Studies on the interaction of two level atoms with quantized electromagnetic field

The present study described about the interaction of a two level atom and squeezed field with time varying frequency. By applying a sinusoidal variation in the frequency of the field, the randomness in population inversion is reduced and the collapses and periodic revivals are regained. Quantum optics is an emerging field in physics which mainly deals with the interaction of atoms with quantised electromagnetic fields. Jaynes-Cummings Model (JCM) is a key model among them, which describes the interaction between a two level atom and a single mode radiation field. Here the study begins with a brief history of light, atom and their interactions. Also discussed the interaction between atoms and electromagnetic fields. The study suggest a method to manipulate the population inversion due to interaction and control the randomness in it, by applying a time dependence on the frequency of the interacting squeezed field.The change in behaviour of the population inversion due to the presence of a phase factor in the applied frequency variation is explained here.This study also describes the interaction between two level atom and electromagnetic field in nonlinear Kerr medium. It deals with atomic and field state evolution in a coupled cavity system. Our results suggest a new method to control and manipulate the population of states in two level atom radiation interaction,which is very essential for quantum information processing.We have also studied the variation of atomic population inversion with time, when a two level atom interacts with light field, where the light field has a sinusoidal frequency variation with a constant phase. In both coherent field and squeezed field cases, the population inversion variation is completely different from the phase zero frequency modulation case. It is observed that in the presence of a non zero phase φ, the population inversion oscillates sinusoidally.Also the collapses and revivals gradually disappears when φ increases from 0 to π/2. When φ = π/2 the evolution of population inversion is identical to the case when a two level atom interacts with a Fock state. Thus, by applying a phase shifted frequency modulation one can induce sinusoidal oscillations of atomic inversion in linear medium, those normally observed in Kerr medium. We noticed that the entanglement between the atom and field can be controlled by varying the period of the field frequency fluctuations. The system has been solved numerically and the behaviour of it for different initial conditions and different susceptibility values are analysed. It is observed that, for weak cavity coupling the effect of susceptibility is minimal. In cases of strong cavity coupling, susceptibility factor modifies the nature in which the probability oscillates with time. Effect of susceptibility on probability of states is closely related to the initial state of the system.

Optical Emission Diagnostics Of Laser Produced Plasma From Graphite And Yba2cu3o7

This thesis is entitled “OPTICAL EMISSION DIAGNOSTICS OF LASER PRODUCED PLASMA FROM GRAPHITE AND YBa2Cu3O7. The work presented in this thesis covers the experimental results on the plasma produced with moderately high power laser with irradiance range in between 10 GW cm 2 to 100 GW cm -2. The characterization of laser produced plasma from solid targets viz. graphite and high temperature superconducting material like YBa2Cu3O7 have been carried out. The fundamental frequency from a Q - switched Nd: YAG laser with 9 ns pulse duration is used for the present studies. Various optical emission emission diagnostic techniques were employed for the the characterization of the LPP which include emission spectroscopy, time resolved studies, line broadening method etc. In order to understand the physical nature of the LPP like recombination, collisional excitation and the laser interaction with plasma, the time resolved studies offer the most logical approach

Evaluation of laser ablation threshold in polymer samples using pulsed photoacoustic technique

The acoustic signals generated in solids due to interaction with pulsed laser beam is used to determine the ablation threshold of bulk polymer samples of teflon (polytetrafluoroethylene) and nylon under the irradiation from a Q-switched Nd:YAG laser at 1.06µm wavelength. A suitably designed piezoelectric transducer is employed for the detection of photoacoustic (PA) signals generated in this process. It has been observed that an abrupt increase in the amplitude of the PA signal occurs at the ablation threshold. Also there exist distinct values for the threshold corresponding to different mechanisms operative in producing damages like surface morphology, bond breaking and melting processes at different laser energy densities.

Chaotic Dynamics of Semiconductor Laser with Current Modulation and optoelectronic feedback

Chaotic dynamics of directly modulated semiconductor lasers have been studied extensively over the last two decades because of their application in secure optical communication. However, chaos is generally suppressed in such systems when the nonlinear gain reduction factor is above 0.01 which is very much smaller than the reported values in semiconductors like InGaAsP. In this paper we show that by giving an optoelectronic feedback with appropriate delay one can increase the range of the values of the gain reduction factor for which chaos can be observed. Numerical studies show that negative feedback is more efficient in producing chaotic dynamics.

Study of Laser Ablation in Liquids Using Pulsed Photoacoustic Technique

Laser ablation processes in liquid benzene, toluene and carbon disulphide have been investigated by pulsed photoacoustic technique using 532 nm radiation from a frequency doubled Q-switched Nd:YAG laser. The nature of variation of photoacoustic signal amplitude with laser energy clearly indicates that different phenomena are involved in the generation of photoacoustic effect and these are discussed in detail. Our results suggest multiphoton induced photofragmentation as the most plausible interaction process occurring during laser ablation in these liquids.

Photosensitivity of Laser Dye Mixtures in Polymer Matrix – A Photoacoustic Study

Laser induced photoacoustic (PA) technique is used in the study of photostability of polymethyl methacrylate (PMMA) films doped with Rhodamine 6G -Rhodamine B dye system. Energy transfer from a donor molecule to an acceptor molecule in a dye mixture affects the output of the dye system. Details of investigations on the role of laser power, modulation frequency and the irradiation wavelength on the photosensitivity of the dye mixture doped PMMA films are presented.

Characterization and Imaging Diagnostics of Laser Induced Plasma from Solid Targets

Laser induced plasma (LIP) emissions from some metal oxide targets were studied with corresponding metal targets of pure quality as a reference. Atomic emissions in the visible region were used in the spectroscopic procedures of LIP characterization. The studies were meant to throw light into LIP dynamics and they provided many experimental results which improved the general awareness of plasma state.When target materials were photo-ablated with an energetically suitable laser pulse, they developed electric charges in them.An electrical signal which was delivered from the target served as an alternative probe signal for the diagnostics of LIP and to track different charged states in the plasma. The signal showed a double peak distribution with positive polarity and a modified time of flight with various voltage levels of a given polarity.The expansion dynamics of LIP in magnetic field were also investigated by monitoring the voltage transients generated at the target.

Backscattering of Laser Light from Colloidal Silica

Light-scattering experiments gained prominence as potential applications of quantum optics, nonlinear optics, and photon localization. The possibility of the realization of lasing action in random media has created much interest in the study of the coherent structure of the backscattered light from disordered media. Backscattering (BS) studies are carried out to analyze the possibilities of photon localization in colloidal silica. The scattering enhancement is best associated with the density of the scatterers. The width of the BS cone and, hence, the mean-free path is related to the concentration of the medium. The dependence of the photon wavelength on the possible characteristics of the scattering is presented.

Fast imaging of laser-blow-off plume:Lateral confinement in ambient environment

The dynamics of plasma plume, formed by the laser-blow-off of multicomponent LiF-C thin film under various ambient pressures ranging from high vacuum to argon pressure of 3 Torr, has been studied using fast imaging technique. In vacuum, the plume has ellipsoidal shape. With the increase in the ambient pressure, sharp plume boundary is developed showing a focusing-like confinement in the lateral space behavior in the front end, which persists for long times. At higher ambient pressure (> 10−1 Torr ), structures are developed in the plasma plume due to hydrodynamic instability/turbulences.

Dynamics of laser produced silver plasma under film deposition conditions studied using optical emission spectroscopy

Laser produced plasma from silver is generated using a Q-switched Nd:YAG laser. Optical emission spectroscopy is used to carry out time of flight (TOF) analysis of atomic particles. An anomalous double peak profile in the TOF distribution is observed at low pressure. A collection of slower species emerge at reduced pressure below 4 X lO-3 mbar and this species has a greater velocity spread. At high pressure the plasma expansion follows the shockwave model with cylindrical symmetry whereas at reduced pressure it shows unsteady adiabatic expansion (UAE). During UAE the species show a parabolic increases in the expansion time with radial distance whereas during shock wave expansion the exponent is less than one. The angular distribution of the ablated species in the plume is obtained from the measurement of optical density of thin films deposited on to glass substrates kept perpendicular to the plume. There is a sharp variation in the film thickness away from the film centre due to asymmetries in the plume.

Collective behavior of laser-produced plasma from a multicomponent YBa2Cu3O7 target in air

The dynamics of diffusion of electrons and ions from the laser-produced plasma from a multielement superconducting material, namely YBa2Cu3O7, using a Q-switched Nd:YAG laser is investigated by time-resolved emission-spectroscopic techniques at various laser irradiances. It is observed that beyond a laser irradiance of 2.6 \xC3\x97 1011 W cm-2, the ejected plume collectively drifts away from the target with a sharp increase in velocity to 1.25 \xC3\x97 106 cm s-1, which is twice its velocity observed at lower laser irradiances. This sudden drift apparently occurs as a result of the formation of a charged double layer at the external plume boundary. This diffusion is collective, that is, the electrons and ions inside the plume diffuse together simultaneously and hence it is similar to the ambipolar diffusion of charged particles in a discharge plasma

High power N2 laser with a modified gas flow system and discharge geometry

A high power Nz laser of the double-Blumlein type having a modified gas flow system, electrode configuration, and discharge geometry with minimum inductance is described. By incorporating a triggere’d-pressurized spark gap switch, arc-free operation was achieved for a wide E/P range. The device gives a peak power in excess of 700 kW with a FWHM of 3 ns and an efficiency of 0.51%, which is remarkably high for a pulsed nitrogen laser system. The dependence of output power on parameters such as operating pressure, voltage, and repetition rate are discussed.

Spatial and temporal analysis of laser induced plasma from a polymer sample

Spatial and temporal analyses of the spectra of the laser induced plasma from a polytetrafluroethylene (PTFE) target obtained with the 1.06 mu m radiation from a Q-switched Nd:YAG laser have been carried out. The spatially resolved spectra of the plasma emission show that molecular bands of C2 (Swan bands) and CN are very intense in the outer regions of the plasma, whereas higher ionized states of carbon are predominant in the core region of the plasma emission. The vibrational temperature and population distribution in the different vibrational levels have been studied as a function of laser energy. From the time resolved studies, it has been observed that there exist fairly large time delays for the onset of emission from all the species in the outer region of the plasma. The molecular bands in each region exhibit much larger time delays in comparison to the ionic lines in the plasma.

Application of laser beam deflection technique to study the diffusion process in electrolyte solutions

A simple method based on laser beam deflection to study the variation of diffusion coefficient with concentration in a solution is presented. When a properly fanned out laser beam is passed through a rectangular cell filled with solution having concentration gradient, the emergent beam traces out a curved pattern on a screen. By taking measurements on the pattern at different concentrations, the variation of diffusion coefficient with concentration can be determined.