Patent ID: 11879975
Assignee: MITUTOYO CORPORATION
Field: Measurement (Instruments)
Classification: CPC G | IPC G

Claim 6:
7. The measurement apparatus according to claim 1, wherein the calculation part calculates a difference d between propagation distances of the reference light and the measurement light by the following equation, using a frequency νB(m, d) of the beat signal obtained by the frequency analyzing part performing a frequency analysis on the beat signal,, d
     =
     
      
       c
       
        2
        ⁢
        
         v
         s
        
        ⁢
        
         v
         c
        
       
      
      ⁢
      
       {
       
        
         
          v
          B
         
         (
         
          m
          ,
          d
         
         )
        
        +
        
         m
         ⁢
         
          v
          c
         
        
       
       }
      
     
    
   
   
    
     (
     1
     ), where c is the speed of light, vs, is a frequency shift amount of the frequency-modulated laser beam, νC is 1/τRT, τRT is the time for light to go around a cavity of the laser apparatus once, and m is an interval of the longitudinal mode numbers of the frequency-modulated laser beam, that is difference between the longitudinal mode numbers of the measurement light and the longitudinal mode numbers of the reference light.