Improvements in or relating to optical masers

摘要

1,083,534. Lasers. WESTERN ELECTRIC CO. Inc. June 16, 1966 [June 23, 1965 (2)], No. 26949/66. Heading H1C. A laser comprises a primary optical cavity resonator formed by first and second reflective elements and has disposed in the cavity an optical energy divider which diverts a portion of the energy from the primary cavity on to a third reflective member disposed external to the primary cavity. In the laser shown in Fig. 1 a gaseous active medium, e.g. helium-neon is disposed in an optical cavity formed by mirrors 11, 12 one of which or both may be partially transmissive and is pumped by an RF discharge as shown or by D.C. excitation. Disposed within the cavity is a half silvered mirror acting as a beam splitter which transmits half of the optical energy incident thereon from the active medium on to mirror 12 and reflects half on to mirror 14. By selecting the difference between L 2 and L 3 to be much greater than the wavelength of the stimulated emission a small change in the wavelength will result in a large change in the reflection coefficient R looking along axis 15 from the active medium towards beam splitter 13. Since this coefficient substantially controls the mode losses the side frequencies of the laser spaced by the order of 150 megacycles from the desired centre frequency will be characterized by significantly lower reflection coefficients and will be suppressed. The distance L 3 is normally varied. In the arrangement of Fig. 3 (not shown) the beam splitter is positioned between mirror 11 and the active medium so that energy propagating to the right along the primary cavity axis towards the beam splitter is split, a portion proceeding on through the active medium to primary cavity mirror 12 and the remainder proceeding to auxiliary cavity reflector (141). A secondary resonance is established for energy propagating between reflectors 11 and (141) via the beam splitter which affects the gain curve of the primary cavity, Fig. 4 (not shown), the secondary cavity being made to have a narrower band reflective characteristic than the primary cavity so that unwanted longitudinal modes are suppressed. The auxiliary cavity is tuned by varying the distance between the beam splitter and the auxiliary reflector.