Comparison of two-color methods based on wavelength and adjacent pulse repetition interval length

This paper describes the characteristics of a two-color method based on the adjacent pulse repetition interval length (APRIL), which functions as a length unit for femtosecond optical frequency combs (FOFCs), and compares the results to the wavelength-based two-color method. The wavelength-based two-color method can eliminate the inhomogeneous disturbance of effects caused by the phase refractive index; therefore, the APRIL-based two-color method can eliminate the air turbulence of errors induced by the group refractive index. Our numerical analysis of the APRIL-based two-color method will contribute to the pulse-laser-based two-color method, which secures traceability to the definition of the meter via APRIL

Using dispersion-induced group delay to solve the integer ambiguity problem: a theoretical analysis

This paper describes a novel approach for solving the integer ambiguity problem when the adjacent pulse repetition interval length (APRIL) from a femtosecond optical frequency comb (FOFC) is used as a length scale. This approach is inspired by the two-color method, which indicates that there is a one-to-one relationship between the integer part of the APRIL and the group delay distance between the two different wavelengths. Accordingly, we numerically investigate the possibility of using dispersion-induced group delay to solve the integer ambiguity problem. The results of theoretical analyses and numerical investigations demonstrate the feasibility of the proposed method. Our results should contribute toward the further development of APRIL-based length measurement methods

Numerical study on uncertainty of two-color method

The two-color method is one of the commonly used approaches for converting a length measured in air to a length in vacuum to eliminate the influence of the refractive index of air. However, the error of the technique is not well known. We investigate this uncertainty based on a generalized expression of the two-color method proposed in this paper and using numerical simulations. Numerical calculations reveal the change of the error with temperature, air pressure, and wavelengths. These characteristics can be used to optimize the two-color method