Right-angle prisms are often preferable to 

an inclined mirror in applications involving 

severe acoustic or inertial loads. This is 

because a right-angle prism is easier to mount 

and deforms much less than a mirror in response 

to external mechanical stress. Very high transmission 

can be achieved by using the hypotenuse face in total 

internal reflection, and by antireflective coating 

on the entrance and exit faces. Alternatively, 

the hypotenuse face can be used in external reflection, 

and coating with a metallic reflective coating.