Double-Clad Antiresonant Hollow-Core Fiber and Its Comparison with Other Fibers for Multiphoton Micro-Endoscopy.

Label-free and multiphoton micro-endoscopy can transform clinical histopathology by providing an in situ tool for diagnostic imaging and surgical treatment in diseases such as cancer. Key to a multiphoton imaging-based micro-endoscopic device is the optical fiber, for distortion-free and efficient delivery of ultra-short laser pulses to the sample and effective signal collection. In this work, we study a new hollow-core (air-filled) double-clad anti-resonant fiber (DC-ARF) as a high-performance candidate for multiphoton micro-endoscopy.

Development of hydrogel-based standards and phantoms for non-linear imaging at depth.

Significance: Rapid advances in medical imaging technology, particularly the development of optical systems with non-linear imaging modalities, are boosting deep tissue imaging. The development of reliable standards and phantoms is critical for validation and optimization of these cutting-edge imaging techniques.

Aim: We aim to design and fabricate flexible, multi-layered hydrogel-based optical standards and evaluate advanced optical imaging techniques at depth.

All-fiberized 1840-nm femtosecond thulium fiber laser for label-free nonlinear microscopy.

We report an all-fiberized 1840-nm thulium-fiber-laser source, comprising a dissipative-soliton mode-locked seed laser and a chirped-pulse-amplification system for label-free biological imaging through nonlinear microscopy. The mode-locked thulium fiber laser generated dissipative-soliton pulses with a pre-chirped duration of 7 ps and pulse energy of 1 nJ. A chirped-pulse fiber-amplification system employing an in-house-fabricated, short-length, single-mode, high-absorption, thulium fiber delivered pulses with energies up to 105 nJ.

Superresolved polarization-enhanced second-harmonic generation for direct imaging of nanoscale changes in collagen architecture.

Superresolution (SR) optical microscopy has allowed the investigation of many biological structures below the diffraction limit; however, most of the techniques are hampered by the need for fluorescent labels. Nonlinear label-free techniques such as second-harmonic generation (SHG) provide structurally specific contrast without the addition of exogenous labels, allowing observation of unperturbed biological systems. We use the photonic nanojet (PNJ) phenomena to achieve SR-SHG.

Selective Imaging of Microplastic and Organic Particles in Flow by Multimodal Coherent Anti-Stokes Raman Scattering and Two-Photon Excited Autofluorescence Analysis.

Microplastic pollution is an urgent global issue. While spectroscopic techniques have been widely used for the identification of plastics collected from aquatic environments, these techniques are often labor-intensive and time-consuming due to sample collection, preparation, and long measurement times. In this study, a method for the two-dimensional detection and classification of flowing microplastic and organic biotic particles with high spatial and temporal resolutions has been proposed based on the simultaneous detection of coherent anti-Stokes Raman scattering (CARS) and two-photon excited autofluorescence (TPEAF) signals.

Widely-tunable synchronisation-free picosecond laser source for multimodal CARS, SHG, and two-photon microscopy.

We demonstrate a continuous wave (CW) seeded synchronization-free optical parametric amplifier (OPA) pumped by a picosecond, 1 µm laser and show its performance when used as a simple yet powerful source for label-free coherent anti-Stokes Raman scattering (CARS), concurrent second harmonic generation (SHG), and two-photon fluorescence microscopy in an epi-detection geometry. The average power level of above 175 mW, spectral resolution of 8 cm, and 2 ps pulse duration are well optimized for CARS microscopy in bio-science and bio-medical imaging systems. Our OPA is a much simpler setup than either the "gold-standard" laser and optical parametric oscillator (OPO) combination traditionally used for CARS imaging, or the more recently developed OPA systems pumped with femtosecond pulses [1].

Live-imaging of Bioengineered Cartilage Tissue using Multimodal Non-linear Molecular Imaging.

Coherent anti-Stokes Raman scattering (CARS) and second harmonic generation (SHG) are non-linear techniques that allow label-free, non-destructive and non-invasive imaging for cellular and tissue analysis. Although live-imaging studies have been performed previously, concerns that they do not cause any changes at the molecular level in sensitive biological samples have not been addressed. This is important especially for stem cell differentiation and tissue engineering, if CARS/SHG microscopy is to be used as a non-invasive, label-free tool for assessment of the developing neo-tissue.

Quantitative temporal interrogation in 3D of bioengineered human cartilage using multimodal label-free imaging.

The unique properties of skeletal stem cells have attracted significant attention in the development of strategies for skeletal regeneration. However, there remains a crucial unmet need to develop quantitative tools to elucidate skeletal cell development and monitor the formation of regenerated tissues using non-destructive techniques in 3D. Label-free methods such as coherent anti-Stokes Raman scattering (CARS), second harmonic generation (SHG) and two-photon excited auto-fluorescence (TPEAF) microscopy are minimally invasive, non-destructive, and present new powerful alternatives to conventional imaging techniques.

Nanoscale dysregulation of collagen structure-function disrupts mechano-homeostasis and mediates pulmonary fibrosis.

Matrix stiffening with downstream activation of mechanosensitive pathways is strongly implicated in progressive fibrosis; however, pathologic changes in extracellular matrix (ECM) that initiate mechano-homeostasis dysregulation are not defined in human disease. By integrated multiscale biomechanical and biological analyses of idiopathic pulmonary fibrosis lung tissue, we identify that increased tissue stiffness is a function of dysregulated post-translational collagen cross-linking rather than any collagen concentration increase whilst at the nanometre-scale collagen fibrils are structurally and functionally abnormal with increased stiffness, reduced swelling ratio, and reduced diameter. In ex vivo and animal models of lung fibrosis, dual inhibition of lysyl oxidase-like (LOXL) 2 and LOXL3 was sufficient to normalise collagen fibrillogenesis, reduce tissue stiffness, and improve lung function in vivo.

Optimising superoscillatory spots for far-field super-resolution imaging.

Optical superoscillatory imaging, allowing unlabelled far-field super-resolution, has in recent years become reality. Instruments have been built and their super-resolution imaging capabilities demonstrated. The question is no longer whether this can be done, but how well: what resolution is practically achievable? Numerous works have optimised various particular features of superoscillatory spots, but in order to probe the limits of superoscillatory imaging we need to simultaneously optimise all the important spot features: those that define the resolution of the system.

Triplet harvesting with 100% efficiency by way of thermally activated delayed fluorescence in charge transfer OLED emitters.

Organic light-emitting diodes (OLEDs) have their performance limited by the number of emissive singlet states created upon charge recombination (25%). Recently, a novel strategy has been proposed, based on thermally activated up-conversion of triplet to singlet states, yielding delayed fluorescence (TADF), which greatly enhances electroluminescence. The energy barrier for this reverse intersystem crossing mechanism is proportional to the exchange energy (ΔEST ) between the singlet and triplet states; therefore, materials with intramolecular charge transfer (ICT) states, where it is known that the exchange energy is small, are perfect candidates.

Tuning the intramolecular charge transfer emission from deep blue to green in ambipolar systems based on dibenzothiophene S,S-dioxide by manipulation of conjugation and strength of the electron donor units.

The efficient synthesis and photophysical properties of a series of ambipolar donor-acceptor-donor systems is described where the acceptor is dibenzothiophene S,S-dioxide and the donor is fluorene, carbazole, or arylamine. The systems exhibit intramolecular charge transfer (ICT) states (of variable ICT character strengths) leading to fluorescence emission ranging from deep blue to green with moderate to high photoluminescence quantum yields. The emission properties can be effectively tuned by systematically changing the position of substitution on both donor and acceptor units (which affects the extent of conjugation) and the redox potentials of the donor units.

Charge transfer in hybrid organic-inorganic PbS nanocrystal systems.

Charge transfer interactions between PbS nanocrystals (NCs) and tetrathiafulvalene (TTF) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) are studied using optical spectroscopy. Selective quenching of PbS NC photoluminescence (PL) by TTF is observed and related to the relative alignment of the highest occupied molecular orbital (HOMO) of TTF and the PbS NC 1s(h) energy level. TCNQ is also found to quench PbS NC PL irrespective of the NC bandgap.