Multimode Phonon Cooling via Three Wave Parametric Interactions with Optical Fields

We discuss the possible cooling of different phonon modes via three wave mixing interactions of vibrational and optical modes. Since phonon modes exhibit a variety of dispersion relations or frequency spectra with diverse spatial structures, depending on the shape and size of the sample, we formulate our theory in terms of relevant spatial mode functions for the interacting fields in any given geometry. We discuss the possibility of Dicke like collective effects in phonon cooling and present explicit results for simultaneous cooling of two phonon modes via the anti-Stokes up conversions. We show that the bimodal cooling should be observable experimentally

Some recent trends in raman spectroscopy

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Surface-enhanced Raman scattering in a two-oscillator electromagnetic model

A two-oscillator model is considered to investigate the effect of a metal substrate of dielectric function ε(ω) on the Raman scattering from a molecule absorbed on the metal surface. In the presence of the metal and an external electric field, the linear motion of the electronic and ionic oscillators in the molecule get coupled, in general. For obtaining Raman scattering at the Stokes frequency, a phenomenological nonlinear force term, which is bilinear in the oscillator amplitudes, is introduced in the equation of motion. The whole problem is considerably simplified when we use the fact that the ionic mass is much larger than the electronic mass and the ionic vibration frequency is much smaller than the electronic and optical frequencies. It is shown that because of different renormalization factors the frequency dependence of the enhancement factor F, taken to be the ratio of Raman intensity with and without the metal, is quite different from that calculated by using the familiar polarizability-derivative theory. Applying the well-known fluctuation-dissipation theorem, the new Raman line shape is also calculated to contrast it with the corresponding line shape in the absence of the metal

Beneficiation of Iron Ore

Wide reserves of iron ore is found in India. Due to the high quality of iron ore available in India, large deposits of Banded Haematite Jasper (BHJ) are left unused because of the presence of silica in unwanted quantity. ROM is put through washing to remove the clayey matter due to the presence of alumina and silica in iron ore leading to slime generation which are disposed of in tailing ponds. Slime in these tailing ponds contains iron values in the range of 45-60%. Appropriate beneficiation process has to be advanced to reduce the waste generation in mines and for the sustainable growth of the iron ore industry some. Major reason for difficulty in beneficiation of BHJ is revealed from characterization studies which show the intergrowth of haematite and quartz. Presence of Kaolonite is proved with the aid of mineralogical studies. For the separation of alumina from iron ore Beneficiation studies have to be carried out

Digital Watermarking Technique used for Security of Digital Images during Broadcasting and Telecasting by Using DWT

Signals are any time varying quantity having lot of Information and have its own frequency. Signal can be classified into random signal, periodic signals, and non-periodic signals, discrete or digital signal. Signal may contain various data like audio, vedio, or in text format. Signal also has information like images. But question arises of security of signal. So; Signals can be making secure by using the different Security techniques such as encryption and decryption by using RSA algorithm, Stegnography, Digital watermarking techniques. In this paper we are going to discuss transmission of Signal and their modulation techniques and its security by using “Digital Watermarking Techniques” with help of “Discrete Wavelet Transform”

Surface-enhanced nonlinear-optical processes in molecules in a two-oscillator electromagnetic model

A two-oscillator electromagnetic model is used to find the effect of a solid or a metal substrate of dielectric function ε(ω) on several nonlinear optical processes in a molecule adsorbed on the surface. In particular, the case of the second-order optical mixing, the stimulated Raman scattering, the third-order polarizability for the four-wave mixing, and the case of two-photon absorption in the molecule have been considered explicitly in the approximation in which the ionic oscillator frequency is assumed to be small compared with both the electronic oscillator frequency and the optical frequencies involved. The two-oscillator model considered here, with a trilinear coupling potential function, is the same as the one recently used by us to investigate the spontaneous Raman process. From our analysis it is quite clear that the enhancement, if any, in each of the processes involves (1) the enhancement of each of the incident optical fields E→ in to E→ (0) at the molecular site, (2) the renormalization of the effective nonlinear polarizabilities at short molecular distances from the surface, and (3) the change of the outgoing radiation propagator (Green's function) from the free-space G0 to G, due to the presence of the surface. For a metal surface of a given shape, each of these factors may contain possible surface-plasmon-polariton resonances at various frequencies involved

Surface-enhanced second-harmonic generation at a metallic grating

The theory of surface-enhanced second-harmonic generation at a metallic grating is developed. Using the form of the nonlinear source polarization given by Bloembergen et al. [Phys. Rev. 174, 813 (1968)], we solve Maxwell's equations to obtain the fields at the second-harmonic frequency. The calculations are done up to second order in the surface-roughness parameter. These perturbation expressions are used to evaluate numerically the second-harmonic intensity, in various directions, produced by a plane wave incident on a metallic grating. The resonant enhancement in the second-harmonic intensity due to surface-plasmon excitation at fundamental frequency ω is discussed and the results compared with some recent experimental observations. The second-harmonic fields are also shown to get enhancement due to excitation of surface plasmons at 2ω; these, however, correspond to local-field enhancements at 2ω and are evanescent in nature