Collection optics for a Raman spectrometer based on the 90° geometry of scattered light collection

In the present work, efficiency of classical lens, mirror-lens, and pure mirror variants of the collection optics for a Raman spectrometer based on 90° geometry of scattered light collection is investigated. It is experimentally established that, despite a smaller collection angle, in the case of a relatively narrow input slit of the spectrometer (<100  μm), the lens optics with corrected off-axis and chromatic aberrations allows larger signal intensities to be registered. However, the low f/# mirror collection optics described in the work provide a more stable adjustment and can be used to increase the Raman signal intensities in cases when the image of the scattering volume formed by them is commensurable with the sizes of the input slit of the spectrometer.