Direct single-shot phase difference retrieval of two wavelengths in off-axis digital holography

A method for direct phase difference reconstruction using single-shot dual-wavelength off-axis digital holography is presented. This approach enables direct imaging of samples with high steps without the need to reconstruct phase images at each individual wavelength. As the dual wavelengths in the reference and object arms pass through a common path in this configuration, single-wavelength arrangements can be applied. Due to the unique capability of the presented method, a sodium-vapor lamp source has been utilized to obtain two closely spaced wavelengths (<i>λ</i>₁=589 nm and <i>λ</i>₂=589.6 nm), with a synthetic wavelength of <i>Λ</i>=578.8 µm in the Michelson configuration. The proposed method is validated by measuring the height of an air wedge using two approaches based on the synthetic and average wavelengths. The capability of the proposed technique to image samples with high-step structures is further demonstrated by measuring four consecutive steps, each separated by a height interval of 30 µm, as well as a glass plate with a thickness of approximately 140 µm.