Browsing by Author "V.N. Rai"

Now showing 1 - 11 of 11

A dc laser pump results in an ac photoacoustic signal
(1989) V.N. Rai; B.N. Singh; S.N. Thakur
[No abstract available]
A simple laser power meter dependent on photoacoustic effect
(1987) V.N. Rai; S.N. Thakur; D.K. Rai
The design and fabrication of a simple laser power meter dependent on the photoacoustic effect is described. This power meter has a sensitivity of 1 mV/3.5 mW laser power and the microphone has a sensitivity of 10 mV/Pa. It can be used in any wavelength region and its calibration is easy.
EFFECT OF NEUTRON AND PROTON IRRADIATION ON SOME PROPERTIES OF KAPTON.
(Plenum Press, 1984) V. Shrinet; U.K. Chaturvedi; S.K. Agrawal; V.N. Rai; A.K. Nigam
[No abstract available]
Electret microphone for use in photoacoustic spectrometer and photoacoustic spectrum of some rare earth oxide powders
(Springer India, 1982) V.N. Rai; L.B. Tiwari; S.N. Thakur; D.K. Rai
We describe a new method for the polarization of an electret foil which has proved very convenient and yields a foil having very good performance in a microphone. The variations in the charge accumulation on the electret foil and its decay with time as well as the variation of the microphone sensitivity with different microphone parameters e.g. different thicknesses of the electret foil, different back plates and different polarization techniques has been investigated. The sensitivity of the home-made microphone is estimated as 1 mV/μbar. The working of this type of microphone and its comparison with a commercial microphone as used in a (laboratory made) single beam photoacoustic spectrometer is discussed. A brief description of the photoacoustic spectrometer including microphone biasing and the photoacoustic cell is given. The photoacoustic spectra of some rare earth oxides in the form of powders have been recorded. It is seen that the atomic levels of triplyionized rare earths which are not fluorescent appear very prominently in the photoacoustic spectrum. The spectra for terbium and praseodymium oxides do not show clear peaks probably due to the presence of different stoichiometric forms. © 1982 Indian Academy of Sciences.
Instrumentation for Laser-Induced Breakdown Spectroscopy
(Elsevier, 2007) V.N. Rai; S.N. Thakur
[No abstract available]
Instrumentation for LIBS and recent advances
(Elsevier, 2020) V.N. Rai; Surya N. Thakur
The basic details on instrumentation for laser-induced breakdown spectroscopy (LIBS) for the study of solid, liquid, and gaseous samples are presented along with portable and handheld LIBS systems. Various new interdisciplinary techniques used for enhancing the sensitivity of LIBS have also been discussed. Applications of LIBS in many advanced fields of research are also described briefly, particularly in nuclear, fusion, and space research. © 2020 Elsevier B.V. All rights reserved.
Optical properties of Rhodamine B and Rhodamine 6G on silver surfaces
(Springer India, 1988) V.N. Rai
The transmission spectra of Rhodamine B and Rhodamine 6G dyes coated on silver island films for various thickness were recorded. A strong coupling between the silver particle plasma resonance and the dye molecules is observed. The absorption of dye molecules increases when the absorption band of individual dyes and silver particles overlaps. In higher silver film thicknesses, transmission increases. The theoretical calculation using Maxwell-Garnett theory and Wang and Kerker's results qualitatively supports the observed phenomenon. A red shift in the absorption peak of dyes on silver surfaces in comparison to solution phase absorption peak indicates photobleaching. © 1988 Indian Academy of Sciences.
Photoacoustic studies on excitation transfer in Rh6G and RhB dye mixture
(Springer India, 1984) V.N. Rai; S.N. Thakur; D.K. Rai
The photoacoustic spectra of Rhodamine 6G (Rh6G), Rhodamine B (RhB) dyes and their mixtures were recorded at different concentrations. It is observed that in the mixture the photoacoustic signal increases due to excitation transfer from Rh6G to RhB in the wavelength region 480-530 nm. The excitation transfer rate estimated from these data show that resonance is dominant rather than the collisional transfer process. © 1984 Indian Academy of Sciences.
PHOTOACOUSTIC STUDIES ON NEUTRON-IRRADIATED RARE EARTH OXIDE POWDERS.
(1986) V.N. Rai; S.N. Thakur; D.K. Rai
The effect of neutron irradiation on the photoacoustic spectra of Er//2O//3 and Nd//2O//3 in powder form has been studied. The irradiation shows a quenching effect on the photoacoustic signal which regains its intensity after a lapse of some time. It is believed that the irradiation changes the oxidation state of the rare-earth ions from M**3** plus to M**2** plus . The half-life of the recovery process Er**2** plus to Er**3** plus in the case of irradiated Er//2O//3 is found to be 46 h.
Physics and dynamics of plasma in laser-induced breakdown spectroscopy
(Elsevier, 2020) V.N. Rai; Surya N. Thakur
The basic physics of laser-plasma interaction, plasma emission, and its different models along with the effects of various parameters (laser and target material) on laser-induced breakdown spectroscopy (LIBS) are presented. Physical processes affecting the plasma dynamics are also discussed with a simple model describing the enhancement in plasma emission during single- and double-pulse LIBS. It has been shown that laser intensity, its time duration, density, and temperature of plasma along with plasma confinement affect the intensity of plasma emission so that the sensitivity of LIBS can be optimized. © 2020 Elsevier B.V. All rights reserved.
Physics of Plasma in Laser-Induced Breakdown Spectroscopy
(Elsevier, 2007) V.N. Rai; S.N. Thakur
[No abstract available]