Littrow prisms are products manufactured by Altechna that can be used as retro-reflecting Brewster prisms. They are specifically designed which makes the beam moving into the Brewster angle falls usual to the flat surface and is bounced back on the same course.
These prisms are best used in laser cavities where the selection of the wavelength returen is possible through tilting the prism slightly. By doing this, the cavity's gain is tuneable to a distinctive laser line. The material used in manufacturing these prisms is the BK7.