A laser beam surgical system provided with a cannula insertable into a body passage leading to a surgical site. The cannula includes a rotatable inner tube whose inlet section has two input ports, one being in line with the tube axis and being coupled to a white light source, the other being at right angles to the axis and being coupled to a carbon dioxide laser projecting a collimated beam. Supported at a 45.degree. angle within the inlet section is a pellicle that is permeable to the beam of white light impinging thereon and reflective to the laser beam whereby both are directed toward an outlet section at the other end of the tube. Supported within the outlet section at a 45.degree. angle with respect to the tube axis is a normally planar reflective membrane which directs both beams through a lateral output port toward the surgical site which is illuminated by the white light. The geometric center of the membrane is coupled at its rear to a controllable actuator which forces the membrane to assume a concave form acting optically to bring the laser beam to a focus at a target surface on the surgical site.