Intracavity Measurement Sensitivity Enhancement without Runaway Noise

A method to increase the sensitivity of an intracavity differential phase measurement that is not made irrelevant by a larger increase of noise is explored. By introducing a phase velocity feedback by way of a resonant dispersive element in an active sensor in which two ultrashort pulses circulate, it is shown that the measurement sensitivity is elevated without significantly increasing the Petermann excess noise factor. This enhancement technique has considerable implications for any optical phase based measurement; from gyroscopes and accelerometers to magnetometers and optical index measurements. Here we describe the enhancement method in the context of past dispersion enhancement studies including the recent work surrounding non-Hermitian quantum mechanics, justify the method with a theoretical framework (including numerical simulations), and propose practical applications.

Electric Transverse Emissivity of Sinusoidal Surfaces Determined by a Differential Method: Comparison with Approximation of Geometric Optics

We present in this paper a numerical study of the validity limit of the optics geometrical approximation in comparison with a differential method which is established according to rigorous formalisms based on the electromagnetic theory. The precedent studies show that this method is adopted to the study of diffraction by periodic rough surfaces. For periods much larger than the wavelength, the mechanism is analog to what happens in a cavity where a ray is trapped and undergoes a large number of reflections. For gratings with a period much smaller than the wavelength, the roughness essentially behaves as a transition layer with a gradient of the optical index. Such a layer reduces the reflection there by increasing the absorption. The code has been implemented for TE polarization. We determine by the two methods such as differential method and the optics geometrical approximation the emissivity of gold and tungsten cylindrical surfaces with a sinusoidal profile, for a wavelength equal to 0.55 microns. The obtained results for a fixed height of the grating allowed us to delimit the validity domain of the optic geometrical approximation for the treated cases. The emissivity calculated by the differential method and that given on the basis of the homogenization theory are satisfactory when the period is much smaller than the wavelength.

Optical Classification of Lower Amazon Waters Based on In Situ Data and Sentinel-3 Ocean and Land Color Instrument Imagery

Optical water types (OWTs) were identified from an in situ dataset of concomitant biogeochemical and optical parameters acquired in the Amazon River and its tributaries, in the Lower Amazon region, at different hydrological conditions from 2014 to 2017. A seasonal bio-optical characterization was performed. The k-means classification was applied to the in situ normalized reflectance spectra (rn(λ)), allowing the identification of four OWTs. An optical index method was also applied to the rn(λ) defining the thresholds of the OWTs. Next, level-3 Sentinel-3 Ocean and Land Color Instrument images representative of the seasonal discharge conditions were classified using the identified in situ OWTs as reference. The differences between Amazon River and clearwater tributary OWTs were dependent on the hydrological dynamics of the Amazon River, also showing a strong seasonal variability. Each OWT was associated with a specific bio-optical and biogeochemical environment assessed from the corresponding absorption coefficient values of colored dissolved organic matter (aCDOM) and particulate matter (ap), chlorophyll-a and suspended particulate matter (SPM) concentrations, and aCDOM/ap ratio. The rising water season presented a unique OWT with high SPM concentration and high relative contribution of ap to total absorption compared to the other OWTs. This bio-optical characterization of Lower Amazon River waters represents a first step for developing remote sensing inversion models adjusted to the optical complexity of this region.

Optical System for the Transit Spectral Observation of Exoplanet-Atmosphere Characteristics

Optical instrumentation with reliable performance is essential for the research of exoplanet atmosphere characteristics. However, due to long distances and weak signals, exoplanets are difficult to be imaged by traditional optical systems. To this end, a novel optical system based on transit spectroscopy is proposed in this paper. On the basis of the principle of the transit-spectroscopy method and the astronomical parameters of observed targets, the optional parameter ranges of a dedicated optical system are analyzed. The transit signal-to-noise ratio (SNR) is introduced for the determination of telescope aperture and throughput. Furthermore, an example of the optical system with a space telescope and spectrometer is proposed according to the above optical index, which is proven to meet the performance requirements. The optical system is required to cover the wavelength of 0.5–8 m and the field of view (FOV) of 27.9′′ within the diffraction limit. The collecting aperture should be greater than 2 m, and spectral resolutions of two spectrometer channels should approximately be 100 (2–4 m) and 30 (4–8 m). The point-spread function (PSF) of each channel at the minimal wavelength should cover 2 pixels. The telescope and dichroic system provide diffraction-limited input beams with the required aperture, FOV, and wavelength for the spectrometer slits. The simulation results of the optical system show that the spectral resolutions of the dual-channel spectrometer were 111–200 and 43–94. The image points of the spectrometer in each wavelength were smaller than the Airy spot within the slit FOV, and the full width at half-maximum (FWHM) of PSF at λmin provided 2 pixels of 18 m sampling. The feasibility of the demonstrated optical parameters is proven by the design.

Longitudinal Impact of Physical Activity on Brain Pulsatility Index and Cognition in Older Adults with Cardiovascular Risk Factors: A NIRS Study

Recent studies have shown that optical indices of cerebral pulsatility, including cerebral pulse amplitude, are linked to cerebrovascular health. A chronically higher cerebral pulsatility is associated with cognitive decline. Although it is widely known that regular physical activity improves cognitive functions, little is known about the association between physical activity and the optical index of cerebral pulsatility. This study assessed the impact of 12 months of regular physical activity on the changes in the optical index of cerebral pulsatility and explored its association with cognition. A total of 19 older adults (aged 59–79 years) with cardiovascular risk factors (CVRF) completed the study. Low-intensity, short-duration walking as a brief cardiovascular challenge was used to study the impact of regular physical activity on post-walking changes in cerebral pulsatility index. The participants walked on a gym track while a near-infrared spectroscopy (NIRS) device recorded hemodynamics data from the frontal and motor cortex subregions. Our data indicated that 12 months of physical activity was associated with lower global cerebral pulse amplitude, which was associated with higher cognitive scores in executive functions. Further, the global cerebral pulsatility index was reduced after short-duration walking, and this reduction was greater after 12 months of regular physical activity compared with the baseline. This may be an indication of improvement in cerebrovascular response to the cardiovascular challenge after regular physical activity. This study suggests that 12 months of physical activity may support cognitive functions through improving cerebral pulsatility in older adults with CVRF.

A novel digital imaging method for measuring cashmere color and its application

The quality of cashmere, such as color and length, determines its price and application. In the current cashmere inspection system, color and length are tested by visual assessment, which is a subjective, time- and labor-consuming process. Herein, the goal of this research is to develop a new method of testing cashmere color using image analysis, and to study the application of color in length measurement. During the color measurement, cashmere was prepared under two sample placement methods, and color features including RGB, XYZ and Lab obtained by the new method were compared with the standard. The calculation method of optical index used in length testing was determined based on theoretical and experimental analysis. Experiments show that fixed weight and pressure are suited for cashmere color measurement. In RGB space, the correlation coefficients ( R2) between the two devices were calculated and were 0.990, 0.995 and 0.996 for parameters R, G and B, respectively. Good agreement also exhibited in XYZ space, with R2 equal to 0.994, 0.996 and 0.999 for X, Y and Z, respectively. This confirmed the accuracy of the proposed color measurement method in RGB and XYZ space. Finally, an accurate fibrogram was obtained by the proposed conversion model for calculating optical index from color values, which is the key curve to testing cashmere length. This study emphasis on methodological aspects and the results acquired are regarded as preliminary, as the experiments studied compose the first stage of research on the exploration of the application of image analysis on cashmere color measurement.

Monitoring the Organic Matter Quality Highlights the Ways in Which Organic Matter Is Removed from Wetland Soil

It has long been considered that ferric phases stabilize organic matter (OM) in soils. Temporarily waterlogged soils, in which Fe is submitted to regular reductive solubilization and oxidizing precipitation, have often been used to study these processes. However, few studies have been interested in the evolution of the OM quality under such conditions. We therefore experimentally investigated the impact of a redox cycle on the quality of the dissolved organic matter (DOM) from wetland soil. The DOM quality was monitored using a combination of analyses run on the elements (%C, %N, C/N), isotopes (δ15N, δ13C), optical index (specific UV absorbance at 254 nm), and fluorescence indexes (FI, HIX, BIX). In addition, the cation and anion concentrations were also determined in the soil solutions throughout the experiment. As classically demonstrated, OM is solubilized as terrestrial aromatic molecules in the first stage of the reducing period, and then as nonaromatic molecules until the end of the reduction, in response to the dissimilatory reductive dissolution of Fe-oxyhydroxides in the soil. More interestingly, we demonstrate that the reintroduction of O2 involves significant lysis of reducing bacterial cells involving the production of small labile organic carbon which represents a significant pathway for OM degradation. Moreover, in response to the physical constraints, the newly formed Fe-OM precipitates produce small aggregates rich in aromatic OM that are expected to disseminate in the environment, representing a second significant way to remove OM.