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A method based on double imaging is proposed for three-dimensional focus manipulation. A thin birefringent plate placed behind a focusing lens was applied to generate two foci with a separation smaller than the original DOF. Depth of focus enlargement of 227% was achieved without serious degradation in lateral resolution. Experimental results obtained by using a confocal arrangement were in good agreement with theory. Both theoretical considerations and experimental results showed that in non-paraxial case the ordinary and extraordinary foci could not be excited independently.

Focus duplication based on birefringence is studied with a ray tracing program with special regard to separation efficiency and aberrations. It was shown that ordinary and extraordinary foci cannot be independently generated by linearly polarized incoming beams, when the numerical aperture exceeds the 0.1 limit. Point-spread-function analysis proved that optical aberrations—especially astigmatism—represent the main limitation of high quality focus duplication.

An ytterbium based all fiber, all normal dispersion fiber oscillator with integrated SESAM can have several operation modes like mode-locked, Q-switched and noise-like. To know and to control the quality of the mode-locking is essential for the application of such laser oscillators, otherwise the whole laser setup can be damaged or the expected operation characteristics of the oscillator driven systems cannot be achieved. Usually the two-photon signal generated by the short pulses is used to indicate the mode locked operation, however such detection can be misleading in certain cases and not always able to predict the forthcoming degradation or vanishing of mode locking. The characterization method that we propose uses only the radio frequency spectrum of the oscillator output and can identify the different operation regimes of our laser setup. The optical spectra measured simultaneously with the RF signals proves the reliability of our method. With this kind of characterization stable mode locking can be initiated and maintained during the laser operation. The method combined with the ability to align the polarization states automatically in the laser cavity leads to the possibility to record a polarization map where the stability domains can be identified and classified. With such map the region where the mode locking is self starting and maintainable with minimal polarization alignment can be selected. The developed oscillator reported here with its compact setup and self alignment ability can be a reliable source with long term error free operation without the need of expensive monitoring tools.

A line-scanning tomographic optical microscope system requires precise rotation of the scanning line. Center of rotation error introduced by both the imprecision of optical and mechanical components is studied experimentally and via simulations. It was shown that a practical tolerance limit can be chosen where the influence of the investigated error on the reconstructed image quality remains insignificant. An effective and simply practical solution was presented to keep the center of rotation error below this tolerance limit and the spatial resolution of the reconstructed image close to the diffraction limit.

In this paper an optical system is proposed to generate radially and azimuthally polarized beams. A focused monochromatic beam is divided into ordinary and extraordinary parts by using a thin plane parallel uniaxial crystal plate. If the optical axis of the crystal is perpendicular to its surface, the two generated foci can be associated with azimuthal and radial polarization states, respectively. The generated foci were studied theoretically and experimentally using a focusing objective with a moderate numerical aperture (NA = 0.45) and different kinds of uniaxial crystal.