Afocal Coupled Etalons. DEM: A High-Reolution Double-Etalon Modulator Spectrometer

摘要

The properties of a spectroscopic device consisting of two etalons coupled by an afocal system, and which behaves as a high-luminosity single-etalon single-aperture Fabry-Perot spectrometer, have been investigated. Although the high luminosity behavior is one of the many states in which a coupled dual-etalon system can exist, mainly the high-luminosity condition has been studied in detail here. This condition is reached when the orders of the etalons comprising the device are related by n sub 01 = n sub 02 1/eta-sq, where the coupling constant is defined as eta = mu 1/mu2 f1 1/f2 and mu sub i and sub i are the indices of refraction and coupling lens focal length associated with the ith etalon. In high-luminosity conditions, one of the etalons serves as a multiple annuli mask for the other thus making it possible to use many of these annuli to achieve the desired high throughput. The limitation on the number of orders usable is given by the (small) nonlinearity in the matching of these orders, because of the different etalon gaps. The results of the study show that luminosity gains near 100 (when compared with a single-etalon single-aperture Fabry-Perot spectrometer) are possible at high resolving powers. This occurs when the coupling constant eta is not too far from unity. It is also shown that this device, or double-etalon modulator (DEM), is a compensated spectrometer since the gain increase with increasing resolving power. Other practical limitations, such as the beam walk-off from the edges of finite size etalons, are discussed. Reprints. (JHD)