Analytical design of an advanced Littrow–Offner spectrometersimultaneously off-axis in meridian and sagittal planes for ultravioletimaging with high performance

A novel, to the best of our knowledge, configuration of a Littrow–Offner spectrometer that is off-axis in both the meridian and sagittal planes is proposed. Through theoretical analysis, the relationship between the distance of each element and the aperture is obtained, and the theoretical basis of the sagittal plane off-axis is given. Extra aberrations are corrected by a spherical lens with a convex grating. An example of design has been presented with an f -number of 4 working in 300–500 nm, according to the theory. Its spectral resolution achieves a 0.1 nm at central wavelength, and its volume decreases by 14.5% compared with the traditional Offner spectrometer.