Double-beam optical method and apparatus for measuring thermal diffusivity and other molecular dynamic processes in utilizing the transient thermal lens effect

An apparatus for measuring thermal diffusivity of a sample material comprising:

• a pulsed laser light source for providing a plurality of laser light pulses directed at a sample material, the duration of each pulse being chosen so that each pulse forms a transient thermal lens in said sample material, and the repetition rate of said pulses being chosen so that each thermal lens formed is substantially dissipated before generation of the next pulse;
• a probe light beam source for providing a probe light beam directed to irradiate said thermal lens during at least a portion of the time said thermal lens is dissipating;
• a probe light beam focusing lens located between said probe light beam source and said sample material, said focusing lens providing a converging/diverging beam with a focal point at a predetermined location with respect to said thermal lens, thereby resulting in an intensity alteration of said probe light beam as a result of irradiating said thermal lens;
• and
• detecting means for providing a plurality of intensity versus time profiles corresponding to a plurality of positions within a portion of said probe light beam after having irradiated said thermal lens, said plurality of intensity versus time profiles being related to the thermal diffusivity of said sample material.

An apparatus for measuring molecular relaxation characteristics of a sample material comprising:

• a pulsed laser light source for providing a pulsed laser light beam directed to irradiate said sample material whose molecular relaxation characteristics are to be measured, said pulsed laser light beam being chosen to cause formation of a thermal lens in said sample material;
• a probe light beam source for providing a probe light beam directed to irradiate said thermal lens;
• a probe light beam focusing lens located between said probe light beam source and said sample material, said focusing lens providing a converging/diverging beam with a focal point at a predetermined location with respect to said thermal lens, thereby resulting in an intensity alteration of said probe light beam as a result of irradiating said thermal lens;
• and
• means for detecting the intensity of at least a portion of said probe light beam after having irradiated said thermal lens during the formation of said thermal lens, thereby providing an intensity versus time profile related to the molecular relaxation characteristics of said sample material.