Dual, parallel cavity Fabry-Perot interferometer

摘要

Laser Doppler shift velocimetry operating in the fringe mode is widely used to record the velocity history of optically reflective solid objects. When the object is rapidly accelerated, the time resolution of the Fabry-Perot Interferometer (FPI)/streak camera system is frequently inadequate to unambiguously record the data. That is, there is a (open quotes)dead time(close quotes) during which fringes form and expand without producing a resolvable record. To remedy this, we have developed a dual, parallel cavity FPI which produces two sets of fringes at the slit of the recording streak camera. The input mirror of the FPI is a conventional flat while the output mirror is stepped so there are two mirror spacings. The input light is divided by the respective areas of the stepped mirror to form two sets of fringes; a higher quality set of fringes (open quotes)A(close quotes) is used to determine the velocity history while a second set of fringes (open quotes)B(close quotes) is used as a (open quotes)referee(close quotes) to determine the number of fringe jumps during the (open quotes)dead time.(close quotes) Since the two sets of fringes are necessarily interleaved, there is a possibility of fringe overlap, i.e., fringes of set A can spatially overlap fringes of set B. To date, two dual cavity FPI's have been successfully constructed and characterized. The theory of operation, details of construction, and the results are described.