Theory of four-photon resonant vacuum-ultraviolet generation with reabsorption via resonant two-photon process

Motivated by the recent experiments of Vallee et al. [IEEE J. Quantum Electron. QE-19, 1331 (1983)], we formulate the theory of the four-photon resonant VUV generation in a media that is positively dispersive. Dispersion characteristics of the medium change as the refractive index becomes intensity dependent. The phase-matching conditions for the third-harmonic generation through a five-photon process are derived. The blue shifts as observed by Vallee et al. are explained as due to the interaction of generated VUV via a two-photon process. Finally the renormalization of the fifth-order polarization due to the generated fields is also considered

Structural, optical and nanomechanical properties of (1 1 1) oriented nanocrystalline ZnTe thin films

Structural, optical and nanomechanical properties of nanocrystalline Zinc Telluride (ZnTe) films of thickness upto 10 microns deposited at room temperature on borosilicate glass substrates are reported. X-ray diffraction patterns reveal that the films were preferentially oriented along the (1 1 1) direction. The maximum refractive index of the films was 2.74 at a wavelength of 2000 nm. The optical band gap showed strong thickness dependence. The average film hardness and Young’s modulus obtained from loaddisplacement curves and analyzed by Oliver-Pharr method were 4 and 70 GPa respectively. Hardness of (1 1 1) oriented ZnTe thin films exhibited almost 5 times higher value than bulk. The studies show clearly that the hardness increases with decreasing indentation size, for indents between 30 and 300 nm in depth indicating the existence of indentation size effect. The coefficient of friction for these films as obtained from the nanoscratch test was ∼0.4.Financial support in the form of fellowships to MSRNK and SK from the ACRHEM project of DRDO is acknowledged

Vacuum-ultraviolet generation using electromagnetic-field-induced transparency

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Tunable nonlinearity in atomic response to a bichromatic field

Atomic response to a probe beam can be tailored, by creating coherences between atomic levels with help of another beam. Changing parameters of the control beam will change the nature of coherences and hence the nature of atomic response as well. Such change can depend upon intensity of both probe and control beams, in a nonlinear fashion. We present a situation where this nonlinearity in dependence can be precisely controlled, as to obtain different variations as desired. We also present a detailed analysis of how this nonlinear dependency arises and show that this is an interesting effect of several Coherent Population Trap(CPT) states that exist and a competition among them to trap atomic population in them.Comment: 16 pages and 6 figure

Quantum theory of the competition between multiphoton ionization and third-harmonic generation

A quantum-mechanical formulation for the generation of third-harmonic radiation in an atomic medium undergoing three-photon resonant multiphoton ionization is given. The generation of the third harmonic is treated as a cooperative emission and its pressure dependence is shown to be in agreement with experiments. The formulation is general enough to include both transient and steady-state phenomena and includes both traveling-wave and standing-wave cases. A comparison of the results of the present theory with those of Jackson and Wynne is given