Optical measurement of refractive index gradients with position-sensitive detectors

This study proposes a PSD-based method for refractive index gradient measurement with advantages of miniaturization and real-time capability. By integrating laser beam deflection principles with PSD detection, we establish a theoretical model correlating spot displacement with refractive index gradients and construct a measurement system achieving 2.22 × 10 −5 refractive index unit (RIU)/m resolution. Theoretical analysis addresses beam deviation caused by collimation misalignment (θ 0 ), proposing an improved method. Ray-tracing simulations demonstrate significantly relaxed collimation requirements: displacement resolution reaches 1μm when |θ 0 |<1.3°. Validation using stratified saline solutions shows integrated PSD gradient measurements agree with refractometer (PRM-2000α) data within <1 × 10 −5 RIU error.