According to certain examples a spectrometer module for use in an imaging spectrometer includes a monolithic spectrometer body component made of an immersion material and including three mirrored surfaces configured to form a reflective triplet having an optical path immersed within the immersion material, the reflective triplet configured to receive incident optical radiation from an entrance face of the monolithic spectrometer body component and reflect the incident optical radiation along the optical path, and a dispersive element configured to receive and disperse the incident optical radiation reflected from the reflective triplet to provide dispersed optical radiation. The reflective triplet is configured to receive the dispersed optical radiation from the dispersive element and to reflect the dispersed optical radiation along the optical path to an exit face of the monolithic spectrometer body component.