Right angle prism is a refractive prism used for optical path adjustment, typically used to achieve 90 ° and 180 ° turns of light beams. Due to the principle of total internal reflection, when light is incident from one right angled surface of a right angled prism, it undergoes total internal reflection at the glass/air interface of the inclined plane and exits from the other right angled surface, causing the incident light to deflect 90 degrees. Therefore, it is very suitable as a substitute for mirrors. When the input light is incident from the inclined plane of the prism, it undergoes total internal reflection at the glass/air interface of the right angle plane, then undergoes a second total internal reflection when passing through the next right angle plane, and finally exits from the inclined plane in a direction parallel to the incident beam. This causes the incident light to deflect 180 degrees, with the same effect as a mirror