Mechanism of Bragg Diffraction-Assisted Light Extraction in GaN-based Light-Emitting Diodes Based on a Self-Consistent Model

By introducing the distribution of the light energy density in GaN-based light-emitting diode (LED),theLED model based on the incoherent regime and the light extraction efficiency are investigated.The energy density asa function of the angle of incidence is calculated to demonstrate the mechanism of the light extraction.The deviationbetween the tendencies of the transmissivity of the output layer and the extraction efficiency is also demonstrated.

Multifrequency Magneto-optic Bragg Diffraction and Radio Frequency Signal Parallel Processing

Magneto-optic(MO)coupling of guided optical waves with microwave magnetostatic waves(MSWs)simultaneously excited by multiple radio frequency(RF)signals can lead to multifrequency diffraction effects and then parallel processing of RF signals can be realized by using of the characteristics that diffraction efficiencies(DEs)are approximately in direct proportion to RF signals intensities and diffraction angles are related to frequencies of the corresponding RF signals within linear MO interaction region.In this paper,studied is the multifrequency MO Bragg diffraction in first-order MO interaction approximation,and obtained was the approximate analytical expression for principle diffraction efficiency(PDE).Also,put forward was a parallel imaging method of relative intensity of RF signals based on single-frequency diffraction.By calculation and analysis,it is shown that the relative error is not more than 0.3dB for the case of three RF signals within the frequency space of 60MHz.

Establishment and study of a polarized X-ray radiation facility

With the advancement in X-ray astronomical detection technology,various celestial polarization detection projects have been initiated.To meet the calibration requirements of polarimeters on the ground,a polarized X-ray radiation facility was designed for this study.The design was based on the principle that X-rays incident at 45°on a crystal produce polarized X-rays,and a second crystal was used to measure the polarization of the X-rays produced by the facility after rotation.The effects of different diaphragm sizes on the degree of polarization were compared,and the facility produced X-rays with polarization degrees of up to 99.55±0.96%using LiF200 and LiF220 crystals.This result revealed that the polarization of incident X-rays is one of the factors affecting the diffraction efficiency of crystals.The replacement of different crystals can satisfy the calibration requirements of polarized X-ray detectors with more energy points in the energy range(4-10)keV.In the future,the facility should be placed in a vacuum environment to meet the calibration requirements at lower energies.

The development,performances and applications of the monochromatic X-rays facilities in(0.218–301)keV at NIM,China

Space scientific exploration is rapidly becoming the primary battlefield for humankind to explore the universe.Countries worldwide have launched numerous space exploration satellites.Accurate calibration of the detectors on the ground is a crucial element for space science satellites to obtain observational results.For the purpose of providing calibration for various satellite-borne detectors,multiple monochromatic X-rays facilities have been built at the National Institute of Metrology,P.R.China(NIM).These facilities mainly pertain to grating diffraction and Bragg diffraction,and the energy range of the produced monochromatic X-rays is 0.218–301 ke V.These facilities have a high performance in terms of energy stability,monochromaticity,and flux stability.The monochromaticity was greater than 3.0%.The energy stability of the facility is 0.02%at 25 ke V over 8 h,and the flux stability was within 1.0%at 25 ke V over 8 h.Calibration experiments on the properties of satellite-borne detectors,such as energy linearity,energy resolution,detection efficiency,and temperature response,can be conducted at the facilities.Thus far,the calibration of two satellites has been completed by the authors,and the work on three other satellites is in progress.This study will contribute to the advancement of X-ray astronomy the development of Chinese space science.

Study of Deep-etched Glass Waveguide Grating

Photoresist grating was fabricated by holography, and it was used in the mask of ion etching. The groovy depth of the etched glass grating was 1.6μm. The glass waveguide was formed by K^+/Na^+ ion exchanging. The laser beam of 633nm was coupled in the waveguide by a prism at one end, then, it passed through the grating and came out of the waveguide at other end. In the experiment, the Bragg diffraction with several orders was observed. The first order Bragg diffraction had the highest efficiency of 90 percent.

THE ANGULAR SPREAD OF THE DEFLECTED SAW BEAM DIFFRACTED BY BRAGG GRATING

In this paper , the angular spread of the SAW beam diffracted by Bragg grating , denoted by δθ1 ,is analysed based on the equations of the deflection angle and the deflection effciency . A parameter δθB is defined to refer to ' Bragg angular spectrum width ' of the grating . The importance of this parameter in distinguishing the angular spread range of the deflected beam for different regimes is discussed as well. It is show from the analysis that if the spread angle of the incident beam labelled with δθinc is larger than the ' Bragg witdth of the angular spectrum ' of the grating , the spread angle δθ1 of the deflected beam will equal to δθB ; but if the angular divergence of the incident beam is less than δθB , then δθ1 =δθinc.Experimentally , four kinds of samples with different configurations are investigated by optical method , two of which operate in the regime of δθinc<<δθB and the others correspond to the case in the regime of δθinc >>δθB . The widths of the angular spread of the incident beam and the deflected beam are estimated by measuring the widths of their own acousto - optical diffraction points . It is demonstrated that the experimental results agree with the theoretical results approximately .

The scattering mechanism of squall lines with C-Band dual polarization radar.Part Ⅱ:the mechanism of an abnormal ZDR echo in clear air based on the parameterization of turbulence deformation

In part I,the clear air echo in front of the squall line is caused by turbulence diffraction,which makes the Z_(DR) echo characteristics different from particle scattering.To study the turbulence deformation phenomenon that is affected by environmental wind,the turbulence-related method is used to analyze the characteristics of three-dimensional turbulence energy spectrum density,and the parametric model of turbulence integral length scale and environmental wind speed is established.The results show that the horizontal scale of turbulence is generally larger than the vertical scale.The turbulence is nearly isotropic in the horizontal direction,presenting a flat ellipsoid with the vertical orientation of the rotation axis when there is no horizontal wind or the horizontal velocity is small.When horizontal wind exists,the turbulence scale increases along the dominant wind direction.The turbulence scale is positively correlated with the wind speed.The power function is used to fit the relationships of turbulence integral length scale and horizontal wind speed,which obtains the best fitting effect,and the goodness of fit(GF)is above 0.99 in each direction.The deforming turbulence can cause 8-9 dB Z_(DR) anomalies in the echo of dual polarization radar,which the ratio of scales in the dominant wind and the vertical direction of deforming turbulence(L_(u)/L_(w))is around 4.3.The variation in Z_(DR) depends on the turbulence shape,orientation and the relative position between turbulence and radar.The shape of turbulence derived from radar detection results is consistent with that of the parametric model,which can provide a parametric scheme for turbulence research.The results reveal the mechanism of abnormal Z_(DR) echo caused by deforming turbulence.