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The features of the formation of the spatial-energy profiles (SEP) of the visibility zones for two methods of observation (MO) are compared by numerical simulation taking the energy of the noise threshold Ent into account. It is confirmed for both MOs that the relationship previously used in the literature in which the length of the visibility zone (VZ) is uniquely determined by the sum of the lengths of the illumination and strobe (photodetector exposure) pulses is valid provided that the maximum value of the signal contrast attained within the confines of the VZ is close to unity. For the second MO the transformation of the SEP for relatively short working distances into a short convex asymmetric peak at half height, for which the maximum in the limiting case is shifted to the beginning of the VZ, is studied in detail. This is explained by the predominant influence of the so-called spatial factor on the formation of the SEP. Despite some spatial shift of the SEP relative to one another for the first and second MO in the case when the durations of the illumination and strobe pulses are unequal, the maximum values of the recorded signals and their contrast, as well as the length of the visibility zone for both MO for the typical parameters in most cases are practically the same. The particular case when the duration of the illumination pulse is shorter than that of the strobe pulse, the experimentally obtained SEPs of the VZ for the first and second MO confirm the results of the calculations. [ABSTRACT FROM AUTHOR]

The regularities of the formation of the spatial-energy profile of the visibility zone of active-pulse vision systems are studied numerically with the noise threshold taken into account. Consideration is limited to the case of objects with a known distance to them, which are observed by moving the visibility zone in their vicinity. It is shown that the equation used previously in the literature, where the length of the visibility zone is uniquely determined by the sum of the lengths of the laser illumination Δtlas and strobe ΔtPhD pulses, is correct for relatively small distances to the objects, where the maximum (peak) values of the signal contrast are close to unity. As the distance is increased, the length of the visibility zone is reduced. When the duration of the illumination pulses Δtlas (beginning with the minimum possible value) and the simultaneous fulfillment of the condition Δtlas + ΔtPhD =const is met the length of the visibility zone increases relatively rapidly in the zone where the maximum values of the signal Emax increase. In the range corresponding to a reduction in Emax, the length of the visibility zone asymptotically approaches the previously known limiting possible value. For the first time a decrease in the length of the visibility zone for fixed durations of the illumination and strobe pulses is confirmed experimentally with increasing distances to the object. [ABSTRACT FROM AUTHOR]

Features of the formation of the spatial-energetic profile of the visibility zone of active-pulse vision systems (APVS) on inclined paths with diffuse reflection of vertical and horizontally oriented objects are studied numerically. It is proposed to take into account the existence of a noise threshold in APVS and to introduce the concept of signal contrast to bring the results of numerical modeling of the potential capabilities of APVS closer to experimental realization. It is shown that the previously used assumption, where the length of the visibility zone is uniquely determined by the sum of the lengths of the illumination and strobe pulses, is valid where the signal contrast is close to unity. For the typical parameters examined here, the limiting range of the observation of vertical objects is~3.8 times higher than for horizontal objects. When the height of the APVS device is increased, the signal for vertical objects decreases monotonically and for horizontal objects this dependence has a maximum. A decrease in the length of the visibility zone is confirmed experimentally for the first time for illumination and strobe pulses of fixed durations with increasing delay distance. [ABSTRACT FROM AUTHOR]

We report a high-performance pulsed optically pumped (POP) Rb clock based on a novel magnetron-type microwave cavity. The cavity has a volume of 30 mL, enabling a highly homogenous microwave field distribution. With the laser frequency tuning to the ground-state hyperfine level ${F}= {2}$ of the ${D}_{{2}}$ line, we observe a Ramsey fringe contrast of 52% in terms of optical absorption detection. The resultant shot noise limit is estimated to be ${1.6} \,\times \, {10}^{-{14}}{\tau }^{-\text {1/2}}$. The clock frequency stability is measured as ${2.3}\,\times \, {10}^{-{13}}\tau ^{-\text {1/2}}$ (1–100 s), which is limited by the relative intensity noise of the light. [ABSTRACT FROM AUTHOR]

Abstract The coherent population trapping (CPT) phenomenon of atoms is used for high precision measurement of weak magnetic field. The sensitivity of the measurement is mainly affected by the resonance spectrum characteristics when this phenomenon occurs. Signal quality factor is defined to represent the characteristics of the CPT resonance signal. Its variation with temperature of the atomic chamber is analyzed and compared with signal contrast. Results show that signal quality factor and signal contrast offer different optimal working temperature which corresponding to the maximum value. The optimal temperature proposed by the signal quality factor is always lower and it makes the magnetic field measurement system to obtain a higher sensitivity. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In the displacement measurement of the wafer stage in lithography machines, signal quality is affected by the relative angular position between the encoder head and the grating. In this study, a two-degree-of-freedom fiber-coupled heterodyne grating interferometer with large operating range of rotation is presented. Fibers without fiber couplers are utilized to receive the interference beams for high-contrast signals under the circumstances of large angular displacement and ZEMAX ray tracing software simulation and experimental validation have been carried out. Meanwhile, a reference beam generated inside the encoder head is adopted to suppress the thermal drift of the interferometer. Experimental results prove that the proposed grating interferometer could realize sub-nanometer displacement measurement stability in both in-plane and out-of-plane directions, which is 0.246 nm and 0.465 nm of 3σ value respectively within 30 s.

Intermolecular multiple-quantum coherences (iMQCs) have been reported to offer a sensitivity to sample structure at a specific user-defined length scale down to the order of 10 μm. When assessing this novel contrast mechanism in controlled phantom experiments, we have observed three different mechanisms whereby residual single-quantum coherences (SQCs) arising from intense high spatial frequencies, stimulated echoes and strong spatially encoding gradients can produce significant changes in signal contrast at particular length scales. These changes which only appear when components arising from SQCs and iMQCs are both present in the detected signal, are similar to changes previously attributed to iMQCs alone. We demonstrate each mechanism by which these residual SQCs arise and describe methods for their suppression. [Copyright &y& Elsevier]

Lanthanide-doped upconversion nanoparticles (UCNPs) can convert two or more lower-energy near-infrared photons to a single photon with higher energy, which makes them particularly suitable for constructing nanoprobes with large imaging depth and minimal interference of autofluorescence and light scattering from biosamples. Furthermore, they feature excellent photostability, sharp and narrow emissions, and large anti-Stokes shift, which confer them the capability of long-period bioimaging and real-time tracking. In recent years, UCNPs-based nanoprobes (UC-nanoprobes) have been attracting increasing interest in biological and medical research. Signal contrast, the ratio of signal intensity after and before the reaction of the probe and target, is the determinant factor of the sensitivity of all reaction-based probes. This progress report presents the methods of constructing UC-nanoprobes, with a focus fixed on recent strategies to improve the signal contrast, which have kept on promoting the bioapplication of this type of probe., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In the displacement measurement of the wafer stage in lithography machines, signal quality is affected by the relative angular position between the encoder head and the grating. In this study, a two-degree-of-freedom fiber-coupled heterodyne grating interferometer with large operating range of rotation is presented. Fibers without fiber couplers are utilized to receive the interference beams for high-contrast signals under the circumstances of large angular displacement and ZEMAX ray tracing software simulation and experimental validation have been carried out. Meanwhile, a reference beam generated inside the encoder head is adopted to suppress the thermal drift of the interferometer. Experimental results prove that the proposed grating interferometer could realize sub-nanometer displacement measurement stability in both in-plane and out-of-plane directions, which is 0.246 nm and 0.465 nm of 3σ value respectively within 30 s. [ABSTRACT FROM AUTHOR]