Nonlinear Negative Absorption of Light in an Inhomogeneously Inverted Semiconductor

Toshikazu Yamada, Kazuhiko Tokoro, Yoshinobu Maeda

Nikolai G. Basov, Oleg N Krokhin, J. M. Popov

Yoshinobu Maeda, Seiichi Ikeda, Masatoshi Migitaka

There has been considerable interest in all-optical devices for achieving the high-speed and parallel processing. Up to the present the amount of absorption in any absorption process has been considered to be proportional to the incident light intensity until in some cases saturation occurs [1]. Recently we observed experimentally negative nonlinear absorption (NNA) phenomena which cause transmission to decrease as the laser intensity increase and confirmed that the transmitted laser intensity with the variation of incident laser showed negative nonlinear (i. e. Maeda's effect) [2, 3]. In this report we demonstrate that the net quantity of light absorbed in an erbium doped yttrium aluminum garnet crystal can be a negative function of the incident laser intensity. The absorbing material has a four-level energy structure: absorption can occur between a ground level and an excited level and between two other excited levels. The input-output characteristic has a negative region due to the absorption between excited states.

Sergei E. Esipov

P. P. Kircheva, S. D. Simeonov

Yoshinobu Maeda, Seiichi Ikeda Seiichi Ikeda, Masatoshi Migitaka

Using a modulated laser diode, dependence of a negative nonlinear absorption effect on both the wavelength and the sample length was observed in an erbium doped yttrium aluminum garnet crystal which has a four-level energy structure. The effect was seen at wavelengths of 787.4 to 788.6 nm in excited state absorption spectra which showed a peak corresponding to the transition from 4 I 13/2 to 2 H 11/2 in Er3+ for sample lengths greater than 2.0 mm. An optical signal inverter which had a negative input-output characteristic was realized using the negative nonlinear absorption effect.