An apparatus for measuring spectral components of Raman-scattered light emitted by target. The apparatus includes: pulsed laser light source to emit light; probe optics to direct light towards target and to collect light scattered by target; optical spectrometer including: input divider to divide collected light into first and second light beams; first spectrograph including input apertures for receiving said light beams and optical disperser to disperse said light beams; second spectrograph comprising input apertures and output apertures; and spatial light modulator to receive dispersed first and second light beams and to selectively provide at least part of at least one of dispersed first and second light beams to input aperture of second spectrograph which reverses dispersion of light beam and focuses light beam to output aperture; detector element to measure spectral components of light beam exiting output aperture. Optical spectrometer further includes delay line(s) line for delaying light beam(s).