Observation of three-photon absorption and saturation of two-photon absorption in amorphous nanolayered Se/As2S3 thin film structures

Abstract

We have studied the nonlinear optical properties of nanolayered Se/ As 2 S 3 film with a modulation period of 10 nm and a total thickness of 1.15 m at two ͓1064 nm ͑8 ns͒ and 800 nm ͑20 ps͔͒ wavelengths using the standard Z-scan technique. Three-photon absorption was observed at off-resonant excitation and saturation of two-photon absorption at quasiresonant excitation. The observation of the saturation of two-photon absorption is because the pulse duration is shorter than the thermalization time of the photocreated carriers in their bands and three-photon absorption is due to high excitation irradiance. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2753581͔The nonlinear optical properties of glasses have recently become the focus of growing scientific and technological interest.1-3 Moreover, glasses have several advantages such as easy handling, easy fabrication of optical waveguides, excellent homogeneity, and low cost over inorganic crystals and organic materials. In particular, chalcogenide glasses have emerged as promising candidates due to their large optical nonlinearity and subpicosecond response time. Recently chalcogenide glasses were prepared in the form of high quality multilayers with nanomodulation and established the possibilities for tailoring the optical properties.4 These amorphous nanolayered chalcogenide structures ͑ANC͒ are similar to the crystalline superlattices, but it is difficult to imagine such structures as ideal crystalline superlattices produced by molecular beam epitaxy. But the ANCs can be considered as well correlated layers with good periodicity, smooth interface, and good surface roughness. Traditional spectroscopic studies such as optical absorption, photoluminescence, and x-ray photoelectron spectroscopy on ANCs indicate that these materials can be used in micro-and optoelectronics.4,5 However, there are not many reports about the nonlinear optical properties of the ANCs despite the considerable interests in photoinduced phenomena. 6 In this article we report the optical and nonlinear optical absorption of amorphous nanomultilayered Se/ As 2 S 3 film on a glass substrate prepared by the conventional thermal evaporation technique. The nonlinear optical absorption was measured at two ͓1064 nm ͑8 ns͒ and 800 nm ͑20 ps͔͒ wavelengths using the standard Z-scan technique. Nanolayered Se/ As 2 S 3 films were prepared by the cyclic thermal evaporation technique from bulk ͑powdered͒ Se and As 2 S 3 . Deposition rates were 2-10 nm/s in a vacuum of 5 ϫ 10 −4 Pa. Periodicity was monitored by the low angle x-ray diffraction method. The modulation period was kept at 10 nm ͑sublayer thickness of As 2 S 3 = 6 nm and Se= 4 nm͒ and the total thickness of the film was 1.15 m. We have used a Bruker Optics IFS 66v/s Fourier-transform infrared spectrometer to obtain the absorption spectrum in the wavelength range from 400 to 1200 nm. A standard Z-scan setup was used for the determination of nonlinear absorption. The experimental setup was the same as described by Sheik-Bahae et al. 7 The sa...

Terahertz emission from ZnGeP_2: phase-matching, intensity, and length scalability

“…With increasing intensity, the transmission for the thinner crystals increases nearly linearly, but for the thicker crystal strong sublinear behavior is observed. Solving equation (2) for a Gaussian pulse while accounting for reflectivity from both surfaces gives the transmittance [35,36] () ln…”

“…Solving equation ( 2) for a Gaussian pulse while accounting for reflectivity from both surfaces gives the transmittance [35,36] () ln…”