Electro-optic comb as synthetic wavelength generator for multiwavelength digital holography

Multi-wavelength digital holography enables high dynamic range surface measurements by combining µm resolution with an unambiguous measurement range of 1 m. However, practical use in an inline production control scenario is limited by the lack of light sources that support fast, reliable, and calibration-free tuning over a wide frequency range. We present a synthetic wavelength generator based on an electro-optic frequency comb with tunable modulation frequency and switchable optical band-pass filters. By combining discrete comb-line selection with continuous radio-frequency tuning, the system provides synthetic wavelengths from meters to millimeters, while maintaining switching times below 25 ms. We demonstrate the potential by applying the setup to multi-wavelength digital holography and investigate the surface of a machine milled part. By the use of 6 synthetic wavelengths between 1874 mm and 1.36 mm, all height-features of the sample, ranging between 0.1 mm and 100 mm are accurately revealed with a precision of ∼ 20 µm within a total acquisition time < 2 s. The approach offers the generation of synthetic wavelengths covering a dynamic range greater than 1 × 103 and inline-capable measuring-time with intrinsic frequency-calibration, providing a promising path towards precise and fast inline production control.