Abstract:We demonstrate imaging through a turbid layer by using digital phase conjugation of the second harmonic field radiated from a beacon nanoparticle. We show that the phase-conjugated focus can be displaced from its initial position by illuminating the same region of the turbid layer with an angular offset. An image is obtained by scanning the phaseconjugated focus through the turbid layer in a region around the nanoparticle. We obtain a clear image of the target by measuring the light transmitted through it when scanning the focused beam.
Abstract:We report Stimulated Emission Depletion (STED) imaging of green fluorescent nanodiamonds containing Nitrogen-Vacancy-Nitrogen (NVN) centers with a resolution of 70 nm using a commercial microscope. Nanodiamonds have been demonstrated to have the potential to be excellent cellular biomarkers thanks to their low toxicity and nonbleaching fluorescence, and are especially appealing for superresolution imaging technique like STED microscopy. However, only red fluorescent nanodiamonds containing Nitrogen-Vacancy (NV) centers have been used with STED microscopy so far. The existence of only one color nonbleaching center limits the possible observations, for instance it complicates spatial correlation studies with STED. To provide a nonbleaching probe in a different color, we characterize here the optical properties of the NVN defect for STED imaging. We demonstrate STED imaging of the green fluorescent nanodiamonds containing NVN centers, opening the door for long term two-color STED observation. Furthermore we exemplify the use of green nanodiamonds as a second color nonbleaching STED biomarker by imaging 70 nm fluorescent crystals up taken into HeLa cells.
Microfluidics and optofluidics have revolutionized high-throughput analysis and chemical synthesis over the past decade. Single molecule imaging has witnessed similar growth, due to its capacity to reveal heterogeneities at high spatial and temporal resolutions. However, both resolution types are dependent on the signal to noise ratio (SNR) of the image. In this paper, we review how the SNR can be enhanced in optofluidics and microfluidics. Starting with optofluidics, we outline integrated photonic structures that increase the signal emitted by single chromophores and minimize the excitation volume. Turning then to microfluidics, we review the compatible functionalization strategies that reduce noise stemming from non-specific interactions and architectures that minimize bleaching and blinking.
Multimode fibers have recently been demonstrated to be a promising candidate for ultrathin and high resolution endoscopy. However, this method does not offer depth discrimination for fluorescence imaging and the numerical aperture of the fiber limits its resolution. In this paper we demonstrate optical sectioning and enhanced resolution using saturated excitation and temporal modulation. Using a continuous wave laser excitation, we demonstrate improved resolution in all three dimensions and increased image contrast by rejecting out of focus light.
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