Laser system having electronically selectable gain

Abstract

A laser system for selectively producing, in response to electronic signals, laser pulses at random intervals and of preselected and variable energy, including a laser cavity capable of being electronically controlled to effect a selectively variable gain. An acousto-optic deflector is disposed in the laser cavity and the amount of acoustic energy applied to the deflector controls the amount of radiation feedback to the laser rod and thus controls the Q or gain of the laser system to any of a wide range of selectable values.

What is claimed is: 
     
       1. A laser system for selectively producing variable energy laser pulses at variable time intervals comprising: a. a laser cavity that includes a lasing medium .Iadd.and at least one reflecting means positioned along a line intersecting the longitudinal axis of the lasing medium and angularly displaced from said longitudinal axis to form a preselected angle therewith.Iaddend.;   b. means for increasing the population inversion in said lasing medium to stimulate emission of a beam of energy therefrom;   c. control means disposed within said laser cavity for selectively controlling both the energy level of respective output pulses and the time duration between successive pulses, said control means effective to deflect a fraction of said beam at .[.a.]. .Iadd.said .Iaddend.preselected angle responsive to application of ultrasonic power thereto, said fraction being a monotonic increasing function of said ultrasonic power; and   d. logic circuitry connected to said control means for selectively applying said ultrasonic power at selected power levels to control the fraction of said beam deflected at said angle, said deflected fraction being reflected .Iadd.by said at least one reflecting means .Iaddend.to provide energy feedback to said lasing medium, a laser output pulse being produced responsive to said reflected fraction lowering the lasing threshold of said cavity to a value below the level of population inversion in said lasing medium at that time, the energy of said pulse being defined by the amount that said lasing threshold is lowered below the population inversion level.   
     
     
       2. A laser system as set forth in claim 1 wherein said control means comprises an acousto-optic beam deflector operable to deflect radiation emitted by said lasing medium, the fraction of radiation from said .[.laser.]. .Iadd.lasing .Iaddend.medium that is deflected being proportional to the power applied to said deflector from said .[.control means.]. .Iadd.logic circuitry.Iaddend. . 
     
     
       3. A laser system for selectively producing at random intervals laser pulses of variable energy comprising: a. a laser cavity that includes a rod of lasing material between first and second reflecting means, said second reflecting means being positioned along a line that forms a preselected angle with the longitudinal axis of said laser rod;   b. means for increasing the population inversion in said lasing material to stimulate emission of a beam of energy therefrom;   c. an acousto-optic beam deflector disposed substantially along said longitudinal axis between said laser rod and said second reflecting means operable to selectively control the lasing threshold of said cavity, said deflector effective to deflect a fraction of said beam at said preselected angle .Iadd.in .Iaddend.response to application of ultrasonic power thereto, said fraction being a monotonic increasing function of said power, said deflected fraction defining the amount of energy feedback to said laser rod; and   d. logic circuitry connected to said deflector for selectively applying said ultrasonic power at selected power levels to control the fraction of said beam deflected, thereby controlling the energy level of respective pulses and the time interval therebetween.   
     
     
       4. A laser system as set forth in claim 3 including third .[.reflective.]. .Iadd.reflecting .Iaddend.means disposed along a line joining said second .[.reflective.]. .Iadd.reflecting .Iaddend.means and said deflector, said third .[.reflective.]. .Iadd.reflecting .Iaddend.means being positioned such that said deflector lies between said second and third .[.reflective.]. .Iadd.reflecting .Iaddend.means. 
     
     
       5. A laser system as set forth in claim 4 and further including a fourth .[.reflective.]. .Iadd.reflecting .Iaddend.means disposed along said longitudinal axis, said fourth reflecting means being positioned on the same side of said deflector as said second .[.reflective.]. .Iadd.reflecting .Iaddend.means and being operable to provide a selected amount of feedback to said laser rod. 
     
     
       6. A laser system for selectively producing variable energy pulses at variable time intervals comprising: a. a laser cavity including a .[.laser rod.]. .Iadd.lasing medium .Iaddend.first and second reflecting means, said first .[.reflective.]. .Iadd.reflecting .Iaddend.means being disposed along and substantially perpendicular to the longitudinal axis of said .[.laser rod.]. .Iadd.lasing medium .Iaddend.and said second reflecting means being displaced from said longitudinal axis;   b. an acousto-optic beam deflector for selectively controlling the lasing threshold of said laser cavity, said deflector disposed within said cavity along said longitudinal axis intermediate said .[.laser rod.]. .Iadd.lasing medium .Iaddend.and said second reflecting means, said second reflecting means being substantially perpendicular to a line joining said second reflecting means and said deflector, said deflector effective to deflect a fraction of an energy beam from said .[.rod.]. .Iadd.lasing medium .Iaddend.at a preselected angle responsive to application of ultrasonic power thereto, said fraction being a monotonic increasing function of said power, said deflected fraction defining the amount of energy feedback to said .[.laser rod.]. .Iadd.lasing medium.Iaddend.,   c. a source of RF power;   d. logic control means for selectively applying said RF power to said acousto-optic beam deflector in amounts and at intervals corresponding to desired laser pulses, said applied RF power being effective to deflect a variable portion of the radiation emitted by said .[.laser rod.]. .Iadd.lasing medium .Iaddend.at said preselected angle to said second reflecting means thereby selectively varying the lasing threshold of said cavity; and   c. means for increasing the population inversion in said .[.laser rod.]. .Iadd.lasing medium .Iaddend.to stimulate emission of radiation therefrom.   
     
     
       7. A laser system as set forth in claim 6 further including third .[.reflective.]. .Iadd.reflecting .Iaddend.means disposed along the line joining said second .[.reflective.]. .Iadd.reflecting .Iaddend.means and said deflector, said third .[.reflective.]. .Iadd.reflecting .Iaddend.means being positioned such that said deflector lies between said second and third reflecting means. 
     
     
       8. A laser system as set forth in claim 7 further including a fourth reflecting means disposed along said longitudinal axis, said fourth reflecting means being positioned on the same side of said deflector as said second reflecting means and being operable to provide a selected amount of feedback to said .[.laser rod.]. .Iadd.lasing medium.Iaddend.. 
     
     
       9. A laser system for selectively producing variable energy laser pulses at variable time intervals comprising: a. a laser cavity including a .[.laser rod.]. .Iadd.lasing medium .Iaddend.intermediate first and second reflecting means disposed along and substantially perpendicular to the longitudinal axis of said .[.laser rod.]. .Iadd.lasing medium.Iaddend., and output means .Iadd.for said lasing medium .Iaddend.displaced from said longitudinal axis;   b. an acousto-optic beam deflector disposed within said cavity along said longitudinal axis between said .[.laser rod.]. .Iadd.lasing medium .Iaddend.and both said output means and said second reflecting means;   c. a source of RF power;   d. logic control means for selectively applying said RF power to said acousto-optic beam deflector at power levels and at intervals corresponding with desired laser pulses, said applied RF power deflecting radiation emitted by said .[.laser rod.]. .Iadd.lasing medium .Iaddend.away from said second .[.reflective.]. .Iadd.reflecting .Iaddend.means to decrease feedback; and   e. means for increasing the population inversion in said .[.laser rod.]. .Iadd.lasing medium .Iaddend.whereby said applied RF power .[.selectivity.]. .Iadd.selectively .Iaddend.varies the amount of radiation reflected back to said .[.laser rod.]. .Iadd.lasing medium .Iaddend.and thus selectively controls the gain of said laser cavity.   
     
     
       10. A laser system as set forth in claim 9 further including third .[.reflective.]. .Iadd.reflecting .Iaddend.means disposed along a line joining said output means and said deflector, said third .[.reflective.]. .Iadd.reflecting .Iaddend.means being positioned such that said deflector lies between said third .[.reflective.]. .Iadd.reflecting .Iaddend.means and said output means. 
     
     
       11. A laser system as set forth in claim 10 .[.further including.]. .Iadd.wherein said output means comprises .Iaddend.a fourth .[.reflective.]. .Iadd.reflecting .Iaddend.means .[.disposed along.]. .Iadd.displaced from .Iaddend.said longitudinal axis, said fourth .[.reflective.]. .Iadd.reflecting .Iaddend.means being positioned on the same side of said deflector as said second reflecting means and being operable to provide a selected amount of feedback to said .[.laser rod.]. .Iadd.lasing medium.Iaddend.. 
     
     
       12. A laser system for selectively producing variable energy laser pulses at variable time intervals comprising: a. a .[.laser rod.]. .Iadd.lasing medium.Iaddend.;   b. first reflecting means positioned from one end of said .[.laser rod.]. .Iadd.lasing medium .Iaddend.along .[.said.]. .Iadd.and .Iaddend.substantially perpendicular to the longitudinal axis of said .[.laser rod.]. .Iadd.lasing medium.Iaddend. ;   c. output means .Iadd.for said lasing medium .Iaddend.positioned from the opposite end of said .[.laser rod.]. .Iadd.lasing medium .Iaddend.along said longitudinal axis;   d. a beam splitter positioned along said longitudinal axis between said .[.laser rod.]. .Iadd.lasing medium .Iaddend.and said output means.Iadd., said beam splitter being disposed to reflect a portion of the beam transmitted from said lasing medium in a direction substantially perpendicular to the longitudinal axis of said lasing medium.Iaddend.;   e. second .[.reflective.]. .Iadd.reflecting .Iaddend.means positioned along a line substantially perpendicular to said longitudinal axis, said second .[.reflective.]. .Iadd.reflecting .Iaddend.means being positioned on the side of said longitudinal axis opposite and in alignment with the direction said beam splitter reflects .Iadd.said portion of .Iaddend.the beam radiated by said .[.laser rod.]. .Iadd.lasing medium.Iaddend.;   f. acousto-optic beam deflector means positioned along a line substantially perpendicular to said longitudinal axis on the opposite side thereof from said second .[.reflective.]. .Iadd.reflecting .Iaddend.means and in alignment with the .Iadd.direction to be taken by the .Iaddend.portion of said beam reflected from said beam splitter;   g. control means connected to said .Iadd.acousto-optic beam .Iaddend.deflector .Iadd.means .Iaddend.for varying the amount of acoustic power applied thereto;   h. means for increasing the population inversion in said .[.laser rod.]. .Iadd.lasing medium.Iaddend., and   i. feedback reflecting means disposed along a line that forms an angle with said beam reflected by said beam splitter whereby in response to applied power to said .Iadd.acousto-optic beam .Iaddend.deflector .Iadd.means .Iaddend.a fraction of the beam from said .[.laser rod.]. .Iadd.lasing medium .Iaddend.reflected by said beam splitter is deflected to impinge upon said feedback reflecting means to be reflected therefrom to provide energy feedback to said .[.laser rod.]. .Iadd.lasing medium.Iaddend., the portion of said feedback energy that is transmitted through said beam splitter being reflected by said second reflecting means back to said beam splitter. .[.13. A laser system as set forth in claim 12 wherein said feedback reflecting means are disposed along a line substantially perpendicular to said longitudinal axis and in alignment with the portion   
     
     
        of said beam reflected by said beam splitter..]. 14. A laser system as set forth in claim 12 including third .[.reflective.]. .Iadd.reflecting .Iaddend.means disposed along a line joining said feedback .[.reflective.]. .Iadd.reflecting .Iaddend.means and said .Iadd.acousto-optic beam .Iaddend.deflector .Iadd.means.Iaddend., said third .[.reflective.]. .Iadd.reflecting .Iaddend.means being positioned such that said .Iadd.acousto-optic beam .Iaddend.deflector .Iadd.means .Iaddend.lies between said third .[.reflective.]. .Iadd.reflecting .Iaddend.means and said feedback .[.reflective.]. .Iadd.reflecting .Iaddend. means. .Iadd. 15. A laser system for producing laser pulses, comprising: a. a laser cavity that includes a rod of lasing material between first and second reflecting means, said second reflecting means being positioned along a line that forms a preselected angle with the longitudinal axis of said laser rod;   b. means for increasing the population inversion in said lasing material to stimulte emission of radiation therefrom;   c. an acousto-optic beam deflector disposed substantially along said longitudinal axis between said laser rod and said second reflecting means operable to control the lasing threshold of said cavity; and   d. third reflecting means disposed along a straight line passing through said deflector and joining said second reflecting means and said deflector, and said third reflecting means being positioned on the opposite side of said deflector from said second reflecting means; and   e. said deflector effective to deflect a fraction of said radiation at said preselected angle in response to application of ultrasonic power thereto, said deflector being further effective to feed back energy from said second reflecting means to said laser rod. .Iaddend. .Iadd. 16. A laser system as set forth in claim 15, further including a fourth reflecting means disposed along said longitudinal axis, said fourth reflecting means being positioned on the same side of said deflector as said second reflecting means and being operable to provide feedback to said laser rod, in an amount less then required for lasing action. .Iaddend. .Iadd. 17. A laser system for producing laser pulses, comprising:   a. a laser cavity including a lasing medium intermediate first and second reflecting means, said first reflecting means being disposed along and substantially perpendicular to the longitudinal axis of said lasing medium and said second reflecting means being displaced from said longitudinal axis;   b. an acousto-optic beam deflector for controlling the lasing threshold of said laser cavity, said deflector disposed within said cavity along said longitudinal axis intermediate said lasing medium and said second reflecting means;   c. third reflecting means disposed along a straight line passing through said deflector and joining said second reflecting means and said deflector, and said third reflecting means being positioned on the opposite side of said deflector from said second reflecting means;   d. said deflector effective to deflect a fraction of an energy beam from said lasing medium to said second reflecting means, responsive to application of ultrasonic power to said deflector;   e. a source of RF power;   f. means for applying said RF power to said acousto-optic beam deflector, thereby varying the lasing threshold of said cavity; and   g. means for increasing the population inversion in said lasing medium to stimulate emission of radiation therefrom. .Iaddend. .Iadd. 18. A laser system as set forth in claim 17, further including a fourth reflecting means disposed along said longitudinal axis on the same side of said deflector as said second reflecting means, said fourth reflecting means being operable to provide feedback to said lasing medium, in an amount less than required for lasing action. .Iaddend..Iadd. 19. A laser system for producing laser pulses, comprising:   a. a lasing medium;   b. first reflecting means positioned from one end of said lasing medium along and substantially perpendicular to the longitudinal axis thereof;   c. output means for said lasing medium positioned from the opposite end of said lasing medium along said longitudinal axis;   d. a beam splitter positioned along said longitudinal axis between said lasing medium and said output means, said beam splitter being disposed to reflect a portion of the beam transmitted from said lasing medium in a direction substantially perpendicular to the longitudinal axis of said lasing medium;   e. second reflecting means positioned along a line substantially perpendicular to said longitudinal axis and on the side of said longitudinal axis opposite and in alignment with the direction said beam splitter reflects said portion of the beam radiated by said lasing medium.   f. an acousto-optic beam deflector positioned along a line substantially perpendicular to said longitudinal axis on the opposite side thereof from said second reflecting means and in alignment with the direction to be taken by the portion of said beam reflected from said beam splitter;   g. means for applying acoustic power to said deflector;   h. means for increasing the population inversion in said lasing medium; and   i. feedback reflecting means disposed along a line that forms an angle with said beam reflected by said beam splitter, whereby in response to applied power to said deflector a fraction of the beam from said lasing medium reflected by said beam splitter is deflected to impinge upon said feedback reflecting means to be reflected therefrom to provide energy feedback to said lasing medium, the portion of said feedback energy that is transmitted through said beam splitter being reflected by said second   
     
     
        reflecting means back to said beam splitter. .Iaddend. .Iadd. 20.  A laser system as set forth in claim 19, further including third reflecting means disposed along a line joining said feedback reflecting means and said deflector, said third reflecting means being positioned such that said deflector lies between said third reflecting means and said feedback reflecting means. .Iaddend.