Point-Spread-Function Engineering
Performance can be improved in many optical applications by engineering
the focused three-dimensional (3D) intensity distribution, or
point-spread-function (PSF), using diffractive optical elements (DOEs). DOEs
are passive optical components that are positioned in the pupil plane of an optical
system to alter the amplitude, phase, and polarization of the light prior to
focusing. Annular multi-phase plates (AMPs) are a special class of phase-only DOE
that are particularly useful for PSF-engineering because they transmit all of
incident optical power altering only the phase of the wavefront.
Optical system incorporating an annular multi-phase plate.
The resolution achieved in scanned-laser imaging techniques, such
as confocal and multi-photon microscopy, is determined by the transverse and
axial extent of the central (most intense) lobe of the diffraction-limited
PSF. AMP designs have been reported that can decrease the lateral or axial
extent of the central lobe, and this is frequently referred to as
super-resolving. In other applications it is beneficial to elongate the PSF
axially so the focused intensity remains peaked over a greater depth of
field.
Comparison of the PSF resulting when a super-resolving AMP is placed before a 1.4 NA lens.
(Top) Normalized axial and transverse intensity distribution within the plane of
polarization (xz-plane) in the diffraction-limit (no AMP) and (bottom) when
the three-zone AMP is present. When the AMP is present the PSF is axially squeezed
yet remains diffraction-limited in the transverse direcion.
The NPM group is developing new algorithms for designing DOEs that fully account
for the vector character of the field. These methods can be used to back-engineer
a DOE based on a set of target PSF criteria achievable under high-numerical-aperture
focusing. The resulting DOEs can be used to improve the resolution achievable in
multi-photon imaging and
multi-photon 3D microfabrication. Click on
the publication below to find out more about our work in this area.
"Vector diffraction analysis of high numerical aperture focused beams modified by two- and three-zone annular multi-phase plates."
T. G. Jabbour and S. M. Kuebler
Opt. Express, 14, 1033-1043 (2006)
