Q-plate enabled spectrally diverse orbital-angular- momentum conversion for stimulated emission depletion microscopy

By Lu Yan, P. Gregg, Ebrahim Karimi, A. Rubano, Lorenzo Marrucci, R. W. Boyd, Siddharth Ramachandran. 2015

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Spin to orbital angular momentum (OAM) conversion using a device known as a q-plate has gained recent attention as a convenient means of creating OAM beams. We show that the dispersive properties of a q=1/2 plate, specifically its group index difference Δng for ordinary and extraordinary polarization light, can be tuned for achieving single-aperture, alignment-tolerant stimulated emission depletion (STED) nanoscopy with versatile control over the color combinations as well as laser bandwidths. Point spread function measurements reveal the ability to achieve single-aperture STED illumination systems with high throughput (transmission >89%) and purity (donut beam extinction ratios as high as |−18.75|  dB, i.e., ∼1% residual light in the dark center of the donut beam) for a variety of color combinations covering the entire visible spectrum, hence addressing several of the fluorescent dyes of interest in STED microscopy. In addition, we demonstrate dual-color STED illumination that would enable multiplexed imaging modalities as well as schemes that could use wide bandwidths up to 19 nm (and hence ultrashort pulses down to ∼50  fs). Switching between any of these color settings only involves changing the bias of the q-plate that does not alter the alignment of the system, hence potentially facilitating alignment-free, spectrally diverse multiplexed nanoscale imaging.

Subfields: Atomic and Molecular Physics, and Optics, Biomedical Engineering

View Paper: https://www.semanticscholar.org/paper/0f126d7e9a3f18d92359be3fa41efd038a32f9fb