Distance measurements by combined method based on a femtosecond pulse laser.

We describe a combined interferometric scheme that enables absolute distance measurements using a femtosecond pulse laser. This method is combined with synthetic wavelength interferometry (SWI), time of flight (TOF) and spectrally-resolved interferometry (SRI) using the optical comb of femtosecond laser. Each technique provides distinct measuring resolutions and ambiguity ranges which are complementary to each other. These separate measurement principles are incorporated and implemented simultaneously and the unified output can enhance the dynamic range of the measuring system. Our experimental results demonstrate an example of absolute distance measurement with the proposed technique and we discuss the possibility of the combined method to measure long distances and the important factors for the implementation.