Non-invasive probing of dynamic ion migration in light-emitting electrochemical cells by an advanced nanoscale confocal microscope.

In this study, we firstly propose an optical approach to investigate the ion profile of organic films in light-emitting electrochemical cells (LECs) without any invasive sputtering processes. In contrast to previous literatures, this pure optical strategy allows us to record clear and non-destructive ion profile images in the (Ru(dtb-bpy)(PF)) consisted organic layer without interferences of complex collisions from the bombardment of secondary sputter induced ions in a conventional time-of-flight secondary ion mass spectrometry. By using the advanced position sensitive detector (PSD)-based Nanoscale Confocal Microscope, ion distribution profiles were successfully acquired based on the observation of nanoscale optical path length difference by measuring the refractive-index variation while the thickness of the LEC layer was fixed.

Correlation between the optical absorption and twisted angle of bilayer graphene observed by high-resolution reflectance confocal laser microscopy.

We report a systematic study of the optical absorption of twisted bilayer graphene (tBLG) across a large range of twist angles from 0° to 30° using a high-resolution reflectance confocal laser microscopy (RCLM) system. The high-quality single crystalline tBLG was synthesized via the efficient plasma enhanced chemical vapor deposition techniques without the need of active heating. The sensitivity of acquired images from the RCLM were better than conventional optical microscopes.

Label-Free Characterization of Collagen Crosslinking in Bone-Engineered Materials Using Nonlinear Optical Microscopy.

Engineered biomaterials provide unique functions to overcome the bottlenecks seen in biomedicine. Hence, a technique for rapid and routine tests of collagen is required, in which the test items commonly include molecular weight, crosslinking degree, purity, and sterilization induced structural change. Among them, the crosslinking degree mainly influences collagen properties.

Imaging of nanoscale birefringence using polarization-resolved chromatic confocal microscopy.

We demonstrate a homebuilt confocal microscope with ∼60 nm axial resolution to visualize the optical path length (OPL) of liquid crystals (LCs) inside a 2-domain alignment LC cell. Since the microscope is sensitive to light polarization, it is capable of determining LC orientation by accounting for the OPL variation, ΔOPL. The resolution of birefringence depends on the measured ΔOPL from two cross-polarized channel detections, of which the concept is different from other polarization-resolved optical imaging techniques, but is relatively simple in optical layout and analysis.

Wave-vector-encoded nonlinear endomicroscopy.

Based on a rigid square fiber for wave vector delivery, we present a novel (to the best of our knowledge) wave-vector-encoded nonlinear-optical endomicroscopy (WENE). WENE overcomes three tangled issues, including femtosecond pulse broadening induced signal degradation, complexity of packaging miniaturized scanners in the distal end, and pixel-like images, which cannot be fully addressed by current distal scanning nonlinear endomicroscopy (NE) or fiber-bundle-based proximal scanning NE. Due to the advantages of its simplicity in overall configuration and package in the distal end, the capability of addressing the issue of pulse broadening, and offering continuous wave vector delivery, the demonstrated WENE shows great promise for future basic research on biomedical processes and minimally invasive utilization for clinical diagnosis.

Label-free characterization of collagen fibers in cancerous esophagus tissues using ratiometric nonlinear optical microscopy.

The issue of classifying esophageal cancer at various developmental stages is crucial for determining the optimized treatment protocol for the patients, as well as the prognosis. Precision improvement in staging esophageal cancer keeps seeking quantitative and analytical imaging methods that could augment histopathological techniques. In this work, we used nonlinear optical microscopy for ratiometric analysis on the intrinsic signal of two-photon excited fluorescence (TPEF) and second harmonic generation (SHG) from single collagen fibers only in submucosa of esophageal squamous cell carcinoma (ESCC).

Ultrahigh-resolution optical coherence tomography/angiography with an economic and compact supercontinuum laser.

In this study, a Q-switch pumped supercontinuum laser (QS-SCL) is used as a light source for imaging via ultrahigh-resolution optical coherence tomography and angiography (UHR-OCT/OCTA). For this purpose, an OCT system based on a spectral-domain detection scheme is constructed, and a spectrometer with a spectral range of 635 - 875 nm is designed. The effective full-width at half maximum of spectrum covers 150 nm, and the corresponding axial and transverse resolutions are 2 and 10 µm in air, respectively.

Tuning the Color Temperature of White-Light-Emitting Electrochemical Cells by Laser-Scanning Perovskite-Nanocrystal Color Conversion Layers.

The development of white-light-emitting electrochemical cells (LECs) has attracted great attention owing to their numerous advantages. Recently, perovskite materials have also shown many outstanding optoelectronic properties in light absorption and emission, and hence they are suitable for serving as the color conversion layers (CCLs) in solid-state white-light-emitting diodes (LEDs). Here, white LECs were fabricated by integrating non-doped blue-green LECs with CCLs made of a single composition of perovskite nanocrystal (NCs).

In situ high-resolution thermal microscopy on integrated circuits.

The miniaturization of metal tracks in integrated circuits (ICs) can cause abnormal heat dissipation, resulting in electrostatic discharge, overvoltage breakdown, and other unwanted issues. Unfortunately, locating areas of abnormal heat dissipation is limited either by the spatial resolution or imaging acquisition speed of current thermal analytical techniques. A rapid, non-contact approach to the thermal imaging of ICs with sub-μm resolution could help to alleviate this issue.

Widely wavelength tunable fast intensity-modulated light source for biophotonic applications.

High modulation depth, fast (megahertz to gigahertz), intensity-modulated light sources of various wavelengths within the 0.7-1.35 μm bio-penetration window are highly desirable for many biophotonic diagnosis systems.

Non-invasive image-guided laser microsurgery by a dual-wavelength fiber laser and an integrated fiber-optic multi-modal system.

A new approach to non-invasive image-guided laser micro-treatment is demonstrated by a dual-wavelength fiber laser source and an integrated fiber-based multi-modal system. The fiber-based source, operated in 1.55 and 1.

Simple approach to three-color two-photon microscopy by a fiber-optic wavelength convertor.

A simple approach to multi-color two-photon microscopy of the red, green, and blue fluorescent indicators was reported based on an ultra-compact 1.03-μm femtosecond laser and a nonlinear fiber. Inside the nonlinear fiber, the 1.

Spiral surface plasmon modes inside metallic nanoholes.

Spiral surface plasmon (SSP) modes that propagate inside a silver (Ag) nanohole are investigated by performing both simulations and theoretical analyses. The SSP modes are formed by a linear combination of two rotating SP eigenmodes of the Ag nanohole in the fast-wave branch. Inside a uniform Ag nanohole, the handedness and the number of strands of the SSP modes are determined by both the component SP eigenmodes and their rotation directions.

Optical coherence tomography-guided laser microsurgery for blood coagulation with continuous-wave laser diode.

Blood coagulation is the clotting and subsequent dissolution of the clot following repair to the damaged tissue. However, inducing blood coagulation is difficult for some patients with homeostasis dysfunction or during surgery. In this study, we proposed a method to develop an integrated system that combines optical coherence tomography (OCT) and laser microsurgery for blood coagulation.

Non-invasive biopsy of doped-ions inside optical substrate by modified two-photon microscopy.

Doped-ion based optical elements play key roles in optical signal processes, including amplification, absorption, wavelength-filtering, lighting, and polarizing plate. Non-invasively mapping the spatial distribution of the ion concentrations in these optical elements is highly desirable either during the fabrication process or to determine their optical qualities. In this work, we applied modified two-photon fluorescence (m-TPF) microscopy to trace the ion-distributions deep inside the optical elements.

Novel wearable and wireless ring-type pulse oximeter with multi-detectors.

The pulse oximeter is a popular instrument to monitor the arterial oxygen saturation (SPO2). Although a fingertip-type pulse oximeter is the mainstream one on the market at present, it is still inconvenient for long-term monitoring, in particular, with respect to motion. Therefore, the development of a wearable pulse oximeter, such as a finger base-type pulse oximeter, can effectively solve the above issue.

High power NIR fiber-optic femtosecond Cherenkov radiation and its application on nonlinear light microscopy.

We reported a record high power (>250 mW) and compact near-infrared fiber-optic femtosecond Cherenkov radiation source and its new application on nonlinear light microscopy for the first time (to our best knowledge). The high power femtosecond Cherenkov radiation was generated by 1.03 μm femtosecond pulses from a portable diode-pumped laser and a photonic crystal fiber as a compact, flexible, and highly efficient wavelength convertor.

Higher-order modulations of fs laser pulses for GHz frequency domain photon migration system.

Except the fundamental modulation frequency, by higher-order-harmonic modulations of mode-locked laser pulses and a simple frequency demodulation circuit, a novel approach to GHz frequency-domain-photon-migration (FDPM) system was reported. With this novel approach, a wide-band modulation frequency comb is available without any external modulation devices and the only electronics to extract the optical attenuation and phase properties at a selected modulation frequency in FDPM systems are good mixers and lock-in devices. This approach greatly expands the frequency range that could be achieved by conventional FDPM systems and suggests that our system could extract much more information from biological tissues than the conventional FDPM systems.

Simultaneous 0.8, 1.0, and 1.3 μm multispectral and common-path broadband source for optical coherence tomography.

Simultaneous multispectral generation in 0.8, 1.0, and 1.

Observation of spontaneous polarization misalignments in periodically poled crystals using second-harmonic generation microscopy.

Periodically poled crystal (PPC) is a key component for nonlinear optical applications. Its poling quality relies largely on successful domain inversion and the alignment of spontaneous polarization (SP) vectors in each domain. Here we report the unexpected observation of bulk second harmonic generation (SHG) in PPC when excitation propagating along its optical axis.

A sub-100 fs self-starting Cr:forsterite laser generating 1.4 W output power.

Without cavity dumping or external amplification, we report a femtosecond Cr:forsterite laser with a 1.4 W output power and 2 W in continuous wave (CW) operated with a crystal temperature of 267 K. In the femtosecond regime, the oscillator generates Kerr-lens-mode-locked 84 fs pulses with a repetition rate of 85 MHz, corresponding to a high 16.

Miniaturized video-rate epi-third-harmonic-generation fiber-microscope.

With a micro-electro-mechanical system (MEMS) mirror, we successfully developed a miniaturized epi-third-harmonic-generation (epi-THG) fiber-microscope with a video frame rate (31 Hz), which was designed for in vivo optical biopsy of human skin. With a large-mode-area (LMA) photonic crystal fiber (PCF) and a regular microscopic objective, the nonlinear distortion of the ultrafast pulses delivery could be much reduced while still achieving a 0.4 microm lateral resolution for epi-THG signals.

Miniaturized multiphoton microscope with a 24Hz frame-rate.

With miniaturized tube lenses and a micro-electro-mechanical system (MEMS) mirror, we constructed a miniaturized multiphoton microscope system. Through a two-dimensional asynchronous scanning of the MEMS mirror, 24Hz frame rate can be realized. With a high numerical aperture objective, sub-micron resolution can also be achieved at the same time.

Cr:Forsterite-laser-based fiber-optic nonlinear endoscope with higher efficiencies.

We demonstrate a beam-scanning nonlinear light endoscope based on a flexible fiber bundle. Excited with a femtosecond Cr:Forsterite laser, the degradation in multiphoton multiharmonic excitation efficiency due to the pulse-broadening effect is significantly reduced without utilizing any external devices. The system resolution has been characterized to be 5.

Thickness dependence of optical second harmonic generation in collagen fibrils.

Simultaneous backward and forward second harmonic generations from isolated type-I collagen matrix are observed. Optical interference behaviors of these nonlinear optical signals are studied with accurately determined fibril thickness by an atomic force microscope. The nonlinear emission directions are strongly dependent on the coherent interaction within and between collagen fibrils.