Imaging apparatus and methods

Abstract

Methods, systems and apparatus for manipulating electromagnetic radiation such as laser beams include a first acousto-optic deflector optimised for efficient transmission at the input beam angle and a second acousto-optic deflector of lower peak efficiency than the first acousto-optic deflector but which accepts beams from a wider range of angles at better transmission efficiency than the first acousto-optic deflector by passing a beam optimised for efficient transmission through the first acousto-optic deflector at the input beam angle, deflecting the beam using the first acousto-optic deflector, passing the deflected beam through the second acousto-optic deflector, which has a lower peak efficiency than the first acousto-optic deflector and accepts beams from a wider range of angles at better transmission efficiency than the first acousto-optic deflector, and deflecting the beam using the second acousto-optic deflector.

1 . Apparatus for deflecting a beam of electromagnetic radiation, said apparatus comprising:
 a first acousto-optic deflector optimised for efficient transmission at the input beam angle; and   a second acousto-optic deflector of lower peak efficiency than said first acousto-optic deflector but which accepts beams from a wider range of angles at better transmission efficiency than said first acousto-optic deflector.   
     
     
         2 . Apparatus according to  claim 1 , wherein said first acousto-optic deflector comprises a first crystal transducer and said second acousto-optic deflector comprises a second crystal transducer, wherein said second crystal transducer is arranged to create a more diverging acoustic wave in the second acousto-optic deflector than the acoustic wave created by said first crystal transducer in said first acousto-optic deflector. 
     
     
         3 . Apparatus according to  claim 1 , wherein said first crystal transducer is wider in the direction of light propagation than said second crystal transducer. 
     
     
         4 . Apparatus according to  claim 1 , wherein said second crystal transducer has a width parallel to the direction of light propagation of less than 1 mm. 
     
     
         5 . Apparatus according to  claim 1 , further comprising:
 a third acousto-optic deflector optimised for efficient transmission at the input beam angle; and
 a fourth acousto-optic deflector of lower peak efficiency than the third acousto-optic deflector but which accepts beams from a wider range of angles at better transmission efficiency than said third acousto-optic deflector. 
   
     
     
         6 . Apparatus according to  claim 5 , wherein said acousto-optic deflectors are arranged in this order along the path of the beam: first, second, third, fourth; or
 wherein said acousto-optic deflectors are arranged in this order along the path of the beam: first, third, second, fourth.   
     
     
         7 . Apparatus according to  claim 1 , wherein said second acousto-optic deflector comprises a crystal cut with less than three degrees deliberate misorientation of the optic axis from the direction of propagation of the acoustic wave; and/or
 wherein the second acousto-optic deflector is oriented such that acoustic waves propagating therethrough will have approximately twenty degrees between their wave vector and their Poynting vector.   
     
     
         8 . Apparatus according to  claim 1 , wherein said acousto-optic deflectors are made from a high efficiency anisotropic acousto-optic crystal, preferably TeO 2  crystals. 
     
     
         9 . A method of deflecting a beam of electromagnetic radiation, said method comprising:
 passing a beam through a first acousto-optic deflector that has been optimised for efficient transmission at the input beam angle;   deflecting said beam using said first acousto-optic deflector;   passing said deflected beam through a second acousto-optic deflector that has a lower peak efficiency than said first acousto-optic deflector but which accepts beams from a wider range of angles at better transmission efficiency that said first acousto-optic deflector; and   deflecting said beam using said second acousto-optic deflector.   
     
     
         10 . A method according to  claim 9 , wherein said step of deflecting said beam using said first acousto-optic deflector comprises creating an acoustic wave in said first acousto-optic deflector, wherein said step of deflecting said beam using said second acousto-optic deflector comprises creating an acoustic wave in said second acousto-optic deflector, and wherein a more diverging acoustic wave is created in the second acousto-optic deflector than in the first acousto-optic deflector. 
     
     
         11 . A method according to  claim 9 , wherein said first acousto-optic deflector comprises a first crystal transducer, said second acousto-optic deflector comprises a second crystal transducer, and wherein said first crystal transducer is wider in the direction of light propagation than said second crystal transducer; and/or
 wherein said second crystal transducer has a width parallel to the direction of light propagation of less than 1 mm.   
     
     
         12 . A method according to  claim 9 , further comprising:
 passing said beam through a third acousto-optic deflector that has been optimised for efficient transmission at the input beam angle;   deflecting said beam using said third acousto-optic deflector;   passing said deflected beam through a fourth acousto-optic deflector that has a lower peak efficiency than said third acousto-optic deflector but which accepts beams from a wider range of angles at better transmission efficiency that said third acousto-optic deflector; and   deflecting said beam using said fourth acousto-optic deflector.   
     
     
         13 . A method according to  claim 12 , wherein said steps of passing said beam through said third acousto-optic deflector and deflecting said beam using said third acousto-optic deflector are carried out prior to passing the beam through said second acousto-optic deflector. 
     
     
         14 . A method according to  claim 9 , wherein said second acousto-optic deflector comprises a crystal cut with less than three degrees deliberate misorientation of the optic axis from the direction of propagation of the acoustic wave; and/or
 wherein the second acousto-optic deflector is oriented such that acoustic waves propagating therethrough will have approximately twenty degrees between their wave vector and their Poynting vector.   
     
     
         15 . A method according to  claim 9 , wherein said acousto-optic deflectors are made from a high efficiency anisotropic acousto-optic crystal, preferably TeO 2  crystals.