Optical modulators

Abstract

An optical modulator comprises a crystal (15) of material exhibiting the pyroelectric effect, and charge-dissipating means for dissipating any charge built up on the optical faces of the prism. The charge-dissipating means may comprise point electrodes (30) positioned adjacent to the optical faces (21) of the crystal and connected to an alternating-current high-voltage power supply (31). The electrodes produce charged ions which neutralize any charge on the optical faces of the crystal. The crystal may be used as the Q-switch in a laser.

We claim: 
     
       1. An optical modulator of the Q-switch type comprising: .Iadd.an optical path; .Iaddend.   a crystal of a material which exhibits the pyroelectric effect .[.and.]. .Iadd.disposed on said optical path, said crystal .Iaddend.having two opposed optical faces through which laser radiation may pass along .[.a.]. .Iadd.said optical .Iaddend.path;   means to apply an electric field to the crystal .[.ransverse.]. .Iadd.transverse .Iaddend.to said path in order to switch said modulator; and   charge-dissipating means for dissipating any static electric charge built up on the two opposed optical faces of the crystal due to the pyroelectric effect.Iadd., said charge dissipating means being disposed adjacent to said optical faces but being disposed so as normally to lie outside of said path. .Iaddend.   
     
     
       2. A modulator as claimed in claim 1 which includes ionising means located adjacent to the optical faces of the crystal and operable to generate ions of opposite polarity to the charge on said optical face. 
     
     
       3. A modulator as claimed in claim 2 in which the ionising means comprise a point electrode connected to a high-voltage power supply. 
     
     
       4. A modulator as claimed in claim 3 in which the high-voltage power supply generates an alternating voltage for application to the point electrodes. 
     
     
       5. A modulator as claimed in claim 2 in which the ionising means comprise a spark gap. 
     
     
       6. A modulator as claimed in claim 2 in which the ionising means comprise a radioactive source capable of emitting ionising radiation towards said optical faces. .[. 
     
     
       7.  A modulator as claimed in claim 1 in which the optical faces of the crystal are provided with a layer of electrically-conducting material connected to the ground..]. 
     
     
       8. A modulator as claimed in claim 1 in which each optical end face is provided with an electrically-conductive wiper movable across the said face and connected to ground. 
     
     
       9. A modulator as claimed in claim 1 which forms the Q-switch of a Q-switched laser. .Iadd.10. An optical modulator of the Q-switch type comprising: a crystal of a material which exhibits the pyroelectric effect and having two opposed optical faces through which laser radiation may pass along a path;   means to apply an electric field to the crystal transverse to said path in order to switch said modulator;   charge-dissipating means for dissipating any static electric charge built up on the two opposed optical faces of the crystal due to the pyroelectric effect; and   a radioactive source located adjacent to the optical faces, said radio active source being capable of emitting ionising radiation towards said optical faces to generate ions of opposite polarity to any static charge   
     
     
        thereon whereby to dissipate the static charge. .Iaddend. .Iadd.11.  An optical modulator of the Q-switch type comprising: a crystal of a material which exhibits the pyroelectric effect and having two opposed optical faces through which laser radiation may pass along a path; means to apply an electric field to the crystal transverse to said path in order to switch said modulator; and   charge-dissipating means for dissipating any static electric charge built up on the two opposed optical faces of the crystal due to the pyroelectric effect, which includes ionising means located adjacent to the optical faces of the crystal and operable to generate ions of opposite polarity to the charge on said optical face. .Iaddend. .Iadd.12. An optical modulator of the Q-switch type comprising:   a crystal of a material which exhibits the pyroelectric effect and having two opposed optical faces through which laser radiation may pass along a path; means to apply an electric field to the crystal transverse to said path in order to switch said modulator; and   charge-dissipating means for dissipating any static electric charge built up on the two opposed optical faces of the crystal due to the pyroelectric effect, which includes ionising means located adjacent to the optical faces of the crystal and operable to generate ions of opposite polarity to the charge on said optical face, in which the ionising means comprise a radioactive source capable of emitting ionising radiation towards said optical faces. .Iaddend.