A high resolution scanning confocal interferometer.
A quasi-paraxial ray tracing calculation is used to investigate the illumination requirements of confocal cavities. It is shown that the additional reflections (four per round trip as compared with two for the traditional Fabry-Perot interferometer) do not degrade the resolving power of the etalon. The need to clarify the concept of free spectral range is established and a tentative revision is suggested and justified. Construction and performance details of a 15-cm confocal interferometer are given. With a free spectral range C/2R(0) of 1 GHz, a finesse of 333 has been achieved yielding a peak width of 3 MHz and resolving power of 1.58 x 10(8) (at 6328 A).
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