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IEEE Journal of Quantum Electronics

Amplification cross section of the 1.052-µ transition of Nd3+in POCl3- SnCl4-(H2O) system by three different methods

F. Collier, G. Girard, M. Michon, Jean-Paul Pocholle

Published Nov 1, 1971• 4 citations
Publisher

Abstract

We report the measurement of the amplification cross section σ21of the Nd3+ion in the POCl3-SnCl4-(H2O) system by three different methods. The first is based on the simultaneous measurement of the variation of fluorescence andQ-spoiled laser emission. The second is purely spectroscopic. The third is based on the measurement of k12at several temperatures. The two last methods give similar results. The most probable value is\sigma_{21} = 8.5 \times 10^{-20}cm2. An explanation for the lowest value\sim 6 \times 10^{-20}cm2found with the first method is given.

DOI
10.1109/jqe.1971.1076567

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Journal of the Optical Society of America B•Mar 16, 2012•4 citations
We report the measurement of the amplification cross section σ21of the Nd3+ion in the POCl3-SnCl4-(H2O) system by three different methods. The first is based on the simultaneous measurement of the variation of fluorescence andQ-spoiled laser emission. The second is purely spectroscopic. The third is based on the measurement of k12at several temperatures. The two last methods give similar results. The most probable value is\sigma_{21} = 8.5 \times 10^{-20}cm2. An explanation for the lowest value\sim 6 \times 10^{-20}cm2found with the first method is given.
The population kinetics of laser levels of neodymium ions in the uranium-containing POCl 3 —SnCl 4 — 235 UO 2 2+ —Nd 3+ laser liquid irradiated in a BARS-6 pulsed reactor is studied experimentally and theoretically. The relations between the populations of the upper and lower laser levels are studied at different time moments with respect to the pump pulse. An inverse population of laser levels is observed and found to be directly proportional to the pump power. The efficiency of pumping of the upper laser level of neodymium ions in the laser medium by uranium fission fragments is determined, and quantitative information is obtained on the inverse population, gain, and their dependences on the pump power.
An experimental method was developed for the determination of the rate of relaxation of the 4I11/2 state and of the absorption cross section of the 4I11/2–4F3/2 transition. These parameters were deduced from the dependences of the intensity of the λ = 0.88 μ luminescence, excited as a result of the 4I11/2–4F3/2 transition by laser pulses of λ = 1.06 μ wavelength, on the energy density and duration of the laser pulses. Estimates of the relaxation time obtained for the investigated silicate (GLS-1) and phosphate (LGS-40, LGS-I) glasses, and also for a liquid based on POCl3-SnCl4, gave τ21 < 2 nsec. A considerable increase in the population of the 4I11/2 level occurred as a result of the Raman scattering of high-power coherent radiation by vibrations of the PO4 group.
In a study of the mechanism of giant pulse amplification in Nd3+doped glass, the following measurements have been made: 1) energy extracted from an amplifier as a function of the input energy, 2) relative fluorescence intensity at 0.9μ in a slab, pumped by the emission of a ruby laser, and 3) gain variation after the transit of an intense, short, rectangular pulse. The experimental results have been compared to theoretical results from a model where both metastable and terminal levels are regarded as comprising two components. The unknown multiplicity of the lower component of the terminal level g11appears as a parameter. It is assumed that during the pulse duration, Boltzmann distribution is maintained between the components of each level. A finite terminal level lifetime τnmay be introduced in the model. Best agreement is obtained with the following values of the parameters: amplification cross section\sigma_{21}\simeq 1.8.10^{-20}cm2,g_{11} = 1or 2, and\tau_{11} \geq 100ns.
This paper reports measurements of the room-temperature laser transition cross section of Nd+3{\mathrm{Nd}}^{+3}Nd+3 in yttrium aluminum garnet at 1.06 \ensuremath{\mu}. One method used is based on the measured upper-state lifetime and a determination of the fluorescence branching ratio for this state. The value thus determined is 3.5\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}19}$ cm2{\mathrm{cm}}^{2}cm2. The second method involves measurement of the ratio of fluorescent intensities from the upper laser level to the ground state and to the lower laser level, and measurement of the cross section in absorption of the transition which involves the ground state. The second method yields a value of 2.7\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}19}$ cm2{\mathrm{cm}}^{2}cm2. The difference represents the contribution of fluorescence to high-lying levels (not included in the determination of branching ratio) and nonradiative transitions. The probable experimental accuracy in both methods is \ifmmode\pm\else\textpm\fi{}15%.
Laser-induced photoionization and fluorescence signals were simultaneously observed in atomic uranium using a single Nd:YAG-pumped dye laser. These signals were recorded in two specific cases. In the first case, the dye laser was resonant to the first-step transition (0–16900.38 cm−1). In the second case, the laser was near-resonant to the first-step transition with a slight detuning (0.15 cm−1) so that it became two-photon resonant at 33801.06 cm−1. The uranium atoms in the ground state were ionized by a single-color, three-photon photoionization technique resulting in the photoionization signal, and the fluorescence signal was simultaneously obtained from the first excited state involved in the photoionization process. The photoionization and the fluorescence signals in the above-mentioned cases were also estimated theoretically for several values of the photoionization cross section for the transition between the second excited state at 33801.06 cm−1 and the autoionization state at 50701.59 cm−1 using density matrix formalism. From the comparison of theoretically calculated ratios of fluorescence signals in the two specific cases with the experimentally obtained values, the photoionization cross section for the 33801.06–50701.59 cm−1 transition has been obtained, which is found to be (5±1)×10−16 cm2.