Achieving High-Fold Optical Subdivision of a Blazed Grating Interferometer Through Near-Littrow Incidence

The multidiffractions model is commonly used to increase the optical subdivision factor. However, in practical applications, as the diffraction order increases, this model requires the size of the mirror above the scale grating to be larger, resulting in the reading unit being too bulky. In addition, the general multiple diffractions arrangement direction is arranged along the relative movement direction of the scale grating and the reading unit, which reduces the measurement range of the scale grating. More importantly, in the current blazed grating interferometer, the incident light beam is generally perpendicular to the grating’s macroscopic surface, which means that the maximum diffraction efficiency characteristics of the blazed grating are not fully utilized. To address these issues, we developed a novel multiple diffractions model. It arranges multiple diffraction positions along the direction of the grating ruling lines and directs the incident light beam onto the blazed grating groove surface at a near-Littrow angle. By slightly adjusting the inclination angle of the beam, the number of diffractions can be controlled. The operating principles of the proposed model are thoroughly elucidated. Subsequently, the corresponding experimental setup is constructed to validate the effectiveness of its optical subdivision and assess the accuracy of its displacement measurements. The results indicate that the measurement model can achieve optical subdivision up to 14 times, with the measurement accuracy reaching 46.54 nm within a travel range of 0.2 mm and 134.42 nm within a travel range of 1 mm. If the corresponding gain material can be inserted between the grating and the reflector to maintain a constant optical power of the diffracted beam, this model presents the potential for substantial optical subdivision multiples when the beam is vertically incident on the surface of the grating groove via the partial reflector. This may establish a fundamental optical design framework for future research on optical subdivision cavities.