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We develop a new method for high-resolution and contactless distance measurement based on self frequency beats of optical frequency combs. We use two optical frequency comb lasers with Rb-stabilized repetition frequencies for doing accurate distance measurement. The repetition frequencies of the optical frequency combs are different, thus parts of the high frequencies such as several gigahertz of self beats are beat-downed to several megahertz without an RF frequency oscillator. The phases of the beat signals of several megahertz frequencies are measured by a lock-in amplifier with a high resolution and high sensitivity. The new method is applied to distance measurement for objects which have rough-surface in the distance range of several-meters.

In this research, we developed a new method for the high precision and contactless profile measurement of rough-surfaced objects using optical frequency combs. The uncertainty of the frequency beats of an optical frequency comb is very small (relative uncertainty is 10−10 in our laboratory). In addition, the wavelengths corresponding to these frequency beats are long enough to measure rough-surfaced objects. We can conduct high-precision measurement because several GHz frequency beats can be used if the capability of the detector permits. Moreover, two optical frequency combs with Rb-stabilized repetition frequencies are used for the measurement instead of an RF frequency oscillator; thus, we can avoid the cyclic error caused by the RF frequency oscillator. We measured the profile of a wood cylinder with a rough surface (diameter is approximately 113.2 mm) and compared the result with that of coordinate measuring machine (CMM).