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The two-photon all-optical physiology system has attracted great interest in deciphering neuronal circuits in vivo , benefiting from its advantages in recording and modulating neuronal activities at single neuron resolutions. However, the interference, or crosstalk, between the imaging and photostimulation beams introduces a significant challenge and may impede the future application of voltage indicators in two-photon all-optical physiology system. Here, we propose the time multiplexed excitation method to distinguish signals from neuronal activities and crosstalks from photostimulation. In our system, the laser pulses of the imaging beam and photostimulation beam are synchronized, and a time delay is introduced into these pulses to separate the fluorescence signal generated by these two beams. We demonstrate the efficacy of our system in eliminating crosstalk signals from photostimulation and evaluate its influence on both genetically encoded calcium indicators (GECIs) and genetically encoded voltage indicators (GEVIs) through in vivo experiments., Competing Interests: The authors declare that there are no conflicts of interest related to this article., (© 2024 Optica Publishing Group.)

Stretchable sensors with multiple sensory functions are in high demand for healthcare monitoring and artificial intelligence. Despite recent advances in wearable electronic sensors, it remains a significant challenge to achieve simultaneous sensing of both thermal and mechanical stimuli with a single sensor while integrating high stretchability. Herein, a stretchable and multifunctional optical sensor (SMOS) with simultaneous readout of temperature and strain is developed for wearable physiological monitoring of the human body. The SMOS primarily consists of a stretchable optical sensing fiber made from polymer nanocomposites containing lanthanide-based upconversion nanoparticles (UCNPs). Temperature measurements are achieved by ratiometric intensity measurements of the dual-emission UCNPs upon near-infrared excitation. By virtue of the ratiometric detection, the temperature readout of the SMOS is independent of strain deformations, enabling stable and continuous measurements of skin temperature during body motions. Furthermore, deformation of the SMOS by stretching leads to detectable and reversible changes in its light transmission, allowing tensile strains to be simultaneously measured. As a proof of concept, we demonstrate the capabilities of the SMOS in real time and simultaneous detection of both skin temperature and motion activities of the human body.

Wide-field fluorescent microscopy (WFFM) is widely employed in biomedical studies, due to its inherent advantages in high-speed imaging of biological dynamics noninvasively and specifically. However, WFFM suffers from the loss of axial resolution and the poor resistance to light scattering in deep tissue imaging. Here we propose a novel WFFM which has the capability in optical sectioning and volumetric imaging. We perform speckle illumination with a digital-micromirror-device for optical sectioning and employ an electrically tunable lens for defocusing modulation so as to quickly switch the image planes. We demonstrate its applications in multi-plane, wide-field imaging of biological dynamics in both zebrafish brains and mouse brains in vivo ., Competing Interests: The authors declare that there are no conflicts of interest related to this article., (© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement.)

To improve imaging speed, multifocal excitation is widely adopted as a parallel strategy in laser-scanning microscopy. Specifically, axial multifocal microscopy is popular in neuroscience as it enables functional imaging of neurons in multiple depths simultaneously. However, previous phase searching algorithms for axial multi-foci generation generally generate foci of uniform intensities, which cannot compensate the scattering-induced power loss in deep tissue and causes inhomogeneous excitation. Here, we propose a novel adaptive optimization-based phase-searching method (AdaPS) to generate axial multi-foci with arbitrary intensity modulations for scattering-induced loss compensation. By adopting Adaptive Moment Estimation (Adam) as the searching algorithm, our method could escape from unsatisfactory local minima and stably converge to the optimal phase pattern with errors at least an order of magnitude lower. We validate AdaPS through both numerical simulations and experiments and demonstrate that AdaPS could provide uniform multi-depth imaging in scattering phantom and enable high-fidelity multi-depth recordings of neural network dynamics in mouse brain in vivo.

Compared to point-scanning multiphoton microscopy, line-scanning temporal focusing microscopy (LTFM) is competitive in high imaging speed while maintaining tight axial confinement. However, considering its wide-field detection mode, LTFM suffers from shallow penetration depth as a result of the crosstalk induced by tissue scattering. In contrast to the spatial filtering based on confocal slit detection, here we propose the extended detection LTFM (ED-LTFM), the first wide-field two-photon imaging technique to extract signals from scattered photons and thus effectively extend the imaging depth. By recording a succession of line-shape excited signals in 2D and reconstructing signals under Hessian regularization, we can push the depth limitation of wide-field imaging in scattering tissues. We validate the concept with numerical simulations, and demonstrate the performance of enhanced imaging depth in in vivo imaging of mouse brains.

Surface enhanced Raman scattering (SERS) fiber sensors have shown great potential in sensitive biosensing and medical diagnostics. However, current SERS fiber probes are most commonly based on stiff silica fibers, which, unfortunately, are not mechanically compliant with soft biological tissues. In addition, the poor biocompatibility of silica fibers sets another barrier that hinders their development for biomedical applications. Here, we present, to the best of our knowledge, the first demonstration of soft-polymer-optical-fiber-based SERS (SPOF-SERS) probes with physio-mechanical properties suitable for implantation, and demonstrate their potential applications for in situ detection of bioanalysts. The SPOFs are made from porous hydrogel materials that are soft, elastic, and biocompatible. The three-dimensional porous structures of the hydrogels enable high loading of metal nanoparticles to provide a large amount of SERS "hot spots" for high sensitivity. We tested the SPOF-SERS sensor for detection and discrimination of rhodamine 6G and 4-mercaptopyridine in situ with detection limits of 10 -7   M and 10 -8   M, respectively. We also demonstrated the capability of SPOF-SERS probes in multiplexing detection. The soft, biocompatible, and highly sensitive SERS probe is promising for bioanalytical and implantable biomedical applications.

Compared with two-photon point-scanning microscopy, line-scanning temporal focusing microscopy breaks the limitation on imaging rate and maintains the axial resolution, which makes it promising for various biomedical studies. However, for deep tissue imaging, it suffers from reduced axial resolution and increased background noise due to sample induced wavefront distortion. Here, we propose a spatio-spectral focal modulation technique to enhance axial resolution and background rejection by simply subtracting an aberrated image, which is induced by a spatial light modulator, from an unaberrated image. The proposed technique could improve the axial resolution by a factor of 1.3 in our implementation, verified by both simulations and experiments. Besides, we show that compared with spatial modulation alone, spatio-spectral modulation induces less peak intensity loss caused by image subtraction. We further demonstrate the performance of our technique on the enhanced axial resolution and background rejection by deep imaging of cleared mouse brains and in vivo imaging of living mouse brains.

We demonstrate a novel and compact FBG interrogation system for multiplexed static strain sensing with a free running mode-locked fiber laser. Multiplexed FBG array in cascading are interrogated by coherent dual-comb pulses generated from a single fiber laser. Dual-comb spectroscopy is achieved with the fiber laser to precisely detect the strain-induced spectral shifts of the FBG sensors. Multi-point strain measurements are performed to characterize the proposed system, where a large dynamic range of 520 με with 0.5 με resolution is achieved.

Optical sectioning imaging with high spatial resolution deep inside scattering samples such as mammalian brain is of great interest in biological study. Conventional two-photon microscopy deteriorates in focus when light scattering increases. Here we develop an optical sectioning enhanced two-photon technique which incorporates structured illumination into line-scanning spatial-temporal focusing microscopy (LTSIM), and generate patterned illumination via laser intensity modulation synchronized with scanning. LTSIM brings scattering background elimination and in-focus contrast enhancement, and realizes nearly 2-fold increase in spatial resolution to ∼208 nm laterally and ∼0.94 µm axially. In addition, the intensity modulated line-scanning implementation of LTSIM enables fast and flexible generation of structured illumination, permitting adjustable spatial frequency profiles to optimize image contrast. The highly qualified optical sectioning ability of our system is demonstrated on samples including tissue phantom, C. elegans and mouse brain at depths over hundreds of microns.

Functional imaging in behaving animals is essential to understanding brain function. However, artifacts resulting from animal motion, including locomotion, can severely corrupt functional measurements. To dampen tissue motion, we designed a new optical window with minimal optical aberrations. Using the newly developed high-speed continuous volumetric imaging system based on an optical phase-locked ultrasound lens, we quantified motion of the cerebral cortex and hippocampal surface during two-photon functional imaging in behaving mice. We find that the out-of-plane motion is generally greater than the axial dimension of the point-spread-function during mouse locomotion, which indicates that high-speed continuous volumetric imaging is necessary to minimize motion artifacts.

In vivo flow cytometry provides a non-invasive way of probing the biology of circulating cells during disease progression and studying cellular response to therapy. However, current methods provide little morphological information which potentially could be new biological marker for early disease diagnosis, and fail to reveal intercellular interactions. Here we report a multi-color, multiphoton in vivo imaging flow cytometry, to image circulating cells within the vasculature of scattering tissues at high spatiotemporal resolution. We apply it in imaging of cellular dynamics in bone marrow through the intact mouse skull, in situ deformability cytometry, distinguishing cellular clusters, and simultaneously monitoring multiple types of trafficking cells based on their morphologies and fluorescence emission colors.

For in vivo deep tissue imaging, high order wavefront measurement and correction is needed for handling the severe wavefront distortion. Towards such a goal, we have developed the iterative multi-photon adaptive compensation technique (IMPACT). In this work, we explore using IMPACT to perform calcium imaging of neocortex through the intact skull of adult mice, and to image through the highly scattering white matter on the hippocampus surface.

Iterative multi-photon adaptive compensation technique (IMPACT) has been developed for wavefront measurement and compensation in highly scattering tissues. Our previous report was largely based on the measurements of fixed tissue. Here we demonstrate the advantages of IMPACT for in vivo imaging and report the latest results. In particular, we show that IMPACT can be used for functional imaging of awake mice, and greatly improve the in vivo neuron imaging in mouse cortex at large depth (~660 microns). Moreover, IMPACT enables neuron imaging through the intact skull of adult mice, which promises noninvasive optical measurements in mouse brain.

Stimulated Raman scattering (SRS) microscopy allows label-free chemical imaging based on vibrational spectroscopy. Narrowband excitation with picosecond lasers creates the highest signal levels and enables imaging speeds up to video-rate, but it sacrifices chemical specificity in samples with overlapping bands compared to broadband (multiplex) excitation. We develop a rapidly tunable picosecond optical parametric oscillator with an electro-optical tunable Lyot filter, and demonstrate multicolor SRS microscopy with synchronized line-by-line wavelength tuning to avoid spectral artifacts due to sample movement. We show sensitive imaging of three different kinds of polymer beads and live HeLa cells with moving intracellular lipid droplets.

A scheme is proposed to enhance the cascaded four-wave mixing (CFWM) generation, by introducing an optical feedback to the input port. Experimental and numerical results show that more efficient CFWM generation can be obtained by the scheme. The number of CFWM products is increased, as well as the powers of most CFWM products are improved.

We numerically studied the polarization dynamics in dissipative soliton lasers mode-locked by nonlinear polarization rotation (NPR). It was found that the polarization states of the intracavity dissipative soliton vary with time across the pulse. Depending on output coupling ratios, the polarization states of the pulse peak before the polarizer can be either nearly circular or nearly linear polarizations. The polarization dependent component in NPR is found to play a role of spectral filter under high and medium output coupling. However, NPR may work as a weak optical limiter under low output coupling, when additional spectral filtering is necessary to maintain steady mode-locking state.