The 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 the entrance and exit faces. Alternatively, the hypotenuse face can be used in external reflection, and coating with a metallic reflective coating。