Optimizing Optomechanical Detection by Spatially Mapping and Masking Measurement Inefficiency

Many optical measurement techniques, such as light scattering from wavelength-scale particles or detecting motion of a surface with an optical lever, encode information in a complex radiation pattern. Extracting all available information is essential for many quantum-enhanced sensing protocols but is often impractical, as it requires multiple detection channels to spatially resolve the scattered signal. We present a new method to visualize how efficiently a measurement scheme captures the information available in the scattered light by mapping out the local contribution to the detection efficiency on the detector surface. We use this tool to experimentally optimize the measurement of the amplitude of motion of a mechanical resonator with a quadrant photodiode. We show that blocking sections of the photodetector enhances sensitivity, counterintuitively yielding a significant improvement in detecting higher-order mechanical modes in the system. We also show how our method can be applied to light scattering measurements of small particles.