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Journal of Applied Physics

Negative nonlinear absorption effects in erbium-yttrium aluminum garnets

Yoshinobu Maeda

Published Oct 15, 1992• 42 citations
Publisher

Abstract

Negative nonlinear absorption, which causes the transmission to decrease as the laser intensity increases, was observed in a 16 at. % Er:YAG crystal using a laser diode operating at 787 and 784 nm. This effect for 787 nm was strong because 787 nm was the center of an absorption peak that is related to the excited-state absorption from 4I13/2 to 2H11/2. It is suggested that these phenomena take place because the absorption cross section from 4I13/2 to 2H11/2 is larger than that from 4I15/2 to 4I9/2 using a double-absorption model.

DOI
10.1063/1.352286

Related papers

Temperature Dependence and Numerical Analysis of Negative Nonlinear Absorption Effect in Erbium-Yttrium Aluminum Garnet

Yoshinobu Maeda, Toshikazu Yamada, Shiho Imai +1 more

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.

Japanese Journal of Applied Physics•Jun 1, 1998•0 citations

Enhanced Absorption Phenomena in Negative Nonlinear Absorption Effects.

Yoshinobu Maeda, Seiichi IKEDA, Masatoshi Migitaka

A negative input-output characteristic was obtained in an erbium doped yttrium aluminum garnet crystal which has multiple-level energy structure: 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 distorted and eventually inverted against the incident one in case that the modulation degree was less than 0.5. It is suggested that an enhanced absorption phenomenon takes place since the excited state absorption from 4I13/2 to 2H11/2 and that a 4S3/2 level plays an important role. Because the time-dependence of this phenomenon matches a life time of the 4S3/2 level. By considering multiple excited state absorption in detail, active functions such as an optical signal inverter could be derived from the negative nonlinear absorption effect.

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A negative input-output characteristic was obtained in an erbium doped yttrium aluminum garnet crystal which has multiple-level energy structure: 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+. It was caused at the wavelength between 786.6 and 788.4nm by the variation of incident laser intensity in the intensity range of 60 nW/cm2 to 100 W/cm2. It is considered that an enhanced absorption occurs due to the excited state absorption from 4I13/2 to 2H11/2. Because its spectra match the wavelength dependence of the incident laser. In addition, optical signal inverter phenomenon was observed using a laser diode modulated with 10 MHz. By considering multiple excited state absorption in detail, active functions such as an optical signal inverter could be derived from the negative nonlinear absorption effect.

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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+.

Japanese Journal of Applied Physics•Aug 1, 1997•6 citations

Numerical Analysis and Dependence of Negative Nonlinear Absorption Effect on Modulation Degree of Incident Laser.

Yoshinobu Maeda, Takao Sakakibara, Masatoshi Migitaka

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 Review of Laser Engineering•Jan 1, 1997•0 citations
Negative nonlinear absorption, which causes the transmission to decrease as the laser intensity increases, was observed in a 16 at. % Er:YAG crystal using a laser diode operating at 787 and 784 nm. This effect for 787 nm was strong because 787 nm was the center of an absorption peak that is related to the excited-state absorption from 4I13/2 to 2H11/2. It is suggested that these phenomena take place because the absorption cross section from 4I13/2 to 2H11/2 is larger than that from 4I15/2 to 4I9/2 using a double-absorption model.
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.
A negative input-output characteristic was obtained in an erbium doped yttrium aluminum garnet crystal which has multiple-level energy structure: 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 distorted and eventually inverted against the incident one in case that the modulation degree was less than 0.5. It is suggested that an enhanced absorption phenomenon takes place since the excited state absorption from 4I13/2 to 2H11/2 and that a 4S3/2 level plays an important role. Because the time-dependence of this phenomenon matches a life time of the 4S3/2 level. By considering multiple excited state absorption in detail, active functions such as an optical signal inverter could be derived from the negative nonlinear absorption effect.
A negative input-output characteristic was obtained in an erbium doped yttrium aluminum garnet crystal which has multiple-level energy structure: 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+. It was caused at the wavelength between 786.6 and 788.4nm by the variation of incident laser intensity in the intensity range of 60 nW/cm2 to 100 W/cm2. It is considered that an enhanced absorption occurs due to the excited state absorption from 4I13/2 to 2H11/2. Because its spectra match the wavelength dependence of the incident laser. In addition, optical signal inverter phenomenon was observed using a laser diode modulated with 10 MHz. By considering multiple excited state absorption in detail, active functions such as an optical signal inverter could be derived from the negative nonlinear absorption effect.
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+.
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.