Abstract: A high power convective flow gas laser having reduced aberration is characterized by negative branch unstable resonator configuration. The present laser is configured to invert an intracavity beam about a focal point within the optical cavity, thereby avoiding a region of high temperature gas located adjacent to the excitation cathode. The present laser has an output beam whose profile corresponds to the theoretical annular shape and is further characterized by an extraction efficiency on par with those of known lasers.

Abstract: An unstable resonator system is controlled in polarization by the use of a compound resonator in which the parent resonator is coupled to a polarization control leg by an aperture that passes a small portion of the output beam into a polarization control element and returns a polarized feedback beam mode-matched to the adjoint mode of the parent resonator.

Abstract: An unstable laser resonator is controlled in polarization by the use of a control leg coupled to the parent resonator and having a linear polarization control element therein, so that control of a low power beam in said control leg serves to control the polarization of the parent resonator.

Abstract: An unstable resonator, dc excited, is pulsed using an adjoint coupled beam of low power as the pulsing element. The resonator feedback consists of the self-feedback and the adjoint beam feedback. The self-feedback can be sufficient for self-oscillation and pulsed operation can be achieved by controlling the repetition rate and the magnitude of the adjoint beam power. Complete control and shut-off between pulses with complete freedom of repetition rate is achieved if the self-feedback is insufficient for laser oscillation. The invention was demonstrated on a 10 kilowatt average power CO.sub.2 laser with pulse control provided by with a 100 watt adjoint feedback beam.

Abstract: A monitoring arrangement monitors the power of a light beam which travels in a predetermined path between a laser and a destination location and is reflected at a predetermined location of the path from a reflecting surface of a deflecting mirror, with attendant inherent light scattering into a space portion. The monitoring arrangement includes at least one sensor situated in a space portion having the reflecting surface and imaginary extensions thereof for its boundary and including the predetermined path. The sensor is located between a reflected portion of the light beam and the boundary, preferably close to the boundary, to intercept and sense scattered light reaching it, especially forward-scattered light of the original laser beam, and generates a signal representative of the intensity of such intercepted scattered light. This signal is then evaluated.

Abstract: A laser pipe welding system for welding 360.degree. around a pipe includes a pair of focusing heads each welding half the pipe circumference, a seam tracker to keep the focal spot on the seam to compensate for axial and radial variations, an active beam alignment system for real-time compensation of angular misalignment, and both passive and active-feedback beam transport systems that flexibly follow the focus head.

Abstract: A damage resistant laser mirror is disclosed comprising a copper substrate highly polished to an optical finish coated with a thin layer of molybdenum or tungsten. The composite has good reflecting properties, is damage-tough, and conducts heat well away from the reflective coating. The superior adhesion of the coating is demonstrated by the fact that severe staining can be removed from the surface of the mirror by abrasive polishing without removing or damaging the coating.

Abstract: An apparatus adapted for rotating a beam of radiation to obtain azimuthal and radial time averaging of the intensity distribution incident onto a workpiece is disclosed. The apparatus includes a housing adapted for rotation about a centerline axis, an entrance port and an exit port adapted for transmitting a beam of radiation through the housing, an inverter disposed within an internal passage within the housing and fixedly attached to the housing for rotation therewith includes a first mirror having a reflective surface angularly disposed to the rotation axis adapted for reflecting radiation incident thereon to a second mirror, a second mirror having a reflective surface adapted for reflecting radiation incident thereon to a third mirror having a reflective surface angularly disposed to the rotation axis adapted for passing radiation incident thereon through the exit port.