  Photonic spin Hall effect (SHE) holds great potential applications in
precision metrology. How to obtain a high measurement precision is an important
issue to detect the photonic SHE. In this letter, we propose using optimal
preselection and postselection in weak measurements to enhance the measurement
precision. We find that the maximum weak value and pointer shift can be
obtained with an optimal overlap of preselection and postselection states.
These findings offer the possibility for improving the precision of weak
measurements and thereby have possible applications for accurately
characterizing the parameters of nanostructures.
