Value Of Two-photon Absorption Coefficient Research Articles

Assessment on third order non linearity and other optical analyses of l-Asparagine Monohydrate single crystal: An efficient candidate for harmonic conversions

Single crystal of l-Asparagine Monohydrate, an organic material has been successfully grown by slow evaporation solution growth technique at ambient condition. The lattice parameters and its strain of the grown crystal have been evaluated from powder X-ray diffraction and found that it belongs to orthorhombic crystal system. The polarizability has been measured by using the Clausius–Mossotti relation. The crystalline perfection of grown single crystal has been examined by high resolution X-ray diffraction and its imperfection in the diffraction plane was clearly visible by recording topographical image of the plane. From the high resolution XRD, it confirms that the crystal contained high crystalline perfection. The optical behavior was analyzed by photoluminescence and birefringence methods. In the photoluminescence, a broad peak has been observed at 475nm which suggest that it emits blue light. The decay tendency of the material has also been observed by calculating decay constant. The optical homogeneity has been determined by the dispersion pattern of the material. The two photon absorption coefficient was further calculated by Z-scan, which gives the information about the third order non linear optical behavior of the material. The value of two-photon absorption coefficient is 4.25×10−12m/W. The thermal parameters like thermal effusivity, thermal diffusivity, specific heat and thermal conductivity was obtained by using photopyroelectric technique. The ferroelectric behavior of the grown specimen was analyzed from PE (polarization VS electric field) loop. The loop suggests that the material was a nearly equivalent to ideal capacitor.

Third-Order Nonlinear Optical Properties of Colloidal Gold Nanorods

We have evaluated the third-order nonlinear optical properties of gold nanorods in water solution in a broad range of wavelengths including both the longitudinal and transverse surface plasmon resonance (SPR) bands. On the basis of the analysis of Z-scan measurements performed with femtosecond laser pulses, we conclude that the optical nonlinearity in the longitudinal-SPR absorption range originates mainly from the saturation of the one-photon absorption, whereas a resonant two-photon absorption process is dominant in the transverse-SPR range of wavelengths. The discrepancies in the values of two-photon absorption coefficients reported by various researchers and the methods of reliable comparison of the results are discussed.

Optical nonlinearities in direct and indirect band gap crystals on the [formula omitted]-scan technique with nanosecond laser

The free carrier optical nonlinearities in direct and indirect band gap crystals have been investigated by the use of a single beam Z -scan technique. The values of two-photon absorption coefficient ( β ) , nonlinear index n 2 ( w ) , the total free carrier absorption cross-section ( σ ab ) and the change in the refractive index per unit carrier density ( σ nr ) are determined in both direct and indirect band gap crystals. Smaller values of ( β ) and ( σ ab ) in the case of indirect band gap crystals have been attributed to phonon assisted transitions, while the smaller value of n 2 ( w ) and ( σ nr ) is due to the rise in saturation taking place in the absorption.

Nonlinear absorption and excited state dynamics in Rhodamine B studied using Z-scan and degenerate four wave mixing techniques

We report our experimental results of nonlinear absorption and excited state dynamics in Rhodamine B solutions at 532 nm, on resonance of the absorption band and 600 nm at the absorption edge, studied using the standard Z-scan and degenerate four wave mixing techniques. We observed saturable absorption at 532 nm and a transition from saturable absorption to reverse saturable absorption at 600 nm with increase in either intensity or concentration. Time-resolved degenerate four wave mixing studies using incoherent light from a broadband dye laser also confirmed the presence of excited state absorption through resonant two-photon absorption. Concentration dependent studies indicate a complex behavior of reverse saturable absorption within saturable absorption. Results are explained using an effective five-level model. The value of two-photon absorption coefficient evaluated using the same model was ∼0.58×10 −8 cm/W.

Picosecond Z-scan measurements on bulk GaN crystals

Bulk GaN crystals were characterized by using picosecond laser pulses at λ=0.527 μm and Z-scan techniques. The role of the free-carrier absorption was evaluated by a dynamical, pump-and-probe-type transmitivity measurement. The values of two-photon absorption coefficient (17–20 cm/GW) and refractive index changes at high optical irradiances due to bound (n2=−4×10−12 esu) and free (σr=−1.0×10−20 cm3) electrons in that material were determined.