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Applied Physics Letters

Enhanced absorption by stimulated emission in three excited states of Er3+ in yttrium aluminum garnet

Yoshinobu Maeda, Masatoshi Migitaka

Published Jan 6, 1997• 31 citations
Publisher

Abstract

Using a laser diode modulated at 250 and 500 MHz, dependence of enhanced absorption on both sample length and temperature was investigated in an erbium doped yttrium aluminum garnet crystal. The transmitted laser intensity decreased with a decay time of 300 ps for sample lengths greater than 3.0 mm and temperatures higher than 50 K when the incident laser intensity increased. In addition, an emission peak was observed near 835 nm corresponding to the transition from the S3/24 level to the I13/24 in Er3+. It was suggested that the enhanced absorption was caused by stimulated emission in three excited states.

DOI
10.1063/1.119302

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Modulation Characteristics of the Negative Nonlinear Absorption Effect in Erbium-Yttrium Aluminum Garnet

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Dependence of the negative nonlinear absorption effect on both modulation degree and frequency was investigated in erbium yttrium aluminum garnet crystals. For a modulation frequency of 1 MHz, two peaks, A and B, were observed in the transmitted waveform. With a decreasing modulation degree, peak C which consists of peaks A and B appeared and a reversed-phase waveform was obtained in the transmitted waveform. Peak A decreased as the modulation frequency increased, and peak B was only observed for modulation frequencies above 50 MHz. In the case of a modulation degree under 35%, the transmitted waveform changed to the opposite phase of incident one for modulation frequencies up to 100 MHz. In addition, the negative nonlinear absorption effect was dependent on the product of the composition of erbium and the sample length. It was suggested that the enhanced absorption was due to stimulated emission in three excited states of Er3+.

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Mechanism of the negative nonlinear absorption effect in a five-level system of the Er3+ ion

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The dependence of the negative nonlinear absorption effect on the modulation degree and frequency, the sample temperature, and the erbium concentration was investigated in erbium yttrium aluminum garnet crystals. With a decreasing modulation degree, a reverse-phased wave form was obtained in the transmitted wave form at modulation frequency lower than 1 MHz. However, the transmitted laser wave form was asymmetrical at higher than 5 MHz and the time-dependent characteristics agreed with the lifetime of the S3/24 level in Er3+. At temperatures lower than 77 K, the negative nonlinear absorption effect weakened because the number of phonons decreased due to low temperature. It is considered that the Er3+ concentration dependence for modulation frequency depends on the lifetime of the S3/24 level. It has been confirmed that a mechanism of negative nonlinear absorption can be explained by calculating the rate equations based on an analytical model for a five-level system of the Er3+ ion. Experimental results agreed well with the calculated values. It is suggested that the effect was due to stimulated emission from the S3/24 level to the I3/24 level.

Journal of Applied Physics•Feb 1, 1998•24 citations
Using a laser diode modulated at 250 and 500 MHz, dependence of enhanced absorption on both sample length and temperature was investigated in an erbium doped yttrium aluminum garnet crystal. The transmitted laser intensity decreased with a decay time of 300 ps for sample lengths greater than 3.0 mm and temperatures higher than 50 K when the incident laser intensity increased. In addition, an emission peak was observed near 835 nm corresponding to the transition from the S3/24 level to the I13/24 in Er3+. It was suggested that the enhanced absorption was caused by stimulated emission in three excited states.
Dependence of the negative nonlinear absorption effect on both modulation degree and frequency was investigated in erbium yttrium aluminum garnet crystals. For a modulation frequency of 1 MHz, two peaks, A and B, were observed in the transmitted waveform. With a decreasing modulation degree, peak C which consists of peaks A and B appeared and a reversed-phase waveform was obtained in the transmitted waveform. Peak A decreased as the modulation frequency increased, and peak B was only observed for modulation frequencies above 50 MHz. In the case of a modulation degree under 35%, the transmitted waveform changed to the opposite phase of incident one for modulation frequencies up to 100 MHz. In addition, the negative nonlinear absorption effect was dependent on the product of the composition of erbium and the sample length. It was suggested that the enhanced absorption was due to stimulated emission in three excited states of Er3+.
Temperature dependence of an enhanced excited state absorption was investigated in erbium-doped garnet crystals using 787.3 and 787.8 nm laser diodes. The enhanced absorption was obtained at temperature ranges of 15–570 K, 15–420 K, and 15–1200 K in a yttrium aluminum garnet, a yttrium scandium gallium garnet, and a lutetium aluminum garnet, respectively. Absorption peaks corresponding to both the I1615/2−I49/2 and the I1613/2−I211/2 transitions of Er3+ in garnets were shifted from those for 300 K at high temperature. The enhanced absorption weakened at high temperature because an absorption cross section from the I413/2 level to the H211/2 level decreased due to the shift of the absorption peaks. It has been confirmed that a mechanism of the enhanced absorption can be explained by calculating the rate equations based on an analytical model for a five-level system of the Er3+ ion. It is suggested that the enhanced absorption weakened at temperatures lower than 12 K because the number of phonons decreased due to low temperature.
Dependence of the negative nonlinear absorption effect on both modulation frequency and sample temperature was investigated in an erbium yttrium aluminum garnet crystal. The phase of transmitted laser was opposite to that of the incident laser at modulation frequencies lower than 1 MHz. However, the transmitted laser waveform was asymmetrical above 5 MHz and the time-dependence characteristics agreed with the lifetime of the 4S3/2 level in Er3+. At temperatures lower than 25 K, enhanced absorption was weakened because the number of phonons decreased due to low temperature. It is suggested that the negative nonlinear absorption effect occurred due to enhanced absorption in three excited states. © 1998 Scripta Technica. Electron Comm Jpn Pt 2, 80(6): 43–48, 1997
The temperature dependence of the negative nonlinear absorption (NNA) effect was investigated in an erbium-doped yttrium aluminum garnet (YAG) crystal using a 787.3 nm laser diode. The NNA effect was obtained in a temperature range of 15 to 400 K. An absorption peak corresponding to both the 4 I 15/2-4 I 9/2 and 4 I 13/2-2 H 11/2 transitions of Er3+ in the YAG at 400 K was displaced from that at 300 K. It is considered that the NNA effect weakened at high temperature because the absorption cross section decreased due to the shift of the absorption peak. In addition, the dependence of the NNA effect on the modulation degree was investigated. The characteristic of the increase in the incident laser intensity was almost the same as that for the decrease. It was confirmed that the mechanism of the NNA effect can be explained by calculating the rate equations based on an analytical model for a five-level system of the Er3+ ion. It is suggested that the NNA effect weakened at the low temperature because the number of phonons decreased due to the low temperature.
The dependence of the negative nonlinear absorption effect on modulation degree of an incident laser was investigated in an erbium doped yttrium aluminum garnet crystal which has a five-level system: absorption can occur between a ground level and an excited level (4I15/2-4I9/2) and between two other excited levels (4I13/2-2H11/2) in Er3+. According as modulation degrees of the incident laser decreased, the transmitted laser waveform was inverted against the incident one for incident modulation degree under 90% and sample lengths greater than 2mm. By calculating rate equations based on an analytical model for the five-level system, it was confirmed that the enhanced absorption was caused by stimulated emission from 4S3/2 level to 4I13/2 level and close agreement between observed and calculated values was obtained in the relation between transmitted modulation degree and incident one.
The dependence of the negative nonlinear absorption effect on the modulation degree and frequency, the sample temperature, and the erbium concentration was investigated in erbium yttrium aluminum garnet crystals. With a decreasing modulation degree, a reverse-phased wave form was obtained in the transmitted wave form at modulation frequency lower than 1 MHz. However, the transmitted laser wave form was asymmetrical at higher than 5 MHz and the time-dependent characteristics agreed with the lifetime of the S3/24 level in Er3+. At temperatures lower than 77 K, the negative nonlinear absorption effect weakened because the number of phonons decreased due to low temperature. It is considered that the Er3+ concentration dependence for modulation frequency depends on the lifetime of the S3/24 level. It has been confirmed that a mechanism of negative nonlinear absorption can be explained by calculating the rate equations based on an analytical model for a five-level system of the Er3+ ion. Experimental results agreed well with the calculated values. It is suggested that the effect was due to stimulated emission from the S3/24 level to the I3/24 level.