Optical Probe System Research Articles

Integrated optical probing scheme enabled by localized-interference metasurface for chip-scale atomic magnetometer

Abstract Emerging miniaturized atomic sensors such as optically pumped magnetometers (OPMs) have attracted widespread interest due to their application in high-spatial-resolution biomagnetism imaging. While optical probing systems in conventional OPMs require bulk optical devices including linear polarizers and lenses for polarization conversion and wavefront shaping, which are challenging for chip-scale integration. In this study, an integrated optical probing scheme based on localized-interference metasurface for chip-scale OPM is developed. Our monolithic metasurface allows tailorable linear polarization conversion and wavefront manipulation. Two silicon-based metasurfaces namely meta-polarizer and meta-polarizer-lens are fabricated and characterized, with maximum transmission efficiency and extinction ratio (ER) of 86.29 % and 14.2 dB for the meta-polarizer as well as focusing efficiency and ER of 72.79 % and 6.4 dB for the meta-polarizer-lens, respectively. A miniaturized vapor cell with 4 × 4 × 4 mm3 dimension containing 87Rb and N2 is combined with the meta-polarizer to construct a compact zero-field resonance OPM for proof of concept. The sensitivity of this sensor reaches approximately 9 fT/Hz1/2 with a dynamic range near zero magnetic field of about ±2.3 nT. This study provides a promising solution for chip-scale optical probing, which holds potential for the development of chip-integrated OPMs as well as other advanced atomic devices where the integration of optical probing system is expected.

High photoelectric conversion efficiency and fast relaxation time of FA0.4MA0.6PbI3 applied in ultrafast modulation of terahertz waves

Active control of terahertz (THz) waves is attracting tremendous attentions in terahertz communications and active photonic devices. Perovskite, due to its excellent photoelectric conversion performance and simple manufacturing process, has emerged as a promising candidate for optoelectronic applications. However, the exploration of perovskites in optically controlled THz modulators is still limited. In this work, the photoelectric properties and carrier dynamics of FA0.4MA0.6PbI3 perovskite films were investigated by optical pumped terahertz probe (OPTP) system. The ultrafast carrier dynamics reveal that FA0.4MA0.6PbI3 thin film exhibits rapid switching and relaxation time within picosecond level, suggesting that FA0.4MA0.6PbI3 is an ideal candidate for active THz devices with ultrafast response. Furthermore, as a proof of concept, a FA0.4MA0.6PbI3-based metadevice with integrating plasma-induced transparency (PIT) effect was fabricated to achieve ultrafast modulation of THz wave. The experimental results demonstrated that the switching time of FA0.4MA0.6PbI3-based THz modulator is near to 3.5 ps, and the threshold of optical pump is as low as 12.7 μJ cm−2. The simulation results attribute the mechanism of ultrafast THz modulation to photo-induced free carriers in the FA0.4MA0.6PbI3 layer, which progressively shorten the capacitive gap of PIT resonator. This study not only illuminates the potential of FA0.4MA0.6PbI3 in THz modulation, but also contributes to the field of ultrafast photonic devices.

Initial probe function construction in ptychography based on zone-plate optics.

X-ray ptychography is a popular variant of coherent diffraction imaging that offers ultrahigh resolution for extended samples. In x-ray ptychography instruments, the Fresnel zone-plate (FZP) is the most commonly used optical probe system for both soft x-ray and hard x-ray. In FZP-based ptychography with a highly curved defocus probe wavefront, the reconstructed image quality can be significantly impacted by the initial probe function form, necessitating the construction of a suitable initial probe for successful reconstruction. To investigate the effects of initial probe forms on FZP-based ptychography reconstruction, we constructed four single-mode initial probe models (IPMs) and three multi-mode IPMs in this study, and systematically compared their corresponding simulated and experimental reconstructions. The results show that the Fresnel IPM, spherical IPM, and Fresnel-based multi-mode IPMs can result in successful reconstructions for both near-focus and defocus cases, while random IPMs and constant IPMs work only for near-focus cases. Consequently, for FZP-based ptychography, the elaborately constructed IPMs that closely resemble real probes in wavefront phase form are more advantageous than natural IPMs such as the random or constant model. Furthermore, these IPMs with high phase similarity to the high-curvature large-sized probe adopted in experiments can help greatly improve ptychography experiment efficiency and decrease radiation damage to samples.

Optically Controlling Broadband Terahertz Modulator Based on Layer-Dependent PtSe2 Nanofilms

In this paper, we propose an optically controlling broadband terahertz modulator of a layer-dependent PtSe2 nanofilm based on a high-resistance silicon substrate. Through optical pump and terahertz probe system, the results show that compared with 6-, 10-, and 20-layer films, a 3-layer PtSe2 nanofilm has better surface photoconductivity in the terahertz band and has a higher plasma frequency ωp of 0.23 THz and a lower scattering time τs of 70 fs by Drude-Smith fitting. By the terahertz time-domain spectroscopy system, the broadband amplitude modulation of a 3-layer PtSe2 film in the range of 0.1-1.6 THz was obtained, and the modulation depth reached 50.9% at a pump density of 2.5 W/cm2. This work proves that PtSe2 nanofilm devices are suitable for terahertz modulators.

Safeguards equipment for the spent nuclear fuel of pressurized heavy water reactors

This paper describes the implementation of newly developed safeguards equipment for the spent nuclear fuel of heavy water reactors stored in a wet interim storage facility. The developed equipment compensates for imperfections in the existing equipment including the optical fiber probe system (OFPS) and improves the performance and user convenience. Specifically, the lithium glass scintillator currently used in the current OFPS was changed to a plastic scintillator with efficient and cost-effective detectors, and the probe design for the radiation measurements was also changed to facilitate replacement of the scintillator. In addition, the manual cable loading method, which is an obstacle method for implementing safeguards, was designed to be automatically loaded onto a drum-shaped structure using a motor. All analog systems such as radiation signal processing systems and cable loading systems that used to run along all the equipment were digitally replaced so that all operations could be done with display panels. Through these efforts, the new equipment resulted in improved performance and enhanced user convenience. The replacement of the scintillators and probes improved the performance by about 10 times, and the new equipment design reduced the number and weight of the parts to less than half that of the existing equipment. The performance of the newly developed equipment was verified so that it can be used as new IAEA safety equipment, and it is expected to have a major role in implementing safeguards for spent nuclear fuel through its registration as IAEA inspection equipment.

Comparison of existing and new optical fiber-based scintillation detectors for spent-fuel verification equipment

The Wolsung Nuclear Power Plant in Korea is under IAEA safeguards. During IAEA physical inventory verifications, the Optical Fiber radiation Probe System has been used since 2007 as the official instrument for verification of spent fuel. Its low sensitivity requires excessive time and labor to perform the IAEA safeguard activities and increases the operator load for preparing a dangerous and time-consuming secondary inspection. The objective of this paper is to develop a superior new optical fiber-based scintillation detector to deal with such issues. To increase the sensitivity of the instrument, a new optical fiber-based scintillation detector was developed by combining a p-terphenyl scintillator with a new type of optical fiber. A field test was carried out in the CANDU Wolsung Unit 1 to characterize the performance of the new detector. The field test showed that the OFPS using the new optical fiber-based scintillation detector has at least 100-times higher sensitivity and can also measure even very weak signals not measurable by the existing detector. From the experimental results, we can conclude that the newly developed OFPS detector would increase the effectiveness and efficiency of nuclear safeguards for verification of spent fuel in wet storage pools of CANDU reactors.

Dual Optical Measurement Probe System for Double-Sided Film Structure

Dual Optical Measurement Probe System for Double-Sided Film Structure

The application of Raman spectroscopy to the diagnosis of mitochondrial muscle disease: A preliminary comparison between fibre optic probe and microscope formats

AbstractMuscle biopsy remains an important component of the diagnostic repertoire for patients with suspected mitochondrial disease, underpinning specialist histopathological and biochemical analyses. Raman spectroscopy has not yet been applied to mitochondrial disease, and new fibre optic systems, with advantages in terms of cost and portability, could provide a rapid means to identify muscle pathology. In this study, we aimed to explore the potential of two different formats of Raman spectroscopy to identify mitochondrial disease: a miniaturised fibre optic Raman system and a standard commercial Raman microscope. Raman spectra were recorded from muscle samples from healthy volunteers (n = 10) and patients with genetically confirmed mitochondrial disease (n = 15). Multivariate classification algorithms demonstrated a high level of disease classification performance with both the fibre optic probe system and microscope (area under receiver operating characteristic curves 0.80–0.82). Key spectral changes associated with mitochondrial disease concerned the α‐helical configuration of proteins. The results suggest that Raman spectroscopy of muscle is worthy of further investigation as a technique for the rapid identification of mitochondrial disease.

Bias-driven terahertz negative conductivity and transmission enhancement

Bias-driven terahertz (THz) negative conductivity and transmission enhancement based on structures composed of monolayer graphene, MXene (Ti 3 C 2 T x ) and poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate):dimethyl sulfoxide (PEDOT:PSS:DMSO) caused by photo-excited or bias-driven are investigated. The THz signals that pass through the monolayer graphene/quartz, MXene/quartz, thinner and thicker PEDOT:PSS:DMSO/quartz structures are enhanced effectively under photo excitation or application of an external bias voltage in a THz time-domain spectroscopy (THz-TDS) system. This enhancement of THz transmission indicates that negative conductivity occurs, which is consistent with the results based on the monolayer graphene, thinner PEDOT:PSS:DMSO samples detected using an optical pump-THz probe (OPTP) system. The conductivity reduction mechanism is explained using an established Drude model. After photo excitation, this results in the generation of photo-induced carriers and an increase in the average scattering rate of the carriers. And as a consequence of the energy injection into the carrier system of the sample after applying a bias, the carrier temperature increases rapidly; this results in the generation of carriers and an increase in the average scattering rate of the carriers. However, the increase in the average scattering rate of the carriers is much higher than the increase in the average carrier density, which leads to the negative conductivity and the increased THz transmission. • THz signals that pass through the structures are enhanced under photo excitation or application of an external bias voltage. • THz transmission enhancement indicates that negative conductivity occurs, which is consistent with the results from optical pump-THz probe system. • This results in the generation of hot carriers and an increase in the average scattering rate of the carriers.

Combined autofluorescence and diffuse reflectance for brain tumour surgical guidance: initial ex vivo study results.

This ex vivo study was conducted to assess the potential of using a fibre optic probe system based on autofluorescence and diffuse reflectance for tissue differentiation in the brain. A total of 180 optical measurements were acquired from 28 brain specimens (five patients) with eight excitation and emission wavelengths spanning from 300 to 700 nm. Partial least square-linear discriminant analysis (PLS-LDA) was used for tissue discrimination. Leave-one-out cross validation (LOOCV) was then used to evaluate the performance of the classification model. Grey matter was differentiated from tumour tissue with sensitivity of 89.3% and specificity of 92.5%. The variable importance in projection (VIP) derived from the PLS regression was applied to wavelengths selection, and identified the biochemical sources of the detected signals. The initial results of the study were promising and point the way towards a cost-effective, miniaturized hand-held probe for real time and label-free surgical guidance.

In situ real-time identification of packaged chemicals using a dual-offset optical probe.

In situ real-time and nondestructive identification of packaged chemicals is essential for applications such as homeland security and terrorism prevention. Although various Raman spectroscopic methods such as spatially offset Raman spectroscopy (SORS) and time-resolved Raman spectroscopy have been investigated for real-time detection, the background interference originating from packaging materials limits the accuracy of the analysis. In principle, the Raman background from the packaging cannot be removed completely. To overcome this limitation, we developed a SORS-based dual-offset optical probe (DOOP) system that offers real-time prediction of 20 chemicals concealed in various containers by completely removing the background signal. The DOOP system selectively acquires the Raman photons generated from both the outer packaging and the inner contents, whose intensities are dependent on the penetration depth of the laser. The Raman spectra obtained at two remote offsets are automatically subtracted after normalization. We demonstrate that the DOOP method provides the pure component spectra by completely removing background interference from three plastic containers for a total of 20 samples in three different containers. In addition, an artificial neural network (ANN) was applied to evaluate the accuracy of the real-time chemical identification system; our system led to drastic improvements of the ANN prediction accuracy.

Core-shell Fe3O4@Au nanocomposite as dual-functional optical probe and potential removal system for arsenic (III) from Water.

We report for the very first time, development of a dual functional nanocomposite to perform as an optical probe as well as removal system for As(III) from ground water. Upon suitable thiolation using dithiothreitol (DTT), the Fe3O4(core)-Au(shell) nanocomposite (DTT-Fe3O4@Au) has been fabricated that can detect As(III) in aqueous solution with significantly low limit of detection and holds potential for selective removal of As(III) from water owing to its magnetic core. Due to high affinity of -SH groups for As(III), the nanoparticles undergo aggregation in the presence of As(III), resulting in a significant decrease in absorbance, yielding the limit of detection (LOD) as 0.86 ppb, which is much lower than the World Health Organisation (WHO) recommended threshold value of 10 ppb. UV-vis spectroscopy in conjunction with dynamic light scattering and electron microscopy techniques have further elaborated the detailed interaction between As(III) and DTT-Fe3O4@Au nanocomposite regarding their size dynamics and solution behaviour during the interaction. Moreover, ca.70% removal of As(III) from aqueous solution by DTT-Fe3O4@Au has been observed by ICP-MS measurement strengthening the potential of this nanocomposite as a dual-functional probe and filter.

An optically multiplexed single-shot time-resolved probe of laser-plasma dynamics.

We introduce a new approach to temporally resolve ultrafast micron-scale processes via the use of a multi-channel optical probe. We demonstrate that this technique enables highly precise time-resolved, two-dimensional spatial imaging of intense laser pulse propagation dynamics, plasma formation and laser beam filamentation within a single pulse over four distinct time frames. The design, development and optimization of the optical probe system is presented, as are representative experimental results from the first implementation of the multi-channel probe with a high-power laser pulse interaction with a helium gas jet target.

Generation and evaluation of an artificial optical signal based on X-ray measurements for bubble characterization in fluidized beds with vertical internals

The performance of fluidized bed reactors strongly depends on the bubble behavior, for which reason knowledge concerning the bubble properties is important for modeling and reactor optimization. X-ray measurements can be used to characterize bubbles within the cross-section of a fluidized bed on a laboratory scale, but cannot easily be extended to hot, pressurized large scale plants. For future measurements at hot conditions in a fluidized bed methanation reactor, we have developed an optical probing system that can be employed under these conditions. However, optical sensors are only able to investigate the local fluidization patterns at a defined position in the bed. The objective of this study is to characterize differences in bubble properties between local optical measurements and an X-ray tomography method that is able to detect bubbles over the entire cross-section. Therefore, an artificial optical signal is created out of existing hydrodynamic X-ray measurement data obtained at a cold flow model of a pilot scale methanation reactor. The determined bubble properties of both methods (i.e. evaluation of the derived artificial optical probe signal and image reconstruction based on the evaluation of original X-ray tomographic data) are compared with regard to the bubble rise velocity and the bubble size (for the X-ray method) or pierced chord length (for the optical evaluation method), respectively. The comparison shows that for the evaluation of the optical probe data, statistical effects have to be considered carefully. The detected mean chord length of the optical method does not immediately correspond to the mean bubble size determined by the X-ray method. Moreover, also differences regarding the bubble rise velocity were detected for some fluidization states. The reason for the discrepancies between both methods could be identified and corrected, amongst others by means of a Monte Carlo simulation in which rising bubbles in a fluidized bed were simulated and characterized by a local virtual optical sensor.

Laser ignition of a multi-injector LOX/methane combustor

This paper reports the results of a test campaign of a laser-ignited combustion chamber with 15 shear coaxial injectors for the propellant combination LOX/methane. 259 ignition tests were performed for sea-level conditions. The igniter based on a monolithic ceramic laser system was directly attached to the combustion chamber and delivered 20 pulses with individual pulse energies of $${33.2 \pm 0.8 \,\text{ mJ }}$$ at 1064 nm wavelength and 2.3 ns FWHM pulse length. The applicability, reliability, and reusability of this ignition technology are demonstrated and the associated challenges during the start-up process induced by the oxygen two-phase flow are formulated. The ignition quality and pressure dynamics are evaluated using 14 dynamic pressure sensors distributed both azimuthally and axially along the combustion chamber wall. The influence of test sequencing on the ignition process is briefly discussed and the relevance of the injection timing of the propellants for the ignition process is described. The flame anchoring and stabilization process, as monitored using an optical probe system close to the injector faceplate connected to photomultiplier elements, is presented. For some of the ignition tests, non-uniform anchoring was detected with no influence onto the anchoring at steady-state conditions. The non-uniform anchoring can be explained by the inhomogeneous, transient injection of the two-phase flow of oxygen across the faceplate. This characteristic is verified by liquid nitrogen cold flow tests that were recorded by high-speed imaging. We conclude that by adapting the ignition sequence, laser ignition by optical breakdown of the propellants within the shear layer of a coaxial shear injector is a reliable ignition technology for LOX/methane combustors without significant over-pressure levels.

Influence of pressure on fluidized bed gasifier: Specific coal throughput and particle behavior

In this work, the influence of pressure on specific coal throughput and particle behavior was investigated. Firstly, mono-gasification of Jincheng anthracite (JCA) and meat and bone meal (MBM) and co-gasification of JCA and MBM were performed in pressurized fluidized bed gasifier pilot plant with a pressure of 0.1–2.6 MPa and a temperature of 900–1050 °C (mono-gasification of MBM at about 750 °C). It was found that the specific coal throughput is approximately directly proportional to the pressure to the power of 0.6–0.75 and co-gasification leads to successful thermochemical conversion of JCA as opposed to mono-gasification. Furthermore, a series of experiments, in a Pseudo-2D cold mode of a pressurized fluidized bed gasifier using an optic fiber probe system, have been performed to investigate the effects of pressure, fluidizing-gas velocity and static bed height on the particle behavior. The bed material used in this study was polystyrene having average diameter of 1.32 mm. It was found that the effect of pressure on vertical local-particle velocities (Vp) at low bed height (LBH) can be ignored at identical excess fluidizing-gas velocity while Vp at high bed height (HBH) decrease slightly with pressure in the lower pressure range (evidently below approximately 1.2 MPa) and increase thereafter. The effects of the fluidizing-gas velocity on Vp at LBH and HBH are also different. However, the effects of static bed height on Vp both at LBH and HBH are the same under pressure.

Integrating spatial, morphological, and textural information for improved cell type differentiation using Raman microscopy

AbstractRaman microscopy is a well‐established tool for distinguishing different cell types in cell biological or cytopathological applications, since it can provide maps that show the specific distribution of biochemical components in the cell, with high lateral and spatial resolution. Currently, established data analysis approaches for differentiating cells of different types mostly rely on conventional chemometrics approaches, which tend to not systematically utilise the advantages provided by Raman microscopic data sets. To address this, we propose 2 approaches that explicitly exploit the large number of spectra as well as the morphological and textural information that are available in Raman microscopic data sets. Spatial bagging as our first approach is based on a statistical analysis of majority vote over classification results obtained from individual pixel spectra. Based on the Condorcet's Jury Theorem, this approach raises the accuracy of a relatively weak classifier for individual spectra to nearly perfect accuracy at the level of characterising whole cells. Our second approach extracts morphological and textural (morpho‐textural) features from Raman microscopic images to differentiate cell types. While using few wavenumbers of the Raman spectrum only, our results indicate on a quantitative basis that Raman microscopic images carry more morphological and textural information than haematoxylin and eosin (H&E) stained images as the current gold standard in cytopathology. Our 2 approaches promise improved protocols for the fast acquisition of Raman imaging data, for instance, for the morphological analysis of coherent anti‐Stokes Raman spectroscopy microscopic imaging data or for improving the accuracy of fibre optical probe systems by resampling spectra and utilising spatial bagging.

Development of a dual optical fiber probe for the hydrodynamic investigation of a horizontal annular drive gas/liquid ejector

A dual-channel optical fiber probe was developed to quantify the bubble characteristics (void fraction, velocity, and bubble size) in a gas–liquid annular ejector system. Water is pumped upstream of the ejector contraction. Since a low pressure region exists downstream in the ejector diffuser, this permits air to be sucked into the flowing liquid by jet pump action and the inlet air volumetric flow rate is measured by a flow meter. Verification of the void fraction (range 0.15–0.5) measured by the optical fiber probe was then possible and deviations were generally around ± 5%. Also, bubble velocity was measured using the optical probe by cross-correlating signals from the two fibers whose tips are separated by a known distance. Alternatively measuring bubble velocity using a particle image velocimetry method provided validation for the optical fiber probe system where a high speed camera was used to capture instantaneous bubble images at time intervals of 0.125ms. Excellent agreement between the velocities using both methods is reported. For bubble size measurements, analyzing the temporal signals from a single probe enabled estimation of the size of a bubble. Bubble sizes measured ranged between 1.5 and 6.0mm and size distributions were constructed for different ejector water volumetric flow rates ranging from 0.0022 to 0.0063m3/s. LabVIEW provided a convenient platform for coding the algorithms for estimating the void fraction, bubble velocity and bubble size. For further comparison, a CFD study of the ejector system was done, and the vertical radial profiles of the void fraction were compared with those obtained by the optical fiber system and these showed good agreement.

Repetitive laser ignition by optical breakdown of a LOX/H2 rocket combustion chamber with multi-injector head configuration

This paper reports on the repetitive laser ignition by optical breakdown within an experimental rocket combustion chamber. Ignition was performed by focusing a laser pulse generated by a miniaturized diode-pumped Nd:YAG laser system. The system, which delivers 33.2 mJ in 2.3 ns, was mounted directly to the combustion chamber. The ignition process and flame stabilization was investigated using an optical probe system monitoring the flame attachment across the 15 coaxial injector configuration. 1195 successful ignitions were performed proving the reliability of this laser ignition system and its applicability to the propellant combination LOX/hydrogen at temperatures of $$T_{{{\text{H}}_{ 2} }}$$ = 120–282 K and $$T_{{{\text{O}}_{ 2} }}$$ = 110–281 K.

Types of Peroral Cholangioscopy: How to Choose the Most Suitable Type of Cholangioscopy.

A number of case studies have described the usefulness of peroral cholangioscopy for diagnosis and therapy, performed by visualizing the inner cavity of the bile duct. Currently available types of peroral cholangioscopy include peroral videocholangioscopy (POCS) using a mother-baby scope system (MBSS), direct peroral videocholangioscopy (D-POCS), and SpyGlass™ Direct Visualization System (SGDVS). POCS started with cholangioscopy using MBSS, requiring two skilled endoscopists using two endoscopic systems. On the other hand, D-POCS and SGDVS were developed as single-operator techniques. In MBSS, the videocholangioscope is inserted into the bile duct through the accessory channel of a conventional therapeutic duodenoscope. MBSS enables comparatively easy scope insertion into the bile duct and stable scope positioning. POCS using MBSS provides excellent images and can be coupled with an image-enhanced function system. However, it has a smaller accessory channel, limiting the devices that can be used. Additionally, scope fragility is serious problem. D-POCS using an ultraslim upper endoscope has been introduced to overcome the drawback of POCS using MBSS. D-POCS has a larger working channel and requires only one endoscopist. D-POCS allows a greater variety of procedures under excellent imaging even with an image-enhanced function system; however, scope insertion is still challenging. SGDVS is designed for single-operator use and is dedicated to procedural purposes. It comprises a reusable optical probe and disposable delivery catheter, which has four-way deflected steering and dedicated irrigation channels. These features lead to good maneuverability, although image quality is poor due to its optical probe system. All systems' features should be recognized and the appropriate system used depending on the need. Cholangioscopy has shown dramatic progress from diagnosis to therapy with high future growth potential.