Performances are presented of three classes of imaging slit spectrometers for extended sources with aberration-corrected gratings. A general analytical expression for minimizing off-axis grating aberrations is obtained, and it is demonstrated that these aberrations are minimized when the spectrometer is operated at a magnification higher than unity. Classical designs with toroidal uniform-line-spaced (TULS) or spherical varied-line-space (SVLS) gratings are compared with a new class of designs that utilize toroidal varied-line-space (TVLS) gratings. Although TULS and SVLS designs with two stigmatic points can be designed to operate at near-unity magnification with excellent on-axis spectral and spatial resolutions, they cannot be made to satisfy the general off-axis condition, and so their off-axis performances are not optimum. On the contrary TVLS designs with two stigmatic points can be operated at almost any magnification, thus satisfying the off-axis condition perfectly. Such designs are suitable for imaging spectrometer observations that require an extended field of view.
© 2004 Optical Society of America
(050.1950) Diffraction and gratings : Diffraction gratings
(080.1010) Geometric optics : Aberrations (global)
(120.6200) Instrumentation, measurement, and metrology : Spectrometers and spectroscopic instrumentation
(220.1000) Optical design and fabrication : Aberration compensation
Luca Poletto and Roger J. Thomas, "Stigmatic Spectrometers for Extended Sources: Design with Toroidal Varied-Line-Space Gratings," Appl. Opt. 43, 2029-2038 (2004)