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Applied Physics Letters

Picosecond excite-and-probe absorption measurement of the 4T2 state nonradiative lifetime in ruby

Swapan Kumar Gayen, W. -B. Wang, Vladimir Petricevic, R. Dorsinville, R. R. Alfano

Published Sep 1, 1985• 24 citations
Publisher

Abstract

In a picosecond excite-and-probe absorption measurement, a 527-nm picosecond pulse excites the 4T2 state of the Cr3+ ion in ruby and a 3.4-μm picosecond probe pulse monitors the growth and decay of population in the 2E state as a function of pump-probe delay. From the growth of population in the metastable 2E state, an upper limit of 7 ps for the nonradiative lifetime of the 4T2 state is determined.

DOI
10.1063/1.96145

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Techniques for the measurement of non-radiative decay rates between the optically excited states in solid-state laser materials are described. Two crystals have been investigated, ruby (Cr3+:Al2O3) and Sm2+:CaF2. A review of the spectroscopy of these materials is presented with particular emphasis on aspects relevant to non-radiative decay. An experiment is described using a second harmonic Nd3+ Nd:glass Q-switched laser to pump ruby crystals. Limiting non-radiative relaxation times were derived from the rise of fluorescence. Rubies varying in concentration between 0.05% and 0.4% were studied over a range of temperatures, 77 -> 7000 K. 4T2 -> 2E(E + 2A), 4T2 -> 2T1 (Eb) and 4T2 -> 2T1 (2A + Ea) non-radiative relaxations were all found to be <4ns in good agreement with the experimental results of other workers. Two experiments employing a ruby laser to pump Sm2+ :CaF2 are described. The first used a Q-switched laser and, apart from some improvements was similar to the ruby experiment. An upper limit of 4f5 5d pump -> metastable non-radiative decay of 2ns was found for Sm2+:CaF2, The fluorescence decay constant at 295 K was also measured to be 63ns. The second experiment employed a mode-locked laser and the Sm2+:CaF2 non-radiative decay time was <0.5ns. A new effect - provisionally called 'surface emission' - discovered during the ruby measurements, has been examined in detail and the results of this investigation are presented. A phase-shift technique for the measurement of non-radiative decay times is examined in detail. A pilot experiment using a self-mode-locked He-Ne laser at 633 nm to pump Sm2+:CaF2 is described. The non-radiative relaxation time found by this method was <33ps. Suggestions for improved experiments, both pulsed and phase-shifts, are made and the application of the techniques to other materials is discussed.

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Transient excited-state absorption measurements in chromium-doped forsterite

Nickolay Zhavoronkov, Valentin P. Petrov, FRANK NOACK

The nonradiative transition dynamics between the excited ${}^{3}{A}^{\ensuremath{''}}{[}^{3}{E(}^{3}{T}_{1a})]$ state and the metastable ${}^{3}{A}^{\ensuremath{''}}{[}^{3}{E(}^{3}{T}_{2})]$ storage state of the tetravalent chromium ion $({\mathrm{Cr}}^{4+})$ in forsterite is investigated using femtosecond excite-and-probe technique. Following excitation to ${}^{3}{T}_{1a}$ with pump pulses at 750 or 773 nm the induced excited state absorption was probed with femtosecond pulses in the ultraviolet (306 nm), visible (650 nm), and infrared (1500 nm). The nonradiative decay time from ${}^{3}{T}_{1a}$ to ${}^{3}{T}_{2}$ was estimated from the rise time of the excited state absorption at 1500 nm using a rate equations model and its value at room temperature is only 3\ifmmode\pm\else\textpm\fi{}1 ps.

Physical review. B, Condensed matter•Jan 15, 2000•3 citations
In a picosecond excite-and-probe absorption measurement, a 527-nm picosecond pulse excites the 4T2 state of the Cr3+ ion in ruby and a 3.4-μm picosecond probe pulse monitors the growth and decay of population in the 2E state as a function of pump-probe delay. From the growth of population in the metastable 2E state, an upper limit of 7 ps for the nonradiative lifetime of the 4T2 state is determined.
Techniques for the measurement of non-radiative decay rates between the optically excited states in solid-state laser materials are described. Two crystals have been investigated, ruby (Cr3+:Al2O3) and Sm2+:CaF2. A review of the spectroscopy of these materials is presented with particular emphasis on aspects relevant to non-radiative decay. An experiment is described using a second harmonic Nd3+ Nd:glass Q-switched laser to pump ruby crystals. Limiting non-radiative relaxation times were derived from the rise of fluorescence. Rubies varying in concentration between 0.05% and 0.4% were studied over a range of temperatures, 77 -> 7000 K. 4T2 -> 2E(E + 2A), 4T2 -> 2T1 (Eb) and 4T2 -> 2T1 (2A + Ea) non-radiative relaxations were all found to be <4ns in good agreement with the experimental results of other workers. Two experiments employing a ruby laser to pump Sm2+ :CaF2 are described. The first used a Q-switched laser and, apart from some improvements was similar to the ruby experiment. An upper limit of 4f5 5d pump -> metastable non-radiative decay of 2ns was found for Sm2+:CaF2, The fluorescence decay constant at 295 K was also measured to be 63ns. The second experiment employed a mode-locked laser and the Sm2+:CaF2 non-radiative decay time was <0.5ns. A new effect - provisionally called 'surface emission' - discovered during the ruby measurements, has been examined in detail and the results of this investigation are presented. A phase-shift technique for the measurement of non-radiative decay times is examined in detail. A pilot experiment using a self-mode-locked He-Ne laser at 633 nm to pump Sm2+:CaF2 is described. The non-radiative relaxation time found by this method was <33ps. Suggestions for improved experiments, both pulsed and phase-shifts, are made and the application of the techniques to other materials is discussed.
The gain dynamics of photoexcited chromium-doped forsterite (Cr4+:Mg2SiO4) were measured by means of a pulsed excite-and-probe technique. The nonradiative relaxation time within the 3T2 vibronic state was determined by measuring the change in the induced gain of the probe pulse as a function of the pumpprobe delay. A 30 ps, 1.064 m pulse from a mode-locked Nd:YAG laser was split into two beams. The first beam provided the pump pulse to populate the 3T2 manifold. The other beam was focused in a calcite crystal to generate a 1.2 m probe pulse by means of stimulated Raman scattering. The transient gain was determined from the measured ratio of the transmitted probe intensity for unpumped and pumped cases as a function of the pumpprobe delay. The rise time (time for growth of the gain from 10% to 90%) was calculated to be 50 ps. A rate-equation analysis of population in the various states was used to extract a value for the vibrational relaxation time from the experimental data under the assumption of Gaussian pump and probe pulses. The best fit to the experimental data of gain as a function of time yields a value of 10 5 ps for the intra-3T2-state vibrational relaxation time.
Depopulation of ground-state Cr ions in ruby (DGS) under optical pumping with a Xe flash light has been measured as a function of time. Experiments have been made by means of measuring the decrease in absorbing power for a probe light (5790 Å or 5461 Å) from a Hg lamp. DGS reaches its maximum value after some delay from the peak of Xe light, and decreases after discontinuation of optical pumping with a time constant of 3.4 ms, which is the lifetime of metastable-state 2E. During laser oscillation mean value of DGS is forced to take a constant value, which varies with the condition of laser oscillation. So long as the input energy to the Xe lamp is not altered, the shorter the duration of Xe flash light is, the higher becomes the maximum value of DGS. On the basis of the rate equation, these experimental results have been explained.
The nonradiative transition dynamics between the excited ${}^{3}{A}^{\ensuremath{''}}{[}^{3}{E(}^{3}{T}_{1a})]$ state and the metastable ${}^{3}{A}^{\ensuremath{''}}{[}^{3}{E(}^{3}{T}_{2})]$ storage state of the tetravalent chromium ion (Cr4+)({\mathrm{Cr}}^{4+})(Cr4+) in forsterite is investigated using femtosecond excite-and-probe technique. Following excitation to 3T1a{}^{3}{T}_{1a}3T1a​ with pump pulses at 750 or 773 nm the induced excited state absorption was probed with femtosecond pulses in the ultraviolet (306 nm), visible (650 nm), and infrared (1500 nm). The nonradiative decay time from 3T1a{}^{3}{T}_{1a}3T1a​ to 3T2{}^{3}{T}_{2}3T2​ was estimated from the rise time of the excited state absorption at 1500 nm using a rate equations model and its value at room temperature is only 3\ifmmode\pm\else\textpm\fi{}1 ps.