Spontaneous Raman Scattering Research Articles

Enhanced Coexistence of Quantum Key Distribution and Classical Communication over Hollow-Core and Multi-Core Fibers.

In this paper, we investigate the impact of classical optical communications in quantum key distribution (QKD) over hollow-core fiber (HCF), multi-core fiber (MCF) and single-core fiber (SCF) and propose wavelength allocation schemes to enhance QKD performance. Firstly, we theoretically analyze noise interference in QKD over HCF, MCF and SCF, such as spontaneous Raman scattering (SpRS) and four-wave mixing (FWM). To mitigate these noise types and optimize QKD performance, we propose a joint noise suppression wavelength allocation (JSWA) scheme. FWM noise suppression wavelength allocation and Raman noise suppression wavelength allocation are also proposed for comparison. The JSWA scheme indicates a significant enhancement in extending the simultaneous transmission distance of classical signals and QKD, reaching approximately 100 km in HCF and 165 km in MCF under a classical power per channel of 10 dBm. Therefore, MCF offers a longer secure transmission distance compared with HCF when classical signals and QKD coexist in the C-band. However, when classical signals are in the C-band and QKD operates in the O-band, the performance of QKD in HCF surpasses that in MCF. This research establishes technical foundations for the design and deployment of QKD optical networks.

Study on effects of ethylene or acetylene addition on the stability of ammonia laminar diffusion flame by optical diagnostics and chemical kinetics

Improvement of ammonia combustion characteristics by carbon-based combustion promoters is currently emphasized, but the impact of carbon‑carbon multi-bond structure on ammonia combustion characteristics and reaction mechanisms has not been sufficiently investigated. In order to investigate the mechanism of molecular structures (C=C and C≡C) of combustion promoters on the stability of ammonia flames, the flame morphology, flame structure, NH3-H2 cracking, and C-N cross-reaction of ammonia/ethylene and ammonia/acetylene laminar diffusion flame are investigated based on a Gu¨lder burner by utilizing high-speed photography, planar laser-induced fluorescence (PLIF) and laser spontaneous Raman scattering (SRS) techniques. The results show that acetylene addition is more effective than ethylene to improve the flame stability. Combined with the flame structure analysis, it is shown that C=C mainly enhances the low-temperature reaction stage intensity of laminar flame, while C≡C can both enhance the intensity of low-temperature and high-temperature reaction stages, thereby enhancing the flame combustion exothermic process. Besides, C=C mainly strengthens the exothermic reactions in the upstream of the flame whereas C≡C can strengthen the exothermic reactions in the upstream and downstream of the flame simultaneously. Investigation of the NH3-H2 cracking reactions reveals that C≡C promotes H2 generation mainly by increasing NH3→H2 cracking, whereas C=C promotes H2 generation mainly by increasing NH2→H2 and NH→H cracking, hence improving the flame stability. Further analysis through the reaction flows revels that C=C acts mainly on H-containing species HCN/HNCO whereas C≡C mainly acts on non-H-containing species CN/NCO to influence the reaction pathways, but C-N cross-reaction does not play an important role in the characteristics of ammonia composite combustion (ACC).

Insights into the flow and scalar structures when shifting from methane to hydrogen turbulent flames using simultaneous PIV – OH PLIF and spontaneous Raman scattering

This study discusses fundamental turbulence-chemistry interactions in a canonical non-premixed bluff body burner fueled with 100% methane or hydrogen. Simultaneous time-resolved PIV&OH-PLIF and 1D Spontaneous Raman Scattering (SRS) have been employed to provide deeper insights into the difference in combustion regimes between CH4 and H2 operations. The analysis of the instantaneous time-resolved PIV and OH-PLIF datasets reveals the presence and absence of local extinctions in methane and hydrogen flames despite the mean flow topology being similar across the test cases. The instantaneous scatter plots of 1D Raman data in the mixture fraction space further quantified the spatial evolution of temperature and major species. Finally, the regime identification scheme is implemented over instantaneous 1D SRS data to identify the different flame/mixture regimes. The change in combustion regime is observed even very close to the burner exit while switching between CH4 and H2, which is attributed to the probability of localized flame extinctions. Overall, this study provides detailed interlinks between flow field aerodynamics and scalar structures in the two different flames whose thermo physical properties are entirely different and form a comprehensive database for cornerstone computational model validation.

Robustness of Intensity-Modulation/Direct-Detection Secret Key Distribution against Spontaneous Raman Scattering in Wavelength-Multiplexed Systems with Existing Optical Transmission Signals

Robustness of Intensity-Modulation/Direct-Detection Secret Key Distribution against Spontaneous Raman Scattering in Wavelength-Multiplexed Systems with Existing Optical Transmission Signals

Applications of the Lambert–Tsallis Wq function in QKD

The Lambert–Tsallis W q function has found applications in several areas of physics, such as quantum optics, astronomy, and semiconductor physics. In this work, we discuss some applications of W q in quantum key distribution (QKD). Three problems are considered: (i) the quantum access network, (ii) analysis of an on-chip SiO2 amplitude modulator used in continuous-variable QKD (CV-QKD), and (iii) parameter estimation of a stochastic quantum channel. In quantum access networks, QKD and classical data travel on the same optical fiber. In this case, an increase of the quantum bit error rate is caused mainly by the spontaneous Raman scattering (SRS) produced by classical data. The amount of SRS produced depends on the fiber length. In the present work, we use the Lambert–Tsallis W q function to calculate analytically the fiber length needed to produce a given level of SRS. Thus, our formula allows the calculation of the QKD channel’s length when the probability of a click on the receiver side without having any incident photons from the quantum transmitter is defined a priori. On the other hand, a crucial step in the security of CV-QKD is the correct channel transmissivity and excess noise estimations. These parameters can be overestimated or underestimated when real devices do not behave as predicted by their models. In this direction, using the W q function, we provide an equation for calculation of the fluctuation of the concentration of free carriers in an integrated amplitude modulator and another equation for calculation of the parameter that models a stochastic quantum channel. These equations are useful in building strategies to avoid quantum hacking.

Intrapulse Correlated Dynamics of Self-Phase Modulation and Spontaneous Raman Scattering in Synthetic Diamond Excited and Probed by Positively Chirped Ultrashort Laser Pulses

In synthetic diamond plates, the intrapulse-correlated dynamics of self-phase modulation and spontaneous nonresonant Raman scattering by center-zone optical phonons were for the first time directly investigated for tightly focused (focusing numerical aperture NA = 0.25) positively chirped visible-range high-intensity laser pulses with variable durations (0.3–9.5 ps) and energies transmitted through the sample. The observed self-phase modulation broadening and modulation of the transmitted light and Stokes Raman spectra for the (sub)picosecond pulse durations indicate the considerable Raman–Kerr contribution to the nonlinear polarization. The latter appears through plasma emission of the optical phonons, which emerges on the (sub)picosecond timescale and dominates at ≈1 ps. Later, this phonon contribution is eventually suppressed in the material due to picosecond-scale electron-lattice thermalization and the related thermally enhanced symmetrical decay of optical phonons into lower-frequency acoustic ones.

88 Microplastic References for Inhalation Studies

Abstract Microplastic research has been increasing due to the uncertainty of potential effects on the environment and human health. However, microplastic references are currently missing. Not only is there a lack of references there is also a lack of diversity in polymer type for references, especially in toxicological studies. In specific, inhalation studies must rely on microplastics that are respirable and/or inhalable (< 10 µm) to result in toxicological outcomes. Therefore, in this project, we focus on using solvent precipitation to produce microplastic references from TPU, PA-6, PET, and LDPE for microplastic inhalation toxicity studies. Particle size distribution of the dispersion is used to verify that the desired size range is achieved. To demonstrate that the produced microplastic references are representative from its original material, molecular and particle descriptors are characterized. Chemical composition, molecular weight, crystallinity, solidity, density, are among the descriptors tested for both the produced microplastic references and its corresponding commercial counterpart. Preliminary results have shown that quantities needed for in-vitro testing and particle size range desired is achieved with successful production of sub-100 nm constituent particle counts and all-respirable mass-based diameters. SEM images confirm the size distribution and show distribution of particle shapes. Chemical composition via spontaneous Raman Scattering illustrates clear polymer spectra signals from the microplastic dispersions. These microplastic reference materials are complemented by toxicology controls. In addition, the in-vitro screening uses both submersed and air-liquid interface cultures to expose cells. This study will thus provide information on microplastic material descriptors relevant for inhalation toxicity.

Integration of QKD Channels to Classical High-speed Optical Communication Networks

Integrating Quantum Key Distribution service with classical high-speed optical data transmission using a dense wavelength division multiplexing technique in a fiber is a cost-effective solution to improve the network's security. In this multichannel system, several noise sources degrade the quality of the quantum channel. The dominant degradation effect is determined by modeling in different cases. Optical filtering cannot decrease spontaneous Raman Scattering caused by the classical optical channels. So this nonlinear optical effect is investigated in detail with different system parameter setups. The optimal channel allocation and the required bandgap between the classical and quantum channels are determined.

Lifetime reductions and read-out oscillations due to imperfect initial level preparations of atoms in a long-lived DLCZ-like quantum memory

Entanglement between a spin-wave qubit (memory qubit) and a photonic qubit is a basic building block for quantum repeaters. Duan-Lukin-Cirac-Zoller (DLCZ) scheme, which generates spin waves via spontaneous Raman scattering (SRS) of Stokes photons in atomic ensemble, provides a promising way to generate such entanglement. In a recent work [arXiv: 2006.05631, accepted by communications physics], DLCZ-like quantum memory that generates long-lived atom-photon entanglement has been experimentally demonstrated, where magnetic-field-insensitive (MFI) coherence is used to store spin waves. For realizing such MFI spin-wave storage, the atoms have to be initially prepared in a specific Zeeman sublevel, which is achieved by applying optical pumping lasers. Here, we demonstrate the memory lifetimes for the cases that the atoms are perfectly and imperfectly prepared in the specific Zeeman level, respectively. The experimental results show that the spin waves associated with magnetic-field-sensitive (MFS) and MFI coherences will be simultaneously created for the case that the atoms are imperfectly prepared in the Zeeman sublevel. Thus, the read outs will experience decay oscillations due to interferences between the two spin waves and the memory lifetime will be shorten due to dephasing of MFS coherence. A detailed theoretical analysis has been developed for explaining the experimental results. The present work will help one to understand decoherence of spin waves (SWs) and then enable one to obtain optimal lifetime of the entanglement storage in the cold atoms.

Trace Analysis of Gases and Liquids with Spontaneous Raman Scattering Based on the Integrating Sphere Principle.

Spontaneous Raman scattering is an attractive optical technique for the analysis of gases and liquids; however, their low densities and notoriously weak scattering cross sections demand an enhancement of the spontaneous Raman scattering signal for detection. Here, we have developed a simple but highly effective and fast technique to enhance the signal of spontaneous Raman scattering from gases and liquids. The technique is developed based on the principle of an integrating sphere, which realizes the multiple pass actions of low-energy pump light and the collection of all Raman scattered light for a sample volume of 2 mL. By measuring the ambient air sample with an exposure time of 180 s, we found the experimental detection limit of our spontaneous Raman scattering setup can reach 3 ppm. CH4 (<2 ppm) in air can be also examined by increasing the exposure time to 300 s. The performance of our setup used for the analysis of trace gases is further illustrated by characterizing ethane, propane, butane, and pentane in methane as well as isotopes of carbon dioxide. The results reveal that the detection limit of our setup for liquids can be improved by nearly 4 orders of magnitude compared to that of confocal Raman scattering spectroscopy with the same experimental conditions.

Modeling and Minimizing Spontaneous Raman Scattering for QKD Secured DWDM Networks

Quantum key distribution (QKD) provides information-theoretic security based on quantum mechanics. Integrating QKD with classical data traffic by using wavelength division multiplexing (WDM) techniques in a single fibre is a cost-efficient way to improve security in legacy infrastructure. In such a system, the main noise source to the quantum channel is spontaneous Raman scattering (SRS) caused by the classical channels. In this letter we introduce a channel allocation strategy for both quantum and classical signals to minimize the SRS noise. A use case that quantum and classical channels co-exist in a dense WDM system is investigated. The results show >26% increase of achievable transmission distance for the QKD system when implementing the introduced channel allocation strategy. Moreover, a network updating plan is proposed, which provides a guideline to light the new wavelengths for classical communications while minimizing the SRS noise to quantum channels.

Investigation of Spontaneous Raman Scattering in Few-Mode Fibers: Dependence on Polarization and Spatial Modes

We study Raman gain in few-mode fibers (FMFs) by measuring spontaneous Raman scattering in polarization-maintaining FMF, mode-maintaining FMF and common FMF. The results show that the intensities of spontaneous Raman scattering in different polarization and spatial modes are affected by vector mode coupling of the degenerate modes in FMFs, which weakens the polarization- and spatial-mode dependence of Raman gain. Our investigation can be used for developing the FMF-based nonlinear-optical devices and sub-systems.

Pulse-burst spontaneous Raman thermometry of unsteady wave phenomena in a shock tube.

A high-speed temperature diagnostic based on spontaneous Raman scattering (SRS) was demonstrated using a pulse-burst laser. The technique was first benchmarked in near-adiabatic ${{\rm H}_2} \text{-} {\rm air}$ flames at a data-acquisition rate of 5 kHz using an integrated pulse energy of 1.0 J per realization. Both the measurement precision and accuracy in the flame were within 3% of adiabatic predictions. This technique was then evaluated in a challenging free-piston shock tube environment operated at a shock Mach number of 3.5. SRS thermometry resolved the temperature in post-incident and post-reflected shock flows at a repetition rate of 3 kHz and clearly showed cooling associated with driver expansion waves. Collectively, this Letter represents a major advancement for SRS in impulsive facilities, which had previously been limited to steady state regions or single-shot acquisition.

Energy relaxation and heating in the afterglow of high electric field ns-discharges in ambient air using spontaneous Raman scattering

The spatio-temporal rovibrational excitation and relaxation mechanisms of N2(X) in the post-discharge of a 10 ns high-voltage diffuse discharge are studied by spontaneous Raman scattering (SRS). It is shown that the vibrational excitation of nitrogen molecules remains high despite the strong electric fields applied during the discharge itself and the relaxation processes are similar to lower voltage ns discharges. The main differences with the lower field discharges are rather visible at the beginning of the discharge with a specific spatial volume distribution and a significant vibrational non-equilibrium between v = 0, 1 and v > 1. The spatial distribution of the rovibrational excitation of the diffuse discharge is very wide radially, consistent with the sustainability of fields greater than 100 Td over nearly 8 mm during propagation. The initial rovibrational excitation is inhomogeneous along the axis. The gas temperature reaches up to about 1200 K close to the pin (85 kV, ambient air) while it remains below 500 K in the rest of the volume. It is possible to control the heating of the discharge without greatly modifying the energy transfer mechanisms by adjusting the duration of the voltage pulse. In terms of reactivity, high atomic oxygen densities seem to be very localized in the vicinity of the pin (1024 m−3 at 1.5 mm from the pin, corresponding to about 20% dissociation). This inhomogeneity reflects the distribution of energy in the volume of the discharge. The main effects of humidity are also studied. It amplifies the fast heating and accelerates the decay of atomic oxygen in the post-discharge. No significant acceleration of the V–T relaxation of nitrogen due to the addition of water vapour was observed for the studied conditions. A shock wave was identified which is triggered at around 500 ns.

Performance of subcarrier-wave quantum key distribution in the presence of spontaneous Raman scattering noise generated by classical DWDM channels

In this paper, we study the performance of the subcarrier-wave quantum key distribution system (SCW QKD) in the presence of spontaneous Raman scattering (SpRS) noise generated by classical channels of the dense wavelength division multiplexing (DWDM) network within a single-mode optical fiber. We present the mathematical model for evaluation of the quantum bit error rate and secure key generation rate with the SpRS noise taken into account. We consider two regimes of the SCW QKD system: the continuous wave regime, which uses a continuous wave laser, and the pulsed regime. For these regimes, performance of the system is analyzed depending on receiver sensitivity of classical DWDM. It is found that the pulsed regime outperforms the continuous wave regime in both the secure key generation rate and maximum achievable distance.

Optical cavity enhancement experiment of Duan-Lukin-Cirac-Zoller writing excitation process in atomic ensemble

The Duan-Lukin-Cirac-Zoller (DLCZ) process in the atomic ensemble is an important means to generate quantum correlation and entanglement between photons and atoms (quantum interface). When a write pulse acts on atoms, the DLCZ quantum memory process will be generated, which has been extensively studied. In the process a spontaneous Raman scattering (SRS) of a Stokes photon is generated, and a spin-wave excitation stored in the atomic ensemble is created at the same time. The higher probability of the generation of Stokes photons will cause more noise and reduce entanglement. On the contrary, the low generation probability of Stokes photons affects the success probability of entanglement distribution on a quantum repeater. How to increase generation probability of Stokes photons without causing more noise is an urgent problem to be resolved. In this work, a &lt;sup&gt;87&lt;/sup&gt;&lt;i&gt;Rb&lt;/i&gt; atomic ensemble is placed in a standing wave cavity which resonates with the Stokes photon. This cavity has a trip length of 0.6 m and a free spectral range (FSR) of 256 MHz. The optical loss of all the optical elements in this cavity is 9%, of which 4% loss originates from the other optical elements and 5% loss from the vacuum chamber of the magneto-optical trap (MOT). The fineness of the cavity with the cold atoms is measured to be ~19.1. By calculating the total probability of Stokes photon emission out of the cavity, we derive the enhancement factor of this standing wave cavity when the cavity loss is &lt;i&gt;l&lt;/i&gt;. When this cavity is locked with PDH frequency locking technique, we observe that the production probability of the Stokes photons is 8.7 times higher than that without cavity due to the optical cavity enhancement effect. Under this condition, the relationship between the generation probability of Stokes photons and the power of write beam is studied. The write excitation probability changes linearly with the power of write beam. This work provides an experimental solution to reducing the noise caused by time multimode operation in DLCZ scheme.

Spontaneous Raman and Surface-Enhanced Raman Scattering Bioimaging.

Raman spectroscopy is a specific, noninvasive and nondestructive optical technique and is able to obtain chemical information from molecules. Optical imaging based on Raman spectroscopy has been a powerful technique for monitoring minute chemical changes of biological samples and generating images through direct or indirect strategies. Two widely applied Raman imaging techniques include spontaneous Raman and surface-enhanced Raman scattering (SERS) imaging. In this chapter, we introduce the basic principles including the physics behind Raman and SERS imaging, design of Raman/SERS labels or probes, and current strategies for further improvements. The progress in the use of spontaneous Raman and SERS spectroscopy for bioimaging is discussed, either in fundamental studies or inbiomedical theranostics. In addition, we give insights into the challenges and opportunities for improving Raman imaging performance.

Establishing of quantum entanglement among three atomic nodes via spontanenous Raman scattering

Quantum entanglement is an essential quantum resource. With the development of quantum information science, quantum network consisting of quantum nodes and quantum channels has attracted extensive attention. The development of quantum information network requires the capability of generating, storing and distributing quantum entanglement among multiple quantum nodes. It is significant to construct the quantum information, and it has very important applications in the distributed quantum computation and quantum internet. Here we propose a simple and feasible scheme to deterministically entangle three distant atomic ensembles via the interference and feedforward network of the light-atom mixed entanglement. Firstly, three atomic ensembles placed at three remote nodes in a quantum network are prepared into the mixed entangled state of light and atomic ensembles via the spontaneous Raman scattering (SRS) process. Then, the first and second Stokes optical field are interfered on an &lt;i&gt;R&lt;/i&gt;&lt;sub&gt;1&lt;/sub&gt;∶&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;1&lt;/sub&gt; optical beam splitter (BS1), and one of the output optical fields from the first optical beam splitter is interfered with the third Stokes field on the second &lt;i&gt;R&lt;/i&gt;&lt;sub&gt;2&lt;/sub&gt;∶&lt;i&gt;T&lt;/i&gt;&lt;sub&gt;2&lt;/sub&gt; optical beam splitter (BS2). The quantum fluctuations of the amplitude and phase quadratures of these three output optical fields from BS1 and BS2 are detected by three sets of balanced homodyne detectors, respectively. Finally, the detected signals of the amplitude and phase quadratures are fed to the three atomic ensembles via the radio frequency coils to establish the entanglement among three remote atomic ensembles. At the user-controlled time, three read optical pulses can be applied to these three atomic ensembles to convert the stored entangled state from the atomic spin waves into the anti-Stokes optical fields via the SRS process. According to the tripartite inseparability criterion, the correlation variance combinations of these three anti-Stokes optical fields can be used to verify the performance of entanglement of three atomic ensembles. This scheme can be extended to larger-scale quantum information network with different physical systems and more atomic nodes. Moreover, the entanglement distillation can be combined with this scheme to realize the entanglement among longer distance quantum nodes.

Spontaneous versus Stimulated Surface-Enhanced Raman Scattering of Liquid Water.

We have observed for the first time the surface-enhanced (SE) signal of water in an aqueous dispersion of silver nanoparticles in spontaneous (SERS) and femtosecond stimulated Raman (SE-FSRS) processes with different wavelengths of the Raman pump (515, 715, and 755 nm). By estimating the fraction of water molecules that interact with the metal surface, we have calculated enhancement factors (EF): 4.8 × 106 for SERS and (3.6–3.7) × 106 for SE-FSRS. Furthermore, we have tested the role of simultaneous plasmon resonance and Raman resonance conditions for the aν1 + bν3 overtone mode of water (755 nm) in SE-FSRS signal amplification. When the wavelength of the Raman pump is within the plasmon resonance of the metal nanoparticles, the Raman resonance has a negligible effect on the EF. However, the Raman resonance with the aν1 + bν3 mode strongly enhances the signal of the fundamental OH stretching mode of water.

High-Performance Raman Distributed Temperature Sensing Powered by Deep Learning

Raman-based distributed temperature sensing (RDTS) can achieve temperature measurement of tens of kilometers and is widely used in temperature monitoring of crucial facilities. The accuracy of RDTS is highly determined by the signal-to-noise ratio (SNR) of the acquired spontaneous Raman scattering (SpRS) signals, which is about 60 dB weaker than the pump pulse. Therefore, the performance of single-mode fiber (SMF) based conventional RDTS is poor. To improve its performance, many methods have been proposed, including the use of special optical fibers, pulse coding techniques, and denoising algorithms. However, these methods have their limitations. Here, we propose and experimentally demonstrate a deep 1-D denoising convolutional neural network (1DDCNN) to enhance the performance of RDTS. A simplified RDTS model is built to train and optimize the 1DDCNN. To verify the performance of the 1DDCNN on actual data, we experimentally measure the SpRS data of a 10-km SMF with an average time of 1 s and a spatial resolution of 3 m. The well-trained 1DDCNN reduces the temperature uncertainty from 6.4 °C to 0.7 °C with high fidelity. As a comparison, the commonly used wavelet denoising algorithm can only reduce it to 3.7 °C. Besides, the 1DDCNN does not require manual parameter adjustment and is not affected by the sampling rate, giving it significant advantages in practical applications compared with conventional denoising algorithms. Moreover, we believe that the proposed 1DDCNN can be applied to other distributed optical fiber sensing systems by fine-tuning the network with appropriate training data.