We demonstrate that it is possible to reduce the focal spot size by inserting a uniform nonlinear thin film at the aperture of a focusing lens. The reduction of spot size is tunable by adjusting the incoming laser power. In comparison with the original diffraction spot, the transverse spot size can be reduced 0.65 times. The nonlinear thin film acts effectively as a Toraldo filter, and the phase and amplitude modulation stems from the laser-induced variances in the transmission of the thin film. The proposed technique removes the need of fabricating annular pupil filters.
© 2008 Optical Society of America
Original Manuscript: December 17, 2007
Revised Manuscript: April 3, 2008
Manuscript Accepted: May 13, 2008
Published: July 11, 2008
Jingsong Wei and Mufei Xiao, "Laser tunable Toraldo superresolution with a uniform nonlinear pupil filter," Appl. Opt. 47, 3689-3693 (2008)