Transmission structured illumination microscopy with tunable frequency illumination using tilt mirror assembly.

We present experimental demonstration of tilt-mirror assisted transmission structured illumination microscopy (tSIM) that offers a large field of view super resolution imaging. An assembly of custom-designed tilt-mirrors are employed as the illumination module where the sample is excited with the interference of two beams reflected from the opposite pair of mirror facets. Tunable frequency structured patterns are generated by changing the mirror-tilt angle and the hexagonal-symmetric arrangement is considered for the isotropic resolution in three orientations. Utilizing high numerical aperture (NA) objective in standard SIM provides super-resolution compromising with the field-of-view (FOV). Employing low NA (20X/0.4) objective lens detection, we experimentally demonstrate [Formula: see text] (0.56 mm[Formula: see text]0.35 mm) size single FOV image with [Formula: see text]1.7- and [Formula: see text]2.4-fold resolution improvement (exploiting various illumination by tuning tilt-mirrors) over the diffraction limit. The results are verified both for the fluorescent beads as well as biological samples. The tSIM geometry decouples the illumination and the collection light paths consequently enabling free change of the imaging objective lens without influencing the spatial frequency of the illumination pattern that are defined by the tilt-mirrors. The large and scalable FOV supported by tSIM will find usage for applications where scanning large areas are necessary as in pathology and applications where images must be correlated both in space and time.

Saturable absorption assisted nonlinear structured illumination microscopy.

We propose a novel, to the best of our knowledge, super-resolution technique, namely saturable absorption assisted nonlinear structured illumination microscopy (SAN-SIM), by exploring the saturable absorption property of a material. In the proposed technique, the incident sinusoidal excitation is converted into a nonlinear illumination by propagating through a saturable absorbing material. The effective nonlinear illumination possesses higher harmonics which multiply fold high frequency components within the passband and hence offers more than two-fold resolution improvement over the diffraction limit. The theoretical background of the technique is presented, supported by the numerical results. The simulation is performed for both symmetric as well as random samples where the raw moiré frames are processed through a blind reconstruction approach developed for the nonlinear SIM. The results demonstrate the super-resolution capability of the proposed technique.

Method for single-shot fabrication of chiral woodpile photonic structures using phase-controlled interference lithography.

In this report, we propose a large-area, scalable and reconfigurable single-shot optical fabrication method using phase-controlled interference lithography (PCIL) to realize submicrometer chiral woodpile photonic structures. This proposed technique involves a 3 + 3 double-cone geometry with beams originated from a computed phase mask displayed on a single spatial light modulator. Simulation studies show the filtering response of such structures for linearly polarized plane wave illumination, with structural features tunable through a single parameter of interference angle. Further, these single chiral woodpile structures show dual chirality on illumination with both right circularly and left circularly polarized light through simulation. Experimentally fabricated patterns on photoresist show resemblance to the desired chiral woodpile structures.

Study of electric fields of diffraction from spatial light modulator: discussion.

A complete study of electric field vectors and efficiencies of diffraction orders for a phase pattern addressed to a pixelated spatial light modulator (SLM) is discussed here. General mathematical expressions of electric field vectors from SLM are explored here analytically for an arbitrary pattern on SLM with a given input electric field. Using the general expression, we calculate orientations of the electric fields of diffraction for sinusoidal and binary patterns of varying duty cycles. The patterns result in diffracted beams of various orders with different efficiencies calculated analytically and matching well with the experimental results. The binary pattern with 50% duty cycle delivers significant distribution of energies where all the even orders are absent, and the diffraction efficiency of the first-order beam can be close to 40% using an appropriately chosen modulation depth. Using the general expression, it is possible to obtain fields and efficiencies of diffraction for any arbitrary pattern on SLM. The discussion might help researchers using SLM in standard optics experiments.