A double-pass dispersion interferometer based on a 9.6-µ m ëé 2 laser with a sensitivity of 〈 n e l 〉 min 1 × 10 13 cm -2 and a temporal resolution of ~50 µ s, designed to measure linear plasma density, is described. A ZnGeP 2 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.

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