bragg reflection
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2022 ◽  
Vol 12 (1) ◽  
Author(s):  
Sunghyun Moon ◽  
Yeojun Yun ◽  
Minhyung Lee ◽  
Donghwan Kim ◽  
Wonjin Choi ◽  
...  

AbstractThin-film vertical cavity surface emitting lasers (VCSELs) mounted onto heatsinks open up the way toward low-power consumption and high-power operation, enabling them to be widely used for energy saving high-speed optical data communication and three-dimensional sensor applications. There are two conventional VCSEL polarity structures: p-on-n and n-on-p polarity. The former is more preferably used owing to the reduced series resistance of n-type bottom distributed Bragg reflection (DBR) as well as the lower defect densities of n-type GaAs substrates. In this study, the p-on-n structures of thin-film VCSELs, including an etch stop layer and a highly n-doped GaAs ohmic layer, were epitaxially grown in upright order by using low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The p-on-n structures of thin-film VCSELs were transferred onto an aluminum heatsink via a double-transfer technique, allowing the top-emitting thin-film VCSELs to keep the p-on-n polarity with the removal of the GaAs substrate. The threshold current (Ith) and voltage (Vth) of the fabricated top-emitting thin-film VCSELs were 1 mA and 2.8 V, respectively. The optical power was 7.7 mW at a rollover point of 16.1 mA.


2021 ◽  
Vol 53 (6) ◽  
pp. 210605
Author(s):  
Iwan Prasetiyo ◽  
Gradi Desendra ◽  
Khoerul Anwar ◽  
Mohammad Kemal Agusta

Several studies have been devoted to increasing the attenuation performance of the Helmholtz resonator (HR). One way is by periodic coupling of HRs in a ducting system. In this study, we propose a different approach, where a membrane (or a thin flexible structure in general) is added to the air cavity of a periodic HR array in order to further enhance the attenuation by utilizing the resonance effect of the membrane. It is expected that three attenuation mechanisms will exist in the system that can enhance the overall attenuation, i.e. the resonance mechanism of the HR, the Bragg reflection of the periodic system, and the resonance mechanism of the membrane or thin flexible structure. This study found that the proposed system yields two adjacent attenuation peaks, related to the HR and the membrane respectively. Moreover, extension of the attenuation bandwidth was also observed as a result of the periodic arrangement of HRs. With the same HR parameters, the peak attenuation by the membrane is tunable by changing its material properties. However, such a system does not always produce a wider attenuation bandwidth; the resonance bandwidths of both mechanisms must overlap.


Crystals ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1389
Author(s):  
Ksenia Kozlovskaya ◽  
Elena Ovchinnikova ◽  
Jun Kokubun ◽  
Andrei Rogalev ◽  
Fabrice Wilhelm ◽  
...  

We propose a new method to determine the absolute structure of chiral crystals, which is based on the chiral asymmetry of multiple scattering diffraction. It manifests as a difference in the azimuthal dependence of the forbidden Bragg reflection intensity measured with left and right circularly polarized X-ray beams. Contrary to the existing ones, the suggested method does not use X-ray anomalous dispersion. The difference between the Renninger scans with circularly polarized X-rays has been experimentally demonstrated for the 001 reflection intensities in the right- and left-handed quartz single crystals. A Jmulti-based code on model-independent three-wave-diffraction approach has been developed for quantitative description of our experimental results. The proposed method can be applied to various structures including opaque, organic and monoatomic crystals, even with only light elements. To determine the type of isomer, the Renninger plot of a single forbidden reflection is sufficient.


Molecules ◽  
2021 ◽  
Vol 26 (22) ◽  
pp. 6889
Author(s):  
Yao Gao ◽  
Yuxiang Luo ◽  
Jiangang Lu

Cholesteric liquid crystals (CLCs) have been widely applied in optical filters due to Bragg reflection caused by their helical structure. However, the reflectivity of CLC filters is relatively low, commonly less than 50%, as the filters can only reflect light polarized circularly either left- or right-handedly. Therefore, a high-reflective CLC filter with a single-layer template was proposed which may reflect both right- and left-handed polarized light. The CLC filters of the red, green, blue color were fabricated by the templating technology, which show good wavelength consistency. Additionally, a multi-phase liquid crystal filter with high reflectance was demonstrated by the single-layer templating technology. The templated CLC or multi-phase liquid crystal filters show great potential applications in the optical community, reflective display, and lasing.


Catalysts ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 1325
Author(s):  
Isabella Kappel ◽  
Sebastian Böcklein ◽  
SoHyun Park ◽  
Michael Wharmby ◽  
Gerhard Mestl ◽  
...  

This study presents information about crystal imperfections in the main phase of industrial vanadium phosphorous oxide catalysts that are used to catalyze the oxidation of n-butane to maleic anhydride, being an important intermediate in the chemical industry. The mechanism of this reaction is still debated, and the catalytically active and selective surface centers have not yet been identified. The results presented are based on X-ray diffraction data obtained by both laboratory-scale and synchrotron powder diffraction experiments, as well as laboratory-scale single-crystal diffraction experiments. It has been proven that pronounced Bragg reflection broadening effects found in laboratory-scale powder diffraction patterns of industrial VPO catalysts are real and not due to an insufficient 2-θ resolution of the apparatus. In the framework of this work, a powder diffraction full profile fitting strategy was developed using the TOPAS software, which was applied to analyze the X-ray diffraction data of four differently activated industrial catalyst samples, originating from one batch after they had been catalytically tested. It was found that the reflection broadening is mainly caused by an anisotropic crystal size, which results in platelet-shaped crystallites of vanadyl pyrophosphate. A further contribution to the reflex broadening, especially for (111), was found to be a result of stacking faults perpendicular to the a direction in the crystal structure of vanadyl pyrophosphate. These results were used to elaborate on possible correlations between structural proxies and catalytic performance. A direct correlation between the extension of coherently scattering domains in the z direction and the catalyst’s selectivity could be proven, whereas the activity turned out to be dependent on the crystallite shape. Regarding the phase contents, it could be shown that sample catalysts containing a higher amount of β-VO(PO3)2 showed increased catalytic activity.


2021 ◽  
Vol 90 (10) ◽  
pp. 104713
Author(s):  
Shin Nakamura ◽  
Takaya Mitsui ◽  
Masayuki Kurokuzu ◽  
Susumu Shimomura

2021 ◽  
Author(s):  
Sunghyun Moon ◽  
Yeojun Yun ◽  
Minhyung Lee ◽  
Donghwan Kim ◽  
Wonjin Choi ◽  
...  

Abstract Thin-film vertical cavity surface emitting lasers (VCSELs) mounted onto heatsinks open up the way toward low-power consumption and high-power operation, enabling them to be widely used for energy saving high-speed optical data communication and three-dimensional sensor applications. There are two conventional VCSEL polarity structures: p-on-n and n-on-p polarity. The former is more preferably used owing to the reduced series resistance of n-type bottom distributed Bragg reflection (DBR) as well as the lower defect densities of n-type GaAs substrates. In this study, the p-on-n structures of thin-film VCSELs, including an etch stop layer and a highly n-doped GaAs ohmic layer, were epitaxially grown in upright order by using low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The p-on-n structures of thin-film VCSELs were transferred onto an aluminum heatsink via a double-transfer technique, allowing the top-emitting thin-film VCSELs to keep the p-on-n polarity with the removal of the GaAs substrate. The threshold current (Ith) and voltage (Vth) of the fabricated top-emitting thin-film VCSELs were 1 mA and 2.8 V, respectively. The optical power was 7.7 mW at a rollover point of 16.1 mA.


2021 ◽  
Vol 28 (6) ◽  
Author(s):  
Yuri Shvyd'ko ◽  
Sergey Terentyev ◽  
Vladimir Blank ◽  
Tomasz Kolodziej

Next-generation high-brilliance X-ray photon sources call for new X-ray optics. Here we demonstrate the possibility of using monolithic diamond channel-cut crystals as high-heat-load beam-multiplexing narrow-band mechanically stable X-ray monochromators with high-power X-ray beams at cutting-edge high-repetition-rate X-ray free-electron laser (XFEL) facilities. The diamond channel-cut crystals fabricated and characterized in these studies are designed as two-bounce Bragg reflection monochromators directing 14.4 or 12.4 keV X-rays within a 15 meV bandwidth to 57Fe or 45Sc nuclear resonant scattering experiments, respectively. The crystal design allows out-of-band X-rays transmitted with minimal losses to alternative simultaneous experiments. Only ≲2% of the incident ∼100 W X-ray beam is absorbed in the 50 µm-thick first diamond crystal reflector, ensuring that the monochromator crystal is highly stable. Other X-ray optics applications of diamond channel-cut crystals are anticipated.


2021 ◽  
Vol 219 (1) ◽  
pp. 260-267
Author(s):  
Chuang Qiao ◽  
Dan Fang ◽  
Li ◽  
Xuan Fang ◽  
Jilong Tang ◽  
...  

Nanomaterials ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 2239
Author(s):  
Olga Rubi Juárez-Rivera ◽  
Reina Araceli Mauricio-Sánchez ◽  
Kenneth Järrendahl ◽  
Hans Arwin ◽  
Arturo Mendoza-Galván

Nanocelluloses are very attractive materials for creating structured films with unique optical properties using different preparation techniques. Evaporation-induced self-assembly of cellulose nanocrystals (CNC) aqueous suspensions produces iridescent films with selective circular Bragg reflection. Blade coating of sonicated CNC suspensions leads to birefringent CNC films. In this work, fabrication of both birefringent and chiral films from non-sonicated CNC suspensions using a shear-coating method is studied. Polarization optical microscopy and steady-state viscosity profiles show that non-sonicated CNC suspensions (concentration of 6.5 wt%) evolve with storage time from a gel-like shear-thinning fluid to a mixture of isotropic and chiral nematic liquid crystalline phases. Shear-coated films prepared from non-sonicated fresh CNC suspensions are birefringent, whereas films prepared from suspensions stored several weeks show reflection of left-handed polarized light. Quantification of linear and circular birefringence as well circular dichroism in the films is achieved by using a Mueller matrix formalism.


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