Absolute distance measurements using the optical comb of a femtosecond pulse laser

Abstract

We describe a new way of implementing absolute displacement measurements by exploiting the optical comb of a femtosecond pulse laser as a wavelength ruler. The optical comb is stabilized by locking both the repetition rate and the carrier offset frequency to an Rb clock of frequency standard Multiwavelength interferometry is then performed using the quasi-monochromatic beams of well-defined generated wavelengths by tuning an external cavity laser diode consecutively to preselected light modes of the optical comb. This scheme of wavelength synthesizing allows the measurement of absolute distances with a high precision that is traceable to the definition of time. The achievable wavelength uncertainty is 1.9 x 10(-10), which allows the absolute heights of gauge blocks to be determined with an overall calibration uncertainty of 15 nm (k = 1). These results demonstrate a successful industrial application of an optical frequency synthesis employing a femtosecond laser a technique that offers many possibilities for performing precision length metrology that is traceable to the well-defined international definition of time.