Sum-frequency generation

<p>Sum-frequency generation (SFG) is a second order <a href="/facts/Nonlinear_optics/maerngXd">nonlinear optical</a> process based on the mixing of two input photons at <a href="/facts/Angular_frequency/VqLm3L3R">frequencies</a> 
  
    
      
        
          ω
          
            1
          
        
      
    
    {\displaystyle \omega _{1}}
  
 and 
  
    
      
        
          ω
          
            2
          
        
      
    
    {\displaystyle \omega _{2}}
  
 to generate a third photon at frequency 
  
    
      
        
          ω
          
            3
          
        
      
    
    {\displaystyle \omega _{3}}
  
. As with any 
  
    
      
        
          χ
          
            (
            2
            )
          
        
      
    
    {\displaystyle \chi ^{(2)}}
  
 optical phenomenon in <a href="/facts/Nonlinear_optics/maerngXd">nonlinear optics</a>, this can only occur under conditions where:
the light is interacting with matter, that lacks <a href="/facts/Centrosymmetry/nIFJqujU">centrosymmetry</a> (for example, surfaces and interfaces);
the light has a very high intensity (typically from a <a href="/facts/Pulsed_laser/PIcW85dx">pulsed laser</a>).
Sum-frequency generation is a "parametric process", meaning that the photons satisfy energy conservation, leaving the matter unchanged:
</p>

ℏ
        
          ω
          
            3
          
        
        =
        ℏ
        
          ω
          
            1
          
        
        +
        ℏ
        
          ω
          
            2
          
        
      
    
    {\displaystyle \hbar \omega _{3}=\hbar \omega _{1}+\hbar \omega _{2}}

Sum-frequency generation open-in-new

Sum-frequency generation