Collagen remodelling and dysregulation are the hallmarks of diverse pathological conditions. In this context, second-harmonic generation (SHG) imaging has emerged as a powerful label-free modality for assessing collagen. This offers submicron resolution, intrinsic optical sectioning, and deeper imaging capabilities without the need for exogenous agents. Additionally, polarisation-resolved SHG (P-SHG) further enhances orientation-sensitive information on collagen architecture. This enables the elucidation of subtle structural alterations that are often invisible to conventional imaging techniques. This nonlinear technique has demonstrated utility in diagnosing diseases, particularly in assessing tumour progression, where collagen remodelling is correlated with disease severity and prognosis. Furthermore, quantitative image analysis, using metrics such as fibre density, orientation, anisotropy, and alignment, provides objective measures of collagen remodelling. P-SHG complements these analyses by enabling the retrieval of molecular susceptibility ratios (e.g., χ33/χ31), degrees of polarisation (DOLP), and orientation distribution functions, yielding more profound insights into the fibrillar ultrastructure and molecular organisation. These quantitative descriptors are being increasingly integrated into clinically relevant feature extraction methods. The incorporation of these features in artificial intelligence (AI) methods has enhanced SHG-based pathological assessment. AI-driven models can automatically classify tissues, detect pathological patterns, and correlate the collagen microstructure with clinical outcomes, addressing the bottleneck of manual interpretation and enhancing reproducibility. Future perspectives highlight the integration of SHG and P-SHG with deep-tissue multiphoton imaging, accompanied by explainable AI/ML-driven quantification, which will improve diagnostic precision, reproducibility, and clinical adoption. Ultimately, the convergence of optical innovation, deep learning, and translational engineering will lead to the establishment of collagen pathology assessment through SHG and P-SHG as reliable, accessible tools for diverse clinical applications.

Establishing quantitative parameters for differentiating between healthy and diseased cartilage tissues by examining collagen fibril degradation patterns facilitates the understanding of tissue characteristics during disease progression. These findings could also complement existing clinical methods used to diagnose cartilage-related diseases. In this study, cartilage samples from normal, osteoarthritis (OA), and rheumatoid arthritis (RA) tissues were prepared and analyzed using polarization-resolved second harmonic generation (P-SHG) imaging and quantitative image texture analysis. The enhanced molecular contrast obtained from this approach is expected to aid in distinguishing between healthy and diseased cartilage tissues. P-SHG image analysis revealed distinct parameters in the cartilage samples, reflecting variations in collagen fibril arrangement and organization across different pathological states. Normal tissues exhibited distinct χ33/χ31 values compared with those of OA and RA, indicating collagen type transition and cartilage erosion with chondrocyte swelling, respectively. Compared with those of normal tissues, OA samples demonstrated a higher degree of linear polarization, suggesting increased tissue birefringence due to the deposition of type-I collagen in the extracellular matrix. The distribution of the planar orientation of collagen fibrils revealed a more directional orientation in the OA samples, associated with increased type-I collagen, while the RA samples exhibited a heterogeneous molecular orientation. This study revealed that the imaging technique, the quantitative analysis of the images, and the derived parameters presented in this study could be used as a reference for disease diagnostics, providing a clear understanding of collagen fibril degradation in cartilage.

The stimulated emission (SE) signal in pump-probe experiment is conventionally measured with lock-in detection to differentiate the weak signals from the relatively large background of spontaneous emission and probe beam. Therefore, direct characterization of signal strength are often major limiting factors in terms of noise, speed, and data acquisition. In contrast, photon counting allows direct quantification of signal strength, while synchronized pump-probe pulse enables precise timing and the separation of signals accordingly. Herein, the SE based pump-probe method is combined with time-correlated single-photon counting to investigate the ultrafast photochemical parameters, digitally and quantitatively. As a proof-of-concept, our technique is applied to investigate, fluorescence lifetime ( tau ) similar to 3.71 ns , optical absorption cross-section ( sigma abs ) similar to 1.23 x 10 - 16 c m 2 , and the SE cross-section ( sigma SE ) similar to 2.22 x 10 - 17 c m 2 , of a fluorescent dye (ATTO 647N) quantitatively. The experimental results are also compared with theoretical photon statistics to further justify the advantages including experimental and statistical critical molecular dynamics parameters extraction with excellent high accuracy.

We report on the design and construction of a laser scanning optical beam-induced current (OBIC) microscope by assembling cost-effective commercial optical and electronic hardware components and developing data acquisition and control software in LabVIEW. A preliminary OBIC image of a Si photodetector acquired by the developed microscope is presented to demonstrate its operational capability. The versatility of the design will allow for the construction of other scanning microscope modalities on the same platform.

We will present the initiative in imaging a hugely expanded drosophila brain via expansion microscopy, which has brought unprecedented opportunities and challenges. 100X expansion has been demonstrated in enlarging the typically 0.6x0.3x0.2 mm brain to 60x30x20 mm, which promises electron microscopy resolution (approximately 3 nm) with optical microscopy (approximately 300 nm) to resolve the synapses connection. A highly sped-up imaging method integrated with an ultrasound-activated microtome is crucial to support the initiative. Critically, photon statistics set the fundamental considerations in selecting the contrasts for optical imaging.

Polarization-resolved second harmonic generation (P-SHG) microscopy is commonly used to analyze the second-order susceptibility, χ(2), tensor, which enables the calculation of the molecular structure of harmonophores. However, despite extensive research on type I collagen, the measured χ(2) ratios vary considerably among published values, which raises the question of whether P-SHG imaging is universally applicable to all tissues containing harmonophores. In this work, we propose that the deviation of χ(2) ratios is primarily due to ignoring the molecular tilt angle and chirality in image analysis. To confirm our hypothesis, we present an analytical model based on C6 symmetry that takes into account these two factors. We also introduce an imaging scheme that splits SHG into X- and Y-polarized image components for χ(2) tensor analysis. Our approach effectively improves the precision of determining χ(2) ratios, depending on how much the two factors affect the P-SHG signals.

Laser scanning optical beam induced current (OBIC) microscopy has become a powerful and nondestructive alternative to other complicated methods like electron beam induced current (EBIC) microscopy, for high resolution defect analysis of electronic devices. OBIC is based on the generation of electron-hole pairs in the sample due to the raster scanning of a focused laser beam with energy equal or greater than the band gap energy and synchronized detection of resultant current profile with respect to the beam positions. OBIC is particularly suitable to localize defect sites caused by metal-semiconductor interdiffusion or electrostatic discharge (ESD). OBIC signals, thus, are capable of revealing the parameters/factors directly related to the reliability and efficiency of the electronic device under test (DUT). In this review, the basic principles of OBIC microscopy strategies and their notable applications in semiconductor device characterization are elucidated. An overview on the developments of OBIC microscopy is also presented. Specifically, the recent progresses on the following three OBIC measurement strategies have been reviewed, which include continuous laser based single photon OBIC, pulsed laser based single photon OBIC, and multiphoton OBIC microscopy for three-dimensional mapping of photocurrent response of electronic devices at high spatiotemporal resolution. Challenges and future prospects of OBIC in characterizing complex electronic devices are also discussed.

Ultrafast spectroscopy techniques are crucial in studying an atom's or molecule's photochemical processes. In this work, the stimulated emission (SE) based pump-probe method is combined with time-correlated single-photon counting (TCSPC) to determine photochemical parameters, the fluorescence lifetime ( τ ~ 3.71 ns), the absorption cross-section (σ abs ~ 1.23 × 10 -16 cm 2 ), and the SE cross-section (σ SE ~ 2.22 × 10 -17 cm 2 ) of a fluorescent dye (ATTO 647N) digitally and quantitatively. Conventionally, the SE signal is measured with lock-in detection to differentiate the weak signals from the relatively large background of spontaneous emission. Therefore, direct characterization and comparison of the signal strength digitally and the corresponding cross-sections are not possible. In contrast, photon counting allows direct quantification of signal strength, while synchronized pump-probe pulse enables precise timing and the separation of signals accordingly. In this way, critical molecular dynamics parameters can be extracted experimentally and statistically with excellent high accuracy. The experimental results are also compared with theoretical photon statistics calculation to further justify the advantages of the photon-counting-based pump-probe technique in photo-chemical analysis, particularly the fluorescence-related ones.

We present a synchronous time delay technique to precisely control the illuminating laser pulses and the ultrasonic wave generation to visualize the ultrasound waveform through the Schlieren imaging method. The proposed time-resolved imaging technique offers the two-dimensional mapping of ultrasound waveform in a temporally evolved manner. The critical physical parameters, such as speed and spatial pulse length of ultrasonic waves, are visualized and calculated from image analysis. Our results suggest a protocol in characterizing ultrasound waveform, and it has the potential to reconstruct the acoustic field by accumulating the time-lapse waveforms.

EDITORIAL article Front. Phys., 21 March 2022Sec. Optics and Photonics https://doi.org/10.3389/fphy.2022.880960

Background: The alcohol patch test (APT) can detect aldehyde dehydrogenase (ALDH) genetic polymorphisms used to diagnose cutaneous erythema. However, the subjective results can vary owing to confounding factors. The hue-saturation-value (HSV) model provides an objective means of image analysis with APT.Methods: This study enrolled 57 participants (27.7 +/- 9.0 years, 52.6% females) with ALDH2*1/*1, ALDH2*1/*2, and ALDH2*2/*2 percentages of 50.9%, 43.8%, and 5.3%, respectively. In total, 56 APT protocols were applied and analyzed employing both visual inspection and the HSV model. The value of the delta standard deviation (SD) of the hue histogram, which manifests the difference between the APT reaction and the baseline skin color, was obtained using the HSV model. The receiver operating characteristic (ROC) curve and area under the ROC curve (AUC) were used to predict the ALDH2*2 allele with the HSV model.Results: Upon visual inspection, a maximal Youden index with a sensitivity of 82.1% and a specificity of 96.6% was determined for the ALDH2 genetic mutation. Using the delta SD of hue obtained in the HSV model, a maximal Youden index with 85.7% sensitivity and 96.6% specificity was determined using the ROC curve analysis (AUC = 0.948, p < 0.001). Thus, the use of the HSV model analysis with APT resulted in equal specificity, but better sensitivity, compared to those obtained upon visual inspection.Conclusion: The HSV model took into account the potential confounding factors, and thus, could help in the prediction of ALDH2 genetic polymorphisms.

Marine Scotland is tasked with reporting on the environmental status of Scottish marine waters, an enormous area of water extending from the shoreline to deep oceanic waters. As one of the most important variables, chlorophyll concentration (Chl) plays an important role in the seawater quality monitoring. Currently, the Chl observation is mostly done by expensive ship-based surveys that have very limited spatio-temporal coverage. Satellite based ocean colour remote sensing has the potential to significantly enhance monitoring capabilities but this opportunity has not been widely adopted by statutory reporting bodies across Europe due to concerns over satellite data quality. To break through this bottleneck, in this paper, we explore to implement advanced machine learning techniques to automatically estimate the Chl via the historic time series of ocean colour remote sensing data during from July 2002 to September 2019.

EDITORIAL article Front. Phys., 04 August 2022Sec. Optics and Photonics https://doi.org/10.3389/fphy.2022.977683

Laser scanning optical beam induced current (OBIC) microscopy has become a powerful and nondestructive alternative to other complicated methods like electron beam induced current (EBIC) microscopy, for high resolution defect analysis of electronic devices. OBIC is based on the generation of electron–hole pairs in the sample due to the raster scanning of a focused laser beam with energy equal or greater than the band gap energy and synchronized detection of resultant current profile with respect to the beam positions. OBIC is particularly suitable to localize defect sites caused by metal–semiconductor interdiffusion or electrostatic discharge (ESD). OBIC signals, thus, are capable of revealing the parameters/factors directly related to the reliability and efficiency of the electronic device under test (DUT). In this review, the basic principles of OBIC microscopy strategies and their notable applications in semiconductor device characterization are elucidated. An overview on the developments of OBIC microscopy is also presented. Specifically, the recent progresses on the following three OBIC measurement strategies have been reviewed, which include continuous laser based single photon OBIC, pulsed laser based single photon OBIC, and multiphoton OBIC microscopy for three‐dimensional mapping of photocurrent response of electronic devices at high spatiotemporal resolution. Challenges and future prospects of OBIC in characterizing complex electronic devices are also discussed.

This paper addresses the application of multimodal nonlinear optical (MNLO) microscopy to clinical research within the context of label-free non-invasive molecular imaging. Here, a compact MNLO microscope based on a laser scanning microscope, a femtosecond laser, a time-correlated single-photon counting system, and a photonic crystal fiber are introduced for biomedical applications. By integrating two-photon fluorescence, two-photon fluorescence lifetime imaging, second-harmonic generation, and coherent anti-Stokes Raman scattering microscopy, the proposed scheme provides profound insights into the physicochemical properties related to 3D molecular orientation distribution, inter- and intra-molecular interactions, and disease progression in biological systems and organs. The high peak power and the low average intensity of near-infrared laser pulses allow for deep-penetration imaging without compromising sample vitality. Linking nonlinear optical phenomena with time/spectral/polarization-resolved imaging also makes it possible to obtain multidimensional information to address complex biomedical questions.

Optical beam-induced current (OBIC) mapping is widely used to characterize semiconductor lasers, particularly for failure analysis, in which the reliability has been a critical issue to be resolved spectrally and temporally. OBIC microscopy is advantageous for its non-invasiveness, when compared with electron beam-induced current (EBIC) microscopy. However, for high-speed devices, conventional OBIC methods may be limited in observing the spectral responses adequately. In this work, we present a modified OBIC microscopy based on a tunable ultrafast laser, to address the need for spectral resolving for precision failure spot analysis in vertical-cavity surface-emitting laser (VCSEL) diodes. The spectral OBIC response of VCSEL diodes is investigated by varying the irradiation wavelengths. Importantly, the ultrafast mode-locked laser provides broadband wavelength range to investigate photocurrent responses of the VCSELs sample. Specifically, the OBIC, electroluminescence (EL) detection, and the reflectance of the normal and the electrostatic discharge (ESD) damaged VCSELs are compared. We have found the ESD damaged VCSELs showing a redshifted spectral response.

In this study, microcirculation on body surface is observed synchronously with electrocardiography and blue LED illumination to enhance the video capturing of the flow of red blood cells and the subsequent extraction of cardiovascular signals accordingly.