A Doppler Shift Interferometric Technique for Measuring Small Absorption Coefficients.
Abstract
An automated laser Doppler interferometer is used to measure low absorption coefficients in infrared transmitting materials. The Hewlett-Packard interferometer employs a He-Ne laser whose lasing level is Zeeman split by an axial magnetic field into two frequencies. Half of the interferometer beam is optically self-heterodyned to supply a local oscillator frequency while the other half of the beam is frequency separated by polarization filters. One frequency is isolated and the other is transmitted through the infrared test window and returned. When the test material is irradiated by a CO2 laser, the transmitted He-Ne beam undergoes a Doppler shift due to thermally induced changes in optical path through the window. The resulting Doppler shift is detected by optically heterodyning the transmitted beam with the isolated portion and subtracting the local oscillator frequency. The shift is thus used to remotely monitor rate of thermal rise in the window sample and thereby to measure the optical absorption coefficient. This technique is compared to standard adiabatic calorimetry with a view toward eliminating many experimental difficulties inherent in the latter method. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Dec 20, 1973
- Accession Number
- AD0778077
Entities
People
- Alfred Kahan
- Audun Hordvik
- Lyn H. Skolnik
- Martin Clark
Organizations
- Air Force Cambridge Research Laboratories