A multi-axis prosthetic ankle for connection of a prosthetic lower leg to a prosthetic foot. In order to adjust the position of the focus of the beam of rays in the direction of the beam of rays, and optical element of the input optics can be displaced relative to the deflecting device. Surface treatment is then performed on a surface of the \u03b1-Si layer. As a result, a current of air is generated from the communication passage to the vacuum passage, and foreign particles are suctioned and removed from the space.