Arun Gaur

Concentration-dependent optical gain characteristics of Coumarin 485, Coumarin 440 and Rhodamine B

Abstract The dye-concentration dependent gain spectra for Rhodamine B (Rh B), Coumarin 485 (C 485) and Coumarin 440 (C 440) in ethanol have been studied by the technique of amplified spontaneous emission (ASE) under N2 laser (337.1 nm) excitation in the concentration range 1 X 10-5 to 1 X 10-2 M. The dependence of the lasing wavelength and peak gain on concentration have been understood in terms of the variation of fluorescence lifetime, which is due to photophysical processes such as radiation trapping and concentration quenching. A comparison of the dynamics of the internal degrees of freedom in C 485 and C 440 has also been made on the basis of different functional groups at different positions of the basic Coumarin.

Multiphoton photoconductivity in an indirect band gap crystal: CdI2

Abstract The photoconducting properties of CdI2, an indirect band gap crystal, have been studied using fundamental and frequency doubled Nd : YAG laser. The ration of three and two photon absorption cross sections ( v 3 v 2 ) has been calculated with the help of experimental results. The value of two photon absorption cross section v2 has been calculated by using third order time dependent perturbation theory and that of v3 has been estimated by making use of the experimental results. Low values of the absorption cross sections obtained in the present case have been attributed to phonon assisted transitions.

Photoquenching in laser grade dyes: Part I

Abstract Optical gain measurements have been made in Rhodamine-B (Rh-B) and Coumarin-495 (C-495) ethanolic solutions at different wavelengths, pump intensities, concentrations and cell length using the amplified spontaneous emission (ASE) technique. A comparison of the experimental results with the theoretical predictions indicates that photoquenching dominates in the case of C-495, while some other processes like dimer formation, intersystem crossing or two-photon excitation may be dominating in the case of Rh-B.

Multiphoton photoconductivity and optical nonlinearities in ZnSe and CdSe direct band gap crystals

The multiphoton photoconductivity properties of ZnSe and CdSe direct band gap crystals have been studied using frequency-doubled Nd:YAG laser excitation. Two-photon absorption in both crystals has been observed. The photoconductivity measurements and nonlinearity in Z-scan traces confirms the existence of a lower valence band, from where one-photon transitions are forbidden but two-photon transitions are allowed. The value of the two-photon absorption cross section γ2 in both crystals has been calculated by using second-order time-dependent perturbation theory.

Preparation of Zinc-Doped CdSe Nanoparticles and Determination of Their Nonlinear Optical Properties using Z-Scan Technique in Thick Media

The present work aims at the synthesis of Zinc-doped CdSe(Zn:CdSe) nanoparticles with average size near the Bohr radius by wet chemical method. The synthesized nanoparticles have been characterized by X-ray diffraction (XRD), UV-Vis spectrometer is used for the determination of bandgap and crystallite size is estimated using Debye–Scherrer formula and Brus equation. The nonlinear optical property that is excitonic nonlinear absorption and the wavelength dependence of nonlinear absorption has also been measured near the excitonic transitions involving the lowest electron state (1S) and one of the hole states 1S3/2(h). We observe the saturable absorption (SA), which can be described by a third-order and a fifth-order nonlinear process for Zn:CdSe nanocrystals. The irradiance and wavelength dependence of the excitonic nonlinearity are explained by two-level model. The calculations have been performed with the help of Z-scan experimental setup using Handy Compact Q-switched pulsed Nd:YAG laser (HYL-101 Quanta System).

Pulsed laser induced photoconductivity in II–VI crystal : ZnSe

Abstract The photoconductivity properties of ZnSe crystal have been studied using Nd: YAG and N 2 -laser excitation. The charge vs intensity characteristics (Q vs I) at low photon densities indicate non-linear behaviour in both the cases. Very low values of the electron mobility at small applied voltage and low photon density with a phenomenal increase with field have been detected.

PHOTOEXCITED CARRIER LIFETIME IN DIRECT AND INDIRECT BAND GAP CRYSTALS ON THE Z-SCAN TECHNIQUE AT 532 nm

The photoexcited carrier lifetime in ZnSe and CdSe (direct band gap crystals) and CdI2 and PbI2 (indirect band gap crystals) has been investigated by the use of a single beam Z-scan technique at 532 nm. The carrier lifetime (τ) is determined to be (1.7 ± 0.5) ns in the case of direct band gap and (1.2 ± 0.03) ps in the case of indirect band gap crystals. Lower values of τ in the case of indirect band gap crystals can be attributed to the reduction in value of the carrier density (N).

Two Photon Absorption And Refraction in Bulk of the Semiconducting Materials

Fast electronic detection systems have opened up a number of new fields like nonlinear optics, optical communication, coherent optics, optical bistability, two/four wave mixing. The interest in this field has been stimulated by the importance of multiphoton processes in many fundamental aspects of physics. It has proved to be an invaluable tool for determining the optical and electronic properties of the solids because of the fact that one gets the information about the bulk of the material rather than the surface one. In this paper we report, the measurement of the nonlinear absorption and refraction from the band gap to half‐band gap region of bulk of semiconductors in the direct and indirect band gap crystals with nanosecond laser. The measured theoretical calculated values of two‐photon absorption coefficients (β) and nonlinear refraction n2 (ω) of direct band gap crystal match the earlier reported theoretical predictions. By making use of these theoretical calculated values, we have estimated β and n...

LASER-INDUCED MULTIPHOTON PHOTOCONDUCTIVITY IN DIRECT AND INDIRECT BAND GAP CRYSTALS USING Z-SCAN TECHNIQUE

Nanosecond laser pulses have employed the photoconductive Z-scan technique. Photoconductivity traces measured by moving the sample across the laser beam waist were used for measuring two and three-photon absorption processes. The value of the three-photon absorption coefficient β3=9.6×10-10cm3/GW2 in the case of direct, and 8.96×10-12cm3/GW2 and 5.0×10-12cm3/GW2 in the case of indirect band gap crystals have been estimated from a comparison of traces measured by exciting the sample with the first and second harmonics of Nd:YAG laser. The low value of β3 in the case of indirect band gap crystals compared to direct band gap crystals is attributed to phonon-assisted transitions.