Abstract: An unstable ring resonator employing grazing incidence telescopic mirrors to expand a high power laser beam after it emerges from the wiggler. The grazing incidence mirror is used to increase the footprint of the laser beam on the mirrors surface to decrease the laser's intensity on the surface of the mirror, and thus increase the power of the laser which can be handled in a ring resonator. The ring resonator consists of a scraper mirror 12, a turning mirror 13, a grazing incident beam reduction telescope 101 comprising mirror components 1 and 2, a wiggler 4, a grazing incident beam expansion telescope 102 comprising mirror components 6 and 7 and a second turning mirror 14. The grazing incident telescopes can have mirror components which are of the cone/cone, hyperbola/parabola, cylinder/cylinder or hyperboloid/paraboloid type. The telescopes may also have three or more optical elements.

Abstract: A self-aligning, high-power, free electron laser (FEL) oscillator 10, comprises a self-aligning feedback, element 12 located near the electron beam input end 14 l of the FEL wiggler 16; a partially transmitting stimulated Brillouin scattering (SBS) plasma mirror 18 located near the output end 20 of the laser wiggler 16; and a plurality of laser beam expansion elements 32-32.sup.n located in succession on the path of the resulting output laser beam 34 for magnifying the output laser beam 34 to a desired output diameter. A totally reflecting, removable start-up mirror 30 is located between SBS plasma mirror 18 and laser beam expansion elements 32-32.sup.n. The removable start-up mirror 30 provides feedback until the SBS threshold is reached.

Abstract: An apparatus and method for enhancing the efficiency of a free electron laser, (10). A plurality of electrodes, (28) are imbedded in an electrically insulating vacuum tube, (18) enclosing the electron beam, (14) and its copropagating electromagnetic wave. A variable computer controlled high voltage d.c. power supply, (29) is connected to the electrodes, (28) for energizing the electrodes, (28) at saturation indicated by detectors, (30) thereby converting d.c. electric potential to electromagnetic radiation without gain degradation.