抄録
Some problems in laser interferometric measurements are discussed. Improvements are described of the rtechnique, for detecting the small fringe shift, which was proposed by one of authors.
A measurement is performed of the electron density in a decaying plasma by using an interferometer of a Ne-He laser, which works at the visible light of 0.63μ, . The plasma is produced in a 20 cm tube by a high-curent pulsed discharge· The fringe shift due to the decay of electron density is pbserved with two photomultipliers, which are located at. positionsaboUt 6m LtIA.18, y from the discharge tube. The two signals from he proemultipliers, are '.dif_ferentially amplified to eliminate the effect of lights from the discharge tube and garp switch, The minimum electron : density detected. in the vresent-re-Dort is. 9 x1013cm-3.for the plasma length. of 20cm. The value corresponds to about a 1/200 fringe. The decaycurve of the electron density determined by the laser interfero meter usedhere reasonably, connects with that measured by the 70-GHz microwave transmission method. This fact shows that the present method detecting the small fringe shift has a sufficient reliability.
