We demonstrate stimulated emission depletion (STED) microscopy implemented in a laser scanning confocal microscope using excitation light derived from supercontinuum generation in a microstructured optical fiber. Images with resolution improvement beyond the far-field diffraction limit in both the lateral and axial directions were acquired by scanning overlapped excitation and depletion beams in two dimensions using the flying spot scanner of a commercially available laser scanning confocal microscope. The spatial properties of the depletion beam were controlled holographically using a programmable spatial light modulator, which can rapidly change between different STED imaging modes and also compensate for aberrations in the optical path. STED fluorescence lifetime imaging microscopy is demonstrated through the use of time-correlated single photon counting.

This article describes a graduate level optics laboratory experiment on the manipulation of the wavefront of a laser beam using a spatial light modulator. A computer generated holography technique is employed to generate a custom defined wavefront, realized in the +1 diffraction order when a collimated laser beam is diffracted by a binary transmission hologram. The hologram is written on a liquid crystal spatial light modulator and can be updated at a video rate using a personal computer interface.

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We describe a zonal-wavefront-sensing technique using an array of plane diffraction gratings. A spatially coherent beam, whose wavefront is to be measured, is incident on the array of gratings. The direction of a diffracted beam of a certain diffraction order is a function of the orientation and periodicity of the corresponding grating. Thus, by choosing the orientation and periodicity of each grating appropriately and by having a lens immediately behind the grating array, it is possible to get an array of focal spots. The profile of the incident wavefront can be estimated from the displacements of these focal spots relative to those due to an unaberrated beam. The arrangement makes it possible to increase the separation between two adjacent focal spots corresponding to two nearby gratings without effecting the areas of the gratings. Consequently, a relatively large dynamic range in wavefront measurement can be achieved without compromising the accuracy. With the arrangement it is also possible to use a photodetector array whose outline is independent of the grating array outline. The proposed wavefront-sensing technique is implemented experimentally using a liquid-crystal spatial-light modulator in conjunction with a CCD camera, and the obtained results are presented.

We show how the effects of azimuthal optical aberrations on singular light beams can result in an intensity modulation in the beam waist or focal point spread function (PSF) that is directly proportional to the amplitude of the applied phase aberration. The resulting distortions are enough to significantly degrade the utility of the singular beams even in well corrected optical systems. However we show that pattern of these intensity modulations is related to the azimuthal order of the applied aberration and we suggest how this can be used to measure those aberrations. We demonstrate a closed loop system using a liquid crystal spatial light modulator as a programmable diffractive optical element to both generate the beam and correct for the sensed aberrations based on feed back from a CCD detected intensity image of the focal point spread function.