| 摘要 |
1,055,398. Lasers. HUGHES AIRCRAFT CO. June 4, 1964 [June 24, 1963], No. 23237/64. Heading H1C. In a laser, Fig. 1, comprising an active medium 13 such as a ruby rod and an optical resonator formed by reflecting surfaces 17, a particular mode of oscillation is preselected from the plurality of oscillation modes within the frequency range selected by the resonator. To this end the reflecting surfaces are appropriately curved and one surface is silvered only at the regions where the required mode or modes emerge. In a modification, Fig. 5, detached reflectors 21 are used and an opaque screen 23 suitably apertured in the shape of the desired mode pattern is placed between the active medium and one reflector. The position of the reflective regions in the embodiment shown in Fig. 1 is determined by the steps of (1) lapping the ends of a ruby rod to form end curvatures corresponding to the desired transverse mode, (2) evaporating silver on to the end surfaces, (3) exciting the active medium by a non- uniform pumping field 19 and examining photographically the mode patterns at the emergent end of the ruby rod during laser action very close to threshold pump power, (4) varying the pump energy distribution around the periphery of the ruby until the desired mode pattern is obtained, and (5) removing, e.g. by etching, the silver from one end surface of the rod except where the required modes are located. Removal of the unwanted silvering on one of the reflecting surfaces may be effected by depositing photo-resist on the surface and exposing it while the laser is operating in the desired mode. Subsequently the unexposed portion of the resist and underlying silver is removed. Fig. 2A to Fig. 2C show the regions where transverse modes emerge for one, two and three electromagnetic field lobes respectively. The non-uniform pumping field may be provided by the use of an elliptical reflector or by placing adjustable opaque strips between the pumping source and the active medium. |
