2波長レーザービート法のプラズマ計測への応用

抄録

When measuring the variation of refractive index of plasmas by the conventional optical interferometry, the light intensity is found to vary with cos φ(t), where φ(t) is the phase shift. Moreover, when the refractive index changes intricately, thereby producing a complex fringe pattern, it is difficult to detect the change in refractive index exactly. An application of an interferometry, which is a modification of the two wavelengths laser interferometry, is introduced here for measuring the variation of the refractive index of a plasma behind a shock front directly from the pattern observed on the oscilloscope. A laser light is split into two components whose spectra are adjacent to each other in the longitudinal laser modes. After one of the light components passes through the medium whose refractive index varies with time, the split components are made to join each other. The beat frequency between the two light components is modulated, and the signal of the beat is integrated after frequency detection.