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Register a new userHigh-resolution Collinear Chiral Sum Frequency Generation Microscopy by Using Vectorial Beam
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In chiral sum frequency generation (C-SFG), the chiral nature of ${chi}^{(2)}$ requires the three involved electric fields to be pairwise non-parallel, leading to the traditional non-collinear configuration which is a hindrance for achieving diffraction limited resolution while utilizing it as a label-free imaging contrast mechanism . Here we propose a collinear C-SFG (CC-SFG) microscopy modality by using longitudinal z-polarized vectorial field. Label-free chiral imaging with enhanced spatial resolution (~1.4 times improvement in one lateral and the longitudinal directions over the traditional non-collinear scheme) is demonstrated, providing a new path for SFG microscopy with diffraction-limited resolution for mapping chirality.
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Super-resolution fluorescence microscopy is an important tool in biomedical research for its ability to discern features smaller than the diffraction limit. However, due to its difficult implementation and high cost, the universal application of super-resolution microscopy is not feasible. In this paper, we propose and demonstrate a new kind of super-resolution fluorescence microscopy that can be easily implemented and requires neither additional hardware nor complex post-processing. The microscopy is based on the principle of stepwise optical saturation (SOS), where $M$ steps of raw fluorescence images are linearly combined to generate an image with a $sqrt{M}$-fold increase in resolution compared with conventional diffraction-limited images. For example, linearly combining (scaling and subtracting) two images obtained at regular powers extends resolution by a factor of $1.4$ beyond the diffraction limit. The resolution improvement in SOS microscopy is theoretically infinite but practically is limited by the signal-to-noise ratio. We perform simulations and experimentally demonstrate super-resolution microscopy with both one-photon (confocal) and multiphoton excitation fluorescence. We show that with the multiphoton modality, the SOS microscopy can provide super-resolution imaging deep in scattering samples.
Beam self-cleaning (BSC) in graded-index (GRIN) multimode fibres (MMFs) has been recently reported by different research groups. Driven by the interplay between Kerr effect and beam self-imaging, BSC counteracts random mode coupling, and forces laser beams to recover a quasi-single mode profile at the output of GRIN fibres. Here we show that the associated self-induced spatiotemporal reshaping allows for improving the performances of nonlinear fluorescence microscopy and endoscopy using multimode optical fibres. We experimentally demonstrate that the beam brightness increase, induced by self-cleaning, enables two and three-photon imaging of biological samples with high spatial resolution. Temporal pulse shortening accompanying spatial beam clean-up enhances the output peak power, hence the efficiency of nonlinear imaging. We also show that spatiotemporal supercontinuum generation is well-suited for large-band nonlinear fluorescence imaging in visible and infrared domains. We substantiated our findings by multiphoton fluorescence imaging in both microscopy and endoscopy configurations.
We present a new flexible high speed laser scanning confocal microscope and its extension by an astigmatism particle tracking device (APTV). Many standard confocal microscopes use either a single laser beam to scan the sample at relatively low overall frame rate, or many laser beam to simultaneously scan the sample and achieve a high overall frame rate. Single-laser-beam confocal microscope often use a point detector to acquire the image. To achieve high overall frame rates, we use, next to the standard 2D probe scanning unit, a second 2D scan unit projecting the image directly on a 2D CCD-sensor (re-scan configuration). Using only a single laser beam eliminates cross-talk and leads to an imaging quality that is independent of the frame rate with a lateral resolution of 0.235unit{mu m}. The design described here is suitable for high frame rate, i.e., for frame rates well above video rate (full frame) up to a line rate of 32kHz. The dwell time of the laser focus on any spot in the sample (122ns) is significantly shorter than in standard confocal microscopes (in the order of milli or microseconds). This short dwell time reduces phototoxicity and bleaching of fluorescent molecules. The new design opens further flexibility and facilitates coupling to other optical methods. The setup can easily be extended by an APTV device to measure three dimensional dynamics while being able to show high resolution confocal structures. Thus one can use the high resolution confocal information synchronized with an APTV dataset.
Nonlinear optical generation has been a well-established way to realize frequency conversion in nonlinear optics, whereas previous studies were just focusing on the scalar light fields. Here we report a concise yet efficient experiment to realize frequency conversion from vector fields to vector fields based on the vectorial nonlinear optical process, e.g., the second-harmonic generation. Our scheme is based on two cascading type-I phase-matching BBO crystals, whose fast axes are configured elaborately to be perpendicular to each other. Without loss of generality, we take the full Poincare beams as the vectorial light fields in our experiment, and visualize the structured features of vectorial second-harmonic fields by using Stokes polarimetry. The interesting doubling effect of polarization topological index, i.e., a low-order full Poincare beam is converted to a high-order one are demonstrated. However, polarization singularities of both C-points and L-lines are found to keep invariant during the SHG process. Our scheme can be straightforwardly generalized to other nonlinear optical effects. Our scheme can offer a deeper understanding on the interaction of vectorial light with media and may find important applications in optical imaging, optical communication and quantum information science.
Label-free imaging approaches seek to simplify and augment histopathologic assessment by replacing the current practice of staining by dyes to visualize tissue morphology with quantitative optical measurements. Quantitative phase imaging (QPI) operates with visible/UV light and thus provides a resolution matched to current practice. Here we introduce and demonstrate confocal QPI for label-free imaging of tissue sections and assess its utility for manual histopathologic inspection. Imaging cancerous and normal adjacent human breast and prostate, we show that tissue structural organization can be resolved with high spatial detail comparable to conventional H&E stains. Our confocal QPI images are found to be free of halo, solving this common problem in QPI. We further describe and apply a virtual imaging system based on Finite-Difference Time-Domain (FDTD) calculations to quantitatively compare confocal with wide-field QPI methods and explore performance limits using numerical tissue phantoms.
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