We present the optical principle of a white-pupil collimator made up of two mirrors with unequal focal lengths. Analytic formulas for third-order aberrations are derived and compared with the results of ray-tracing experiments. It is shown that the image quality is good if the second mirror has a suitable conic coefficient and the <i>F</i> ratio is not too small. Furthermore, third-order coma and astigmatism can be zeroed simultaneously if the angles are also appropriately selected. When implemented in high-resolution echelle spectrographs, this design permits smaller cross dispersers and cameras, with considerable savings in cost.
© 2000 Optical Society of America
(120.1680) Instrumentation, measurement, and metrology : Collimation
(120.6200) Instrumentation, measurement, and metrology : Spectrometers and spectroscopic instrumentation
(220.1000) Optical design and fabrication : Aberration compensation
Raffaele G. Gratton, Rajiv Bhatia, and Andrea Cavazza, "Asymmetric White-Pupil Collimators for High-Resolution Spectrographs," Appl. Opt. 39, 2614-2619 (2000)