School of Physics

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  • Item
    Cooperative effects in optical double resonance
    ( 1980-01-01) Agarwal, G. S. ; Anantha Lakshmi, P.
    A theory of optical double resonance which takes into account the cooperative interactions among atoms is formulated. The analytical result for the double resonance spectra in the conventional situation when the probe field is weak, is given. The changes in the nature of the spectra as one sweeps from cooperative to single atom branch are discussed. The cooperative interaction is shown to reduce considerably the asymmetry of the Autler-Towne's doublet. © 1980, All rights reserved.
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    Optical Hanle effect in fields of arbitrary strength and bandwidth
    ( 1981-01-01) Lakshmi, P. Anantha ; Agarwal, G. S.
    A quantum-statistical theory of optical Hanle effect is developed for arbitrary intensities and bandwidths of the pump field. The excited- and ground-state level shifts, caused by another light field with appropriate polarization, are directly included in the theory by using the method of time averaging. The laser fluctuations are taken into account exactly by using the phase-diffusion model of the pump laser. The analytical and numerical results for the fluorescence signals are presented for a variety of excitations. Our results in the limiting case reduce to those of Kaftandjian, Klein, and Hanle. Finally, the case of a very broadband excitation under saturation conditions is analyzed and the results for signals in various directions and the polarizations are obtained. © 1981 The American Physical Society.
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    Modulation spectroscopy in partially coherent fields of arbitray intensity
    (University of Hyderabad, 1981-05-30) Saxena, Ragini ; Agarwal, G.S.
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    One-dimensional quark gas
    ( 1982-01-01) Nambu, Y. ; Bambah, Bindu ; Gross, Mark
    Based on a recently developed method, the thermodynamic properties of a one-dimensional quark gas are investigated. The quarks are treated as classical particles except for their SU(N) spin. General formulations as well as specific calculations for SU(2) and SU(3) are given. © 1982 The American Physical Society.
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    Many-quark problem in two-dimensional gauge theory
    ( 1982-01-01) Nambu, Y. ; Bambah, Bindu
    General theorems are given for enumerating and constructing the singlet eigenstates of interaction energy for an arbitrary number of static quarks in SU(N) gauge theory in 1+1 dimensions. © 1982 The American Physical Society.
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    Fourier tranform techniques in electron spin echo modulation
    (University of Hyderabad, 1982-06-23) Ramakrishna, Y.V.S. ; Sastry, V.S.S.
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    Effect of spontaneous emission and recombination on the four-wavemixing profiles involving autoionizing resonances
    ( 1983-01-01) Agarwal, G. S. ; Lakshmi, P. Anantha
    A general expression for the four-wavemixing profiles in situations involving autoionizing resonances is derived by taking fully into account the spontaneous-emission characteristics of the autoionizing states. The signals are valid for arbitrary values of Fano asymmetry parameters, field strengths, and spontaneous-emission rates. The dramatic increase in the four-wavemixing signal for field strengths corresponding to the confluence is demonstrated. The spontaneous emission is shown to affect the line shapes not only in weak fields but also in strong fields. The effects of spontaneous emission are found to be most important for field strengths corresponding to confluence which is similar to the problem of laser-induced autoionization. © 1983 The American Physical Society.
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    An alternative derivation of the reduced electron-phonon hamiltonian
    ( 1983-03-28) Chatterjee, Ashok ; Mitra, T. K.
    Using the concept of the rigidity of the electronic wave function in the superconducting phase the reduced electron-phonon hamiltonian is derived very simply without the Fröhlich-Nakajima-Bardeen-Pines transformations. The remainder term is furthermore obtained in a closed form and the connection with the Born-Oppenheimer approximation is discussed. © 1983.
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    Measurement of Curie temperature and magnetization of ferromagnetic materials employing an rf oscillator
    ( 1983-04-01) Rama Rao, K. V.S. ; Seshu Bai, V. ; Ramasastry, C. ; Weiden, Norbert ; Weiss, Alarich
    Details of a method which employs an rf oscillator to determine the Curie temperature and magnetization of ferromagnetic materials have been described. the results obtained on some intermetallic compounds viz. CrTe, Mn1.1Sb, Mn1.2Sb, Mn0.9Co0.1Sb and Mn0.9Fe0.1Sb are presented. © 1983.
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    Theory of optical Hanle effect in atomic beams and in cavities under arbitrary pumping conditions
    (University of Hyderabad, 1983-08-20) Anantha Lakshmi, P. ; Agarwal, G.S.
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    Ferromagnetic and spin-wave resonance studies in Mn < inf > 1-x < /inf > Fe < inf > x < /inf > Sb and Mn < inf > 1-x < /inf > Co < inf > x < /inf > Sb
    ( 1983-12-01) Seshu Bai, V. ; Rama Rao, K. V.S.
    Ferromagnetic resonance studies have been carried out in thin films of Mn1-xFexSb (0 < or=x < or=0.3) and Mn 1-xCoxSb (0 < or=x < or=0.3) to study the variation of the strain-anisotropy field and the g value. The composition dependence of the strain-anisotropy field showed that the spins reorient from the basal plane in hexagonal MnSb to a direction parallel to the c axis at x=0.21 in Mn 1-xFexSb and at x=0.16 in Mn1-xCo xSb, at 300K. The spin-wave resonance spectra were analysed and the variation of the exchange coupling constant with composition was obtained.
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    Evidence of a critical Mn-Mn distance for the onset of ferromagnetism in NiAs type compounds
    ( 1984-01-01) Seshu Bai, V. ; Rajasekharan, T.
    Recently, the technique of spin wave resonance has been used to measure the exchange coupling constants as a function of composition in several solid solutions of MnSb. From an examination of the results we show that in those alloys in which the linear chains of magnetic atoms are not disturbed, the exchange coupling constants become positive leading to ferromagnetic coupling when the distance between Mn atoms becomes equal to 2.83 Å or more. This experimental value of the Mn-Mn distance for the onset of ferromagnetism is equal to the critical distance derived by Forrer after examining a large number of materials which owe their ferromagnetism predominantly to the direct exchange interaction. © 1984.
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    Estimation of plasma frequency from IR reflectivity in doped GaAs
    ( 1984-01-01) Tata, B. V.R. ; Arora, A. K.
    The influence of the phonon-plasmon coupling on the IR reflectivity spectra of doped GaAs is examined for the range of plasma frequencies which are close to the optical phonon frequencies. An analytic expression for the plasma frequency in terms of the frequencies of the reflectivity minima, which requires knowledge of the dielectric constant at the reflectivity minima and the carrier lifetime, is obtained. Empirical relations are suggested to estimate the required dielectric constant. Lifetime is estimated by a graphical method. These relations are used to estimate the plasma frequencies from the reported reflectivity spectra of doped GaAs samples. © 1984.
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    Photon-counting statistics of squeezed states in resonance fluorescence
    ( 1984-01-01) Lakshmi, P. Anantha ; Agarwal, G. S.
    The properties of the photon-counting distribution, for arbitrary intervals, produced by a mixture of coherent radiation and the radiation scattered by a strongly pumped two-level atom are calculated. Such properties reflect in an important way on the squeezing characteristics and the anomalous correlators of the scattered radiation. © 1984 The American Physical Society.
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    Thermodynamics of quark jets. II. Baryon production
    ( 1984-01-01) Crawford, M. ; Bambah, B.
    A Monte Carlo analysis based on a recent thermodynamic model for jets is used to model quark fragmentation into hadrons. Quantitative estimates of the baryon-to-meson ratio NBNM and kaon and hyperon production are made. © 1984 The American Physical Society.
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    Thermodynamics of quark jets. I
    ( 1984-01-01) Bambah, Bindu
    A model for quark jets based on the thermodynamics of a one-dimensional quark gas in a grand canonical ensemble is presented. The model makes predictions about such properties of jets as multiplicity and Koba-Nielsen-Olesen (KNO) scaling. A generalization to higher dimensions is out-lined. KNO scaling in the statistical description of many-particle phenomena is also examined. © 1984 The American Physical Society.
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    Effect of cooperativity on squeezing in resonance fluorescence
    ( 1984-10-15) Anantha Lakshmi, P. ; Agarwal, G. S.
    Squeezing characteristics of the radiation field produced by a collective system of atoms driven by a coherent field are calculated. The collective behavior is found to affect the squeezing behavior considerably. © 1984.
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    Solid solutions of MnSb as recording media in optical memory applications
    ( 1984-12-01) Seshu Bai, V. ; Rama Rao, K. V.S.
    We show in this paper that many of the difficulties, encountered in using the ferromagnetic MnSb films as storage media in memory devices employing the technique of laser Curie point writing and magneto-optic readout, can be overcome by forming solid solutions of MnSb with Fe, Co, In, and excess Mn, viz. Mn1-xFexSb, Mn1-xCo xSb, MnSb1-xInx and Mn 1+xSb (0≤x≤0.25 or 0.3). Spins that are in basal plane of MnSb at 300 K are found to reorient to be along the film normal, from ferromagnetic resonance work, beyond a critical composition (xc=0.16, 0.21, 0.16, and 0.14 for the systems containing Co, Fe, In, and excess Mn, respectively) ensuring a large readout efficiency. Moreover, the lowering of Curie temperature for higher compositions can enable us to work with low power lasers which help to achieve sharper writing without diffusion of heat into neighboring domains. In addition, the absence of any crystallographic phase transformation in the temperature range of operation (unlike in MnBi) makes the MnSb alloys potentially more attractive for use as recording media.
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    Some characteristics of icosahedral aluminium alloys
    ( 1985-01-01) Sekhar, J. A. ; Rao, K. N. ; Rajasekharan, T. ; Seshu Bai, V.
    Preliminary results of a study of the transformation behaviour, and those of microhardness measurements on quasi-crystalline Al-14 at.% Mn and Al-22 at.% Mn alloys are reported. © 1985.