The answer depends on what specifically you are trying to achieve.

(I) In a spectrometer, rather than using a prism, more often a grating is being used.

(II) If the purpose is to measure the index of refection of the materials that is used to make the prism then you may use the angle of minimum deviation to determine the index of refraction: https://www.teachengineering.org/activities/view/uoh_invisible_activity1

(III) The other approach might be based on the critical angle: http://www.kpatents.com/assets/files/downloads/refractive_index_principle.pdf

(IV) You may also use index matching techniques: https://notes.tyrocity.com/refractive-index-of-material-of-a-prism-i-d-curve-method/

(V) Some other approaches are described in the following link: https://www.aplustopper.com/measure-refractive-index/.

hi,

Apart from agreeing with what Bahram Roughani said, you could also use a simple approach by integrating xerox scanner tube (from a thrown away machine if funding is the problem!!!) and use its data for measuring the displace path of the ray of light. For an inferior option would be to use an array of discrete optical sensors like some photodiodes/LDR alongwith either programmable instrumentation or simple measure voltages across them, you will get a workable refractometer at your disposal.

Regards

To my mind in project like You have, for determination refraction index (RI) You can use Brewster refractometry: RI=tan(brw) where (brw) is angle for which exists minimum of power reflection p-polarized laser beam. Your material has to have just one optical surface to make measurement. Accuracy of measurement: if angle was measured up to 1 minute, RI get known in third sign after coma (1.123)