Laser tuning by spectrally dependent spatial filtering

Abstract

A laser tuning mechanism which embodies “spectrally dependent spatial filtering” (SDSF) and contemplates two key elements of the tuning mechanism. The first element of the SDSF tuning mechanism is a spectrally dependent beam distortion (i.e. alteration of the amplitude and/or phase profile of the beam) provided by an SDSF tuning element in a laser cavity. The second element of the SDSF tuning mechanism is an intracavity spatial filter which makes the round trip cavity loss a sensitive function of both beam distortion and cavity alignment. Such a laser can be aligned so that a specific beam distortion, which is provided by the SDSF tuning element at a tunable wavelength, is required to obtain minimum round trip cavity loss, thereby providing tunable laser emission. A preferred embodiment of the SDSF tuning mechanism is an external cavity semiconductor laser having a zeroth order acousto-optic tuning element.

1 . A laser comprising an optical resonator, said optical resonator comprising: 
 a) a pumped gain medium; and    b) a tuning element comprising a tunable optical spectral notch filter;    wherein said optical resonator is aligned such that radiation is emitted from said optical resonator at substantially a single emission wavelength which is selected by said tuning element.    
     
     
         2 . The laser of  claim 1  wherein said tuning element comprises a volume hologram.  
     
     
         3 . The laser of  claim 1  wherein a three wave parametric interaction occurs within said tuning element.  
     
     
         4 . The laser of  claim 3  wherein said three wave parametric interaction is an acousto-optic interaction and an optical beam circulating within said optical resonator passes through said tuning element as a zeroth order beam.  
     
     
         5 . The laser of  claim 1  wherein said optical resonator further comprises a grid fixing etalon.  
     
     
         6 . The laser of  claim 1  wherein a parasitic etalon within said optical resonator provides discrete tunability.  
     
     
         7 . The laser of  claim 1  wherein the round trip path length of said optical resonator is selected so as to provide discrete tunability.  
     
     
         8 . The laser of  claim 1  further comprising means for monitoring said single emission wavelength.  
     
     
         9 . The laser of  claim 1  further comprising means for monitoring a wavelength difference between said single emission wavelength and a center wavelength of said tuning element.  
     
     
         10 . A method for generating a laser beam comprising: 
 a) pumping a gain medium positioned within an optical resonator, said optical resonator defining an intracavity beam path; and    b) passing light traveling on said beam path through a tunable optical spectral notch filter provided by a tuning element;    wherein said optical resonator is aligned such that radiation is emitted from said optical resonator at substantially a single emission wavelength which is selected by said tuning element.    
     
     
         11 . The method of  claim 10  further comprising passing light traveling on said beam path through a spatial filter.  
     
     
         12 . The method of  claim 10  wherein said tuning element comprises a volume hologram.  
     
     
         13 . The method of  claim 10  wherein a three wave parametric interaction occurs within said tuning element.  
     
     
         14 . The method of  claim 13  wherein said three wave parametric interaction is an acousto-optic interaction.  
     
     
         15 . The method of  claim 10  further comprising passing light traveling on said beam path through a grid fixing etalon.  
     
     
         16 . The method of  claim 10  wherein a parasitic etalon within said optical resonator provides discrete tunability.  
     
     
         17 . The method of  claim 10  wherein the optical length of said beam path is selected so as to provide discrete tunability.  
     
     
         18 . The method of  claim 10  wherein an acousto-optic interaction occurs within said tuning element, said method further comprising: 
 c) emitting a portion of a first order beam from said optical resonator to provide a first order signal;    d) emitting a portion of a zeroth order beam from said optical resonator to provide a zeroth order signal;    e) deriving a normalized first order signal from said first order signal and said zeroth order signal; and    f) controlling the center wavelength of said tuning element to hold said normalized first order signal fixed to a predetermined value.    
     
     
         19 . A laser comprising an optical resonator, said optical resonator comprising: 
 a) a pumped gain medium; and    b) means for selecting an emission wavelength;    wherein said optical resonator is aligned such that radiation is emitted from said optical resonator at substantially said emission wavelength which is selected by said means in accordance with a spectrally dependent spatial filtering (SDSF) tuning mechanism.