Journal of Applied Physics

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

Yoshinobu Maeda

Published Feb 1, 1998• 24 citations

Abstract

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.

DOI: 10.1063/1.366814

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