Superresolution with an apodization film in a confocal setup

Generation of an axially super-resolved quasi-spherical focal spot using an amplitude-modulated radially polarized beam

An axially super-resolved quasi-spherical focal spot can be generated by focusing an amplitude-modulated radially polarized beam through a high numerical aperture objective. A method based on the unique depolarization properties of a circular focus is proposed to design the amplitude modulation. The generated focal spot shows a ratio of x:y:z=1:1:1.48 for the normalized FWHM in three dimensions, compared to that of x:y:z=1:0.74:1.72 under linear polarization (in the x direction) illumination. Moreover, the focusable light efficiency of the designed amplitude-modulated beam is 65%, which is more than 3 times higher than the optimized case under linear polarization and thus make the amplitude-modulated radial polarization beam more suitable for a wide range of applications.

Quasi-spherical focal spot in two-photon scanning microscopy by three-ring apodization

We present a beam-shaping technique for two-photon excitation (TPE) fluorescence microscopy. We show that by inserting a properly designed three-ring pupil filter in the illumination beam of the microscope, the effective optical sectioning capacity of such a system improves so that the point spread function gets a quasi-spherical shape. Such an improvement, which allows the acquisition of 3D images with isotropic quality, is obtained at the expense of only a small increase of the overall energy in the axial sidelobes. The performance of this technique is illustrated with a scanning TPE microscopy experiment in which the image of small beads is obtained. We demonstrate an effective narrowing of 12.5% in the axial extent of the point spread function, while keeping the 82% of the spot-fluorescence efficiency.

Tunable phase-only optical filters with a uniaxial crystal

A novel method of fabricating phase-only optical filters that is based on the properties of a uniaxial crystal is proposed. With these optical filters, the phase differences are tunable among the different filter zones. Many focal patterns can be obtained if these optical filters are placed in front of a lens; furthermore, these optical filters can also be used to make up for the distortions in fabrications in which they were used only as untunable optical filters.

3D behaviour of Frieden filters in confocal imaging

The three-dimensional (3D) focal behaviour of the super-resolving Frieden filters is investigated numerically. It is shown that, as the central bright spot is sharpened, super-giant secondary maximums are formed on the optic axis. These lobes are much higher that the well-known side-lobes inherent to spatial filtering that surround the restricted, utilisable field, whose characteristics in the meridional plane are depicted for various values of the space-bandwidth parameter and for various numbers of terms that compose the window function. The two-terms filter is found to present, for the first time to my knowledge, some axial apodizing properties. To be compatible with practical realisation, the use of this class of filters in a single- and two-photon confocally scanned system is discussed in terms of 3D super-resolution with an intentionally limited light-power loss. It is shown that these filters match particularly well with recently designed axial apodizers for the transmission-mode confocal scanning microscope and provide a 3D intensity point-spread volume reduction of variable amount as high as 37 percent. The filtering process is shown to vary significantly with the mode of operation.

Axial apodization in 4Pi-confocal microscopy by annular binary filters

We present a novel technique for considerably decreasing the sidelobe height of the axial point-spread function of one-photon 4Pi-confocal microscopes. By means of a numerical example, in which the ratio between the excitation and the fluorescence wavelengths was set to epsilon = lambdaexc/lambdadet = 0.8, we show that simply inserting a pair of properly designed two-ring binary masks in the illumination set allows the height of the axial sidelobes to be reduced from 20% to 5% of the height of the central peak. This allows one to receive the full benefit of the strong narrowness of the central lobe provided by the 4Pi-confocal technique.

New class of axially apodizing filters for confocal scanning microscopy

A new class of axially apodizing continuously transmitting filters is analytically determined and numerically implemented. The longitudinal and lateral properties of the associated point-spread function are displayed both for a single filtered lens and for a combination with a laterally superresolving mask in a confocal configuration. Interesting imaging properties relative to the increase in axial contrast and transverse resolving power for dephasing ring-free pupil filters of moderate losses in luminosity are predicted.

Binary optics and confocal imaging

The use of two-level phase masks or spatial light modulators in confocal imaging systems is considered. It is shown how, although such masks can modify or correct the effective point-spread function of a system, their behavior for planar objects may not be as desired as a result of phase-wrapping effects. Overcoming this problem with a multilevel mask or a pair of two-level masks is discussed.

Resolution enhancement in a reflection-type confocal microscope with a phase-conjugate mirror

Theoretical and experimental results for a new reflection-type confocal microscope with a phase-conjugate mirror (PCM) are presented. The microscope achieves better lateral and axial resolution than the conventional confocal microscope. The observation volume is reduced considerably (approximately 63%). Owing to the properties of the PCM, the system is self-aligning.