Cavity-enhanced direct frequency comb spectroscopy

Cavity-enhanced direct frequency comb spectroscopy combines broad spectral bandwidth, high spectral resolution, precise frequency calibration, and ultrahigh detection sensitivity, all in one experimental platform based on an optical frequency comb interacting with a high-finesse optical cavity. Precise control of the optical frequency comb allows highly efficient, coherent coupling of individual comb components with corresponding resonant modes of the high-finesse cavity. The long cavity lifetime dramatically enhances the effective interaction between the light field and intracavity matter, increasing the sensitivity for measurement of optical losses by a factor that is on the order of the cavity finesse. The use of low-dispersion mirrors permits almost the entire spectral bandwidth of the frequency comb to be employed for detection, covering a range of ~10% of the actual optical frequency. The light transmitted from the cavity is spectrally resolved to provide a multitude of detection channels with spectral resolutions ranging from a several gigahertz to hundreds of kilohertz. In this review we will discuss the principle of cavity-enhanced direct frequency comb spectroscopy and the various implementations of such systems. In particular, we discuss several types of UV, optical, and IR frequency comb sources and optical cavity designs that can be used for specific spectroscopic applications. We present several cavity-comb coupling methods to take advantage of the broad spectral bandwidth and narrow spectral components of a frequency comb. Finally, we present a series of experimental measurements on trace gas detections, human breath analysis, and characterization of cold molecular beams.Comment: 36 pages, 27 figure

The effects of moisture and micro-structural modifications in drying mortars on vibration-based NDT methods

In this paper, we investigate the utility of vibration-based NDT tests to detect the subtle microstructural modifications and cracking damage in Portland cement mortars subjected to oven drying treatment. Both linear (resonant mode frequency and damping) and nonlinear (nonlinear hysteretic behavior) vibration test data are reported, collected from samples having a range of water to cement ratios and at two different aggregate contents. All test data are affected by the drying treatments, but it appears that the resonant mode frequency response is dominated by the reduction in internal moisture content with drying and changing aggregate cement ratio of the mixture. On the other hand, the linear mode damping, and more so the nonlinear hysteretic parameter, are more influenced by the microstructural modification and cracking damage caused by drying. In particular it appears that the nonlinear hysteretic parameter is very sensitive to internal damage and microstructural modifications caused by oven drying, but not notably sensitive to pore moisture content, and water to cement and aggregate to cement ratios. (C) 2015 Elsevier Ltd. All rights reserved.The authors want to acknowledge the financial support of the Ministerio de Economia y Competitividad (MINECO), Spain, and FEDER funding (Ondacem Project: BIA 2010-19933). J.N. Eiras wants to acknowledge the financial support provided by Ministerio de Economia y Competitividad (MINECO), Spain, grant BES-2011-044624 and grants EEBB I-13-06609, and EEBB-I-14-08993 for supporting extended visits to the University of Illinois.Eiras Fernández, JN.; Popovics, JS.; Borrachero Rosado, MV.; Monzó Balbuena, JM.; Paya Bernabeu, JJ. (2015). The effects of moisture and micro-structural modifications in drying mortars on vibration-based NDT methods. Construction and Building Materials. 94:565-571. https://doi.org/10.1016/j.conbuildmat.2015.07.078S5655719

The Atacama Cosmology Telescope: A Catalog of >4000 Sunyaev–Zel’dovich Galaxy Clusters

We present a catalog of 4195 optically confirmed Sunyaev–Zel'dovich (SZ) selected galaxy clusters detected with signal-to-noise ratio >4 in 13,211 deg2 of sky surveyed by the Atacama Cosmology Telescope (ACT). Cluster candidates were selected by applying a multifrequency matched filter to 98 and 150 GHz maps constructed from ACT observations obtained from 2008 to 2018 and confirmed using deep, wide-area optical surveys. The clusters span the redshift range 0.04 1 clusters, and a total of 868 systems are new discoveries. Assuming an SZ signal versus mass-scaling relation calibrated from X-ray observations, the sample has a 90% completeness mass limit of M500c > 3.8 × 1014 M⊙, evaluated at z = 0.5, for clusters detected at signal-to-noise ratio >5 in maps filtered at an angular scale of 2farcm4. The survey has a large overlap with deep optical weak-lensing surveys that are being used to calibrate the SZ signal mass-scaling relation, such as the Dark Energy Survey (4566 deg2), the Hyper Suprime-Cam Subaru Strategic Program (469 deg2), and the Kilo Degree Survey (825 deg2). We highlight some noteworthy objects in the sample, including potentially projected systems, clusters with strong lensing features, clusters with active central galaxies or star formation, and systems of multiple clusters that may be physically associated. The cluster catalog will be a useful resource for future cosmological analyses and studying the evolution of the intracluster medium and galaxies in massive clusters over the past 10 Gyr

Co-limitation towards lower latitudes shapes global forest diversity gradients

The latitudinal diversity gradient (LDG) is one of the most recognized global patterns of species richness exhibited across a wide range of taxa. Numerous hypotheses have been proposed in the past two centuries to explain LDG, but rigorous tests of the drivers of LDGs have been limited by a lack of high-quality global species richness data. Here we produce a high-resolution (0.025° × 0.025°) map of local tree species richness using a global forest inventory database with individual tree information and local biophysical characteristics from ~1.3 million sample plots. We then quantify drivers of local tree species richness patterns across latitudes. Generally, annual mean temperature was a dominant predictor of tree species richness, which is most consistent with the metabolic theory of biodiversity (MTB). However, MTB underestimated LDG in the tropics, where high species richness was also moderated by topographic, soil and anthropogenic factors operating at local scales. Given that local landscape variables operate synergistically with bioclimatic factors in shaping the global LDG pattern, we suggest that MTB be extended to account for co-limitation by subordinate drivers