P. S. Gupta

Short-time squeezing in spontaneous Raman and stimulated Raman scattering

The non-classical effect of squeezing of light in spontaneous Raman and stimulated Raman processes are investigated under a short-time approximation based on a fully quantum mechanical approach. A Raman process is looked upon as a two-photon and one-phonon interaction process. Squeezing in amplitude, amplitude squared and amplitude cubed have been investigated. The occurrence of squeezing is observed in the fundamental mode in spontaneous Raman and stimulated Raman scattering. The squeezing in a Stokes field is found to be dependent on squeezing of the initial pump field.

Short-time squeezing effects in spontaneous and stimulated six-wave mixing process

The concept of squeezing of the electromagnetic field is investigated in the fundamental mode in spontaneous and stimulated six-wave mixing process under short-time approximation based on a fully quantum mechanical approach. The interaction is looked upon as a process involving absorption of two pump photons and emission of three probe photons and one signal photon at different frequency. The coupled Heisenberg equations of motion involving real and imaginary parts of the quadrature operators are established. The occurrence of squeezing in amplitude, amplitude squared and amplitude-cubed in the fundamental mode are investigated. The dependence of squeezing on photon number is brought out and the degree of squeezing in the first- and higher-order are also investigated.

The squeezing of radiation in four-wave mixing processes

Squeezing of the electromagnetic field is investigated in the pump, Stokes and parametric mode in spontaneous and stimulated four-wave mixing processes under a short-time approximation based on a fully quantum mechanical approach. The occurrence of squeezing in amplitude and amplitude squared of the fundamental mode has been investigated. The dependence of squeezing on the photon number is noticed and the degree of squeezing in the first and second-order is also investigated. Squeezing occurs in the fundamental mode in both spontaneous and stimulated processes, whereas squeezing in the Stokes and parametric modes is found to be dependent on squeezing of the initial pump field.

Comparative study of optical, structural and electrical properties of zinc phthalocyanine Langmuir–Blodgett thin film on annealing

Zinc phthalocyanine (ZnPc) in the mixture of N-methyl pyrroldione (NMP) and chloroform (CHCl3) [1 : 10 (v/v)] spreading solvent was observed to have only a monomeric absorption peak. However, on processing the solution into a thin film using the Langmuir–Blodgett (LB) technique, it shows absorption peaks corresponding to H, J and monomer aggregates, as confirmed by UV-Vis absorption spectroscopy. The Q-band absorption spectra of ZnPc LB thin film was observed to have a sharp change on annealing at 65 °C, indicating a change in the aggregation configuration of molecules over the surface. The annealed ZnPc LB thin film is found to have H and monomer aggregates only, which indicates that ZnPc molecules are arranged in an edge on face-to-face conformation. The ZnPc LB thin film remains in this aggregation until the higher annealing temperature. The ZnPc LB thin film shows an α-phase characteristic when annealed at 65 °C, and it remains intact in this phase up to 200 °C. The α–β phase transformation starts occurring from 200 °C and is completed at 290 °C. The large increase in crystallite size, as obtained from the XRD study, and the change in the shape of the ZnPc nanoparticles from spherical to nanorod structure, as observed from FESEM and AFM images, confirms the transformation of the ZnPc film from metastable α phase to stable β phase. Electrical conductivity is found to be enhanced considerably for β-phase with respect to α-phase in dark and under photoexcitation because of better charge carrier transport.

Higher-order squeezing of the electromagnetic field in spontaneous and stimulated Raman processes

The occurrence of fourth and fifth-order squeezing in the fundamental mode of the electromagnetic field in spontaneous and stimulated Raman processes under the short-time approximation is investigated on the basis of a fully quantum-mechanical approach. In an idealized model, the Raman process is looked upon as a two-photon on a one phonon interaction process. The coupled Heisenberg equations of motion involving real and imaginary parts of the quadrature operators are established. The dependence of fourth- and fifth-order squeezing in terms of the signal-to-noise ratio on the number of photons is investigated. We have also established the amplitude squeezing effects in the Stokes and vibrational modes, which is found to be dependent on higher-order difference squeezing showing a difference squeezing that can be converted to normal squeezing.

Higher-order amplitude squeezing in hyper-Raman scattering under short-time approximation

The nonclassical effect of squeezing of light in hyper-Raman processes is investigated under the short-time approximation based on a fully quantum mechanical approach. Effects of squeezing in spontaneous and stimulated processes are studied. A hyper-Raman process is looked upon as a three-photon and one-phonon interaction process. Squeezing in amplitude, squared amplitude and cubed amplitude have been investigated. Squeezing occurs invariably in the fundamental mode in both spontaneous and stimulated processes, whereas the squeezing in the Stokes mode is found to be dependent on amplitude-squared squeezing of the initial pump field.

Sum squeezing in four-wave sum frequency generation

Abstract Sum squeezing is a higher-order multimode squeezing effect. Sum squeezing of the electromagnetic field in four-wave sum frequency generation is investigated under short-time approximation based on a fully quantum mechanical approach. It is shown that for uncorrelated modes the normal squeezing in the sum frequency field depends directly on the sum squeezing of the input field modes and that sum squeezing can be turned into normal squeezing through it. Further, the occurrence of sum squeezing in the three input modes is found to be dependent on the normal squeezing in any one or more of the modes.

DIFFERENCE SQUEEZING IN FOUR-WAVE DIFFERENCE-FREQUENCY GENERATION

The multimode difference squeezing of the electromagnetic field in the four-wave mixing process is investigated under the short-time approximation based on a fully quantum mechanical approach. It is shown that for uncorrelated modes the normal squeezing in the difference-frequency field depends on the difference squeezing of input field modes, which can generate normal squeezing in the difference-frequency field mode. Various possibilities for obtaining difference squeezing in three modes and its dependence on squeezing of individual field modes are investigated. If one of the high-frequency modes is squeezed and the other two modes are in coherent states, difference squeezing can be generated when the amplitude of the low-frequency mode is large enough. Difference squeezing can be generated in the three modes if one of the high-frequency modes is in a coherent state and the other two modes are difference squeezed. It is also shown that when the low-frequency mode is in a coherent state and the high-frequency modes are sum squeezed, then difference squeezing can be generated for large amplitude of the low-frequency mode.

Dynamics of roughening and growth kinetics of CdS–polyaniline thin films synthesized by the Langmuir–Blodgett technique

Thin films of cadmium sulphide (CdS) nanoparticle induced polyaniline (PANI) nanocomposites have worked as a better system for application in photovoltaics due to the efficient charge separation and charge transfer. In this communication, we have chosen such a system of varying thickness deposited by the Langmuir–Blodgett (LB) technique in order to study the growth and roughness phenomena by dynamic scaling theory. Different techniques such as X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and X-ray reflectivity (XRR) are used for characterization of these films. In the study, the growth exponent, β, is found to have a correlation with the invariant logarithmic scaling law. A very large value of β = 1.18 ± 0.23 as calculated is a result of the rapid roughening in the multilayer film growth process. We have investigated the dynamic scaling behavior of the multilayer system which shows a difference in the value of the coarsening factor and this confirms the breakdown of self-affinity as a consequence of some nonlocal growth effects. The normal grain formation with deposition at the initial stage and the increase in grain abnormality with increase in thickness is also verified in support of the dynamic scaling ansatz. In the present study the layer-by layer deposition is confirmed by XRR fitting for a 3 layer film whereas the multilayer shows diffusing behavior due to H-bonding or electrostatic interactions.

nTH-ORDER SQUEEZING OF THE FIELD AMPLITUDE IN RAMAN PROCESS AS A GENERALIZATION OF THE HIGHER-ORDER SQUEEZING

The concept of nth-order amplitude squeezing is introduced in the fundamental mode in Raman process as a generalization of the higher-order squeezing under short-time approximation based on a fully quantum mechanical approach. The condition for occurrence of nth-order squeezing is obtained from which higher-order squeezing up to n = 5 are studied. The coupled Heisenberg equation of motion involving real and imaginary parts of the quadrature operators is established. Dependence of squeezing on photon number is also established.