A design for focusing an incoming light into an ultrasmall spot with a long depth of focus is proposed. We use a phase plate with three concentric regions to modulate the incoming light from radial polarization into outward–inward–outward polarization. The analysis shows that the design is more suitable for a lens with a high numerical aperture because much energy is concentrated in the main lobe of the focus spot.
© 2003 Optical Society of America
(050.1380) Diffraction and gratings : Binary optics
(120.5060) Instrumentation, measurement, and metrology : Phase modulation
(210.4680) Optical data storage : Optical memories
(260.5430) Physical optics : Polarization
Ching-Cherng Sun and Chin-Ku Liu, "Ultrasmall focusing spot with a long depth of focus based on polarization and phase modulation," Opt. Lett. 28, 99-101 (2003)