Optics: measuring and testing – For light transmission or absorption
Patent
1979-01-31
1981-01-06
Sacher, Paul A.
Optics: measuring and testing
For light transmission or absorption
73 15R, G01N 2101
Patent
active
042433274
ABSTRACT:
A method and apparatus for measuring thermal diffusivity and molecular relaxation processes in a sample material utilizing two light beams, one being a pulsed laser light beam for forming a thermal lens in the sample material, and the other being a relatively low power probe light beam for measuring changes in the refractive index of the sample material during formation and dissipation of the thermal lens. More specifically, a sample material is irradiated by relatively high power, short pulses from a dye laser. Energy from the pulses is absorbed by the sample material, thereby forming a thermal lens in the area of absorption. The pulse repetition rate is chosen so that the thermal lens is substantially dissipated by the time the next pulse reaches the sample material. A probe light beam, which in a specific embodiment is a relatively low power, continuous wave (cw) laser beam, irradiates the thermal lens formed in the sample material. The intensity characteristics of the probe light beam subsequent to irradiation of the thermal lens is related to changes in the refractive index of the sample material as the thermal lens is formed and dissipated. A plot of the changes in refractive index as a function of time during formation of the thermal lens as reflected by changes in intensity of the probe beam, provides a curve related to molecular relaxation characteristics of the material, and a plot during dissipation of the thermal lens provides a curve related to the thermal diffusivity of the sample material.
REFERENCES:
Twarowski, A. J. et al., "Multiphoton Absorption Spectra Using Thermal Blooming", Chem. Physics 20, (1977), pp. 253-258.
Buser, A. G. et al., "Transient Thermal Blooming of Single and Multiple Short Laser Pulses", Applied Optics, vol. 14, No. 11, Nov. 1975, pp. 2740-2742.
Sooy, W. R. et al., "Switching Semiconductor Reflectivity by a Giant Pulse Laser", Applied Physics Letters, vol. 5, No. 3, pp. 54-56, Aug. 1964.
Pridmore-Brown "Absorption Saturation Effects on High-Power CO.sub.2 Laser Beam Transmission", Applied Optics, vol. 12, No. 9, Sep. 1973, pp. 2188-2191.
Hu et al., "Now Thermooptical Measurement Method and a Comparison with Other Methods", Applied Optics, vol. 12, No. 1, Jan. 1973 pp. 72-79.
Frosch Robert A. Administrator of the National Aeronautics and Space
Gupta Amitava
Hong Su-Don
Moacanin Jovan
Arnold Bruce Y.
Grifka Wilfred
Manning John R.
Mott Monte F.
Sacher Paul A.
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