Question

What effect would you expect a spectroscope with a diffraction grating of 600 lines mm to have on sharpness and resolution in your spectrum

Answer 1

Answer :)

Spectral resolution in a dispersive spectrometer is determined by four main factors. In the discussions below, the effect of each factor is considered under the assumption that all other factors remain unchanged.

(i) Spectrometer focal length – the longer the focal length (e.g., the distance between the dispersing grating and detector) of the spectrometer the higher the spectral resolution.

(ii) Diffraction grating – the higher the groove density of the grating (typically measured as number of grooves per millimetre), the higher the spectral resolution.

(iii) Laser wavelength – the dispersing power of a grating/spectrometer pair can usually be considered constant in terms of wavelength. number, cm^-1) which means that the spectral resolution decreases as the laser excitation is changed from infra-red to visible to ultra-violet wavelengths. As an example, if a 600gr/mm grating is used with an infra-red laser, a 1200gr/mm or 1800gr/mm will be required with a green laser to achieve a similar resolution.

(iv) Detector – most systems have a single detector, so practically the user does not have control of this factor. However, it should be noted that different detectors can be configured with different pixel sizes. The smaller the pixel the higher the achievable spectral resolution