Configuration of singular optical cones in gyrotropic crystals with dichroism

Merkulov, V. S.

doi:10.1134/s106377611502003x

Cited by 4 publications

(7 citation statements)

References 14 publications

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“…As the wave properties of the ordinary ray depends only on the magnitude of the in-plane wave vector component (Equation (39a)), in the case of a degeneration of the wave properties, the magnitude of the eight wave vectors is the same for all orientations and the components of the wave vector differ only in their sign. An inspection of Equation ( 39), (41), and (43) yields that the solutions for the out-of-plane Table 5. Symmetry relations of the Euler angles for the optically anisotropic crystals.…”

Section: Uniaxial Crystalsmentioning

confidence: 99%

Electromagnetic Waves in Crystals: The Presence of Exceptional Points

Sturm

2024

Advanced Photonics Research

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Although the investigation of the propagation of electromagnetic waves in crystals dates back to the 19th century, the presence of singular optic axes in optically anisotropic materials has not been fully explored until now. Along such an axis, either a left or a right circular polarized wave can propagate without changing its polarization state. More generally, these singular optic axes belong to exceptional points (EPs) in the momentum space and correspond to a simultaneous degeneration of the eigenmodes and their propagation properties. Herein, a comprehensive discussion on EPs in optically anisotropic materials, their occurrence, and properties as well as the properties of the electromagnetic waves propagating along such EPs is presented. The presence of such EPs, their spatial and spectral distribution in bulk, and semi‐infinite and finite crystals are discussed. It is shown that the presence of interfaces has a strong impact on the presence of the EPs and their spatial distribution. At an EP, the propagation of an arbitrarily polarized wave cannot be described by a superposition of two eigenmodes, as typically described in textbooks. This leads to singularities if the reflection and transmission coefficients have to be calculated. Here, two approaches are presented to overcome these limitations.

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Section: Uniaxial Crystalsmentioning

confidence: 99%

Electromagnetic Waves in Crystals: The Presence of Exceptional Points

Sturm

2024

Advanced Photonics Research

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“…A theoretical description of the phenomenon measured in this work (Alshits & Lyubimov, 2008) and simulated conoscopic patterns for various crystal parameters near an isotropic point (Vasylkiv et al, 2006) are found in the literature. Recent work considers the more complex optical response from optically active crystals with significant linear dichroism in the spectral region near an isotropic point in the real portion of the electric permittivity tensor (Alshits & Lyubimov, 2004;Merkulov, 2014Merkulov, , 2015Sturm & Grundmann, 2016). This scenario results in the splitting of double cones of eigendirections into cones of singular optical axes.…”

Section: Polar Mappingmentioning

confidence: 99%

“…A full analysis of the double cones of eigendirections in EDSeO 4 is made here. Theoretical crystal optical analyses of these phenomena were described previously (Semchenko et al, 2000;Vasylkiv et al, 2006;Alshits & Lyubimov, 2008;Merkulov, 2014Merkulov, , 2015.…”

Section: Introductionmentioning

confidence: 99%

Double cone of eigendirections in optically active ethylenediammonium selenate crystals

Martin

Nichols

et al. 2017

J Appl Cryst

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Circular birefringence (CB) is generally responsible for only a small perturbation to the state of light polarization in crystals that also exhibit linear birefringence (LB). As such, the magnetoelectric tensor of gyration, which gives rise to CB and optical activity, is less well determined than the electric permittivity tensor in optical models of the Mueller matrix. To visualize the effect of the magnetoelectric tensor on polarimetric measurements, reported here are experimental mappings of the Mueller matrix and of the CB in a new chiral crystal with accidental null LB at an accessible optical frequency. Single crystals of ethylenediammonium selenate (EDSeO) were synthesized and characterized by X-ray diffraction and Mueller matrix measurements in transmission and reflection. The crystals are isomorphous with the corresponding sulfate salt. They are tetragonal, space group 422. The constitutive relations of EDSeO were recovered using a partial wave summation of incoherent reflections. The extraordinary and ordinary refractive indices cross at 364 nm (3.41 eV), a scenario commonly called the 'isotropic point' or 'iso-index point'. At this wavelength, the magnetoelectric tensor fully describes the polarization transformation, giving rise to a double cone of eigendirections.

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“…Exciton absorption in GaN is observed at room temperature with an excitonic absorption peak of = 3.44 eV at zero field, where GaN has an F = 0 exciton binding energy of 20.4 meV. 42 As pointed out by Dow and Redfield, 32 Blossey, 43 and Merkulov, 33 the Coulombic electron-hole interaction modifies the absorption spectrum (exciton absorption), which has a qualitatively distinct fielddependence compared with the band-to-band transition treated by the FKA theory. This excitonmodified FK effect was previously observed in GaN electroabsorption spectra.…”

mentioning

confidence: 92%

“…34 36 As our data span a wide range of photon energy deficit, , including the range where is comparable to the exciton binding energy ( ), the values of the absorption coefficient are greatly underestimated by the non-excitonic FKA model; when the electric field distortion of the exciton wave function enhances the absorption coefficient (see Supplementary Material for comparison of FKA versus XFK spectral lineshape). To model the XFK effect, we utilize the theory developed by Merkulov, 33 where the sub-band gap field-dependent absorption coefficient is,…”

mentioning

confidence: 99%

Local electric field measurement in GaN diodes by exciton Franz–Keldysh photocurrent spectroscopy

Verma

Adnan

Rahman

et al. 2020

Applied Physics Letters

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The eXciton Franz-Keldysh (XFK) effect is observed in GaN p-n junction diodes via the spectral variation of photocurrent responsivity data that redshift and broaden with increasing reverse bias. Photocurrent spectra are quantitatively fit over a broad photon energy range to an XFK model using only a single fit parameter that determines the lineshape, the local bias ( ), uniquely determining the local electric field maximum and depletion widths. As expected, the spectrally determined values of vary linearly with the applied bias ( ) and reveal a large reduction in the local electric field due to electrostatic non-uniformity. The built-in bias ( ) is estimated by extrapolating at , which compared with independent C-V measurements indicates an overall ±0.31 V accuracy of . This demonstrates sub-bandgap photocurrent spectroscopy as a local probe of electric field in wide bandgap diodes that can be used to map out regions of device breakdown (hot spots) for improving electrostatic design of high voltage devices.GaN is a III-V compound semiconductor with a wide bandgap (Eg~3.4 eV) and a high breakdown electric field ( > 3.3 MV/cm), making it useful for power devices and optoelectronics. 1 5Heterostructures based on GaN result in high responsivity Metal-Heterojunction-Metal (MHM) ultraviolet photodetectors. 6,7 However, the stability and lifetime at high voltages for GaN based power electronics still remains a challenge to the device industry. 7 12 Vertical devices such as p-n junctions have electric field peaks near the device edge, which are managed using junction termination structures such as field plates and guard rings. 13 16 Lateral devices such as AlGaN/GaN HEMTs also show field variation across the gate-drain region. The built-in electric field in such heterostructures can be measured using contactless electroreflectance, 17,18 however it is not suitable at high fields when the reflectance oscillations decay. It is a challenge to measure the actual field distribution in such devices, and device engineers usually rely on device simulations to estimate the electric field profiles.Furthermore models used to estimate electric field profiles may ignore inhomogeneity, and thus may not

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Configuration of singular optical cones in gyrotropic crystals with dichroism

Cited by 4 publications

References 14 publications

Electromagnetic Waves in Crystals: The Presence of Exceptional Points

Electromagnetic Waves in Crystals: The Presence of Exceptional Points

Double cone of eigendirections in optically active ethylenediammonium selenate crystals

Local electric field measurement in GaN diodes by exciton Franz–Keldysh photocurrent spectroscopy

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