Luminescence from Surfactant-Free ZnO Quantum Dots Prepared by Laser Ablation in Liquid

Highly transparent, luminescent and biocompatible ZnO quantum dots were prepared in water, methanol, and ethanol using liquid-phase pulsed laser ablation technique without using any surfactant. Transmission electron microscopy analysis confirmed the formation of good crystalline ZnO quantum dots with a uniform size distribution of 7 nm. The emission wavelength could be varied by varying the native defect chemistry of ZnO quantum dots and the laser fluence. Highly luminescent nontoxic ZnO quantum dots have exciting application potential as florescent probes in biomedical applications.

Laser Induced Photoacoustic Technique for the Detection of Phase Transitions in Liquid Crystals

In this paper we report the use of a laser induced phoroacoustic technique for the detection of multiple phase transitions in heptyl-oxy-cyanobiphenyl (70CB) and octyl-oxy-cyanobiphenyl (80CB) liquid crystals. The observed photoacoustic signal amplitude profile carries clear signatures of two tirst order transitions in 70CB and two tirst order and a second order transitions in 80CB. Analysis of the experimental data using Rosencwaig-Gersho theory shows that the sudden decrease in the photoacoustic (PA) signal amplitude during phase transitions is due to a sharp increase in the heat capacity of the samples near the transition temperatures.

Use of photoacoustic effect for the detection of phase transitions in liquid crystal mixtures

We report on a laser induced photoacoustic study of the nematic-to-isotropic transition in certain commercial nematic liquid crystal mixtures, namely BL001, BL002, BL032 and BL035. A simple analysis of the experimental data using the Rosencwaig–Gersho theory shows that the heat capacities of all these compounds exhibit a sharp peak as the temperature of the sample is varied across the transition region. Also, substantial differences in the photoacoustic signal amplitudes in nematic and isotropic phases have been noticed for all the mixtures. The increased light scattering property of the nematic phase may be the reason for the enhanced photoacoustic signal amplitude in this phase.

Use of photoacoustic effect for the detection of phase transitions in liquid crystal mixtures

We report on a laser induced photoacoustic study of the nematic-to-isotropic transition in certain commercial nematic liquid crystal mixtures, namely BL001, BL002, BL032 and BL035. A simple analysis of the experimental data using the Rosencwaig–Gersho theory shows that the heat capacities of all these compounds exhibit a sharp peak as the temperature of the sample is varied across the transition region. Also, substantial differences in the photoacoustic signal amplitudes in nematic and isotropic phases have been noticed for all the mixtures. The increased light scattering property of the nematic phase may be the reason for the enhanced photoacoustic signal amplitude in this phase

Use of photoacoustic effect for the detection of phase transitions in liquid crystal mixtures

We report on a laser induced photoacoustic study of the nematic-to-isotropic transition in certain commercial nematic liquid crystal mixtures, namely BL001, BL002, BL032 and BL035. A simple analysis of the experimental data using the Rosencwaig–Gersho theory shows that the heat capacities of all these compounds exhibit a sharp peak as the temperature of the sample is varied across the transition region. Also, substantial differences in the photoacoustic signal amplitudes in nematic and isotropic phases have been noticed for all the mixtures. The increased light scattering property of the nematic phase may be the reason for the enhanced photoacoustic signal amplitude in this phase.

Laser Induced Photothermal Investigations on Thermal and Transport Properties of Certain Selected Photonic Materials

Discovery of coherent optical sources four decades ago has revolutionized all fields of scientific development. One of the path breaking applications of lasers is the emergence of various thermo optic techniques to unravel some of the mysteries of light matter interactions.Thermo optic technique is a valuable tool to evaluate optical and thermal properties of materials in solid,liquid and gaseous states .This technique can also be employed effectively in nondestructive quality evaluation. In this doctoral thesis , the use of photothermal techniques based on photoacoustic and photothermal deflection phenomena for the study of certain class of photonics materials such as semiconductors, nano metal dispersed ceramics, composites of conducting polymers and liquid crystals is elaborated.

Liquid phase benzoylation of arenes over iron promoted sulphated zirconia

The present work undertakes the preparation and physico-chemical characterisation of iron promoted sulphated zirconia (SZ) with different amounts of iron loading and their application to Friedel-Crafts benzoylation of benzene, toluene and xylene under different experimental conditions, XRD and laser Raman techniques reveal the stabilisation of the tetragonal phase of zirconia and the existence of iron in highly dispersed form as Fe203 on the catalyst surface. The surface acidic properties were determined by ammonia temperature programmed desorption (TPD) and perylene adsorption, The results were supported by the TGA studies after adsorption of pyridine and 2,6-dimethylpyridine (2,6-DMP), Strong Lewis acid sites on the surface, which are evident from TPD and perylene adsorption studies. explain the high catalytic activity of the systems towards benzoylation. The experimental results provide evidence for the truly heterogeneous nature of the reaction. The studies also establish the resistance to deactivation in the metal incorporated sulphated systems.

Use of mirage effect for the detection of phase transitions in liquid crystals

he phenomenon of single beam mirage effect, otherwise known as photothermal deflection (PTD) effect using a He–Ne laser beam has been employed to detect phase transitions in some liquid crystals. It has been observed that anomalous changes in amplitude occur in the PTD signal level near the transition temperature. The experimental details and the results of measurements made in liquid crystals E8, M21 and M24 are given in this paper.

A comparative study of energy transfer in dye mixtures in monomer and polymer matrices under pulsed laser excitation

This study was conducted to identify the concentration dependence of the operating wavelengths and the relative intensities in which a dye mixture doped polymer optical fibre can operate. A comparative study of the radiative and Forster type energy transfer processes in Coumarin 540:Rhodamine 6G, Coumarin 540:Rhodamine B and Rhodamine 6G:Rhodamine B in methyl methacrylate (MMA) and poly(methyl methacrylate) (PMMA) was done by fabricating a series of dye mixture doped polymer rods which have two emission peaks with varying relative intensities. These rods can be used as preforms for the fabrication of polymer optical fibre amplifiers operating in the multi-wavelength regime. The 445 nm line from an Nd:YAG pumped optical parametric oscillator (OPO) was used as the excitation source for the first two dye pairs and a frequency doubled Nd:YAG laser emitting at 532 nm was used to excite the Rh 6G:Rh B pair. The fluorescence lifetimes of the donor molecule in pure form as well as in the mixtures were experimentally measured in both monomer and polymer matrices by time-correlated single photon counting technique. The energy transfer rate constants and transfer efficiencies were calculated and their dependence on the acceptor concentration was analysed. It was found that radiative energy transfer mechanisms are more efficient in all the three dye pairs in liquid and solid matrices.

Simultaneous determination of nonlinear optical and thermo-optic parameters of liquid samples

The authors apply the theory of photothermal lens formation and also that of pure optical nonlinearity to account for the phase modulation in a beam as it traverses a nonlinear medium. It is used to simultaneously determine the nonlinear optical refraction and the thermo-optic coefficient. They demonstrate this technique using some metal phthalocyanines dissolved in dimethyl sulfoxide, irradiated by a Q-switched Nd:YAG laser with 10 Hz repetition rate and a pulse width of 8 ns. The mechanism for reverse saturable absorption in these materials is also discussed.

Observation of Multiphoton Process in Liquid CS2 Using Pulsed Photoacoustic Technique

Pulsed photoacoustic measurements have been carried out in liquid CS2 using 532 nm radiation from a frequency doubled Nd:YAG laser. Variation of signal amplitude with laser fluence clearly indicates the role of multiphoton processes in the generation of photoacoustic effect. It is also shown that four photon induced dissociation and five photon induced ionization are likely processes in CS2 and 532 nm radiation.

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.

Laser induced thermal lens and near infrared absorption studies of ch overtones in some organic compounds

Vibrational overtone spectroscopy of X-H (X=C,N,O) containing molecules is an area of recent interest. The spectroscopic studies of higher vibrational levels yield valuable informations, regarding,the molecular structure, intra- and inter-molecular interactions, radiationless transitions, intra-molecular vibrational relaxations, multiphoton excitations and chemical reactivities, which cannot be z obtained by other spectroscopic methods. This thesis presents the results of experimental investigations on the overtone spectra of some organic compounds in the liquid phase for the characterization of CH bonds. The spectra in the fifth overtone region (1fiV=6) are recorded using a dual beam thermal lens setup and the lower overtones (.AV=2-5) are recorded spectrophotometrically.The thesis is presented in six chapters.

NIR Spectroscopic and Laser Induced Fluorescence studies of some organic molecules

Vibrational overtone spectroscopy of molecules containing X-H oscillators (X = C, N, O...) has become an effective tool for the study of molecular structure, dynamics, inter and intramolecular interactions, conformational aspects and substituent effects in aliphatic and aromatic compounds. In the present work, the author studied the NIR overtone spectra of some liquid phase organic compounds. The analysis of the CH, NH and OH overtones yielded important structural information about these systems. In an attempt to get information on electronic energy levels, we studied the pulsed Nd:YAG laser induced fluorescence spectra of certain organic compounds. The pulsed laser Raman spectra of some organic compounds are also studied. The novel high resolution technique of near infrared tunable diode laser absorption spectroscopy (TDLAS) is used to record the rotational structure of the second OH overtone spectrum of 2-propanol. The spectral features corresponding to the different molecular conformations could be identified from the high resolution spectrum. The whole work described in this thesis is divided into five chapters.