of 4p /sup 2/P states of Ca/sup +/ following pulsed-laser pumping of the 4s/sup 2/ /sup 1/S/sub 0/-4s4p /sup 3/P/sub 1/ transition of Ca

Muhammad Arshad Khan, M.A. Gondal, M. H. Rais

European Quantum Electronics Conference (EQEC)•Aug 24, 2005•0 citations
We have studied Superfluorescence (SF) under highly unfavorable conditions of rapid collisional and radiative distribution in a Doppler broadened medium. Nanosecond SF pulses at 5.5 {mu} were generated from a 50 cm column of calcium vapor buffered with argon by optically pumping the Ca (4s{sup 2} {sup 1}S{sub 0} - 4s4p{sup 1}P{sub 1} - 3d4s{sup 1}D{sub 2}) Raman Amplifier scheme. Power broadening due to an intense 13 nsec pump pulse precludes the evolution of SF for essentially this duration. As a result, the scaling laws which govern the properties of SF in a transversely excited system are shown to apply in our situation in which the conditions resemble swept excitation.
We have studied superfluorescence (SF) under highly unfavorable conditions of rapid collisional and radiative distribution in a Doppler-broadened medium. Nanosecond SF pulses at 5.5 \ensuremath{\mu}m were generated on the Ca 4s4p1P1−−3d4s1D24s4p{}^{1}{P}_{1}--3d4s{}^{1}{D}_{2}4s4p1P1​−−3d4s1D2​ transition from a column of calcium vapor buffered with Ar by optically pumping the 4s21S0−−4s4p1P1{4s}^{2}{}^{1}{S}_{0}--4s4p{}^{1}{P}_{1}4s21S0​−−4s4p1P1​ transition. The Rabi frequency associated with the intense pump pulse prevents the occurrence of SF while the pump laser is on. As a result, the predicted scaling laws that describe the properties of SF in a transversely excited system, such as peak heights, pulse widths, and delay times, are shown to apply in our situation in which the conditions resemble swept excitation. The delay times were found to be in agreement with a fully quantum mechanical calculation which describes the initiation of SF. Measurements of the densities of the three levels, the absolute SF photon yield, and the spatial distribution of the excited states indicate that the system has a quantum yield of unity. The SF intensity increases with an increase in Ar pressure due to collisional redistribution until the collisional dephasing rate inhibits SF. The conditions describing the transition of SF to amplified spontaneous emission allow us to measure the collisional broadening rate for the SF transition.
We have studied superfluorescence (SF) in Ca vapor evolving on the 3d4s ^3 D_J -4s4p ^3 P_J-1 transitions at 1.9 µm by exciting the 4s^21 S_0 -4s4p ^1 P_1 with a pulsed dye laser. SF is generated following population transfer by spin-changing collisions with an inert gas Ar from the 4s4p ^1 P_1 and 3d4s ^1 D_2 levels. We show for the first time to our knowledge that the time delay for SF evolution follows the 1/sqrt N dependence expected for the case of uniform excitation of the vapor column by collisional transfer. Here, N is the number of participating atoms that was measured directly from the photon yield. The measured photon yield for the signal as a function of Ar pressure was found to be consistent with rate equations that simulate the buildup of populations in the ^3 D_J levels based on known collisional rates. This suggests that collisional rates can be directly inferred on the basis of SF photon yields and the atomic level populations. The pulse shapes for SF show temporal oscillations that depend on two distinct factors. The first is the presence of a number of independently evolving regions in the gain medium, and the second is the presence of spatial modes. Temporal ringing is a well-known effect related to the exchange of energy between the atoms and the radiation field during pulse propagation. However, the temporal ringing observed in this experiment is far more pronounced than in previous SF experiments due to a particular choice of evolution parameters. This should make it feasible to compare our results with detailed numerical simulations that have been carried out previously.
We have studied effects of magnetic sublevel degeneracy on the polarization of superfluorescent pulses generated on the Ca 4s4p1P1−−3d4s1D24s4p{}^{1}{P}_{1}--3d4s{}^{1}{D}_{2}4s4p1P1​−−3d4s1D2​ transition at $5.5\ensuremath{\mu}\mathrm{m}.$ These pulses were generated from a cell of length 50 cm by optically pumping calcium vapor on the 4s21S0−−4s4p1P1{4s}^{2}{}^{1}{S}_{0}--4s4p{}^{1}{P}_{1}4s21S0​−−4s4p1P1​ transition in the presence of Ar gas. The axis of ellipticity of superfluorescence (SF) polarization is oriented parallel to the axis of the pump-laser polarization at large detunings, and undergoes an abrupt rotation through $90\ifmmode^\circ\else\textdegree\fi{}$ for detunings close to resonance. The distribution of populations in the magnetic sublevels of the 1P1{}^{1}{P}_{1}1P1​ state can be estimated using a simple model based on previously calculated cross sections for collisionally aided absorption in the presence of an intense (pump) field. For large detunings, these estimates are consistent with the polarized SF intensity measured in the experiment. A direct measurement of the populations of the 1P1{}^{1}{P}_{1}1P1​ magnetic sublevels also supports the collisional redistribution predicted by the calculated cross sections. We therefore suggest that SF polarization can be a useful signature of collisional redistribution. However, the change in ellipticity is unexpected, and probable causes for this effect are discussed.
Time-resolved nsec kinetic methods are used to measure state specific electronic excitation transfer for the near-resonant process: Ca(4s5p /sup 1/P/sub 1/) +Ar /sup k//sub 1/arrow-right-left/sub k//sub -/1 Ca(4s5p /sup 3/P/sub 2,1,0/)+Ar. In stimulated emission experiments it is found that the Ca(4s5p /sup 3/P/sub 2/) level is preferentially populated. The rate constant k/sub 1/ for the specific /sup 3/P/sub 2/ channel is 5.2 +- 0.5 x 10/sup -11/ cm/sup 3/ molecule/sup -1/ sec/sup -1/. These results are discussed in terms of near-resonant spin changing collision mechanisms. Radiative lifetimes for Ca(4s5p /sup 1/P/sub 1/) and Ca(4s5p /sup 3/P/sub 1/) are also determined to be 77 +- 2 nsec and 67 +- 2 nsec, respectively.