DETECTION OF PROBE DITHER MOTION IN NEAR-FIELD SCANNING OPTICAL MICROSCOPY

The probe-to-sample separation in near-field scanning optical microsco pes can be regulated by a noncontact shear-force sensing technique. Th e technique requires the measurement of a minute dither motion applied to the probe. We have characterized an optical detection method for m easuring this motion to determine the optimum detection configuration in terms of sensitivity and stability. A scalar diffraction model of t he detection method is developed for calculating sensitivity, and expe rimental results are found to be in good agreement with the theoretica l predictions. We find that maximum sensitivity and stability cannot b e achieved simultaneously, and it may be desirable in practice to trad e sensitivity for enhanced stability. (C) 1995 Optical Society of Amer ica