Acousto-optical tunable filter element

Abstract

An acousto-optical filter element ( 114 ) is provided which has an acousto-optical crystal ( 118 ) having an acoustic signal transmitter ( 120 ) for generating acoustic signals in the acousto-optical crystal ( 118 ). The acousto-optical crystal ( 118 ) is designed to selectively spatially deflect light of a target wavelength from an input light beam ( 116 ) entering into the acousto-optical crystal ( 118 ), as a function of a high frequency applied to the acoustic signal transmitter ( 120 ), and to thereby produce a target light beam ( 126 ) having the target wavelength. In addition, the acousto-optical filter element ( 114 ) includes a spatial filter element ( 132 ) which is located in the target light beam ( 126 ) and is designed to selectively suppress the intensity of the target light beam ( 126 ) in a plane perpendicular to the propagation direction of the target light beam ( 126 ).

1 . An acousto-optical filter element ( 114 ) comprising an acousto-optical crystal ( 118 ) having an acoustic signal transmitter ( 120 ) for generating acoustic signals in the acousto-optical crystal ( 118 ), the acousto-optical crystal ( 118 ) being designed to selectively spatially deflect light of a target wavelength from an input light beam ( 116 ) entering into the acousto-optical crystal ( 118 ), as a function of a high frequency applied to the acoustic signal transmitter ( 120 ), and to thereby produce a target light beam ( 126 ) having the desired target wavelength,
 characterized by a spatial filter element ( 132 ) that is located in the target light beam ( 126 ), the spatial filter element ( 132 ) being designed to selectively suppress the intensity of the target light beam ( 126 ) in a plane perpendicular to the propagation direction of the target light beam ( 126 ).   
   
   
       2 . The acousto-optical filter element ( 114 ) as claimed in  claim 1 , the spatial filter element ( 132 ) including a lens element ( 134 ,  138 ). 
   
   
       3 . The acousto-optical filter element ( 114 ) as claimed in  claim 2 , the lens element ( 134 ,  138 ) including a lens element ( 134 ,  138 ) having a variable focal length, in particular, having a focal length that is adjustable by motor and/or electronically. 
   
   
       4 . The acousto-optical filter element ( 114 ) as claimed in  claim 1 , the spatial filter element ( 132 ) including a pinhole ( 136 ). 
   
   
       5 . The acousto-optical filter element ( 114 ) as claimed in  claim 4 , the pinhole ( 136 ) including at least one of the following apertures: a slit aperture, a square aperture, a rectangular aperture, a circular aperture, an iris aperture. 
   
   
       6 . The acousto-optical filter element ( 114 ) as claimed in  claim 1 ,
 the spatial filter element ( 132 ) including an optical waveguide ( 144 ) and a lens element ( 134 ,  138 ), which is located between one end ( 146 ) of the optical waveguide ( 144 ) and the acousto-optical crystal ( 118 ) and is adapted to couple a portion of the target light beam ( 126 ) into the end ( 146 ) of the optical waveguide ( 144 ).   
   
   
       7 . The acousto-optical filter element ( 114 ) as claimed in  claim 6 , the optical waveguide ( 144 ) including a single mode fiber. 
   
   
       8 . The acousto-optical filter element ( 114 ) as claimed in  claim 6 , a distance and/or an orientation of the lens element ( 134 ,  138 ) relative to the end ( 146 ) of the optical waveguide ( 144 ) being adjustable, preferably electronically. 
   
   
       9 . The acousto-optical filter element ( 114 ) as claimed in  claim 1 , the spatial filter element ( 132 ) being adjusted in such a way that secondary maxima of an order higher than 2 of a spatial intensity distribution of the target light beam ( 126 ) are suppressed. 
   
   
       10 . The acousto-optical filter element ( 114 ) as claimed in  claim 9 , in addition, secondary maxima of the 1st order being suppressed in such a way that merely the principal maximum of the spatial intensity distribution of the target light beam ( 126 ) is transmitted. 
   
   
       11 . The acousto-optical filter element ( 114 ) as claimed in  claim 1 , in addition including a calibration device ( 156 ), the calibration device ( 156 ) including a tunable, coherent test light source ( 158 ) and a detector ( 168 ), and the calibration device ( 156 ) being designed to implement at least one of the following calibration procedures to ascertain a transfer function of the acousto-optical filter element ( 114 ):
 given a fixed high frequency of the acoustic signal transmitter ( 120 ), the wavelength of the test light source ( 158 ) is varied, and the intensity of the target light beam ( 126 ) is measured;   given a fixed wavelength of the test light source ( 158 ), the high frequency of the acoustic signal transmitter ( 120 ) is varied, and the intensity of the target light beam ( 126 ) is measured.   
   
   
       12 . An adjustable light source ( 110 ) comprising a broadband coherent light source ( 112 ), as well as an acousto-optical filter element ( 114 ) as claimed in  claim 1  the broadband coherent light source ( 112 ) being designed to produce the input light beam ( 116 ) of the acousto-optical filter element ( 114 ). 
   
   
       13 . The adjustable light source ( 110 ) as claimed in  claim 12 , the broadband coherent light source ( 112 ) including at least one of the following light sources: a broadband laser, in particular a white-light laser; a plurality of laser light sources and a device for superposing the beams of the laser light sources; an optical waveguide having a spectrally broadening doping and a pump laser, the doping encompassing, in particular, a rare-earth doping, in particular, a doping with Er, Nd, Yb, Ho and/or a semiconductor doping, in particular, a Ge doping; a spectrally broadening optical waveguide, in particular having a tapered fiber, a microstructured fiber, a photonic crystal fiber, a holey fiber, a photonic bandgap fiber. 
   
   
       14 . A microscope ( 170 ) for capturing image information from a specimen ( 180 ), comprising a beam optics ( 176 ,  178 ,  184 ) and an adjustable light source ( 110 ) as claimed in  claim 12 . 
   
   
       15 . The microscope ( 170 ) as claimed in  claim 14 , the microscope ( 170 ) being designed as a confocal microscope and having a beam splitter ( 174 ) for separating excitation light and detection light, the beam splitter ( 174 ) having a beam-splitter transfer function ( 194 ); by adjusting the spatial filter element, the transfer function ( 194 ) of the acousto-optical filter element ( 114 ) of the adjustable light source ( 110 ) being implemented in such a way that the spectral width of the target light beam ( 126 ) is smaller than the spectral width of the principal maximum of the beam-splitter transfer function ( 194 ).