| 摘要 |
1,211,119. Scanning lasers. INTERNATIONAL BUSINESS MACHINES CORP. 3 April 1968 [28 April, 1967], No. 16015/68. Heading H1C. A laser 8, having a partially light transmitting resonator reflector 5a and elements 5, 7 for selecting a particular spatial mode, is associated with a light amplifier 10, which amplifies light which is transmitted through reflector 5a and reflects the amplified light back into laser 8. As a result the energy density within laser 8 prior to selection of a particular mode is relatively high and the delay in the production of the selected mode after actuation of the selection elements is reduced. Elements 5, 7 each Consist of a stack of laminar electro-optic crystals, the crystals in the two stacks extending in mutually perpendicular directions. Also included in laser 8 are lenses 2, 3 and-a polarizer 6. Initially a voltage is applied to all the crystals in both stacks so that light from active medium 1, after being plane polarised by polarizer 6 becomes elliptically polarized by element 7. The light reflected from 7a then loses energy in passing through polarizer 6, a similar process occurring with element 5. Light passing through element 5 and reflector 5a, however, is amplified before being returned to the main resonator. The energy density in the cavity is thus maintained just below the laser threshold for each mode prior to selection. To select a mode the bias voltage is removed from one crystal in each stack so that the selected mode does not become elliptically polarized in elements 5, 7. The losses having been thus reduced this mode is amplified and the lasing threshold is rapidly exceeded. |
