Path Length Difference Research Articles

Disrupted Patterns of Rich-Club and Diverse-Club Organizations in Subjective Cognitive Decline and Amnestic Mild Cognitive Impairment

BackgroundSubjective cognitive decline (SCD) and amnestic mild cognitive impairment (aMCI) were considered to be a continuum of Alzheimer’s disease (AD) spectrum. The abnormal topological architecture and rich-club organization in the brain functional network can reveal the pathology of the AD spectrum. However, few studies have explored the disrupted patterns of diverse club organizations and the combination of rich- and diverse-club organizations in SCD and aMCI.MethodsWe collected resting-state functional magnetic resonance imaging data of 19 SCDs, 29 aMCIs, and 28 healthy controls (HCs) from the Alzheimer’s Disease Neuroimaging Initiative. Graph theory analysis was used to analyze the network metrics and rich- and diverse-club organizations simultaneously.ResultsCompared with HC, the aMCI group showed altered small-world and network efficiency, whereas the SCD group remained relatively stable. The aMCI group showed reduced rich-club connectivity compared with the HC. In addition, the aMCI group showed significantly increased feeder connectivity and decreased local connectivity of the diverse club compared with the SCD group. The overlapping nodes of the rich club and diverse club showed a significant difference in nodal efficiency and shortest path length (Lp) between groups. Notably, the Lp values of overlapping nodes in the SCD and aMCI groups were significantly associated with episodic memory.ConclusionThe present study demonstrates that the network properties of SCD and aMCI have varying degrees of damage. The combination of the rich club and the diverse club can provide a novel insight into the pathological mechanism of the AD spectrum. The altered patterns in overlapping nodes might be potential biomarkers in the diagnosis of the AD spectrum.

Range-Angle Coupling and Near-Field Effects of Very Large Arrays in mm-Wave Imaging Radars

In order to improve the resolution of imaging radars, electrically large arrays and a high absolute modulation bandwidth are needed. For radar systems with simultaneously high range resolution and very large aperture, the difference in path length at the receiving antennas is a multiple of the range resolution of the radar, in particular for off-boresight angles of the incident wave. Therefore, the radar response of a target measured at the different receiving antennas is distributed over a large number of range cells. This behavior depends on the unknown incident angle of the wave and is, thus, denoted as range-angle coupling. Furthermore, the far-field (FF) condition is no longer fulfilled in short-range applications. Applying conventional signal processing and radar calibration techniques leads to a significant reduction of the resolution capabilities of the array. In this article, the key aspects of radar imaging are discussed when radars with both large aperture size and high absolute bandwidth are employed in short-range applications. Based on an initial mathematical formulation of the physical effects, a correction method and an efficient signal processing chain are proposed, which compensate for errors that occur with conventional beamforming techniques. It is shown by measurements that with an appropriate error correction an improvement of the angular resolution up to a factor of 2.5 is achieved, resulting in an angular resolution below 0.4° with an overall aperture size of nearly 200λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> .

Toward monochromated sub-nanometer UEM and femtosecond UED

A preliminary design of a mega-electron-volt (MeV) monochromator with 10−5 energy spread for ultrafast electron diffraction (UED) and ultrafast electron microscopy (UEM) is presented. Such a narrow energy spread is advantageous in both the single shot mode, where the momentum resolution in diffraction is improved, and the accumulation mode, where shot-to-shot energy jitter is reduced. In the single-shot mode, we numerically optimized the monochromator efficiency up to 13% achieving 1.3 million electrons per pulse. In the accumulation mode, to mitigate the efficiency degradation caused by the shot-to-shot energy jitter, an optimized gun phase yields only a mild reduction of the single-shot efficiency, therefore the number of accumulated electrons nearly proportional to the repetition rate. Inspired by the recent work of Qi et al. (Phys Rev Lett 124:134803, 2020), a novel concept of applying reverse bending magnets to adjust the energy-dependent path length difference has been successfully realized in designing a MeV monochromator to achieve the minimum energy-dependent path length difference between cathode and sample. Thanks to the achromat design, the pulse length of the electron bunches and the energy-dependent timing jitter can be greatly reduced to the 10 fs level. The introduction of such a monochromator provides a major step forward, towards constructing a UEM with sub-nm resolution and a UED with ten-femtosecond temporal resolution. The one-to-one mapping between the electron beam parameter and the diffraction peak broadening enables a real-time nondestructive diagnosis of the beam energy spread and divergence. The tunable electric–magnetic monochromator allows the scanning of the electron beam energy with a 10−5 precision, enabling online energy matching for the UEM, on-momentum flux maximizing for the UED and real-time energy measuring for energy-loss spectroscopy. A combination of the monochromator and a downstream chicane enables “two-color” double pulses with femtosecond duration and the tunable delay in the range of 10 to 160 fs, which can potentially provide an unprecedented femtosecond time resolution for time resolved UED.

Single wavelength measurements of absorption coefficients based on iso-pathlength point.

In optical sensing, to reveal the chemical composition of tissues, the main challenge is isolating absorption from scattering. Most techniques use multiple wavelengths, which adds an error due to the optical pathlength differences. We suggest using a unique measurement angle for cylindrical tissues, the iso-pathlength (IPL) point, which depends on tissue geometry only (specifically the effective radius). We present a method for absorption assessment from a single wavelength at multiple measurement angles. The IPL point presented similar optical pathlengths for different tissues, both in simulation and experiments, hence it is optimal. Finally, in vivo measurements validated our proposed method.

Neural correlates of conscious tactile perception: An analysis of BOLD activation patterns and graph metrics

Theories of human consciousness substantially vary in the proposed spatial extent of brain activity associated with conscious perception as well as in the assumed functional alterations within the involved brain regions. Here, we investigate which local and global changes in brain activity accompany conscious somatosensory perception following electrical finger nerve stimulation, and whether there are whole-brain functional network alterations by means of graph metrics. Thirty-eight healthy participants performed a somatosensory detection task and reported their decision confidence during fMRI. For conscious tactile perception in contrast to undetected near-threshold trials (misses), we observed increased BOLD activity in the precuneus, the intraparietal sulcus, the insula, the nucleus accumbens, the inferior frontal gyrus and the contralateral secondary somatosensory cortex. For misses compared to correct rejections, bilateral secondary somatosensory cortices, supplementary motor cortex and insula showed greater activations. The analysis of whole-brain functional network topology for hits, misses and correct rejections, did not result in any significant differences in modularity, participation, clustering or path length, which was supported by Bayes factor statistics. In conclusion, for conscious somatosensory perception, our results are consistent with an involvement of (probably) domain-general brain areas (precuneus, insula, inferior frontal gyrus) in addition to somatosensory regions; our data do not support the notion of specific changes in graph metrics associated with conscious experience. For the employed somatosensory submodality of fine electrical current stimulation, this speaks for a global broadcasting of sensory content across the brain without substantial reconfiguration of the whole-brain functional network resulting in an integrative conscious experience.

Noise-suppressing and lock-free optical interferometer for cold atom experiments.

A novel noise-suppressing and lock-free interferometer is proposed and experimentally demonstrated in the study of the quantum non-destructive (QND) interaction of cold atoms. A QND measurement based on far-off resonant dispersive probing is usually carried out by a Mach-Zehnder type interferometer. It is an experimental challenge in its own right to reduce the classical noise, such as acoustic noise, phase noise and amplitude noise of lasers, and to lock the interferometer at the white-light position that corresponds to a nearly zero path-length difference. Here, we report an interferometer with an inserted acousto-optic modulator (AOM). It is noise immune and lock-free in principle. The experiments show that the new interferometer is able to measure cold atoms for more than 30 minutes and reduce the phase noise by about 30 dB.

Impacts of Laboratory Vibrations and Laser Flicker Noise on Digital Holography

In this paper, we experimentally demonstrate the impacts of laboratory vibrations and laser flicker noise on digital holography (DH). Specifically, we measure both the vibration efficiency and the coherence efficiency of our DH system at various focal-plane array integration times and path-length differences between the signal and reference. These efficiencies, in practice, contribute to the overall mixing efficiency, which is a measure for how well the detected signal and reference interfere. The results show that when the integration time is ≤1ms, the laboratory vibrations are negligible with a vibration efficiency of 100%; however, when the integration time equals 100 ms, the laboratory vibrations lead to a 94% vibration efficiency. In addition, the results show that the effective coherence length of the master-oscillator (MO) laser increases by 280% when the integration time decreases from 100ms to 100 $\mu \text{s}$ . To account for this outcome, we present a model of the coherence efficiency based on the frequency noise of the MO laser. The model fit to the DH data then shows that the frequency of the MO laser is flicker-noise dominated. As a result, decreasing the integration time improves the overall mixing efficiency because of high-pass filtering in both the vibration efficiency and the coherence efficiency. Based on previous published efforts, these results have direct ties to the achievable signal-to-noise ratio of a DH system.

An assessment study of three indirect methods for estimating leaf area density and leaf area index of individual trees

Field measurements of leaf area density (LAD) and leaf area index (LAI) for individual trees have increased in importance and relevance with the advent of high spatial resolution remote sensing for the urban landscape. However, indirect field measurements of LAD/LAI for widely dispersed individual trees have not been comprehensively evaluated. The present study compares the accuracy of three indirect LAD/LAI estimation methods, including single-return terrestrial laser scanning (TLS), LAI-2200, and digital hemispherical photography (DHP) on urban trees. To this end, field measurements were inter-compared and physically modeled by discrete anisotropic radiation transfer (DART). The inter-comparisons of field data revealed substantial inconsistencies between DHP and the other two approaches. For the physical modeling, reference LAI was obtained from realistic 3-D tree objects in DART, and the LAD/LAI was derived from simulated TLS, LAI-2200, and DHP acquisitions and was evaluated against the references. The physical modeling results showed that TLS could reasonably estimate LAD/LAI for LAD < 3 and LAI < 6 using a small (0.3 m) voxel size. However, the measurements became saturated for dense foliage (LAD > 3 and LAI > 6). The LAD/LAI accuracy was sharply reduced as voxel size increased. In addition, the trunks caused overestimation for both of LAD and LAI, while branches caused LAD underestimation and LAI overestimation. Further research is needed to compensate for the effects of occlusions and clumping in the estimates of LAD/LAI for dense-foliated trees using TLS. LAI-2200 grossly underestimated LAD for all cases, while it accurately estimated LAI for LAI < 5 and became gradually saturated for LAI > 5. The estimation accuracy of LAI-2200 declined markedly with increasing uncertainty in crown shape. The 90° view cap had higher accuracy than the 180° or 270° view caps using four or all five LAI-2200 rings. Additional sensors or algorithms for crown shape measurement should be developed for LAI-2200 to reduce its reliance on other data sources. DHP is not recommended for individual trees as the LAI estimations were biased from the reference values, and improvements in reliability will depend on new algorithms to account for differences in path length. These results serve as a benchmark for evaluating the accuracy of in situ LAD/LAI measurement techniques and for optimizing the configurations required for each indirect measurement method applied to individual trees.

Large-field step-structure surface measurement using a femtosecond laser.

We present a femtosecond laser-based interferometry for step-structure surface measurement with a large field of view. A height axial scanning range of 348 µm is achieved by using the method of repetition frequency scanning with reference to the Rb atomic clock and the optical path length difference design for 21 times of the pulse interval. A combined method, which includes the envelope peak positioning method for rough measurement, synthetic-wavelength interferometry for connection, and carrier wave interferometry for fine measurement, is proposed to reconstruct the surface. A three-step specimen with heights of approximately 20, 50, and 70 µm was successfully measured with a height precision of 7 nm, and the accuracy was verified by a commercial white light interferometer. The diameter of the field of view that was demonstrated was 17.3 mm, which could be much larger owing to the high spatial coherence of the femtosecond laser. The results show that the femtosecond laser system combines the step-structure measurement performance of white light interferometry and the high-precision large-field performance of phase shifting interferometry, indicating its potential for widespread use in ultra-precision manufacturing of micro/nano-devices, such as semiconductor chips, integrated circuits, and micro-electro-mechanical systems.

Large-format X-Ray Reflection Grating Operated in an Echelle-like Mounting

Abstract We report on resolving power measurements of an X-ray reflection grating designed for use in an astronomical soft X-ray spectrograph. The grating was patterned via electron-beam lithography (EBL) to have fanned grooves to match the convergence of an illuminating beam. Grating measurements were conducted in an echelle-like mounting, which yields access to high diffraction orders in the soft X-ray bandpass (0.2–2.0 keV). By comparing the zeroth-order line-spread function to the telescope focus, we find evidence for minimal broadening (&lt;1″) introduced by the figure of the grating. In addition, we fit for the spectral resolution (R = λ/Δλ) intrinsic to this grating using a Bayesian Markov Chain Monte Carlo approach. Using an ensemble fitting technique, we find that the grating resolution R exceeds 2200 (3σ lower bound). This current grating resolution meets the performance required for a notional soft X-ray grating spectroscopy mission measuring hot baryonic material in the extended halos of galaxies. Using ray-trace simulations, we identify a geometric aberration resulting from path length differences across the width of the grating as a limiting factor in assessing the resolution of these gratings and discuss methods for placing better constraints on the inherent resolution of X-ray astronomical reflection gratings fabricated using EBL.

On-sky verification of Fast and Furious focal-plane wavefront sensing: Moving forward toward controlling the island effect at Subaru/SCExAO

Context. High-contrast imaging (HCI) observations of exoplanets can be limited by the island effect (IE). The IE occurs when the main wavefront sensor (WFS) cannot measure sharp phase discontinuities across the telescope’s secondary mirror support structures (also known as spiders). On the current generation of telescopes, the IE becomes a severe problem when the ground wind speed is below a few meters per second. During these conditions, the air that is in close contact with the spiders cools down and is not blown away. This can create a sharp optical path length difference between light passing on opposite sides of the spiders. Such an IE aberration is not measured by the WFS and is therefore left uncorrected. This is referred to as the low-wind effect (LWE). The LWE severely distorts the point spread function (PSF), significantly lowering the Strehl ratio and degrading the contrast. Aims. In this article, we aim to show that the focal-plane wavefront sensing (FPWFS) algorithm, Fast and Furious (F&amp;F), can be used to measure and correct the IE/LWE. The F&amp;F algorithm is a sequential phase diversity algorithm and a software-only solution to FPWFS that only requires access to images of non-coronagraphic PSFs and control of the deformable mirror. Methods. We deployed the algorithm on the SCExAO HCI instrument at the Subaru Telescope using the internal near-infrared camera in H-band. We tested with the internal source to verify that F&amp;F can correct a wide variety of LWE phase screens. Subsequently, F&amp;F was deployed on-sky to test its performance with the full end-to-end system and atmospheric turbulence. The performance of the algorithm was evaluated by two metrics based on the PSF quality: (1) the Strehl ratio approximation (SRA), and (2) variance of the normalized first Airy ring (VAR). The VAR measures the distortion of the first Airy ring, and is used to quantify PSF improvements that do not or barely affect the PSF core (e.g., during challenging atmospheric conditions). Results. The internal source results show that F&amp;F can correct a wide range of LWE phase screens. Random LWE phase screens with a peak-to-valley wavefront error between 0.4 μm and 2 μm were all corrected to a SRA &gt; 90% and an VAR ⪅ 0.05. Furthermore, the on-sky results show that F&amp;F is able to improve the PSF quality during very challenging atmospheric conditions (1.3–1.4″seeing at 500 nm). Closed-loop tests show that F&amp;F is able to improve the VAR from 0.27–0.03 and therefore significantly improve the symmetry of the PSF. Simultaneous observations of the PSF in the optical (λ = 750 nm, Δλ = 50 nm) show that during these tests we were correcting aberrations common to the optical and NIR paths within SCExAO. We could not conclusively determine if we were correcting the LWE and/or (quasi-)static aberrations upstream of SCExAO. Conclusions. The F&amp;F algorithm is a promising focal-plane wavefront sensing technique that has now been successfully tested on-sky. Going forward, the algorithm is suitable for incorporation into observing modes, which will enable PSFs of higher quality and stability during science observations.

Portable quantitative phase microscope for material metrology and biological imaging

Quantitative phase microscopy (QPM) has emerged as an important tool for material metrology and biological imaging. For broader adoption in those applications, we have proposed and demonstrated a new portable off-axis QPM method, which works in both transmission and reflection modes to meet different sample measurement requirements. The temporal and spatial sensitivities of our system, as quantified by optical path-length difference values, are 0.65 nm and 1.04 nm, respectively. To demonstrate its applicability for a wide range of applications, we deployed our system for profiling transistor gold electrode samples, observing red blood cell membrane fluctuations, imaging living cells flowing in a microfluidic chip, etc. Our portable QPM system has a low-cost design and involves a simple and robust phase-retrieval algorithm that we envision will allow for broader deployment at different environmental settings, including in resource-limited sites and integration with other metrology or imaging modalities.

Comparison of DEKA Arm and Body-Powered Upper Limb Prosthesis Joint Kinematics

ObjectivesTo study the effects of advancements in upper-limb prosthesis technology on the user through biomechanical analyses at the joint level to quantitatively examine movement differences of individuals using an advanced upper-limb device, the DEKA Arm, and a conventional device, a body-powered Hosmer hook. DesignClinical measurement. SettingLaboratories at the United States Food and Drug Administration. ParticipantsConvenience sample of participants (N=14) with no upper limb disability or impairment. InterventionsAll participants were trained on either an upper limb body-powered (n=6) or DEKA Arm (n=8) bypass device. Main Outcome MeasuresParticipants completed the Jebsen-Taylor Hand Function Test (JHFT) and targeted Box and Blocks Test within a motion capture framework. Task completion times and joint angle trajectories for each degree of freedom of the right elbow, right shoulder, and torso were collected and analyzed for range of motion, mean angle, maximum angle, and angle path length during each task. ResultsSignificant differences between devices were observed across metrics in at least one task for each degree of freedom. Completion times were significantly higher for DEKA users (eg, 30.51±19.29s vs 9.30±1.44s) for JHFT–simulated feeding. Some kinematic measures, such as angle path length, were significantly lower in DEKA users, with the greatest difference in the right elbow flexion path length during JHFT–Page Turning (0.29±0.14 units vs 0.11±0.04 units). ConclusionsResults from this work elucidate the effect of the device on the user’s movement approach and performance, as well as emphasizing the importance of capturing movement quality into the assessment of function for advanced prosthetic technology to fully understand and evaluate potential benefits.

A Novel Cooperative Path Planning for Multirobot Persistent Coverage in Complex Environments

In this paper, a new path planning algorithm is developed to address the problem of persistent and cooperative coverage using a group of robots in a complex environment. Previous works have mainly used geometric division to achieve collaborative coverage search, but ignored the environmental complexity and the path length difference of each robot. In contrast, this paper presents a novel strategy for multi-robot persistent coverage, which aims to obtain more equal coverage route for each robot while guaranteeing both the obstacle avoidance and the minimization of the coverage period. The strategy first deploys the sensors in the target region to satisfy coverage requirements. Then it classifies the sensor points by improved k-means clustering which introducing the feedback mechanism to balance the length of each route. Finally, the approach solves the travelling salesman problem to obtain the closed route for each robot. The numerical simulations show that the proposed approach is feasible to implement the cooperative and persistent coverage in consideration of complicated obstacles, equilibrium of the path length, and the minimization of total cost.

Optical Interferometric Fringe Pattern-Incorporated Spectrum Calibration Technique for Enhanced Sensitivity of Spectral Domain Optical Coherence Tomography.

Depth-visualizing sensitivity can be degraded due to imperfect optical alignment and non-equidistant distribution of optical signals in the pixel array, which requires a measurement of the re-sampling process. To enhance this depth-visualizing sensitivity, reference and sample arm-channeled spectra corresponding to different depths using mirrors were obtained to calibrate the spectrum sampling prior to Fourier transformation. During the process, eight interferogram patterns corresponding to point spread function (PSF) signals at eight optical path length differences were acquired. To calibrate the spectrum, generated intensity points of the original interferogram were re-indexed towards a maximum intensity range, and these interferogram re-indexing points were employed to generate a new lookup table. The entire software-based process consists of eight consecutive steps. Experimental results revealed that the proposed method can achieve images with a high depth-visualizing sensitivity. Furthermore, the results validate the proposed method as a rapidly performable spectral calibration technique, and the real-time images acquired using our technique confirm the simplicity and applicability of the method to existing optical coherence tomography (OCT) systems. The sensitivity roll-off prior to the spectral calibration was measured as 28 dB and it was halved after the calibration process.

MP47-07 MOTION ANALYSIS TO PROMOTE UNDERSTANDING OF LAPAROSCOPIC SURGERY-DEXTERITY AND OBJECTIVE ASSESSMENT-BASED SIMULATION TRAINING

You have accessJournal of UrologySurgical Technology & Simulation: Training & Skills Assessment II (MP47)1 Apr 2020MP47-07 MOTION ANALYSIS TO PROMOTE UNDERSTANDING OF LAPAROSCOPIC SURGERY-DEXTERITY AND OBJECTIVE ASSESSMENT-BASED SIMULATION TRAINING Takashige Abe*, Koki Ebina, Madoka Higuchi, Jun Furumido, Naoya Iwahara, Masafumi Kon, Kiyohiko Hotta, Shunsuke Komizunai, Yo Kurashima, Hiroshi Kikuchi, Ryuji Matsumoto, Takahiro Osawa, Sachiyo Murai, Atsushi Konno, and Nobuo Shinohara Takashige Abe*Takashige Abe* More articles by this author , Koki EbinaKoki Ebina More articles by this author , Madoka HiguchiMadoka Higuchi More articles by this author , Jun FurumidoJun Furumido More articles by this author , Naoya IwaharaNaoya Iwahara More articles by this author , Masafumi KonMasafumi Kon More articles by this author , Kiyohiko HottaKiyohiko Hotta More articles by this author , Shunsuke KomizunaiShunsuke Komizunai More articles by this author , Yo KurashimaYo Kurashima More articles by this author , Hiroshi KikuchiHiroshi Kikuchi More articles by this author , Ryuji MatsumotoRyuji Matsumoto More articles by this author , Takahiro OsawaTakahiro Osawa More articles by this author , Sachiyo MuraiSachiyo Murai More articles by this author , Atsushi KonnoAtsushi Konno More articles by this author , and Nobuo ShinoharaNobuo Shinohara More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000000902.07AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: Based on the recent widespread use of laparoscopic surgery, working-hour restrictions, and ethical considerations, there is a growing need for an efficient simulation training program for laparoscopic surgery. Our aim was to promote understanding of the dexterity of laparoscopic surgery using a motion tracking system and develop an objective assessment-based simulation training program in a wet lab. METHODS: Participants performed lymphadenectomy around the aorta, dividing encountered mesenteric vessels after applying Hem-o-locks (task 1), and renal parenchymal closure (task 2: suturing only, task 3: suturing and tying), using swine cadaveric organs (Figures 1a and 1b). The optical based motion capture (Mocap) system that we newly developed was utilized to capture forceps movements (Figure 1c). Briefly, infrared reflective marker sets with an individual arrangement pattern were attached to handles of grasping forceps, scissors forceps, a clip applier, and needle holders (Figure 1d). Mocap, which consisted of 6 infrared cameras, simultaneously tracked the movements of multiple surgical instruments during a series of training steps. The tip movements were calculated based on the positional relationship between the tip and handle. Measurements were compared according to participants’ surgical experiences (experts: >50 laparoscopic surgeries, intermediates: 10-49, novices: 0-9). RESULTS: A total of 15 experts, 12 intermediates, and 18 novices participated in the training. In task 1, there were significant differences in the path length of grasping forceps (Kruskal Wallis test, p<0.001), scissors forceps (p<0.001), and a clip applier (p<0.035) among the three groups, showing economic motions in experts (Figure 1e and 1f, representative samples). Similar results were observed in tasks 2 and 3. CONCLUSIONS: Our novel Mocap system recognized the difference in path length of multiple surgical instruments during a series of surgical flow according to the skill level. We are now analyzing other parameters, including speed, acceleration, and jerk. Our results strongly show the possibility of digitizing laparoscopic surgical skills and a novel surgical simulation program whereby trainees are able to immediately receive objective feedback during wet lab training. Source of Funding: KAKENHI © 2020 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 203Issue Supplement 4April 2020Page: e686-e686 Advertisement Copyright & Permissions© 2020 by American Urological Association Education and Research, Inc.MetricsAuthor Information Takashige Abe* More articles by this author Koki Ebina More articles by this author Madoka Higuchi More articles by this author Jun Furumido More articles by this author Naoya Iwahara More articles by this author Masafumi Kon More articles by this author Kiyohiko Hotta More articles by this author Shunsuke Komizunai More articles by this author Yo Kurashima More articles by this author Hiroshi Kikuchi More articles by this author Ryuji Matsumoto More articles by this author Takahiro Osawa More articles by this author Sachiyo Murai More articles by this author Atsushi Konno More articles by this author Nobuo Shinohara More articles by this author Expand All Advertisement PDF downloadLoading ...

The resolution of the MIEZE setup on the longitudinal neutron resonance spin-echo spectrometer at CMRR

A longitudinal neutron resonance spin echo (L-NRSE) spectrometer combined with a MIEZE (modulated intensity with zero effort) configuration will be constructed at the C33 beam port at China Mianyang Research Reactor (CMRR) . In the MIEZE mode, the analyzer is placed in front of the sample, and between the sample and the detector there is no other optical device. The MIEZE signal is sensitive to the neutron path length differences from the sample to the detector. In this work, we have analytically studied the effects of sample geometry, detector thickness, and experimental setup on the resolution function.

Cellular-resolution in vivo tomography in turbid tissue through digital aberration correction

Noninvasive tomographic imaging of cellular processes in vivo may provide valuable cytological and histological information for disease diagnosis. However, such strategies are usually hampered by optical aberrations caused by the imaging system and tissue turbidity. State-of-the-art aberration correction methods require that the light signal be phase stable over the full-field data acquisition period, which is difficult to maintain during dynamic cellular processes in vivo. Here we show that any optical aberrations in the path length difference (OPD) domain can be corrected without the phase stability requirement based on maximum intensity assumption. Specifically, we demonstrate a novel optical tomographic technique, termed amplitude division aperture synthesis optical coherence tomography (ADAS-OCT), which corrects aberrations induced by turbid tissues by physical aperture synthesis and simultaneously data acquisition from sub-apertures. Even with just two sub-apertures, ADAS-OCT enabled in vivo visualization of red blood cells in human labial mucosa. We further demonstrated that adding sub-apertures could significantly scale up the aberration correction capability. This technology has the potential to impact a number of clinical areas where noninvasive examinations are preferred, such as blood count and cancers detection.

Enhanced spectral resolution for broadband coherent anti-Stokes Raman spectroscopy.

The spectral resolution of broadband Fourier-transform coherent anti-Stokes Raman spectroscopy is limited by the maximum optical path length difference that can be scanned within a short time in an interferometer. However, alternatives to the Fourier transform exist which can bypass this limitation with certain assumptions. We apply one such approach to broadband coherent Raman spectroscopy using interferometers with a short delay line (low Fourier spectral resolution) and large delay line (high Fourier spectral resolution). With this method, we demonstrate that broadband coherent Raman spectroscopy of closely spaced vibrational bands is possible using a short delay line interferometer with comparable spectral resolution to the longer delay line instrument. We discuss how this approach may be particularly useful for more complex Raman spectra, such as those measured from biological samples.

Band-Limited Reference-Free Speckle Spectroscopy: Probing the Fluorescent Media in the Vicinity of the Noise-Defined Threshold

A method of reference-free speckle spectroscopy based on the statistical analysis of intensity spatial fluctuations of the spectrally-selected multiple-scattered fluorescence radiation is examined in the case of the finite-band spectral selection of fluorescence light emitted by the laser-pumped random medium, and detection conditions far from the ideal case. Intensity fluctuations are recorded during point-to-point scanning of the surface of a random multiple-scattering medium, which is characterized by the dependences of the second- and third-order statistical moments of intensity on the wavelength of detected spectrally selected light. In turn, the statistical moments of intensity fluctuations are determined by the average propagation path of fluorescent radiation in the medium. This makes it possible to analyze the features of the light-medium interactions at a scale of the order of the transport mean free path of radiation propagation in the medium. Depending on the spectral selection conditions, the method is applicable for characterizing micro- or nano-structured fluorescent layers with thicknesses from tens of micrometers to several millimeters. In the examined case, the finite-band spectral selection results in the values of coherence length of the detected fluorescence radiation compared with the ensemble-averaged absolute value of the path-length difference between the stochastically interfering and spectrally selected partial contributions to the fluorescence field. In addition, non-ideal detection conditions (usage of a multimode optical fiber in the light-collecting unit) cause additional strong damping of the detected speckle intensity fluctuations. These factors lead to a remarkable suppression of spatial fluctuations of the fluorescence intensity in the course of spatially- and spectrally-resolved surface scanning of the laser-pumped probed random medium. Nevertheless, with appropriate procedures of the intrinsic noise reduction and data correction, the obtained spectral dependencies of the normalized third-order statistical moment of the band-limited fluorescence intensity clearly indicate the fluorescence propagation features in the probed multiple-scattering random media (such as a strong influence of the scattering strength and multiple self-absorption–re-emission events on the average propagation path of light in the medium).The possibilities of noise reduction and data correction in the case of applying the band-limited reference-free spectroscopic instrumentation with low spectral and spatial resolution are illustrated by the experimental results obtained using the Rhodamine-6G-doped and continuous wave (CW)-laser-pumped layers of the densely packed titania and silica particles.