Abstract
The analytical description of the twin-etalon scanning spectrometer (TESS), i.e., an enhanced Fabry-Perot spectrometer, is presented in detail. Practical gains of >100 are attainable with this device, and it is also shown that this instrument is competitive with the spherical Fabry-Perot but with the ability to change the resolution at will. The spectral properties of the TESS are investigated for the determination of Doppler widths and shifts to emphasize the similarities and slight differences between this instrument and the single-etalon single-aperture Fabry-Perot. Practical considerations and tolerances required for operation of the TESS are discussed.