Compact Offner-Wynne imaging spectrometers

Some ideas that were developed by Wynne to improve the performance of the Offner unit magnification imaging system are used to design Offner imaging spectrometers to which a concentric meniscus lens has been added. The new degrees of freedom associated to the meniscus lens allow removing image aberrations far from the paraxial region in a wide annular area or even more, in two concentric annular areas. This provides a great flexibility of design as it is shown below in four examples. In these examples, the slit length, the f-number or the spectral resolution has been optimized while retaining almost diffraction-limited spot size, with rather separate slit and image, and getting quite compact designs in comparison to the original Offner system. In particular, the most compact system (~50×40×30mm3) has an f-number of 1.86, a slit length of 9.6 mm and covers a spectral range from 400 to 1000 nm, being diffraction-limited for wavelengths longer than 450 nm.