In Fabry–Perot interferometry a large fraction of light can be reflected by the etalon; thus, it is lost for spectroscopic purposes. The present article shows the possibility of recovering this light, collecting it by means of reflectors and sending it back to the etalon under a different angle. Some devices are examined and some experimental proofs of the device are reported. The gain achieved is of the order of five.
© 1967 Optical Society of America
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