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Modern Physics Letters B

OPTICAL EXTENSION OF DICKE'S SUPERRADIANCE: A CASE STUDY OF THALLIUM IN THALLIUM MERCURY SYSTEM

Shubhada Adhi

Published Apr 30, 2001• 0 citations
Publisher

Abstract

A detailed study of superradiance at the Thallium green line (λ=535.0 nm ) in Thallium–Mercury (Tl–Hg) system is reported. High peak power of 1 kW delivered in short pulse duration of 4 nsec (FWHM) has been obtained. Attempts have also been made experimentally to determine the various time constants viz. inhomogeneous dephasing time, decay time, characteristic time, delay time etc. along with their inequality relations for the Tl–Hg system. The experimental results of superradiance in Tl are compared with those predicted theoretically by M. S. Feld et al.2

DOI
10.1142/s0217984901001756

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The transfer of excitation from excited mercury atoms to ground-state thallium atoms was investigated using techniques of sensitized fluorescence. A Hg–Tl vapor mixture contained in a quartz cell was irradiated with Hg 2537 Å resonance radiation which caused the mercury atoms to become excited to the 63P1, state. Subsequent collisions between the Hg(63P1) and Tl(62P1/2) atoms resulted in the population of the 82S1/2, 62D, and 72S1/2 thallium states, whose decay gave rise to sensitized fluorescence of wavelengths 3231, 3520, 3776, and 5352 Å. Intensity measurements on the sensitized fluorescence and on the Hg 2537 Å resonance fluorescence, observed at right angles to the direction of excitation, yielded cross sections of 3.0, 0.3, and 0.05 Å2 for collisional excitation transfer from Hg(63P1) to the 82S1/2, 62D, and 72S1/2 states in thallium, respectively. The results are fully consistent with previously determined cross sections for excitation transfer in other binary metallic vapor systems.

Canadian Journal of Physics•Jul 1, 1978•10 citations
A detailed study of superradiance at the Thallium green line (λ=535.0 nm ) in Thallium–Mercury (Tl–Hg) system is reported. High peak power of 1 kW delivered in short pulse duration of 4 nsec (FWHM) has been obtained. Attempts have also been made experimentally to determine the various time constants viz. inhomogeneous dephasing time, decay time, characteristic time, delay time etc. along with their inequality relations for the Tl–Hg system. The experimental results of superradiance in Tl are compared with those predicted theoretically by M. S. Feld et al.2
Inversion and superradiance at the Tl green line (5351 Å) has been observed using Tl-Hg and Tl-Cd-Ar systems pumped optically via the excimer channel with a pulsed nitrogen dye laser. Superradiant power outputs up to 200 W averaged over the pulse (without any mirrors) have been obtained with a 90-cm-long Tl-Hg tube. The general applicability of this method to other excimer systems should provide a means of generating coherent radiation at new wavelengths and in understanding collision processes.
ABSTRACT We have applied the concept of superradiance introduced by Dicke in 1954 to astrophysics by extending the corresponding analysis to the magnetic dipole interaction characterizing the atomic hydrogen 21 cm line. Although it is unlikely that superradiance could take place in thermally relaxed regions and that the lack of observational evidence of masers for this transition reduces the probability of detecting superradiance, in situations where the conditions necessary for superradiance are met (close atomic spacing, high velocity coherence, population inversion, and long dephasing timescales compared to those related to coherent behavior), our results suggest that relatively low levels of population inversion over short astronomical length-scales (e.g., as compared to those required for maser amplification) can lead to the cooperative behavior required for superradiance in the interstellar medium. Given the results of our analysis, we expect the observational properties of 21 cm superradiance to be characterized by the emission of high-intensity, spatially compact, burst-like features potentially taking place over short periods ranging from minutes to days.
The problem of superradiant emission from a small atomic system is treated under conditions in which the effects of inhomogeneous broadening are important, as in a solid. The treatment is semiclassical, with the assumption that all atoms see the same electromagnetic field. A set of coupled integrodifferential equations is obtained characterizing the state of each atom of resonant frequency \ensuremath{\omega} at time ttt. It is found that, in general, atoms of different frequencies evolve differently in time, whether or not they start from the same initial state. The effect of the inhomogeneous broadening is generally to delay the onset and to reduce the amplitude of the superradiant pulse. Some effects of inhomogeneous broadening are manifest even when the inhomogeneous lifetime is much longer than the usual superradiance time. When the atomic system starts in the ground state and is then exposed to a coherent excitation pulse, superradiant effects can appear even when the inhomogeneous lifetime is very short compared with the usual superradiance time.
Recently, Jaroszynski and King found superradiance(SR) occurring in photodissociatively created systems using NaI and n-C3F7I moleculesl) , and Hahn and Lee have performe2)d the amplified spontaneous emission(ASE) experiment in an iodine photodissociation laser(IPL) amplifier . In general, to observe SR experimentally, a very short intense pumping pulse of which FWHM is about a few tens of nanoseconds, is used for making a totally inverted system. But in this work, the amplifier is pumped with conventional flashlamps of FWHM=3us, yet we have detected a output pulse which is a superposition of ASE and SR. The temporal behaviour of the pulse is investigated in detail, and the experimental results are compared with theoretical results.
The transfer of excitation from excited mercury atoms to ground-state thallium atoms was investigated using techniques of sensitized fluorescence. A Hg–Tl vapor mixture contained in a quartz cell was irradiated with Hg 2537 Å resonance radiation which caused the mercury atoms to become excited to the 63P1, state. Subsequent collisions between the Hg(63P1) and Tl(62P1/2) atoms resulted in the population of the 82S1/2, 62D, and 72S1/2 thallium states, whose decay gave rise to sensitized fluorescence of wavelengths 3231, 3520, 3776, and 5352 Å. Intensity measurements on the sensitized fluorescence and on the Hg 2537 Å resonance fluorescence, observed at right angles to the direction of excitation, yielded cross sections of 3.0, 0.3, and 0.05 Å2 for collisional excitation transfer from Hg(63P1) to the 82S1/2, 62D, and 72S1/2 states in thallium, respectively. The results are fully consistent with previously determined cross sections for excitation transfer in other binary metallic vapor systems.