The laser interferometer: Application to plasma diagnostics

A laser interferometer employing a reference arm with a spherical mirror is discussed. This interferometer is extremely promising in many fields of scientific endeavor, for instance, in plasma physics, due to its simplicity and high sensitivity. Its sensitivity is greater than that of a similar interferometer with planar mirrors because the closely spaced normal modes with nonzero transverse indexes can easily be resolved in the former but not in the latter. Special attention is given to describing the principle of operation, discussing the optimum geometrical conditions for both the laser resonant structure and the reference arm, and discussing the sensitivity limitations. Some experimental measurements of electron densities in gaseous plasmas are also presented.