|
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. |