CO2-Laser Interferometer for the Measurement of Transient Low-Density Plasmas

A coupled cavity CO2-laser interferometer is described. The feedback is achieved either with (a) a rotating corner mirror or (b) an oscillating mirror. For method (a) a sensitivity of ∫ndl≥5×1014cm−2 and time resolution of 0.2 μsec is obtained. Method (b) is more sensitive (∫ndl≥1013cm−2) but the time resolution is limited by the fact that signal amplitudes are strongly frequency dependent above 350 kc. The interferometer has been used to measure plasma densities of the Scylla IA θ pinch.