A Dispersion Interferometer Based on a CO2 Laser

A double-pass dispersion interferometer based on a 9.6-µm CO2 laser with a sensitivity of 〈 n e l〉min ∼ 1 × 1013 cm−2 and a temporal resolution of ∼50 µ s, designed to measure linear plasma density, is described. A ZnGeP2 nonlinear crystal is used as the frequency doubler. The main advantages of the interferometer are its compactness and a low sensitivity to vibrations of optical elements. The interferometer requires no special vibration isolation. Its main components are arranged compactly on an optical bench outside the apparatus, except for a window for radiation injection and a retroreflector; these are mounted on the wall of the experimental facility's vacuum chamber. The advantages of the dispersion interferometer have been demonstrated in an experiment with a gas-dynamic trap.