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Applied Physics Letters

Selective optical excitation and inversions via the excimer channel: Superradiance at the thallium green line

Santaram Chilukuri

Published Feb 15, 1979• 9 citations
Publisher

Abstract

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.

DOI
10.1063/1.90761

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Journal of Physics B Atomic and Molecular Physics•Dec 14, 1981•1 citation
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.
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
Stimulated emission of the 535 nm line of thallium was observed when a Tl-He mixture was pumped optically in the violet wing of a pressure-broadened resonance line of thallium at 377.6 nm by a recombination He–Ca laser emitting at λ = 373.7 nm. Pumping resulted from the absorption transitions between repulsive terms of the Tl-He quasimolecule. The average stimulated radiation power reached 5 mW when the pulse repetition frequency was 6 kHz. The efficiency of conversion of the useful part of the pump pulse was 45%.
Lasing on the D(1) transition (6P1/22-->6S1/22) of Cs has been observed by photoassociating Cs-Kr atomic pairs with a tunable, pulsed dye laser. Pumping of the blue or red satellites of the Cs D(2) line (62P3/2<==>62S1/2), peaking at approximately 841.1 nm and approximately 853 nm (respectively) in Cs/Kr/C(2)H(6) gas mixtures, provides a photodissociation laser in which the CsKr excimer parent molecule is not, at any point in the pumping process, in a bound electronic state. Relative to the absorbed pump pulse energy, laser slope efficiencies greater than or approximately 5% have been measured when the Cs number density is in the range of 5x10(14)-1.5x10(15) cm(-3) and the pump wavelength is 841.1 nm. Direct photoexcitation of the Cs 6P3/22 state at 852.1 nm under these conditions is a less efficient pathway for pumping the 894.3 nm laser, presumably as a result of competing nonlinear optical processes such as 1+2 resonantly enhanced multiphoton ionization of the alkali atom.
Photodissociation of TlBr and CsBr by the 1850-Å mercury resonance line could lead to laser transitions at 5350 Å and 2.93 μ in Tl and Cs, respectively. The transition probabilities of Cs are such that radiative decay will maintain a population inversion between the 72P3/2 and 72S½ levels. Calculations indicate that a gain of 4% per m is expected at a temperature of 890° for photodissociation into the 72P3/2, ½ Cs levels. In Tl, however, the 62P3/2 level is metastable. A suitable quenching gas must be found before oscillation is possible at 5350 Å from photodissociation into the 72S½ level. Nitrogen and CO2 have been tried thus far without success.
RbXe bands are observed using pulsed dye laser excitation of atomic alkali transitions in Rb/Xe mixtures containing 193 and 465 Torr xenon. Bands observed in absorption (A) or emission (E) at 427.0 nm (E), 497.8 nm (A), 501.8 nm (A, E), 509.0 nm (A, E), 520.0 nm (A, E) and 535.0 nm (E) are assigned to molecular potentials associated with the 6 2 P 1/2 atomic rubidium states for the first, 6 2 S 1/2 for the next two and 4 2 D 3/2,5/2 for the remaining three. The time evolution of the emission bands depends on the population mechanism of the parent atomic state which involves superradiant transitions from the pumped excited state. Monitoring of the corresponding infrared emission allows a control over the population mechanisms and an evaluation of the lifetimes, collisional quenching and reaction rates of the excimer and parent states. This in turn allows a determination of the atomic parent states of the bands observed.