Abstract: Articulated arm for guiding infrared radiation, with preferred wavelength between about 1 .mu.m and about 100 .mu.m, from a typically stationary radiation source to a moving or movable target. The inventive arm comprises hollow waveguides of the Marcatili-Schmeltzer type, with preferred bore diameter between about 50 and about 200 wavelengths of the radiation to be guided in the bore. Preferred waveguides consist of glass or quartz tubes of cylindrical cross section. The waveguides are typically held coaxially inside straight tubular members, the members being connected movably in end-to-end fashion. Beam direction altering means, for instance, reflecting means such as plane mirrors, serve to direct the radiation from the output end of one waveguide into the input end of the next waveguide. The articulated arm according to the invention typically is mode preserving, e.g., single mode radiation remains single mode, has high pointing accuracy, i.e.

Abstract: A laser surgical instrument uses a CO.sub.2 laser source and an articulated arm structure to maintain single mode transmission of a 10.6 .mu.m beam to probe. In one configuration, high power is maintained for photo-transection and/or photocauterization. A second probe embodiment introduces other degrees of functionality such as aspiration, irrigation and internal viewing. Internal illumination is achieved by using the sheaths of quartz waveguides to transmit visible light while the laser beam is propagated internally in the waveguide structure.