| 摘要 |
A sensitive, noise-free ellipsometer measures depolarization of an incident beam by forming from the reference and signal components of the incident beam a signal component polarized in one direction, and a frequency shifted local oscillator component polarized in the same direction, with these latter components being optically heterodyned at a detector. In the formation of the local oscillator component, the reference component of the incident beam is shifted in frequency from that of the signal component of the incident beam and rotated 90 DEG from its original orientation so that optical heterodyning can take place. This is accomplished by passing the incident beam through a shear-wave, traveling wave acoustic modulator which forms local oscillator and signal beams, each having rotated and frequency shifted components, and unrotated and unshifted components. Thereafter, all the light from the modulator is incident on a polarization analyzer which selects for heterodyning the unshifted, unrotated components of the signal beam and shifted, rotated components of the local oscillator beam. The shear wave action of the modulator operates to provide the rotation, while the traveling wave action of the modulator assures that the frequency shift is in only one direction.
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