Sub-millimeter Spatial Resolution Research Articles

Optical frequency domain reflectometry with broadened frequency sweep range assisted by a dual electro-optic frequency comb.

We propose an optical frequency domain reflectometry (OFDR) with the assistance of a dual electro-optic frequency comb (EOFC), which is intended to improve the system spatial resolution. As the spatial resolution of an OFDR system is inversely proportional to the frequency sweep range, the EOFC acts as a multi-frequency light source for collecting Rayleigh backscattering signals, which are combined to extend the effective frequency sweep range. By utilizing this technique, we have successfully expanded the experimental frequency sweep range to hundreds of gigahertz, achieving a sub-millimeter spatial resolution.

Three-dimensional oxygen concentration monitoring in hydrogels using low-cost phosphorescence lifetime imaging for tissue engineering.

Oxygen concentration measurement in 3D hydrogels is vital in 3D cell culture and tissue engineering. However, standard 3D imaging systems capable of measuring oxygen concentration with adequate precision are based on advanced microscopy platforms, which are not accessible in many laboratories due to the system's complexity and the high price. In this work, we present a fast and low-cost phosphorescence lifetime imaging design for measuring the lifetime of oxygen-quenched phosphorescence emission with 0.25 µs temporal precision and sub-millimeter spatial resolution in 3D. By combining light-sheet illumination and the frequency-domain lifetime measurement using a commercial rolling-shutter CMOS camera in the structure of a conventional optical microscope, this design is highly customizable to accommodate application-specific research needs while also being low-cost as compared to advanced instruments. As a demonstration, we made a fluidic device with a gas-permeable film to create an artificial oxygen gradient in the hydrogel sample. Dye-embedded beads were distributed in the hydrogel to conduct continuous emission lifetime monitoring when nitrogen was pumped through the fluidic channel and changed oxygen distribution in the sample. The dynamics of the changes in lifetime co-related with their location in the gel of size 0.5 mm×1.5 mm×700 µm demonstrate the ability of this design to measure the oxygen concentration stably and precisely in 3D samples.

Angular correction methodology and characterization of a high-resolution CMOS array for patient specific quality assurance on a robotic arm linac.

To develop an angular correction methodology and characterize a high-resolution complementary metal-oxide-semiconductor (CMOS) array for patient specific quality assurance on a robotic arm linear accelerator. Beam path files from the treatment planning software (TPS) were used to calculate the angle of radiation beam with respect to the detector plane. Beams from multiple discrete angles were delivered to the CMOS detector array and an angular dependency look up table (LUT) was created. The LUT was then used to correct for the angular dependency of the detector. An iso-centric 5mm fixed cone, non iso-centric multi-target fixed cone, 10mm Iris and a multi-leaf collimator (MLC) based collimated plan were delivered to the phantom and compared to the TPS with and without angular correction applied. Additionally, the CMOS array was compared to gafchromic film and a diode array. Large errors of up to 30% were observed for oblique angles. When angular correction was applied, the gamma passing rate increased from 99.2% to 100% (average gamma value decreased from 0.29 to 0.14) for the 5-mm iso-centric cone plan. Similarly, the passing rate increased from 84.0% to 100% for the Iris plan and from 49.98% to 98.4% for the MLC plan when angular correction was applied. For the multi-target plan, applying angular correction improved the gamma passing rate from 94% to 99.6%. The 5mm iso-centric fixed cone plan was also delivered to film, and the gamma passing rate was 91.3% when using gafchromic film as the reference dataset, whereas the diode array provided insufficient sampling for this plan. A methodology of calculating the beam angle based on the beam path files was developed and validated. The array was demonstrated to be superior to other quality assurance tools because of its sub-millimeter spatial resolution and immediate read out of the results.

MoS2 Photoelectrodes for Hydrogen Production: Tuning the S-Vacancy Content in Highly Homogeneous Ultrathin Nanocrystals.

Tuning the electrocatalytic properties of MoS2 layers can be achieved through different paths, such as reducing their thickness, creating edges in the MoS2 flakes, and introducing S-vacancies. We combine these three approaches by growing MoS2 electrodes by using a special salt-assisted chemical vapor deposition (CVD) method. This procedure allows the growth of ultrathin MoS2 nanocrystals (1-3 layers thick and a few nanometers wide), as evidenced by atomic force microscopy and scanning tunneling microscopy. This morphology of the MoS2 layers at the nanoscale induces some specific features in the Raman and photoluminescence spectra compared to exfoliated or microcrystalline MoS2 layers. Moreover, the S-vacancy content in the layers can be tuned during CVD growth by using Ar/H2 mixtures as a carrier gas. Detailed optical microtransmittance and microreflectance spectroscopies, micro-Raman, and X-ray photoelectron spectroscopy measurements with sub-millimeter spatial resolution show that the obtained samples present an excellent homogeneity over areas in the cm2 range. The electrochemical and photoelectrochemical properties of these MoS2 layers were investigated using electrodes with relatively large areas (0.8 cm2). The prepared MoS2 cathodes show outstanding Faradaic efficiencies as well as long-term stability in acidic solutions. In addition, we demonstrate that there is an optimal number of S-vacancies to improve the electrochemical and photoelectrochemical performances of MoS2.

Feasibility of 4D HDR brachytherapy source tracking using x-ray tomosynthesis: Monte Carlo investigation.

High dose rate (HDR) brachytherapy rapidly delivers dose to targets with steep dose gradients. This treatment method must adhere to prescribed treatment plans with high spatiotemporal accuracy and precision, as failure to do so may degrade clinical outcomes. One approach to achieving this goal is to develop imaging techniques to track HDR sources in vivo in reference to surrounding anatomy. This work investigates the feasibility of using an isocentric C-arm x-ray imager and tomosynthesis methods to track Ir-192 HDR brachytherapy sources in vivo over time (4D). A tomosynthesis imaging workflow was proposed and its achievable source detectability, localization accuracy, and spatiotemporal resolution were investigated in silico. An anthropomorphic female XCAT phantom was modified to include a vaginal cylinder applicator and Ir-192 HDR source (0.5 × 0.5 × 5.0 mm3 ), and the workflow was carried out using the MC-GPU Monte Carlo image simulation platform. Source detectability was characterized using the reconstructed source signal-difference-to-noise-ratio (SDNR), localization accuracy by the absolute 3D error in its measured centroid location, and spatiotemporal resolution by the full-width-at-half-maximum (FWHM) of line profiles through the source in each spatial dimension considering a maximum C-arm angular velocity of 30° per second. The dependence of these parameters on acquisition angular range (θtot = 0°-90°), number of views, angular increment between views (Δθ = 0°-15°), and volumetric constraints imposed in reconstruction was evaluated. Organ voxel doses were tallied to derive the workflow's attributable effective dose. The HDR source was readily detected and its centroid was accurately localized with the proposed workflow and method (SDNR: 10-40, 3D error: 0-0.144 mm). Tradeoffs were demonstrated for various combinations of image acquisition parameters; namely, increasing the tomosynthesis acquisition angular range improved resolution in the depth-encoded direction, for example from 2.5 mm to 1.2 mm between θtot = 30o and θtot = 90o , at the cost of increasing acquisition time from 1 to 3 s. The best-performing acquisition parameters (θtot = 90o , Δθ = 1°) yielded no centroid localization error, and achieved submillimeter source resolution (0.57 × 1.21 × 5.04 mm3 apparent source dimensions, FWHM). The total effective dose for the workflow was 263 µSv for its required pre-treatment imaging component and 7.59 µSv per mid-treatment acquisition thereafter, which is comparable to common diagnostic radiology exams. A system and method for tracking HDR brachytherapy sources in vivo using C-arm tomosynthesis was proposed and its performance investigated in silico. Tradeoffs in source conspicuity, localization accuracy, spatiotemporal resolution, and dose were determined. The results suggest this approach is feasible for localizing an Ir-192 HDR source in vivo with submillimeter spatial resolution, 1-3 second temporal resolution and minimal additional dose burden.

High-spatial-resolution φ-OFDR shape sensor based on multicore optical fiber with femtosecond-laser-induced permanent scatter arrays.

An optical fiber φ-OFDR shape sensor with a submillimeter spatial resolution of 200 µm was demonstrated by using femtosecond-laser-induced permanent scatter array (PS array) multicore fiber (MCF). A PS array was successfully inscribed in each slightly twisted core of the 400-mm-long MCF. The two-dimensional (2D) and three-dimensional (3D) shapes of the PS-array-inscribed MCF were successfully reconstructed by using PS-assisted φ-OFDR, vector projections, and the Bishop frame based on the PS-array-inscribed MCF. The minimum reconstruction error per unit length of the 2D and 3D shape sensor was 2.21% and 1.45%, respectively.

Micro-dispenser-based optical packaging scheme for grating couplers.

Due to their sub-millimeter spatial resolution, ink-based additive manufacturing tools are typically considered less attractive than nanophotonics. Among these tools, precision micro-dispensers with sub-nanoliter volumetric control offer the finest spatial resolution: down to 50 µm. Within a sub-second, a flawless, surface-tension-driven spherical shape of the dielectric dot is formed as a self-assembled µlens. When combined with dispersive nanophotonic structures defined on a silicon-on-insulator substrate, we show that the dispensed dielectric µlenses [numerical aperture (NA) = 0.36] engineer the angular field distribution of vertically coupled nanostructures. The µlenses improve the angular tolerance for the input and reduces the angular spread of the output beam in the far field. The micro-dispenser is fast, scalable, and back-end-of-line compatible, allowing geometric-offset-caused efficiency reductions and center wavelength drift to be easily fixed. The design concept is experimentally verified by comparing several exemplary grating couplers with and without a µlens on top. A difference of less than 1 dB between incident angles of 7° and 14° is observed in the index-matched µlens, while the reference grating coupler shows around 5 dB contrast.

Forward modelling of [formula omitted] camera view in ST40 informed by experimental data

Embedding diagnostics in future pilot plants will be a challenging task, because of space- and irradiation-related concerns. Relying on high-fidelity synthetic diagnostics would then be valuable.The 3D Monte-Carlo ray-tracing code CHERAB allows the development of numerous synthetic spectroscopic diagnostics. Focus of the present work is the introduction of new CHERAB models. The forward modelling of a synthetic Dα camera in ST40, the privately funded, high-field spherical tokamak, owned and operated by Tokamak Energy Ltd, and the comparison against experimental data is chosen as a testbed for quality assessment. Main output of the study then consists of estimates of the neutral particle densities throughout the chamber, of crucial relevance within edge plasma studies.Starting from simple analytical models, a 2D Dα source in the poloidal plane is generated. However, the centre column limited plasmas in ST40 display an intrinsically-3D Dα emission, mostly localised around the discrete poloidal limiters on the centre column, not captured by any axisymmetric source model. Hence, a novel methodology is introduced in CHERAB to approximate the 3D non-toroidally-symmetric pattern via a piece-wise emission distribution.Irrespective of the geometry of the emission and size of the tokamak, the pronounced non-homogeneity in the edge plasma emission requires sub-millimetric (∼ power fall-off length) spatial resolution to guarantee an accurate estimate of the peak emission. Minimising the associated burden via implementation of a non-uniform source sampling algorithm, which is a modification of the standard CHERAB uniform sampling, results in a >10-fold reduction of the computational cost.The significantly-shortened simulation time also makes the inclusion of more sophisticated models affordable. Of potential appeal in view of highly-detached divertors, the approximation of optically thin plasma is dropped, and photon-plasma interactions are accounted for. Brand-new CHERAB models able to take into account phenomena of photon absorption and scattering are so introduced.

Layer-specific correlates of detected and undetected auditory targets during attention.

In everyday life, the processing of acoustic information allows us to react to subtle changes in the auditory scene. Yet even when closely attending to sounds in the context of a task, we occasionally miss task-relevant features. The neural computations that underlie our ability to detect behavioral relevant sound changes are thought to be grounded in both feedforward and feedback processes within the auditory hierarchy. Here, we assessed the role of feedforward and feedback contributions in primary and non-primary auditory areas during behavioral detection of target sounds using submillimeter spatial resolution functional magnetic resonance imaging (fMRI) at high-fields (7T) in humans. We demonstrate that the successful detection of subtle temporal shifts in target sounds leads to a selective increase of activation in superficial layers of primary auditory cortex (PAC). These results indicate that feedback signals reaching as far back as PAC may be relevant to the detection of targets in the auditory scene.

Simulation study of a brain PET scanner using TOF-DOI detectors equipped with first interaction position detection

Objective. The aim of this study is to evaluate the performance characteristics of a brain positron emission tomography (PET) scanner composed of four-layer independent read-out time-of-flight depth-of-interaction (TOF-DOI) detectors capable of first interaction position (FIP) detection, using Geant4 application for tomographic emission(GATE). This includes the spatial resolution, sensitivity, count rate capability, and reconstructed image quality. Approach. The proposed TOF-DOI PET detector comprises four layers of a 50 × 50 cerium-doped lutetium–yttrium oxyorthosilicate (LYSO:Ce) scintillator array with 1 mm pitch size, coupled to a 16 × 16 multi-pixel photon counter array with 3.0 mm × 3.0 mm photosensitive segments. Along the direction distant from the center field-of-view (FOV), the scintillator thickness of the four layers is 2.5, 3, 4, and 6 mm. The four layers were simulated with a 150 ps coincidence time resolution and the independent readout make the FIP detection capable. The spatial resolution and imaging performance were compared among the true-FIP, winner-takes-all (WTA) and front-layer FIP (FL-FIP) methods (FL-FIP selects the interaction position located on the front-most interaction layer in all the interaction layers). The National Electrical Manufacturers Association NU 2-2018 procedure was referred and modified to evaluate the performance of proposed scanner. Main results. In detector evaluation, the intrinsic spatial resolutions were 0.52 and 0.76 mm full width at half-maximum (FWHM) at 0° and 30° incident γ-rays in the first layer pair, respectively. The reconstructed spatial resolution by the filter backprojection (FBP) achieved sub-millimeter FWHM on average over the whole FOV. The maximum true count rate was 207.6 kcps at 15 kBq ml−1 and the noise equivalent count rate (NECR_2R) was 54.7 kcps at 6.0 kBq ml−1. Total sensitivity was 45.2 cps kBq−1 and 48.4 cps kBq−1 at the center and 10 cm off-center FOV, respectively. The TOF and DOI reconstructions significantly improved the image quality in the phantom studies. Moreover, the FL-FIP outperformed the conventional WTA method in terms of the spatial resolution and image quality. Significance. The proposed brain PET scanner could achieve sub-millimeter spatial resolution and high image quality with TOF and DOI reconstruction, which is meaningful to the clinical oncology research. Meanwhile, the comparison among the three positioning methods indicated that the FL-FIP decreased the image degradation caused by Compton scatter more than WTA.

Nondestructive testing and 3D imaging of PE pipes using terahertz frequency-modulated continuous wave.

Polyethylene (PE) pipes are widely used as the main carrier for the transportation of natural gas, so nondestructive testing techniques for PE pipes are essential for the safety of natural gas transportation. In order to compensate for the shortcomings of conventional inspection methods, a terahertz (THz) three-dimensional imaging system for nondestructive inspection of PE pipes is designed. The system is based on frequency-modulated continuous-wave (FMCW) technology, with a THz source bandwidth of 0.225-0.330THz and an output power of over 5mW, which can achieve submillimeter spatial resolution in three dimensions. The system is used to scan PE pipes in three dimensions in a laboratory environment, and the results show that the system could achieve nondestructive testing and three-dimensional imaging of different defects in PE pipes. In addition, combined with the deep-learning-based THz transformer network, the intelligent identification of different defects is realized, and the accuracy rate can reach up to 88%. The above results provide technical guidance for the application of THz FMCW systems in the actual detection of PE pipes, and provide supplements and improvements for traditional detection methods.

High-resolution optical magnetic resonance imaging of electronic spin polarization in miniaturized atomic sensors

Miniaturized atomic sensors of magnetic field and inertia have great potential to be applied as geophysical instruments and in the detection of biomolecules. The distribution of the electronic spin polarization plays a key role as it defines the amount of noble gas that can achieve a state of hyperpolarization, which in turn determines the technique's accuracy and, consequently, its resolution. However, the current techniques for electronic spin polarization imaging are unsuited for the operating conditions of miniaturized atomic sensors besides only accomplishing submillimeter spatial resolution. In this study, optical magnetic resonance is applied to obtain electronic spin polarization images with a spatial resolution of 60 μm experimentally and 10 μm theoretically. This corresponds to an increase by one order of magnitude in resolution when compared to previous reports of electronic spin polarization imaging. By sweeping the RF frequency of the magnetic field while applying a magnetic field gradient of 0.22 μT/mm, it is possible to measure electronic spin polarization images for different average photon spins and pump beam positions. Spin polarization images present a high degree of correlation with pump beam images. Furthermore, this image method can be applied to suppressing the inhomogeneities in miniaturized cells, leading to a gain in signal-to-noise ratio. It also offers an opportunity to experimentally perform two-dimensional atomic polarization manipulation in the gas phase, optically transparent solids, and liquids.

Toward evaluation of multiresolution cortical thickness estimation with FreeSurfer, MaCRUISE, and BrainSuite.

Advances in Magnetic Resonance Imaging hardware and methodologies allow for promoting the cortical morphometry with submillimeter spatial resolution. In this paper, we generated 3D self-enhanced high-resolution (HR) MRI imaging, by adapting 1 deep learning architecture, and 3 standard pipelines, FreeSurfer, MaCRUISE, and BrainSuite, have been collectively employed to evaluate the cortical thickness. We systematically investigated the differences in cortical thickness estimation for MRI sequences at multiresolution homologously originated from the native image. It has been revealed that there systematically exhibited the preferences in determining both inner and outer cortical surfaces at higher resolution, yielding most deeper cortical surface placements toward GM/WM or GM/CSF boundaries, which directs a consistent reduction tendency of mean cortical thickness estimation; on the contrary, the lower resolution data will most probably provide a more coarse and rough evaluation in cortical surface reconstruction, resulting in a relatively thicker estimation. Although the differences of cortical thickness estimation at the diverse spatial resolution varied with one another, almost all led to roughly one-sixth to one-fifth significant reduction across the entire brain at the HR, independent to the pipelines we applied, which emphasizes on generally coherent improved accuracy in a data-independent manner and endeavors to cost-efficiency with quantitative opportunities.

Beyond a 107 range-resolution-1 product in an OFDR based on a periodic phase noise estimation method.

We present and demonstrate a method based on a periodic phase noise estimation in an optical frequency domain reflectometry (OFDR) capable of a beyond 107 range-resolution-1 product (RRP) for the first time, which corresponds to 2.5 × improvement compared with the state-of-the-art. The moving average filter is employed to suppress the amplification of noise in the derivation process. Further, with the help of a third-order Taylor expansion, this method provides a highly precise estimation of periodic phase noise, which is the main factor impacting the performance of OFDR systems with medium-to-long measurement range combined with a submillimeter spatial resolution. A spatial resolution within 535 μm over the measurement range of 8 km is obtained. The proposed method offers a promising technique for fiber network monitoring and sensing applications.

Comparative Role of MDCT and FDG-PET/CT in the Diagnostic Evaluation of Mediastinal Mass Lesions: An Institutional Experience.

Background Mediastinal mass lesions span a wide histopathological and radiological spectrum. Partition of the mediastinum into specific compartments aids in differential diagnosis of mass lesions, assistance in biopsies, and other surgical procedures. Multidetector row computed tomography (MDCT) is a promising three-dimensional imaging tool allowing substantial anatomical volumes to be routinely covered with isotropic submillimeter spatial resolution to precisely localize lesions and biopsy needles for both benign and malignant disease lesions of the mediastinum. Objective The aim of this study was to categorize mass lesions according to the mediastinal compartments to study their MDCT characteristics and to provide a comparative role of fluorodeoxyglucose positron emission tomography/computed tomography (FDG-PET/CT) in the diagnostic evaluation of mediastinal mass lesions. Materials and Methods Patients with clinical or radiological suspicion of mediastinal lesions on the basis of an abnormal chest radiograph were referred to the department of radiodiagnosis at a tertiary care center between April 2015 and December 2019 for MDCT evaluation. A total of 80 cases were correlated with the histopathological diagnosis excluding aneurysms. Size, CT density (Hounsfield unit [HU] mean), and maximum standardized uptake value (SUV max ) of mediastinal and chest wall lesions were determined on FDG-PET/CT. Results This study included a total of 102 cases, 72 males and 29 females. Mediastinal mass lesions were most common in the age group 46 to 60 years. Anterior mediastinum ( n = 43, 42.2%) is the most commonly involved compartment followed by posterior mediastinum ( n = 37, 35.9%) and middle mediastinum ( n = 22, 21.8%). Transcompartmental involvement is more commonly seen involving the anterior and middle mediastinum. The SUV max , HU mean, and size were higher in malignant cases ( p = 0.001, p = 0.003, and p = 0.004, respectively). The current study found a cutoff value of 4.61 for SUV max to discriminate benign lesions from malignant ones with a sensitivity and specificity of 73.7 and 75.9%, respectively (area under the curve: 0.841, 95% confidence interval: 0.793–0.965, p = 0.0001). The values of SUV max and HU mean were higher in solid benign lesions than those of cystic benign lesions ( p = 0.007 and p = 0.003, respectively). Conclusion In the current study, MDCT has high diagnostic accuracy of ∼94% overall as compared with histopathology, and 97 and 92% for benign and malignant lesions, respectively, in the evaluation of mediastinal mass lesions. FDG-PET/CT may be complementary to conventional imaging methods for the evaluation of mediastinal and chest wall mass lesions. However, confirmatory tissue sampling is required to confirm PET positive findings for the definite diagnosis.

Polymer-based planar waveguide chirped Bragg grating for high-resolution tactile sensing.

A novel tactile sensor for two-dimensional force location measurements, based on polymer-based planar waveguide chirped Bragg gratings (PPCBGs) fabricated on sheet PMMA substrate, is presented. The planar waveguide and chirped Bragg grating are simultaneously generated using a KrF excimer laser and a phase mask covered by a quartz chrome mask. Location and magnitude of an applied force is measured by observing the change of the wavelength of a dip in the measured spectrum and a change in the reflectivity intensity. Experimental characterization indicates submillimeter spatial resolution of applied force in the range of 1-4 N with a sensitivity of 947.02 pm/mm.

Filament-induced nonlinear hyperspectral fluorescence imaging

Hyperspectral fluorescence imaging is promising for many applications including gas sensing and imaging. However, achieving spectrally and spatially resolved images for quantitative multi-gas and multi-parameter analysis remains challenging, especially in a non-cooperative environment. Here, we report a simple technique, based on filament-induced nonlinear spectroscopy, for information-rich gas imaging. We obtained three-dimensional (3D) hyperspectral images for an alcohol/air flame with sub-millimeter spatial resolutions. For each hypercube, a broadband fluorescence fingerprint spectrum, containing 2500 spectral elements (350–600 nm at a spectral resolution of 0.1 nm), was acquired. This technique, with backward fluorescence detection, enabled high-spatial-resolution point-wise imaging in a non-cooperative situation, e.g., in a sealed tube. Without meticulously arranged cameras, the technique may open up new opportunities for remote gas imaging and tomography.

Ultrasound Localization Microscopy in Liquid Metal Flows

Liquid metal convection plays an important role in natural and technical processes. In experimental studies, an instrumentation with a sub-millimeter spatial resolution is required in an opaque fluid to resolve the flow field near the boundary layer. Using ultrasound methods, the trade-off between the frequency and imaging depth of typical laboratory experiments limits the spatial resolution. Therefore, the method of ultrasound localization microscopy (ULM) was introduced in liquid metal experiments for the first time in this study. To isolate the intrinsic scattering particles, an adaptive nonlinear beamformer was applied. As a result, an average spatial resolution of 188 μm could be achieved, which corresponded to a fraction of the ultrasound wavelength of 0.28. A convection experiment was measured using ULM. Due to the increased spatial resolution, the high-velocity gradients and the recirculation areas of a liquid metal convection experiment could be observed for the first time. The presented technique paves the way for in-depth flow studies of convective turbulent liquid metal flows that are close to the boundary layer.

Study of a position-sensitive scintillator neutron detector prototype based on 6LiF/ZnS scintillator and silicon photomultiplier arrays readout

Due to the shortage of the 3He gas and its rapidly increasing price, scintillator detectors, the advantages of which are high spatial resolution and capability of detection in real time, become widely used in many neutron instruments. In this work, a position-sensitive neutron detector consisting of a 6LiF/ZnS scintillation screen and a silicon photomultiplier array linked to a capacitive network to detect the positions of incident neutrons, is constructed and tested. To evaluate the detector performance, a series of neutron beam experiments with the detector prototype were performed in the BL20 at the China Spallation Neutron Source. The spatial resolution was measured, and the energy-selective neutron imaging and Bragg edge measurements of a 316L stainless steel sample were performed. A sub-millimeter spatial resolution could be obtained for the detector prototype under study. The detector with such a high spatial resolution is promising for applications in neutron scattering experimental installations, especially for neutron single-crystal diffractometers.

Chemical analysis from a distance: Spatially resolved, remote sensing using backward transient absorption

Identification of chemical species from a distance is achieved with backward transient absorption spectroscopy. The experiments employ UV excitation followed by a Rydberg-Rydberg transition that gives the method its inherent molecule-specificity. Using three similar amines, we demonstrate that backward transient absorption spectroscopy can identify closely related compounds. The distance of the vapors is measured independently with a sub-millimeter spatial resolution, limited by the duration of the laser pulses and the signal level. The combination of high sensitivity and excellent spatial resolution makes backward transient absorption spectroscopy an excellent choice for applications where chemical structures can be identified from a distance.