Raman Scattering Research Articles

Raman scattering impairments caused by 50G-PON introduction and mitigation techniques

We explore the impact of stimulated Raman scattering (SRS) in the context of multiple PON generations sharing the same optical distribution network. The 50G-PON, being the last specified ITU-T PON, imposes the use of high launch power to meet strong optical path loss requirements. We show that the XGS-PON upstream could be the first victim of the introduction of 50G-PON since its wavelength spacing maximizes Raman scattering. We exploit a model to describe both in simulation and experiment the SRS-induced depletion on XGS-PON. Assuming that 50G-PON will be deployed on the current passive infrastructure, we also exploit field data to precisely predict the amount of terminations exceeding the requirements. The results show that up to 1.8 dB can be lost on XGS-PON upstream signals, 1.3 dB on the 50G-PON upstream, and 0.5 dB on the G-PON upstream, over a distance of 20 km of fiber. Up to 3% of terminations may be affected, according to our field data exploitation. Improving the receivers’ sensitivity through either better photodiodes, signal processing, or forward error correction could relax the high launch power constraints, and thus the SRS. Deploying an optical splitter at the central office could also limit the power actually launched into the fiber while meeting high split ratios. Finally, decreasing the 50G-PON downstream wavelength seems a possible option to mitigate the Raman scattering.

Unmixing Autoencoder for Image Reconstruction from Hyperspectral Data.

Due to the complexity of samples and the limitations in spatial resolution, the spectra in hyperspectral imaging (HSI) are generally contributed to by multiple components, making univariate analysis ineffective. Although feature extraction methods have been applied, the chemical meaning of the compressed variables is difficult to interpret, limiting their further applications. An unmixing autoencoder (UAE) was developed in this work for the separation of the mixed spectra in HSI. The proposed model is composed of an encoder and a fully connected (FC) layer. The former is used to compress the input spectrum into several variables, and the latter is employed to reconstruct the spectrum. Combining reconstruction loss and sparse regularization, the weights and the spectral profiles of the components will be encoded in the compressed variables and the connection weights of FC, respectively. A simulated and three experimental HSI data sets were adopted to investigate the performance of the UAE model. The spectral components were successfully obtained, from which the handwriting under papers was revealed from the image of near-infrared (NIR) diffusive reflectance spectroscopy, and the images of lipids, proteins, and nucleic acids were reconstructed from the Raman and stimulated Raman scattering (SRS) images.

Study on Stimulated Raman Scattering Threshold Over Two-Mode Fiber

Study on Stimulated Raman Scattering Threshold Over Two-Mode Fiber

System Performance Estimation Accounting for Stimulated Raman Scattering in 14.1-THz Bandwidth S+C+L Inline-Amplified Transmission

System Performance Estimation Accounting for Stimulated Raman Scattering in 14.1-THz Bandwidth S+C+L Inline-Amplified Transmission

Absolute signal of stimulated Raman scattering microscopy: A quantum electrodynamics treatment.

The advent of stimulated Raman scattering (SRS) microscopy has launched a rapidly growing field in chemical imaging with broad impact. Although the physical picture seems to be well understood from classical models, prediction of absolute SRS signals remains a challenge. Here, we present a quantum electrodynamics treatment of the newly introduced stimulated Raman cross section. The resulting formula for calculating the absolute SRS signal is simple and differs from the commonly used relations by only one factor. We demonstrate the utility of this formula in a broad range of crucial applications of SRS microscopy, including stimulated Raman enhancement factor (>108 times), signal-to-noise ratio (SNR) of typical imaging experiments, population saturation under high power excitation, and energy deposition during stimulated Raman photothermal microscopy. In particular, the theory predicts that SRS microscopy is almost always more sensitive than spontaneous Raman microscopy for chemical imaging.

Temperature-Dependent Raman Scattering and Correlative Investigation of AlN Crystals Prepared Using a Physical Vapor Transport (PVT) Method

Ultrawide bandgap (UWBG) AlN c- and m-face crystals have been prepared using the physical vapor transport (PVT) method and studied penetratively using temperature-dependent (TD) Raman scattering (RS) measurements under both visible (457 nm) and DUV (266 nm) excitations in 80–870 K, plus correlative atomic force microscopy (AFM) and variable-angle (VA) spectroscopic ellipsometry (SE). VASE identified their band gap energy as 6.2 eV, indicating excellent AlN characteristics and revealing Urbach energy levels of about 85 meV. Raman analyses revealed the residual tensile stress. TDRS shows that the E2(high) phonon lifetime decayed gradually in the 80–600 K range. Temperature has the greater influence on the stress of m-face grown AlN crystal. The influence of low temperature on the E2(high) phonon lifetime of m-plane AlN crystal is greater than that of the high-temperature region. By way of the LO-phonon and plasma coupling (LOPC), simulations of A1(LO) modes and carrier concentrations along different faces and depths in AlN crystals are determined. These unique and significant findings provide useful references for the AlN crystal growth and deepen our understanding on the UWBG AlN materials.

Mid‐Infrared on‐Chip Soliton Self‐frequency Shift in Chalcogenide Glass Waveguide

AbstractMid‐infrared soliton lasers leveraging the Raman self‐pumping induced soliton self‐frequency shift (SSFS) effect offer continuously tunable, highly efficient, femtosecond coherent sources that are essential for applications such as spectroscopy, metrology, and quantum optics. However, despite significant advancements in fluoride and chalcogenide fiber platforms, realizing mid‐infrared Raman soliton lasers on on‐chip platforms remains challenging. In this study, the first experimental demonstration of a mid‐infrared Raman soliton laser in an on‐chip Ge28Sb12Se60 (GeSbSe) chalcogenide glass waveguide is presented. A fully fiberized femtosecond fiber laser, centered at 1.96 µm and emitting 246 fs pulses at a 50 MHz repetition rate, is utilized as the pump source, establishing a fiber‐to‐chip configuration. The waveguides are meticulously fabricated using e‐beam lithography and plasma etching, achieving high optical quality and precision in the mid‐infrared regime. Through precise geometrical dispersion engineering, a Raman soliton laser is achieved that continuously tunes from 1960 to 2145 nm within a 32.5 mm long snakelike GeSbSe strip waveguide. The threshold for pump peak power is remarkably low, at just 14.1 W (3.47 pJ). Additionally, a more than one‐octave‐spanning near to mid‐infrared supercontinuum (1320–2760 nm at 22.9 pJ), reinforced by the combined Kerr and Raman effects, is also realized, confirming the versatile performance of the proposed GeSbSe waveguide. These findings pave the way for mid‐infrared on‐chip Raman soliton lasers, highlighting their potential for power‐efficient, low‐cost, and field‐deployable on‐chip applications in the mid‐infrared regime.

Surface-Enhanced Raman Scattering to Improve the Sensitivity of the MTT Assay

Surface-Enhanced Raman Scattering to Improve the Sensitivity of the MTT Assay

Competitive Binding Strategy for Reliable Signal-off Surface Enhanced Raman Scattering Sensing in Protecting Apples from Patulin without External Interference

Patulin is a toxin that can be found in damaged or moldy fruits, especially apples. Very high detection sensitivity can be achieved using the SERS (Surface Enhanced Raman Scattering) technique, which provides information about molecular vibrations. However, unexpected desorption of target toxins from the surface of the SERS substrate and interference from other substances pose a major challenge. Here we investigate a competitive binding strategy for reliable SERS analysis of PAT. Core-Raman molecule-shell (CMS) structures and programmable, specific DNA interactions are utilized to regulate Raman signal intensity without affecting the embedded Raman molecules. Specfically, aptamer-functionalized CMS structures are combined with metal-organic scaffold nanoparticles that possess complementary DNA sequences. In the presence of PAT, binding of the aptamer to the toxin leads to degradation of the hybrid nano assembly, which can be measured by a change in the SERS signal. This SERS strategy enables turn-off sensing in apple juice over a wide range (10pg/mL to 1μg/mL), with a detection limit as low as 0.02ng/mL. Analysis of real samples gives results consistent with high-performance liquid chromatography (HPLC) test. The excellent selectivity and sensitivity of the SERS sensor demonstrate its potential for a wide range of SERS sensor applications.

Ultrasensitive NIR-II Surface-Enhanced Resonance Raman Scattering Nanoprobes with Nonlinear Photothermal Effect for Optimized Phototheranostics.

Surface-enhanced resonance Raman scattering (SERRS) in the second near-infrared (NIR-II) window has great potential for improved phototheranostics, but lacks nonfluorescent, resonant and high-affinity Raman dyes. Herein, it is designed and synthesize a multi-sulfur Raman reporter, NF1064, whose maximum absorption of 1064nm rigidly resonates with NIR-II excitation laser while possessing absolutely nonfluorescent backgrounds. Ultrafast spectroscopy suggests that the fluorescence quenching mechanism of NF1064 originates from twisted intramolecular charge transfer (TICT) in the excited state. Gold nanorods (AuNRs) decorated with such nonfluorescent NF1064 (AuNR@NF1064) show remarkable SERRS performances, including zero-fluorescence background, femtomolar-level sensitivity as well as superb photostability without fluorescence photobleaching. More importantly, AuNR@NF1064 exhibits a nonlinear photothermal effect upon plasmonic fields of AuNRs by amplifying the non-radiative decay of nonfluorescent NF1064, thus achieving a high photothermal conversion of 68.5% in NIR-II window with potential for further augmentation. With remarkable SERRS and photothermal properties, the NIR-II nanoprobes allow for high-precision intraoperative guided tumor resection within 8min, and high-efficient hyperthermia combating of drug-resistant bacterial infection within living mouse body. This work not only unlocks the potential of nonfluorescent resonant dyes for NIR-II Raman imaging, but also opens up a new method for boosting photothermal conversion efficiency of nanomaterials.

A simple, rapid, and low-cost approach for colloidal nanoparticle-based surface enhanced Raman Scattering detection of endosulfan pesticide at trace levels

Abstract Surface Enhanced Raman Spectroscopy (SERS) is a highly specific, sensitive, and portable technique with great potential for on-site pesticide detection and monitoring. Endosulfan, an organochlorine pesticide known for its high toxicity, slow degradation, and bioaccumulation, has poor affinity for metallic SERS substrates. This study presents a label-free SERS detection method for endosulfan, using aggregating agents like potassium chloride (KCl), potassium hydroxide (KOH), potassium bromide (KBr), and sodium hydroxide (NaOH) to modify the behavior of Ag colloidal nanoparticles (NPs) and enhance the SERS signal of endosulfan molecules trapped within formed hot-spots. We analyzed the UV–Vis spectra, the hydrodynamic diameter, and zeta-potential of Ag NPs with the addition of these agents and endosulfan. Successful detection of both α- and ß- endosulfan isomers at μM concentrations in both ethanol and methanol was achieved with KOH-treated Ag NPs. The method was also applied to detect endosulfan in real water samples, along with simultaneous detection of λ-cyhalothrin, showcasing its capability to identify multiple analytes. The selectivity and specificity were confirmed using a mixture of endosulfan and thiabendazole, highlighting the crucial role of selecting the appropriate aggregating agent for each analyte. Overall, the findings emphasize the potential of aggregating agents to mediate the SERS enhancement of endosulfan, facilitating simple and rapid protocols for environmental pollutant detection, while shedding light on the intricate interplay between NP behavior, surface chemistry, and analyte interaction.

Digital-twin-based active input refinement for insertion loss estimation and QoT optimization in C and C + L networks

Quality of transmission (QoT) prediction is a fundamental function in optical networks. It is typically embedded within a digital twin and used for operational tasks, including service establishment, service rerouting, and (per-channel or per-amplifier) power management to optimize the working point of services and hence to maximize their capacity. Inaccuracy in QoT prediction results in additional, unwanted design margins. A key contributor to QoT inaccuracy is the uncertain knowledge of fiber insertion loss, e.g., the attenuation due to connector losses at the beginning or at the end of each fiber span, as such loss cannot be directly monitored. Indeed, insertion losses drive the choice of the launch power in fiber spans, which in turn drive key physical effects, including the Kerr and stimulated Raman scattering (SRS) effects, which affect services’ QoT. It is thus important to estimate (and detect possibly anomalous) fiber insertion losses at each span. We thereby propose a novel active input refinement (AIR) technique using active probing to estimate insertion losses in C and C + L systems. Here, active probing consists of adjusting amplifier gains span by span to slightly alter SRS. The amount of adjustment must be sufficient to be measurable (such that insertion losses can be inferred from the measures) but small enough to have a negligible impact on running services in a live network. The method is validated by simulations on a European network with 30 optical multiplex sections (OMSs) in C and C + L configurations and by lab experiments on a C-band network, demonstrating that AIR significantly improves insertion loss estimation, network QoT optimization, and QoT prediction compared with other state-of-the-art monitoring techniques. This work underscores the critical role of accurate estimation of QoT inputs in enhancing optical network performance.

Development of an Enhanced Surface-Enhanced Raman Scattering (SERS) Plasmonic Sensor for the Detection of Klebsiella Pneumoniae Bacteria

Development of an Enhanced Surface-Enhanced Raman Scattering (SERS) Plasmonic Sensor for the Detection of Klebsiella Pneumoniae Bacteria

Efficient generation of multi-order Raman radiation in aqueous solutions derived from -CH2 and -NH2 vibrations via cascaded four-wave mixing and Stokes processes.

Multiple coherent radiations are achieved in a water-3-aminopropanol (3AP) mixed solution through cascaded four-wave mixing (C-FWM) and cascaded Stokes (C-Stokes) processes, both driven by stimulated Raman scattering (SRS) in this work. The O-H vibration peak from water is replaced by the emergence of the -NH2 symmetric stretching Raman peaks from 3AP, with intensity approaching that of the -CH2 symmetric stretching peak. The dual-wavelength SRS signals for the -NH2 and -CH2 stretching vibrations have a relatively small frequency interval of about 400 cm-1 (16 nm). By varying the 3AP concentration and pump energy, these two peaks from 3AP act as new pump sources, enabling the successful generation of up to 16th-order Stokes and 5th-order anti-Stokes radiation through C-FWM and C-Stokes processes. The resulting spectrum spans a broad wavenumber range from -3318 to 6629 cm-1 (452 to 822 nm), offering a new approach for broadband coherent light sources and multi-order Raman spectra in liquid media.

Correction to “Customization of Nanogap Arrays Using Stereolithography and Nanoskiving for Surface-Enhanced Raman Scattering”

Correction to “Customization of Nanogap Arrays Using Stereolithography and Nanoskiving for Surface-Enhanced Raman Scattering”

An Activity-Based Sensing Approach to Multiplex Mapping of Labile Copper Pools by Stimulated Raman Scattering.

Molecular imaging with analyte-responsive probes offers a powerful chemical approach to studying biological processes. Many reagents for bioimaging employ a fluorescence readout, but the relatively broad emission bands of this modality and the need to alter the chemical structure of the fluorophore for different signal colors can potentially limit multiplex imaging. Here, we report a generalizable approach to multiplex analyte imaging by leveraging the comparably narrow spectral signatures of stimulated Raman scattering (SRS) in activity-based sensing (ABS) mode. We illustrate this concept with two copper Raman probes (CRPs), CRP2181 and CRP2153.2, that react selectively with loosely bound Cu(I/II) and Cu(II) ions, respectively, termed the labile copper pool, through copper-directed acyl imidazole (CDAI) chemistry. These reagents label proximal proteins in a copper-dependent manner using a dye scaffold bearing a 13C≡N or 13C≡15N isotopic SRS tag with nearly identical physiochemical properties in terms of shape and size. SRS imaging with the CRP reagents enables duplex monitoring of changes in intracellular labile Cu(I) and Cu(II) pools upon exogenous copper supplementation or copper depletion or genetic perturbations to copper transport proteins. Moreover, CRP imaging reveals reciprocal increases in labile Cu(II) pools upon decreases in activity of the antioxidant response nuclear factor-erythroid 2-related factor 2 (NRF2) in cellular models of lung adenocarcinoma. By showcasing the use of narrow-bandwidth ABS probes for multiplex imaging of copper pools in different oxidation states and identifying alterations in labile metal nutrient pools in cancer, this work establishes a foundation for broader SRS applications in analyte-responsive imaging in biological systems.

One‐Pot Polyol Syntheses of Ag Right Bipyramids and Nanocubes, and their Surface‐Enhanced Raman Scattering Properties

One‐Pot Polyol Syntheses of Ag Right Bipyramids and Nanocubes, and their Surface‐Enhanced Raman Scattering Properties

Dynamic Phase Behavior of Amorphous Solid Dispersions Revealed with In Situ Stimulated Raman Scattering Microscopy.

This study reports the application of in situ stimulated Raman scattering (SRS) microscopy for real-time chemically specific imaging of dynamic phase phenomena in amorphous solid dispersions (ASDs). Using binary ritonavir and poly(vinylpyrrolidone-vinyl acetate) films with different drug loadings (0-100% w/w) as model systems, we employed SRS microscopy with fast spectral focusing to analyze ASD behavior upon contact with a dissolution medium. Multivariate unmixing of the SRS spectra allowed changes in the distributions of the drug, polymer, and water to be (semi)quantitatively imaged in real time, both in the film and the adjacent dissolution medium. The SRS analyses were further augmented with complementary correlative sum frequency generation and confocal reflection for additional crystallinity and phase sensitivity. In the ASDs with drug loadings of 20, 40, and 60% w/w, the water penetration front within the film, followed by both surface-directed and bulk phase separation in the film, was apparent but differed quantitatively. Additionally, drug-loading and phase-dependent polymer and drug release behavior was imaged, and liquid-liquid phase separation was observed for the 20% drug loading ASD. Overall, SRS microscopy with fast spectral focusing provides quantitative insights into water-induced ASD phase phenomena, with chemical, solid-state, temporal, and spatial resolution. These insights are important for optimal ASD formulation development.

Strategic modal management for enhanced stimulated Raman scattering in optical fibers

Raman fiber lasers have attracted significant attention for their unique ability to generate high-power output at specific wavelengths. Theoretically, the quantum loss associated with the nonlinear Stokes frequency shift in Raman scattering is lower than that from energy level transitions in conventional ytterbium-doped lasers, suggesting that Raman lasers should achieve higher conversion efficiencies. However, in practice, the efficiency of high-power Raman lasers often fails to reach these theoretical limits, with power scaling being impeded by 2 nd order Raman effects. In this article, we delve into the dynamics of stimulated Raman scattering within few-mode fibers, offering an in-depth analysis of the underlying physical mechanisms from multiple perspectives. Our research combines theoretical analysis with experimental research, covering the frequency domain, spatial domain, and nonlinear behavior. The experimental findings indicate that strategically increasing the proportion of higher-order modes in the injected light can enhance the conversion efficiency of the Raman process and effectively suppress higher-order Raman and four-wave mixing nonlinear processes. This study provides profound theoretical insights and practical guidance, contributing significantly to the ongoing development and optimization of Raman laser technology.

Rapid Surface-Enhanced Raman Scattering Imaging and Deep Learning for Highly Sensitive Discrimination of Amino Acids and Peptides

Rapid Surface-Enhanced Raman Scattering Imaging and Deep Learning for Highly Sensitive Discrimination of Amino Acids and Peptides