Reflection Configuration Research Articles

Direct-imaging DOEs for high-NA multi-spot confocal microscopy

Abstract Diffractive lens arrays with overlapping apertures can produce spots with high numerical apertures (NAs). Such diffractive optical elements (DOEs) can replace high-NA objectives and measure a large area with high resolution in transmission microscopes. However, in reflection microscopes for surface measurements, the axial resolution is still limited by the objectives. Direct-imaging DOEs are proposed to solve the problem. They can perform high-NA multi-spot measurement in reflection configurations in both lateral and axial directions. Experiments demonstrate a lateral non-vanishing contrast up to 1448 lp/mm and an axial response on a plane mirror with a full width at half maximum (FWHM) of 2.24 μm.

Differentiable model-based adaptive optics with transmitted and reflected light.

Aberrations limit optical systems in many situations, for example when imaging in biological tissue. Machine learning offers novel ways to improve imaging under such conditions by learning inverse models of aberrations. Learning requires datasets that cover a wide range of possible aberrations, which however becomes limiting for more strongly scattering samples, and does not take advantage of prior information about the imaging process. Here, we show that combining model-based adaptive optics with the optimization techniques of machine learning frameworks can find aberration corrections with a small number of measurements. Corrections are determined in a transmission configuration through a single aberrating layer and in a reflection configuration through two different layers at the same time. Additionally, corrections are not limited by a predetermined model of aberrations (such as combinations of Zernike modes). Focusing in transmission can be achieved based only on reflected light, compatible with an epidetection imaging configuration.

Improving the width of lossy mode resonances in a reflection configuration D-shaped fiber by nanocoating laser ablation.

The full width at half maximum (FWHM) of lossy mode resonances (LMRs) in the optical spectrum depends on the homogeneity of the thin film deposited. In this Letter, a method for improving the FWHM is applied for an LMR generated by a D-shaped optical fiber in reflection configuration. For this purpose, three samples with different attenuation were deposited with DC sputtering thin films of SnO2-x, and a further controlled immersion of the samples in water was performed. A laser-cleaner method was used to improve the FWHM characteristics of one of the samples from 106 to 53 nm. This improvement can be applied to thin-film-based sensors where there is a problem with the inhomogeneity of the coating thickness. Moreover, with this technique, it was proved that a coated length of just 3-4 mm permits the generation of an LMR, with implications for the miniaturization of the final device.

In-cell infrared difference spectroscopy of LOV photoreceptors reveals structural responses to light altered in living cells

Proteins are usually studied in well-defined buffer conditions, which differ substantially from those within a host cell. In some cases, the intracellular environment has an impact on the mechanism, which might be missed by in vitro experiments. IR difference spectroscopy previously has been applied to study the light-induced response of photoreceptors and photoenzymes in vitro Here, we established the in-cell IR difference (ICIRD) spectroscopy in the transmission and attenuated total reflection configuration to investigate the light-induced response of soluble proteins in living bacterial cells. ICIRD spectroscopy on the light, oxygen, or voltage (LOV) domains of the blue light receptors aureochrome and phototropin revealed a suppression of the response of specific secondary structure elements, indicating that the intracellular environment affects LOV photoreceptor mechanisms in general. Moreover, in-cell fluorescence spectroscopy disclosed that the intracellular environment slows down the recovery of the light-induced flavin adduct. Segment-resolved ICIRD spectroscopy on basic-region leucine zipper (bZIP)-LOV of aureochrome 1a from the diatom Phaeodactylum tricornutum indicated a signal progression from the LOV sensor to the bZIP effector independent of unfolding of the connecting A'α-helix, an observation that stood in contrast to in vitro results. This deviation was recapitulated in vitro by emulating the intracellular environment through the addition of the crowding agent BSA, but not by sucrose polymers. We conclude that ICIRD spectroscopy is a noninvasive, label-free approach for assessing conformational changes in receptors in living cells at ambient conditions. As demonstrated, these near-native responses may deviate from the mechanisms established under in vitro conditions.

Morphodynamic response to extreme wave events of microtidal dissipative and reflective beaches

In this work, the morphodynamic response of microtidal dissipative and reflective beaches to extreme wave events generated by hurricanes and cold fronts in the Colombian Caribbean was established. Two sandy beaches were used as case studies, Bocagrande (Cartagena, Bolívar Department) (dissipative) and Costa Verde (Ciénaga, Magdalena Department) (intermediate–reflective). The numerical models SWAN and XBeach were used to investigate wave propagation during storm conditions for selected cases and to determine morphological changes on the two beaches. Both models were calibrated using hydrodynamic and bathymetric data obtained in field campaigns pre and post-cold fronts. The results of the numerical models satisfactorily represented the real conditions on both beaches. It was shown that regardless of beach configuration, whether dissipative or intermediate–reflective, erosive processes had a greater magnitude during cold fronts (March 2009 and December 2017) than under hurricanes conditions. Bocagrande beach is more exposed to extreme wave events, mainly due to its characteristic dissipative profile. Infragravity wave energy, fundamental in sediment transport dynamics, is not reflected on the beach front, but is dissipated along the swash zone and drags sediment to the sea. By contrast, Costa Verde shows conservative coastline retreats: its intermediate–reflective morphologic configuration played a transcendental role. Infragravity wave reflection on the beach front does not allow a longer water extension over dry areas in the swash zone under storms.

Evaluation of optical fibre sensors in the electrical domain

Abstract. Optical fibre sensors cover a wide range of applications. They offer versatile advantages including resilience to electromagnetic interference, biocompatibility and chemical resistivity. Even in environments with restricted accessibility, integration difficulties can be overcome by using radio-over-fibre (RoF) technology that allows a wireless read-out. Conventionally, optical fibre sensors are evaluated in the optical domain by analysing the amplitude or spectrum of either the transmitted or the reflected light. A novel approach is to feed a radio frequency-modulated laser into the optical sensor and carry out a full electrical analysis of the resulting radio frequency (RF) signal, which is changed by the sensor's characteristics. This method will be investigated in this paper for fibre Bragg grating-based and chirped fibre Bragg grating-based sensors in reflection and transmission configuration. Their applicability for this new evaluation scheme will be discussed. Subsequent studies may cover additional types of sensors and the testing of the novel evaluation method within an application-related scenario, including packaging.

Lithostratigraphy and Sequence Stratigraphy of Ultra-Deep E-Field, Eastern Niger Delta: Reservoir, Geological and Biostratigraphical Evidence

The ultra-deep offshore, eastern Niger Delta is marked by rapid, cyclic deposition of thick units of siliciclastic sediments ranging from deep marine to non-marine environments, deposited into rapidly subsiding sub-basins occurring along the slope of the continental margin. This rapid deposition resulted in thick third-order sequences and systems tracts. Patterns of deposition were analysed from seismic reflection configuration and well-log patterns. Lithofacies patterns critical for systems tract recognition were interpreted from well logs and tied to seismic sections where possible. Sediment accumulation plots were constructed and employed to interpret the location of stratigraphic condensation, key surfaces, diffuse boundaries between systems tracts and evaluate the significance of condensed sections. The origin of these condensed sections is caused by major allocyclic changes associated with transgression and shifting of the deltaic depocenter that fed the area. The regional change in condensation through time was interpreted as reflecting avulsion of the shallow marine sediment source. The compilation of sediment accumulation plots also showed a major increase in sedimentation approximately 2.4 Ma; caused by the influx of the prograding shallow marine sediments. Wells located in distal regions in this field are more condensed [steeper slope] than proximal locations. The resulting analyses of this study showed that the basin-floor fan has the highest rate of deposition and could be identified as a gentle slope in the line of sediment accumulation. In the distal regions of the field, TST’s are characterized by sediment starvation because most of the sediments are trapped in the proximal areas. The maximum flooding surfaces [MFS’s] were recorded in deep water as condensed sections. Secondary condensed sections were delineated and interpreted to have deposited above the top basin-floor fan surface [tbfs] and top slope fan surface [tsfs]. In addition to traditional first downhole occurrence biostratigraphy, the database also contains information on nannofossil abundance. The sands encountered in the reservoirs are correlatable indicating a relatively longer period of depositional cycle. Keywords : Lithostratigraphy, Sequence stratigraphy, Eustacy, Reservoir geology, Biostratigraphy, Ultra-deep Offshore, Eastern Niger Delta. DOI : 10.7176/JEES/10-7-06 Publication date :July 31st 2020

Self-referenced optical networks for remote interrogation of quasi-distributed fiber-optic intensity sensors

Abstract Different multiplexing techniques for passively addressing fiber-optic sensors and compensation schemes for overcoming the undesirable optical signal losses to provide self-referenced quasi-distributed sensing from intensity-based fiber-optic point sensors are revisited. Furthermore, a passive wavelength division multiplexing (WDM) network operating in reflective configuration with remote Radio-Frequency self-referenced fiber-optic intensity sensors with electro-optical configuration is proposed. Delay lines in the electrical domain provide more compact sensor-heads and easy-reconfigurable performance of the sensing points. The technique is analyzed following the Z-transform formalism and measurements validating the theoretical model are reported. There are two measurement parameters providing self-referenced remote interrogation for the sensing heads. The paper shows their experimental validation in a 2-sensor network based on tapered SMF micro-displacement sensors, testing sensor self-referencing as well as sensor crosstalk. Those results provide the background to extrapolate them to a quasi-distributed passive CWDM-based 16-sensor network at around 65 km of remote distance from the central office, with possible upgrade to a 25 km-long DWDM-based 48-sensor network.

Optical System Based on Multiplexed FBGs to Monitor Hand Movements

This contribution reports the development and characterization of an optical system based on parallel Fiber Bragg Gratings (FBGs) to monitor the movements of the wrist and fingers of a hand. The system consisted of a reflective configuration made of FBGs detecting the movements of the fingers and one more located on the wrist as a reference. All FBGs were multiplexed in order to collect the basic movements of the hand. Fibers were embedded in polydimethylsiloxane for protection and to give flexibility to the optical detection setup. Measurements of strain, angle and torsion were performed during the experiments, obtaining sensitivities up to 1.29 pm/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \varepsilon $ </tex-math></inline-formula> in strain and 64.23 pm/° in angle. Also, a study on the influence of a single sensor on the performance of the whole system was analyzed for a complete study of this proof of concept. The obtained results present a simple system that can be used to monitor the positions of the hand or for the rehabilitation of patients suffering from neuromotor or post-stroke diseases.

Towards Fingerprint Spoofing Detection in the Terahertz Range.

Spoofing attacks using imitations of fingerprints of legal users constitute a serious threat. In this study, a terahertz time domain spectroscopy (TDS) setup in a reflection configuration was used for the non-intrusive detection of fingerprint spoofing. Herein, the skin structure of the finger pad is described with a focus on the outermost stratum corneum. We identified and characterized five representative spoofing materials and prepared thin and thick finger imitations. The complex refractive index of the materials was determined in TDS in the transmission configuration. For dataset collection, we selected a group of 16 adults of various ages and genders. The reflection results were analyzed both in the time (reflected signal) and frequency (reflectivity) domains. The measured signals were positively verified with the theoretical calculations. The signals corresponding to samples differ from the finger-related signals, which facilitates spoofing detection. Thanks to deconvolution, we provide a basic explanation of the observed phenomena. We propose two spoofing detection methods, predefined time–frequency features and deep learning based. The methods achieved high true detection rates of 87.9% and 98.8%. Our results show that the terahertz technology can be successfully applied for spoofing detection with high detection probability.

Cylindrical IR-ATR Sensors for Process Analytics.

Infrared attenuated total reflection (ATR) spectroscopy is a common laboratory technique for the analysis of highly absorbing liquids and solids. However, in a process environment, maintaining a sufficient sample exchange and cleaning of the sensitive surface of the element is a crucial issue. An important industrial application is the measurement of isocyanate concentrations. Isocyanates are necessary for the fabrication of polyurethane materials and are among the chemicals with the highest production volume worldwide. For process applications, narrowband photometers or MEMS spectrometers are more appropriate than the use of bulky FTIR instruments frequently encountered in a laboratory environment. Toluene diisocyanate (TDI) and hexamethylene diisocyanate (HDI) concentrations are measured with a planar ATR photometer setup. Using a miniature Fabry–Perot interferometer (FPI), trace concentrations below 100 ppm (m/m) are detected. By employing an ATR element of the cylindrical shape, sensors can be realized with a smooth surface ideally suited for an automatic cleaning system in a process environment. A laboratory setup with sapphire tubes as ATR elements for incorporation in a liquid flow system is described. Reflection and transmission configurations were investigated. Measurements with acetonitrile as a less toxic substitute showed that with cylindrical ATR sensors’ detection limits for isocyanate concentrations below 100 ppm (m/m) are feasible.

In situ detection of gas chromatography analytes by active illumination with quantum cascade lasers

Gas chromatography (GC) is a staple analytical technique used to separate chemical mixtures (analytes) prior to identification with a hyphenated technique, such as mass spectrometry or Fourier transform infrared (IR) spectroscopy. Traditionally, analytes elute through the GC separation column where they are detected when they exit. We have developed a technique to perform in situ IR spectroscopy during the process of separating the analytes along the GC column. This is achieved by spin coating the stationary phase onto a germanium prism and actively probing the stationary phase in an attenuated total reflectance configuration with a quantum cascade laser.. The GC column is formed by pressing a molded epoxy lid, with grooves that form the tubular column, onto the stationary phase coated prism.

TiOxNy Thin Film Sputtered on a Fiber Ball Lens as Saturable Absorber for Passive Q-Switched Generation of a Single-Tunable/Dual-Wavelength Er-Yb Double Clad Fiber Laser.

The use of titanium oxynitride (TiOxNy) thin films as a saturable absorber (SA) element for generation of passive Q-switched (PQS) laser pulses, from a linear cavity Er-Yb double-clad fiber (EYDCF) laser, is demonstrated. Additionally, the deposition of the material as a thin film covering a fiber micro-ball lens (MBL) structure is reported for the first time. The TiOxNy coating is deposited by a direct current (DC) magnetron-sputtering technique. The MBL is inserted within the laser cavity in a reflection configuration, alongside a reflecting mirror. As a result, the coated fiber MBL simultaneously acts as a SA element for PQS laser pulses generation and as an interference filter for wavelength selection and tuning of the generated laser line. Tunable single-laser emission in a wavelength range limited by dual-wavelength laser generation at 1541.96 and 1547.04 nm is obtained. PQS laser pulses with a repetition rate from 18.67 to 124.04 kHz, minimum pulse duration of 3.57 µs, maximum peak power of 0.359 W, and pulse energy of 1.28 µJ were obtained in a pump power range from 1 to 1.712 W.

Seismic sedimentary characteristics and filling structure of the Upper Triassic Yanchang Formation, Ordos Basin, China

Following the analysis of cores, outcrops, well log, and seismic sections, we have studied the seismic reflection configuration and depositional history of the hydrocarbon-rich Yanchang Formation in the Ordos Basin. We divided the seismic reflection configurations into five types: subparallel reflection, parallel reflection, tangential progradational reflection, shingled progradational reflection, and chaotic reflection. Based on our study results, we concluded that the slopes exhibit differences in the different regions of the Ordos Basin during the sedimentary period of the Yanchang Formation: The slope with the largest gradient of approximately 10°–20° occurred in the southwestern basin, followed by the northwestern basin (with a slope of approximately 1.6°–3.3°), but the slope was relatively gentle in the northeastern basin (approximately 0.8°–1.2°). We also found that the paleocurrent direction of the basin mainly includes two directions: The paleocurrent direction of the southwest region is 186°–259°, which indicates the provenance came from the southwestern region, whereas the paleocurrent direction of the northeast region is 10°–79°, which indicates that the provenance came from the northeastern region. In addition, the Ordos Basin was under isostatic subsidence as a whole during this period, and its sedimentary infilling evolution underwent five stages: the initial depression, intense depression, progradational filling, uplifting and denudation, as well as shrinking and extinction stages, just corresponding with the Chang 10-Chang 9, the Chang 8-Chang 7, the Chang 6-Chang 4+5, the Chang 3-Chang 2, and the Chang 1 depositional age, respectively.

Oblique angle transient-reflectivity laser-scanning microscopy for mineral imaging in natural ores.

The microscopic arrangement of different minerals in ores is of high interest for mine planning, mineral processing and extractive metallurgy. Many economically important, naturally occurring minerals are highly absorbing semiconductors. To characterize these materials, we have implemented pump-probe laser scanning microscopy (LSM) in a two-lens reflective configuration that offers efficient collection of signal light by using a combination of galvanometer and sample stage scanning. We show that the short-time (∼10 ps) pump-probe response of a material allows us to distinguish economically important sulfide minerals.

Optimization of SERS Sensing With Micro-Lensed Optical Fibers and Au Nano-Film

We present the fabrication and characterization of optical fiber reflection probes based on surface-enhanced Raman scattering (SERS) and micro-lensed multimode fibers. For the SERS substrate, a nano-sphere lithography method is used. Comparison of SERS measurements with three different fiber probe configurations is presented. The proposed optimized structure shows a five times increase in SERS signal for dried Rhodamine 6G (R6G) and two times for aqueous R6G in comparison to a standard reflection configuration. Measurements of different concentrations of R6G in a water solution with an limit of detection (LOD) equal to 10−7 M are demonstrated.

Reflective plasmonic super-oscillatory metasurfaces with simultaneous phase and amplitude controls for sub-diffraction focusing

Optical super-oscillatory phenomena, coming from the delicate interference of the propagating light through an elaborate-designed structure, have been successfully applied to realize far-field focusing and imaging with a resolution beyond the diffraction limit. However, most reported super-oscillatory lenses only modulate either the amplitude or phase of the incident light. Here, a reflective plasmonic super-oscillatory metasurface (RSOM), made of aluminum-nanorods/glass-spacer-layer/aluminum-mirror, is proposed to simultaneously engineer a desired amplitude and phase profile of the incoming light and realize far-field sub-diffraction focusing. The used reflective configuration with a high polarization conversion can be helpful to concentrate more energy into the super-oscillatory spot. Sub-diffraction hotspots are further numerically verified and precisely formed at the preset plane. The compressed spot sizes for one RSOM are 0.666 and 0.714 times the diffraction limit along the x and y directions, respectively. The numerical results agree well with theoretical predictions. The novel complex amplitude control of the light field gives more degrees of freedom in manipulating the propagation of light and provides a better tradeoff among conflicting factors of a super-oscillatory field.

Sequence architecture and depositional evolution of Dongying Formation in steep slope zone of northern Liaodong Bay and its responses to tectonism

The sequence architecture and depositional evolution of Dongying Formation in the steep slope zone are mainly developed in response to tectonism. The comprehensive analysis of cores, wireline logs, and seismic volumes is employed to reveal the relationship among sequence architecture, depositional evolution, and tectonism. The results indicate that the whole Dongying Formation can be divided into three third‐order sequences based on regional unconformity along the basin margin and slope and its correlative conformity in the basin centre. In addition, seven fourth‐order sequences are further divided based on regression surfaces within third‐order sequences. The sequence architecture of different‐order sequences is discussed and revealed in terms of systems tracts, stratal thickness and distribution, and seismic reflections. Four genetic types of sedimentary facies including fan delta, sublacustrine fan, near‐shore subaqueous fan, and braided delta are identified according to core observations, stacking patterns of wireline logs, internal configuration, and external geometry of seismic reflections. The depositional evolution in Dongying Formation is related to tectonic intensity and tectonic evolution stage in the steep slope. The whole Dongying Formation is in the midst of a strike‐slip and rifting stage during its depositional period. When tectonic movements are intensively active, it is mainly characterized by fan delta and near‐shore subaqueous fan along the steep slopes and sublacustrine fan in the basin centre. However, the opposite case is dominated by fan delta and braided delta around and along the uplifts. In addition, the palaeogeomorphology and sediment supply also play an important role in controlling facies distributions in the steep slope zone. The subsidence rate resulted from tectonism controls the sequence architecture and depositional filling in terms of fault activities and accommodation space in the steep slope.

Terahertz diffractive structures for compact in-reflection inspection setup.

Two diffractive optical elements are used to create a compact raster THz scanning setup in reflective configuration. The first one focuses the radiation into the small focal spot on the sample, while the second one collects reflected radiation and focuses it on the detector. To assure small size of the setup and large apertures of optical elements, structures work in the off-axis geometry. Thus, the focal spot is formed 100 mm after and 60 mm below the optical axis of the element, which measures 75 mm in diameter. The designed iterative algorithm allows further minimization of these values.

Reflective Photoplethysmography Acquisition Platform With Monitoring Modules and Noninvasive Blood Pressure Calculation

Modularity is one of the most important aspects of the continuous development of a system. With a modular platform, it is possible to scale the functionalities, adding more features or keeping just the needed ones. A very robust and effective solution for the real-time monitoring problem is an automotive monitoring system whose architecture will be used as the base for a modular photoplethysmography (PPG) acquisition platform. The PPG acquisition platform uses the reflective configuration on the wrist for u-health applications to allow the medical data management of an individual anytime and anywhere. The acquisition platform is equipped with LED voltage control to capture a wave morphology without any interference from skin color, thickness of the fat layer, or stiffness from the subject’s artery walls. This article also provides a technique to obtain blood pressure (BP) in a noninvasive way, based only on the PPG signal with an initial calibration. We also study a technique to obtain the BP parameter, also with PPG and without calibration from an auxiliary device. Our results proved the success of the platform in capturing noninvasive BP calculation in real time, achieving the tolerance errors allowed by the Association for the Advancement of Medical Instrumentation (AAMI). The BP calculation without calibration by an auxiliary device showed promising results, but further studies are needed. Main contributions are the development of a modular human monitoring system based on PPG; improvements on the existing BP calculation algorithm based on PPG; and development of a BP estimation algorithm based on PPG, without calibration from an external device.