Why in professional spectroscopes diffraction gratings are used instead of prisms? Why in professional spectroscopes diffraction gratings are used instead of prisms?
I guess transparency is not an issue, as we need optics anyway.
 A: I found a comparison  of the two possibilities and it seems that prisms are better.
This manual  for a spectroscope used for jewelry stones, gives higher marks to the diffraction grating towards the red part of the spectrum, where the crystal gets lower efficiency. It seems the efficiency for the grating is uniform for the whole spectrum. It is also possible that economically it might be cheaper to use a grating than three crystals, as this particular brand proposes to solve the efficiency for crystals.
A: Just compare the resolution of the two:


*

*Prism depending on n, there is no good material n>1.7 (besides diamond)

*depending on base length if you use a equilateral triangle

*have to use more than one to overcome this

*prism absorb light, you have got scattering (stray light) too


Now a grating:


*

*optimize it for your wavelength

*choose lines per milimeter

*resolution depending on the number of lines that are illuminated

*compact device

*just transmission gratings have got absorption, you can do your measurement in reflection with a blazed grating

*design your blazed grating to get the most light in e.g. 2nd order


Quantitatively
Prism: $\frac{\lambda}{\Delta \lambda} = t \frac{dn}{d\lambda}$
Grating: $\frac{\lambda}{\Delta \lambda} = \frac{zD}{g}=zN$
where t is your base length, z... order of spectrum, g...grating constant, D...entrance beam diameter, N...number of illuminated lines
So just use a grating, nowadays they can be fabricated in excellent quality. On my university learning the pros of a diffraction grating is part of the 1st year laboratory exercises.
A: One reason prisms are not preferred is that their quality is directly proportional to their size; if you want to make a decent spectroscope using a prism, you may not be able to carry it.
A: In addition, glass prism will experience its resonance frequency absorption at certain wavelength (eg: some glasses absorb UV). That why it is not a brilliant choice to disperse the light spectrum in most of the professional spectroscopy.
