We examine the use of defocus for changing the effective spot size in fluctuation microscopy. Our conclusions relate to other coherent techniques. While it is possible to increase the illuminated spot size by defocusing, the number of phase oscillations inside the illuminated spot increases. As a result the stationary phase region increases with defocus at a slower rate than the spot size. Therefore, the effective spot size for fluctuation microscopy is not the beam size, and the phase interference is increasingly diluted by incoherent contributions, rendering defocus an ineffective means of changing the spot size for fluctuation microscopy.
ASJC Scopus subject areas
- Physics and Astronomy(all)