Bindhu, C V; Dr.Girijavallabhan,C P(Cochin University of Science and Technology, June 22, 1998)
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Abstract:
In the pre—laser era it was difficult to believe that the optical properties of a medium
depend upon the intensity of the radiation incident on it. The basis for this conclusion is
that the electric field strength associated with the conventional light sources used before
the advent of lasers was much smaller than (103 V/cm) the field sttrengths of atomic or
interatomic fields (2 107 —- 10” V/cm). The radiation with such low intensity is not able
to affect atomic fields to the extent of changing optical parameters. The invention of laser
in 1960 was a turning point. The high degree of coherence of the laser radiation provides
high spatial concentration of optical power. With the availability of the femtosecond lasers
it has become possible to get extremely high peak powers 2 1013 W/cmz). At such high
fields, the relationship between electric ‘polarization P and the electric field strength E ceases
to be linear and several nonlinear effects begin to occur. Nonlinear absorption, a branch
of nonlinear optics, refers to the interaction between radiation and matter accompanied by
absorption of more than one photon. Nonlinear absorption has acquired great importance
after the invention of high power lasers.
One of the objectives of the present work is to investigate the nonlinear absorption processes
occurring in fullerene, selected organic solvents and laser dyes. Fullerenes and laser
dyes were chosen because of their highly nonlinear behaviour. Fullerenes, the most beautiful
among molecules, offer fascinating field of research owinglto their significant structural
properties. As toluene, benzene and carbon disulphide are themost widely used solvents for
fullerenes, it seems important to study the nonlinear properties of these liquids as well. Like
fullerenes, laser dyes also possess highly delocalized 7r electrons which are responsible for their
nonlinear absorption. Dye lasers were the fulfillment of an experimenter’s pipe dream - to
have a laser that is easily tunable over a wide range of wavelengths. A better understandingof the photophysical properties of laser dyes can significantly enhance the development and
technology of dye lasers. We studied the nonlinear absorption properties of two rhodamine
dyes to have some insight into their nonlinear optical properties.
Description:
International School of Photonics, Cochin University of Science & Technology
Manjusha, M V; Dr. Jacob, Philip(Cochin University of Science and Technology, May , 2008)
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Abstract:
Photothermal spectroscopy is a group of high sensitivity methods used to measure optical absorption and thermal characteristics of a sample.The basis of photothermal spectroscopy is a photo-induced change in the thermal state of the sample.Light energy absorbed and not lost by subsequent emission results in sample heating.This heating results in a temperature change as well as changes in thermodynamic parameters of the sample which are related to temperature.Measurements of the temperature,pressure,or density changes that occur due to optical absorption are ultimately the basis for the photothermal spectroscopic methods.This is a more direct measure of optical absorption than optical transmission based spectroscopies.Sample heating is a direct consequence of optical absorption and so photothermal spectroscopy signals are directly dependent on light absorption.Scattering and reflection losses do not produce photothermal signals.Subsequently,photothermal spectroscopy more accurately measures optical absorption in scattering solutions,in solids,and at interfaces.This aspect makes it particularly attractive for application to surface and solid absorption studies,and studies in scattering media.
Description:
Department of Instrumentation,
Cochin University of Science and Technology