On-chip non-dispersive infrared CO2 sensor based on an integrating cylinder

In this paper, we propose a novel, miniaturized non-dispersive infrared (NDIR) CO2 sensor implemented on a silicon chip. The sensor has a simple structure, consisting of a hollow metallic cylindrical cavity along with access waveguides. A detailed analysis of the proposed sensor is presented. Simulation with 3D ray tracing shows that an integrating cylinder with 4 mm diameter gives an equivalent optical path length of 3 . 5 cm. The sensor is fabricated using Deep Reactive Ion Etching (DRIE) and wafer bonding. The fabricated sensor was evaluated by performing a CO2 concentration measurement, showing a limit of detection of ∼100 ppm. The response time of the sensor is only ∼2.8 s, due to its small footprint. The use of DRIE-based waveguide structures enables mass fabrication, as well as the potential co-integration of flip-chip integrated midIR light-emitting diodes (LEDs) and photodetectors, resulting in a compact, low-power, and low-cost NDIR CO2 sensor

Liquid Crystals on Ferroelectric Thin Films

Barium titanate (BTO) and lead zirconate titanate (PZT) are two of the most common ferroelectric materials used in applications. These two materials offer excellent dielectric, piezo-electric, electro-optic and pyro-electric properties. The excellent electro-optic properties of our PZT and BTO deposited thin films may lead to cheap and versatile ultra-fast electro-optic modulators on existing photonic platforms [1], such as the Si or the SiN nanophotonic platform. In this work however, we exploit the extremely high dielectric permittivity of PZT (in the order of 500 to 1000). The permittivity is quasi independent of the underlying substrate material (glass, glass + ITO, glass + Pt, Si, etc.). Liquid crystals exhibit electro-optic effects that are an order of magnitude larger compared to PZT, which makes them ideal materials for use in beam steering applications of focus tunable lenses. In these applications the liquid crystal imposes a spatially varying optical path length to light passing through the liquid crystal layer. By working with a number of separately addressable electrodes the optical path length variation can be accurately controlled. Using multi-electrode designs for example, tunable lenses with high optical quality have been demonstrated. One major problem of multi-electrode designs is the appearance of fringe fields which leads to unwanted behavior of the liquid crystal and may eventually lead to the formation of disclination lines which reduces the optical performance drastically. Using a PZT thin film, we demonstrate that the fringe fields are eliminated and that designs with fewer separately addressable electrodes are necessary. Tunable lenses with a liquid crystal layer integrated on top of a PZT layer are demonstrated [2]. Next to the experimental demonstration we provide numerical simulations of the effect of the high permittivity layer on the liquid crystal. [1] J.P. George, et al. Lanthanide-Assisted Deposition of Strongly Electro-optic PZT Thin Films on Silicon: Toward Integrated Active Nanophotonic Devices. ACS Appl. Mater. Inter. 7 13350-9 (2015) [2] O. Willekens, et al., Ferroelectric thin films with liquid crystal for gradient index applications, Optics Express (submitted

Reflective liquid crystal hybrid beam-steerer

We report on efficient optical beam-steering using a hot-embossed reflective blazed grating in combination with liquid crystal. A numerical simulation of the electrical switching characteristics of the liquid crystal is performed and the results are used in an FDTD optical simulator to analyze the beam deflection. The corresponding experiment on the realized device is performed and is found to be in good agreement. Beam deflection angles of 4.4° upon perpendicular incidence are found with low applied voltages of 3.4V. By tilting the device with respect to the incoming optical beam it can be electronically switched such that the beam undergoes either total internal reflection or reflection with a tunable angle

High quality beam produced by tightly focused laser driven wakefield accelerators

We propose to use tightly focused lasers to generate high quality electron beams in laser wakefield accelerators. In this scheme, the expansion of the laser beam after the focal position enlarges the size of wakefield bubble, which reduces the effective phase velocity of the wake and triggers injection of plasma electrons. This scheme injects a relatively long beam with high charge. The energy spread of the injected beam can be minimized if an optimal acceleration distance is chosen so that the beam chirp is suppressed. Particle-in-cell simulations indicate that electron beams with the charge in the order of nanocoulomb, the energy spread of $\sim 1\%$, and the normalized emittance of $\rm \sim 0.1\ mm\cdot mrad$ can be generated in uniform plasma using $\sim 100\ \rm TW$ laser pulses. An empirical formula is also given for predicting the beam charge. This injection scheme, with a very simple setup, paves the way towards practical high-quality laser wakefield accelerators for table-top electron and radiation sources.Comment: 7 pages, 9 figure

Bridging the electrode gap with ferroelectric thin films

Close to the edges of electrodes, strong electric fields are present which often give rise to unwanted effects in liquid crystal behavior. In liquid crystal microdisplays for projector applications, the gap between electrodes should be as small as possible and the liquid crystal orientation should vary sharply from one pixel to the other in order to achieve the highest possible resolution. In other applications however, a smooth variation in the liquid crystal orientation is desirable and fringe field effects are highly unwanted. Electrode based tunable lenses or beam steering devices are examples in which fringe fields should be suppressed as much as possible. A common way to alleviate the fringe field problem and to smoothen out the spatial variation of liquid crystal orientation is to deposit weakly conductive layers on top of the highly conductive electrodes. In such devices there is a trade-off between high electrical power consumption (high conductivity) and reduced smoothing effect (low conductivity). Also, it is technologically not always straightforward to obtain layers with the desired sheet conductivity. In this work, we demonstrate a new technique exploiting the extremely high dielectric permittivity of ferroelectric thin films based on lead zirconate titanate (PbZrxTi1-xO3, PZT). The high dielectric permittivity of the layer leads to similar effects as the conductivity of a weak conductor. The smoothening and spreading of the electrical field lines between two electrodes is clearly demonstrated in figure 1. At the same time we also prove the excellent reduction of fringe fields near electrode edges. Using multi-electrode designs with a PZT top layer, tunable lenses with high optical quality are demonstrated [1]. Also one-dimensional beam steering is demonstrated. In both cases a reference device was fabricated without PZT layer. The benefit of using a PZT layer is obvious when comparing the PZT and non-PZT devices. [1] O. Willekens, J.P. George, K. Neyts & J. Beeckman, Ferroelectric thin films with liquid crystal for gradient index applications, Optics Express 24, 8088-8096 (2016

Inversion of Different Cultivated Soil Types’ Salinity Using Hyperspectral Data and Machine Learning

Soil salinization is one of the main causes of global desertification and soil degradation. Although previous studies have investigated the hyperspectral inversion of soil salinity using machine learning, only a few have been based on soil types. Moreover, agricultural fields can be improved based on the accurate estimation of the soil salinity, according to the soil type. We collected field data relating to six salinized soils, Haplic Solonchaks (HSK), Stagnic Solonchaks (SSK), Calcic Sonlonchaks (CSK), Fluvic Solonchaks (FSK), Haplic Sonlontzs (HSN), and Takyr Solonetzs (TSN), in the Hetao Plain of the upper reaches of the Yellow River, and measured the in situ hyperspectral, pH, and electrical conductivity (EC) values of a total of 231 soil samples. The two-dimensional spectral index, topographic factors, climate factors, and soil texture were considered. Several models were used for the inversion of the saline soil types: partial least squares regression (PLSR), random forest (RF), extremely randomized trees (ERT), and ridge regression (RR). The spectral curves of the six salinized soil types were similar, but their reflectance sizes were different. The degree of salinization did not change according to the spectral reflectance of the soil types, and the related properties were inconsistent. The Pearson’s correlation coefficient (PCC) between the two-dimensional spectral index and the EC was much greater than that between the reflectance and EC in the original band. In the two-dimensional index, the PCC of the HSK-NDI was the largest (0.97), whereas in the original band, the PCC of the SSK400 nm was the largest (0.70). The two-dimensional spectral index (NDI, RI, and DI) and the characteristic bands were the most selected variables in the six salinized soil types, based on the variable projection importance analysis (VIP). The best inversion model for the HSK and FSK was the RF, whereas the best inversion model for the CSK, SSK, HSN, and TSN was the ERT, and the CSK-ERT had the best performance (R2 = 0.99, RMSE = 0.18, and RPIQ = 6.38). This study provides a reference for distinguishing various salinization types using hyperspectral reflectance and provides a foundation for the accurate monitoring of salinized soil via multispectral remote sensing

On Gravitational anomaly and Hawking radiation near weakly isolated horizon

Based on the idea of the work by Wilczek and his collaborators, we consider the gravitational anomaly near weekly isolated horizon. We find that there exists a universal choice of tortoise coordinate for any weakly isolated horizon. Under this coordinate, the leading behavior of a quite arbitrary scalar field near horizon is a 2-dimensional chiral scalar field. This means we can extend the idea of Wilczek and his collaborators to more general cases and show the relation between gravitational anomaly and Hawking radiation is a universal property of black hole horizon.Comment: 14 page

Microbial Properties Depending on Fertilization Regime in Agricultural Soils with Different Texture and Climate Conditions: A Meta-Analysis

Over-fertilization has a significant impact on soil microbial properties and its ecological environment. However, the effects of long-term fertilization on microbial properties on a large scale are still vague. This meta-analysis collected 6211 data points from 109 long-term experimental sites in China to evaluate the effects of fertilizer type and fertilization duration, as well as soil and climate conditions, on the effect sizes on various microbial properties and indices. The organic fertilizers combined with straw (NPKS) and manure (NPKM) had the highest effect sizes, while the chemical fertilizers N (sole N fertilizer) and NPK (NPK fertilizer) had the lowest. When compared with the control, NPKM treatment had the highest effect size, while N treatment had the lowest effect size on MBN (111% vs. 19%), PLFA (110% vs. −7%), fungi (88% vs. 43%), Actinomycetes (97% vs. 44%), urease (77% vs. 25%), catalase (15% vs. −11%), and phosphatase (58% vs. 4%). NPKM treatment had the highest while NPK treatment had the lowest effect size on bacteria (123% vs. 33%). NPKS treatment had the highest while N treatment had the lowest effect sizes on MBC (77% vs. 8%) and invertase (59% vs. 0.2%). NPKS treatment had the highest while NPK treatment had the lowest effect size on the Shannon index (5% vs. 1%). The effect sizes of NPKM treatment were the highest predominantly in arid regions because of the naturally low organic carbon in soils of these regions. The effect sizes on various microbial properties were also highly dependent on soil texture. In coarse-textured soils the effect sizes on MBC and MBN peaked sooner compared with those of clayey or silty soils, although various enzymes were most active in silty soils during the first 10 years of fertilization. Effect sizes on microbial properties were generally higher under NPKM and NPKS treatments than under NPK or N treatments, with considerable effects due to climate conditions. The optimal field fertilizer regime could be determined based on the effects of fertilizer type on soil microorganisms under various climate conditions and soil textures. This will contribute to the microbial biodiversity and soil health of agricultural land. Such controls should be used for adaptation of fertilization strategies to global changes

Soil Chemical Properties Depending on Fertilization and Management in China: A Meta-Analysis

The long-term overuse of fertilizers negatively affects soil chemical properties and health, causing unsustainable agricultural development. Although many studies have focused on the effects of long-term fertilization on soil properties, few comparative and comprehensive studies have been conducted on fertilization management over the past 35 years in China. This meta-analysis (2058 data) evaluated the effects of the fertilizer, climate, crop types, cultivation duration and soil texture on the soil chemical properties of Chinese croplands. NPKM (NPK fertilizers + manure) led to the highest increase in pH (−0.1), soil organic carbon (SOC) (+67%), total nitrogen (TN) (+63%), alkali-hydrolysable nitrogen (AN) (+70%), total phosphorus (TP) (+149%) and available potassium (AK) (+281%) compared to the unfertilized control, while the sole nitrogen fertilizer (N) led to the lowest increase. The SOC (+115%) and TN (+84%) showed the highest increase under the influence of NPKM in an arid region. The increase in the chemical properties was higher in unflooded crops, with the maximum increase in the wheat–maize rotation, compared to rice, under NPKM. The SOC and TN increased faster under the influence of organic fertilizers (manure or straw) compared to mineral fertilization. Fertilizers produced faster effects on the change in the SOC and TN in sandy loam compared to the control. Fertilizers showed the highest and lowest effects on change in pH, organic C to total N ratio (C/N), TP and TK in clay loam with the cultivation duration. NPKM greatly increased the C/N compared to NPK in an arid region by 1.74 times and in wheat by 1.86 times. Reaching the same SOC increase, the lowest TN increase was observed in wheat, and the lowest increase in TP and AK was observed in rice, compared to the other crops. These results suggest that organic fertilizers (manure or straw) play important roles in improving soil fertility and in acidification. NPKM greatly increased the potential for soil C sequestration in wheat and in the arid region. The small increases in TP and TK can increase the SOC in rice and in the humid region. Therefore, considering the crop types and climatic conditions, reduced fertilization and the combination of mineral fertilizers with manure may be the best ways to avoid agricultural soil deterioration and increase soil carbon sequestration