An apparatus for measuring time-gated Raman spectrum, the apparatus comprising: - a light source for generating a pulse of light towards a target, wherein the target will subsequently emit an optical radiation comprising at least a first portion (208, 508, 604) and a second portion of a planar wave front of the emitted optical radiation; - a sensor arrangement (118, 200) for measuring the intensity of the optical radiation; and - a controller (120, 228) operatively coupled to the light source and the sensor arrangement; wherein the sensor arrangement comprises: - at least one optical delay element (212, 214, 402, 404, 406) to provide a time delay to the first portion (208, 508, 604) of the emitted optical radiation (210, 302, 412, 706), wherein the second portion of the emitted optical radiation bypasses the at least one optical delay element; - an optical spectral disperser arranged in the optical path after the at least one optical delay element (212, 214, 402, 404, 406) to disperse the delayed first portion and the second portion of the emitted optical radiation into a dispersed radiation having a plurality of wavelengths, wherein each wavelength of the dispersed radiation is split into an angularly separate direction, and wherein the dispersed radiation of each portion exits the optical spectral disperser with predetermined relative delays; and - a sensor element (226, 314, 426, 612) configured to receive each wavelength of the dispersed radiation on a different spatial region thereof, and to measure light intensity associated with each wavelength of the dispersed radiation; and wherein the controller is operable to record the measured light intensity associated with each wavelength of the dispersed radiation measured by the sensor element to form a time-resolved optical spectrum. - a light source for generating a pulse of light towards a target, wherein the target will subsequently emit an optical radiation comprising at least a first portion (208, 508, 604) and a second portion of a planar wave front of the emitted optical radiation; - a sensor arrangement (118, 200) for measuring the intensity of the optical radiation; and - a controller (120, 228) operatively coupled to the light source and the sensor arrangement; - at least one optical delay element (212, 214, 402, 404, 406) to provide a time delay to the first portion (208, 508, 604) of the emitted optical radiation (210, 302, 412, 706), wherein the second portion of the emitted optical radiation bypasses the at least one optical delay element; - an optical spectral disperser arranged in the optical path after the at least one optical delay element (212, 214, 402, 404, 406) to disperse the delayed first portion and the second portion of the emitted optical radiation into a dispersed radiation having a plurality of wavelengths, wherein each wavelength of the dispersed radiation is split into an angularly separate direction, and wherein the dispersed radiation of each portion exits the optical spectral disperser with predetermined relative delays; and - a sensor element (226, 314, 426, 612) configured to receive each wavelength of the dispersed radiation on a different spatial region thereof, and to measure light intensity associated with each wavelength of the dispersed radiation;