| 摘要 |
A body transparent to laser radiation, such as an optical fiber or a preform thereof, is transluminated by a monochromatic beam of a frequency in the THz range split off from a composite laser beam with two closely spaced frequencies produced by the Zeeman effect; the width of that beam in a plane transverse to the body axis is at least equal to the diameter of that body. Another monochromatic beam at the second laser frequency bypasses the transparent body and is recombined with the first beam downstream of the transluminated body to form a field of radiation which is photoelectrically sampled at closely spaced locations in the aforementioned transverse plane to provide a multiplicity of electrtical signals in the MHz range differing in phase from a reference wave of the same frequency photoelectrically obtained from the same monochromatic beams. The phase differences, determined by a comparator, are fed to a calculator computing the refractive-index profile therefrom.
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