Laser with narrow bandwidth antireflection filter for frequency selection

Abstract

A laser includes a narrow bandwidth AR coating for defining a frequency range for laser emission within the laser cavity. Advantageously, the narrow-band AR coating has a very low loss, which can be particularly useful if the gain medium has low gain. The narrow-band AR coating can be used to narrow the laser emission from a broadband gain medium (e.g. Cr:LiSAF), or to select from among discrete transition lines (e.g. Nd:YAG) without the use of cumbersome tuning elements. An etalon, which may be substantially uncoated, may be utilized to further narrow the fundamental wavelength. For a solid state gain medium, the AR coating may be formed on one of the optical faces. A nonlinear element may be included for frequency-conversion, and the AR coating constrains the lasing frequency in the presence of this nonlinear loss and assists in maintaining single frequency operation to provide a stable frequency-converted output.

1 . A frequency-converted laser comprising: 
 a laser cavity including a first and a second end mirror;    a gain medium situated within said laser cavity, said gain medium defining a gain-bandwidth;    a pump source arranged to pump said gain medium to thereby excite laser emission within said laser cavity;    a nonlinear element situated within said laser cavity, said nonlinear element arranged for frequency conversion of said laser emission within a required spectral range for efficient frequency conversion; and    a AR coating formed on a transmissive surface within said laser cavity, said AR coating defining a minimum loss point within said gain-bandwidth of said gain medium;    wherein said AR coating constrains the bandwidth of said laser emission within said required spectral range for frequency conversion.    
     
     
         2 . The laser of  claim 1  wherein said gain medium and said laser cavity are arranged to suppress at least three adjacent longitudinal modes by spatial hole burning.  
     
     
         3 . The laser of  claim 1  wherein said fundamental emission is substantially single frequency.  
     
     
         4 . The laser of  claim 1  wherein said AR coating has a minimum loss point of less than about 1%.  
     
     
         5 . The laser of  claim 4  wherein said AR coating has a minimum loss point of less than about 0.5%.  
     
     
         6 . The laser of  claim 4  wherein said AR coating has a minimum loss point of less than about 0.2%.  
     
     
         7 . The laser of  claim 1  wherein said gain medium comprises a solid state gain medium.  
     
     
         8 . The laser of  claim 1  wherein said laser cavity defines an optical axis, said gain medium comprises a first optical face and a second optical face situated along the optical axis, and said AR coating is formed on said second optical face.  
     
     
         9 . The laser of  claim 8  wherein at least one of said optical faces has a nonzero angle with respect to said optical axis.  
     
     
         10 . The laser of  claim 1  wherein said laser cavity defines an optical axis, said nonlinear element includes a first optical face and a second optical face situated along the optical axis, and said AR coating is formed on at least one of said optical faces.  
     
     
         11 . The laser of  claim 1  wherein said gain medium provides a gain amplification of said laser emission of less than about 4% per pass.  
     
     
         12 . The laser of  claim 1  wherein said gain medium comprises a broadband gain medium.  
     
     
         13 . The laser of  claim 12  wherein said gain medium comprises a chromium-doped solid state gain medium.  
     
     
         14 . The laser of  claim 1  wherein said gain medium comprises a gain medium that lases at discrete transitions, and said AR coating selects one of said transitions.  
     
     
         15 . The laser of  claim 14  wherein said gain medium comprises a rare-earth doped solid state gain medium.  
     
     
         16 . The laser of  claim 1  wherein said pump source comprises: 
 an optical pump source; and    means for focusing optical radiation from said optical pump source into said gain medium.    
     
     
         17 . The laser of  claim 16  wherein said optical pump source comprises a laser diode arranged to end pump said gain medium.  
     
     
         18 . The laser of  claim 1  wherein said laser cavity defines a linear configuration.  
     
     
         19 . The laser of  claim 1  wherein said nonlinear element is arranged for frequency doubling of said laser emission.