Collinear second harmonic generations in a nonlinear photonic quasicrystal

LiNbO₃ nonlinear photonic quasicrystal with octagonal symmetry was fabricated. The collinear quasiphase matched second harmonic generations at 22 wavelengths were observed. It is shown that not only the standard type quasiphase matching but also the recently proposed projection-based quasiphase matching plays an important role in these harmonic generations.The financial support of Chinese Academy of Science, Max Plank Society, and Deutscher Akademischer Austauschdienst DAAD is gratefully acknowledged

Generation of clear light source sequence in two-dimensional ten-fold quasi-periodic photonic crystals

Using the noncollinear quasi-phase matching technology, ″clear light source″ sequence of different colors at different positions can be obtained in a two-dimensional LiNbO3 nonlinear photonic crystal with ten-fold quasi-periodic superlattice. When th

Collinear second harmonic generation of 20 wavelengths in a single two-dimensional decagonal nonlinear photonic quasi-crystal

We report on the observation of quasi-phase matched collinear second harmonic generation (SHG) at 20 wavelengths in a two-dimensional nonlinear photonic quasi-crystal with decagonal lattice. We show that at some wavelengths the second harmonics are generated via standard quasi-phase matching, namely a reciprocal vector exists that equals the phase-mismatch vector, while at others the SHG is as a result of the projection-based quasi-phase matching in which the momentum conservation is satisfied up to a projection of a reciprocal vector onto the direction of propagation. In spite of different generation mechanisms, the reciprocal vectors (or their projections) involved in the collinear QPM SHG can be described by a generalized equation

Evaluating crop response and environmental impact of the accumulation of phosphorus due to long-term manuring of vertisol soil in northern China

The availability of soil phosphorus (P) is one of the key factors that regulate crop productivity. Fertilization practices with P fertilizers carry a high risk of non-point environmental pollution due to water run-off and leaching. The present work discusses data from a 29-year (1982-2011) fertilization experiment with wheat-soybean rotation. Its aim was to quantify and evaluate the dynamic of soil P availability in relation to P accumulation, crop yield, and environmental safety in northern China. This study included six treatments with four field replicates: CK (no fertilizer), NPK (mineral fertilizers), 1/2SNPK (mineral fertilizers plus 50% wheat straw return), SNPK (mineral fertilizers plus 100% wheat straw return), PMNPK (mineral fertilizers plus pig manure), and CMNPK (mineral fertilizers plus cattle manure). Continual additional application of farmyard manure (i.e., PMNPK and CMNPK) produced significantly (P <0.01) better soil total P and Olsen-P than NPK treatment, and both factors showed increasing trends. However, straw incorporation (i.e., 1/2SNPK and SNPK) had no effect on soil P or Olsen-P. There were significant positive correlations between P budget and increase in Olsen-P and total P. These correlations indicated that, with each 100 kg ha-1 of P budget, there were about 1.0-1.1 and 22.5-26.0 mg kg-1 increases in Olsen-P and total P for the straw incorporation treatments, whereas there were 5.7-5.9 and 26.5-30.8 mg kg-1 increases in Olsen-P and total P for use of manure. Average P activation coefficients for soil Olsen-P in the PMNPK and CMNPK treatments increased sharply by 87.2% and 121.3% compared to the NPK treatment (P <0.01). Two segment regression analyses indicated there to be observable changes in the relationships between Olsen-P and relative crop yield, and in Olsen-P and soluble-P, indicating critical Olsen-P levels of 11 mg kg-1 for crop yield, and 18 mg kg-1 for soluble P, respectively. In conclusion, much more P is available in the soil under long-term farmyard manure than crop straw incorporation when the amount of P accumulation is uniform. Long-term, continuous, excessive use of farmyard manure to increase crop yield is not sustainable and has a high risk of P environmental pollution. The incorporation of crop straw is a recommended means of managing which decreases the risk of P environmental pollution without compromising crop productivity of vertisol soil in northern China

Experimental Investigation of Relationship between the object- and Image Distance

Abstract-We experimentally investigate the focusing properties of a triangular two-dimensional photonic crystals of which all the cylinders are coated. The relationship between the location of object and image point is analyzed. It&apos;s demonstrated that at a certain frequency with relative refractive index of −1, the position of image point obey the geometric-optics analysis and non-near-field imaging can be achieved

Development of a New Tropical Cyclone Strip Segment Retrieval Model for C-Band Cross-Polarized SAR Data

Compared with co-polarized (HH/VV) normalized radar cross-section (NRCS) backscattered from the sea surface, there is no saturation phenomenon in cross-polarized (HV/VH) NRCS when wind speed is greater than about 20 m/s, so cross-polarized synthetic aperture radar (SAR) images can be used for high wind speed monitoring. In this work, a new geophysical model function (GMF) is proposed to describe the relation of the C-band cross-polarized NRCS with wind speed and radar incidence angle. Here, sixteen ScanSAR wide mode SAR images acquired by RADARSAT-2 (RS-2) under tropical cyclone (TC) conditions and the matching wind speed data from the European Centre for Medium-Range Weather Forecasts (ECMWF) and the Stepped-Frequency Microwave Radiometer (SFMR) are collected and divided into datasets A and B. Dataset A is used for analyzing the effects of the wind field and radar incidence angle on the reference noise-removed cross-polarized NRCS, and for proposing the new GMF for each sub-swath of the SAR images, while dataset B is used to retrieve wind speed and evaluate the validity of the new GMF. The comparisons between the wind speeds retrieved by the new GMF and the collocated ECMWF and SFMR data demonstrate the excellent performance of the new GMF for wind speed retrieval. To analyze the universality of the new GMF, wind speed retrievals based on 32 Sentinel-1A/B (S-1A/B) extra-wide-swath (EW) mode images acquired under TC conditions are also compared with the collocated wind speeds measured by the Soil Moisture Active Passive (SMAP) radiometer, and the retrieved wind speeds have RMSE of 3.667 m/s and a bias of 2.767 m/s. The successful applications in high wind speed retrieval of different tropical cyclones again supports the availability of the new GMF

Development of a New Tropical Cyclone Strip Segment Retrieval Model for C-Band Cross-Polarized SAR Data

Compared with co-polarized (HH/VV) normalized radar cross-section (NRCS) backscattered from the sea surface, there is no saturation phenomenon in cross-polarized (HV/VH) NRCS when wind speed is greater than about 20 m/s, so cross-polarized synthetic aperture radar (SAR) images can be used for high wind speed monitoring. In this work, a new geophysical model function (GMF) is proposed to describe the relation of the C-band cross-polarized NRCS with wind speed and radar incidence angle. Here, sixteen ScanSAR wide mode SAR images acquired by RADARSAT-2 (RS-2) under tropical cyclone (TC) conditions and the matching wind speed data from the European Centre for Medium-Range Weather Forecasts (ECMWF) and the Stepped-Frequency Microwave Radiometer (SFMR) are collected and divided into datasets A and B. Dataset A is used for analyzing the effects of the wind field and radar incidence angle on the reference noise-removed cross-polarized NRCS, and for proposing the new GMF for each sub-swath of the SAR images, while dataset B is used to retrieve wind speed and evaluate the validity of the new GMF. The comparisons between the wind speeds retrieved by the new GMF and the collocated ECMWF and SFMR data demonstrate the excellent performance of the new GMF for wind speed retrieval. To analyze the universality of the new GMF, wind speed retrievals based on 32 Sentinel-1A/B (S-1A/B) extra-wide-swath (EW) mode images acquired under TC conditions are also compared with the collocated wind speeds measured by the Soil Moisture Active Passive (SMAP) radiometer, and the retrieved wind speeds have RMSE of 3.667 m/s and a bias of 2.767 m/s. The successful applications in high wind speed retrieval of different tropical cyclones again supports the availability of the new GMF