Dispersive prisms are typically used at the minimum angle of deviation. This is the angle for which the wavelength of interest will travel parallel to the base of the prism, and the angle of incidence is equal to the angle of refraction when measured with respect to the normal of the prism face at the respective interface. At the minimum angle of deviation, a maximum clear aperture is achieved and reflective loss of P-polarized light is reduced since the angle of incidence is nearly Brewster's angle. For S-polarization, a custom antireflective coating can be used to minimize surface reflections.

Highly recommended Equilateral Prism list from Yutai Optics:
UV Fused Silica Equilateral Prism,
H-K9L(BK7) Equilateral Prism,
F4(nd data=1.62005) Equilateral Prism, 
H-ZF13(nd data=1.78472) Equilateral Prism, 
CaF2 Equilateral Prism,
ZnSe Equilateral Prism,
Si/Ge Equilateral Prism.