Two-photon absorption in layered TlGaSe2, TlInS2, TlGaS2 and GaSe crystals

We measured two-photon absorption (TPA) coefficients for layered chalcogenide crystals TlGaSe2, TlInS2, TlGaS2 and GaSe. The measurements were performed at room temperature using single-wavelength excitation by an YAG:Nd laser at lambda = 1.06 mu m and pulse duration of 35 ps. The absorption coefficients for direct interband transitions for TlGaSe2, TlInS2 and GaSe were measured by the non-linear transmittance method. For TlGaS2, the TPA coefficient for indirect transitions was determined. TPA coefficients were found to be beta = (9.5 +/- 0.5) x 10(-9) cm/W for TlGaSe2, beta = (9.4 +/- 1.5) x 10(-9) cm/W for TlInS2, beta = (6.5 +/- 0.7) x 10(-8) cm/W for TlGaS2 and beta = (6.3 +/- 2.2) x 10(-9) cm/W for GaSe. The measured value of the TPA coefficient for GaSe was compared with the existing experimental and theoretical values. (C) 1999 Elsevier Science Ltd. All rights reserved.