Birefringence Effect Research Articles

Experimental investigation on the effect of crystal birefringence on the performance of nanosecond-pulsed diamond Raman laser

The impact of crystal birefringence on the performance of diamond Raman lasers has been studied previously at power levels slightly above the threshold. However, the diamond Raman lasers operating far above the threshold usually exhibit different properties. Using the Metripol polarimetry, we obtained the birefringence intensity and fast-axis distribution of a home-made single-crystal diamond. The effects of crystal birefringence on the performance of Stokes laser were then investigated in an external nanosecond-laser pumped Raman cavity with a low Q-factor. When the pump power exceeds 1.5 times the Stokes threshold, the Stokes output performance is significantly affected by birefringence, if the birefringence intensity is high or the fast axis angle is far from the diamond maximum gain angle. In regions where the birefringence intensity is low and the fast axis angle is close to the maximum gain direction, the output is mainly influenced by gain variations. This work can provide valuable insights for the development of single-crystal diamond and polarization-related nanosecond-pulsed diamond Raman laser applications.

Film thickness dependence of nanoscale arrangement of a chiral electron donor in its blends with an achiral electron acceptor.

The nanoscale chiral arrangement in a bicomponent organic material system comprising donor and acceptor small molecules is shown to depend on the thickness of a film that is responsive to chiral light in an optoelectronic device. In this bulk heterojunction, a previously unreported chiral bis(diketopyrrolopyrrole) derivative was combined with an achiral non-fullerene acceptor. The optical activity of the chiral compound is dramatically different in the pure material and the composite, showing how the electron acceptor influences the donor's arrangement compared with the pure molecule. Mueller matrix polarimetric imaging shows the authenticity of this effect and the homogeneity of short range chiral orientations between the molecules, as well as more heterogeneous short and longer range arrangements in the films observed in linear dichroic and birefringent effects. The two-dimensional circular dichroism (CD) maps and spectra show the uniformity of the short range supramolecular interactions both in spun-cast films on quartz and blade-coated films on photovoltaic device substrates, where evidence for the chiral arrangement is uniquely provided by the synchrotron CD measurements. The external quantum efficiency of the devices depends upon the handedness of the light used to excite them and the film thickness, that influences the supramolecular arrangement and organization in the film, and determines the selectivity for left or right circularly polarised light. The difference in external quantum efficiency of the photovoltaic devices between the two handedness' of light correlates with the apparent differential absorbance (g-factor) of the films.

Applications of Isosceles Triangular Coupling Structure in Optical Switching and Sensing.

In the case of waveguide-based devices, once they are fabricated, their optical properties are already determined and cannot be dynamically controlled, which limits their applications in practice. In this paper, an isosceles triangular-coupling structure which consists of an isosceles triangle coupled with a two-bus waveguide is proposed and researched numerically and theoretically. The coupled mode theory (CMT) is introduced to verify the correctness of the simulation results, which are based on the finite difference time domain (FDTD). Due to the existence of the side mode and angular mode, the transmission spectrum presents two high transmittance peaks and two low transmittance peaks. In addition, the four transmission peaks exhibit different variation trends when the dimensions of the isosceles triangle are changed. The liquid crystal (LC) materials comprise anisotropic uniaxial crystal and exhibit a remarkable birefringence effect under the action of the external field. When the isosceles triangle coupling structure is filled with LC, the refractive index of the liquid crystal can be changed by changing the applied voltage, thereby achieving the function of an optical switch. Within a certain range, a linear relationship between refractive index and applied voltage can be obtained. Moreover, the proposed structure can be applied to biochemical sensing to detect glucose concentrations, and the sensitivity reaches as high as 0.283 nm·L/g, which is significantly higher than other values reported in the literature. The triangular coupling structure has advantages such as simple structure and ease of manufacturing, making it an ideal choice for the design of high-performance integrated plasmonic devices.

Cationic Coordination Modification Drives Birefringence and Nonlinear Effect Double Lifting in Sulfate.

As nonlinear optical (NLO) crystals, sulfates have the superiority of transparency for ultraviolet (UV) light, but they are often troubled by small nonlinear coefficients and birefringence owing to the high symmetry of the [SO4]2- group. By introducing two neutral diethylenetriamine (DETA) molecules to replace the six coordinated water molecules of the [Zn(H2O)6]2+ complex cation in [Zn(H2O)6](SO4)(H2O), a new sulfate with an acentric structure, namely, [Zn(DETA)2](SO4)(H2O)3, has been designed and synthesized. Structural investigation reveals that the coordination modification of Zn2+ ion tremendously enhances its intraoctahedral distortion. The formed distorted [Zn(DETA)2]2+ cations and the [SO4]2- groups feature an optimized arrangement, endowing [Zn(DETA)2](SO4)(H2O)3 with enhancements in both second harmonic generation (SHG) intensity, from undetectable to 0.25 × KH2PO4 (KDP), and birefringence, from 0.014 to 0.042 at 1064 nm. Despite the slight compromise made in the light transmission range, [Zn(DETA)2](SO4)(H2O)3 still possesses a short absorption edge of 220 nm, retaining the majority of the light transmission range in the solar-blind region. Our work provides a novel and applicable approach of cationic coordination modification to improve the nonlinear optical coefficient and birefringence of sulfates.

VACUUM BIREFRINGENCE AND DICHROISM IN A STRONG PLANE-WAVE BACKGROUND

In the present study, we consider the effects of vacuum birefringence and dichroism in strong electromagnetic fields. According to quantum electrodynamics, the vacuum state exhibits different refractive properties depending on the probe photon polarization and one also obtains different probabilities of the photon decay via production of electron-positron pairs. Here we investigate these two phenomena by means of several different approaches to computing the polarization operator. The external field is assumed to be a linearly polarized plane electromagnetic wave of arbitrary amplitude and frequency. Varying the probe-photon energy and the field parameters, we thoroughly examine the validity of the locally-constant field approximation (LCFA) and techniques involving perturbative expansions in terms of the external-field amplitude. Within the latter approach, we develop a numerical method based on a direct evaluation of the weak-field Feynman diagrams, which can be employed for investigating more complex external backgrounds. The polarization operator depends on two parameters: classical nonlinearity parameter ξ and the product η = ωq0/m2 of the laser field frequency ω and the photon energy q0 (m is the electron mass). The domains of validity of the approximate techniques in the ξη plane are explicitly identified.

Fabry–Perot enhancement of liquid crystals birefringence effects in terahertz range

Abstract THz technology is a rapidly advancing field in both fundamental and applied research, integrating novel approaches from optical and microwave ranges. Despite the wide applications of liquid crystals (LCs) in the visible range, their efficiency in the THz range is limited due to the low optical path length of existing anisotropic LC materials. In this work, we propose and explore the advantages of incorporating a LC core layer into the Fabry-Perot resonator as a simple strategy to enhance the observed birefringence effects. This enhancement is achieved through multiple wave passes through the LC layer, effectively increasing the effective optical path length.
In particular, we demonstrate a more than tenfold improvement in the efficiency of wave transformation within a plane-parallel LC layer.
Our findings are well correlated with the THz response of an LC cell composed of two parallel thick quartz substrates infiltrated with commercially available E48 liquid crystal, as observed in our experiments. The low switching voltage for cells with pyrocarbon-based electrodes is also demonstrated.

Theoretical and experimental study on optical polarization states in overhead optical cables under complex weather conditions such as real lightning

Abstract By analyzing the changes in three Stokes vectors, the trajectory of polarization state on the Poincaré sphere, and the polarization change rate, both theoretical and practical aspects of polarization state variations in signal light within optical fiber composite overhead power ground wires (OPGWs) during real thunderstorm conditions, were examined. Our findings reveal that lightning and mechanical vibrations both impact the polarization state of the signal light in OPGW. Theoretical models demonstrate that lightning induces polarization changes through the Faraday magneto-optic effect and exhibits nonlinear electro-optic effects, leading to a maximum polarization change rate of Mrad s−1. In contrast, mechanical vibrations cause long-term, low-intensity polarization rate changes, with a maximum polarization rate of Krad s−1, highlighting a significant optical birefringence effect. Digital signal processing algorithms for coherent receivers with over 100G polarization multiplexing provide valuable guidance for recovering polarization states.

Kerr birefringent switching mechanism in core-shell nanowires transformed by stark anti-crossing

Stark anti-crossing (SAC) serves as a new approach to switch the Kerr birefringence effect of the off-centered core-shell square nanowires (OSN). The intensity of SAC induced by an electric field is inversely correlated with the degree of the core displacement from the center. To the best of our knowledge, it is the first demonstration that SAC is equipped with efficacy in suppressing Kerr birefringence of OSN by intensifying energy degeneracy and mitigating the parity symmetry distortion of wavefunction due to core displacement. Such a novel mechanism lies in the formation of two quasi-degenerate energy levels with nearly identical energies but opposite parity wavefunctions. It demonstrates a transform from polarization-dependent to -independent response of refractive index changes at mid-infrared wavelengths longer than 10 µm.

Resonant conversion of gravitational waves in neutron star magnetospheres

High-frequency gravitational waves are the subject of rapidly growing interest in the theoretical and experimental community. In this work we calculate the resonant conversion of gravitational waves into photons in the magnetospheres of neutron stars via the inverse Gertsenshtein mechanism. The resonance occurs in regions where the vacuum birefringence effects cancel the classical plasma contribution to the photon dispersion relation, leading to a massless photon in the medium which becomes kinematically matched to the graviton. We set limits on the amplitude of a possible stochastic background of gravitational waves using X-ray and IR flux measurements of neutron stars. Using Chandra (2–8 keV) and NuSTAR (3–79 keV) observations of RX J1856.6-3754, we set strain limits hclim≃10−26–10−24 in the frequency range 5×1017 Hz≲f≲2×1019 Hz. Our limits are many orders of magnitude stronger than existing constraints from individual neutron stars at the same frequencies. We also use recent JWST observations of the Magnetar 4U 0142+61 in the range 2.7×1013 Hz≲f≲5.9×1013 Hz, setting a limit hclim≃5×10−19. These constraints are in complementary frequency ranges to laboratory searches with CAST, OSQAR and ALPS II. We expect these limits to be improved both in reach and breadth with a more exhaustive use of telescope data across the full spectrum of frequencies and targets. Published by the American Physical Society 2024

Pre- and post-compensation to suppress birefringent walk-off effects of entangled photons.

Photon-based entanglement sources, crucial for obtaining entangled states, are typically generated via spontaneous parametric down-conversion. However, birefringence in nonlinear crystals causes spatial or temporal walk-off, reducing entangled photon quality. The theoretical analysis attributes birefringent walk-off to dispersive materials curbed by pre- and post-compensation. We experimentally validate this method, enhancing polarization-entangled photon quality. We measured the Bell state along with a violation of CHSH-Bell's inequality by ∼366 standard deviations (S = 2.623 ± 0.0017). Our approach, simple and stable, does not complicate setups. Its applicability extends to optimizing various entanglement source schemes, aiding optical quantum technologies such as computation, sensing, and communication.

Detecting axion dark matter with black hole polarimetry

The axion, as a leading dark matter candidate, is the target of many ongoing and proposed experimental searches based on its coupling to photons. Ultralight axions that couple to photons can also cause polarization rotation of light which can be probed by the cosmic microwave background. In this work, we show that a large axion field is inevitably developed around black holes due to the Bose-Einstein condensation of axions, enhancing the induced birefringence effects. Therefore, measuring the modulation of supermassive black hole imaging polarization angles is a strong probe to the axion-photon coupling due to the formation of the axion condensation (axion star) which enhances the axion field. The oscillating axion field around black holes induces polarization rotation on the black hole image, which is detectable and distinguishable from astrophysical effects on the polarization angle, as it exhibits distinctive temporal variability and frequency invariability. In this work, we perform the theoretical calculation on the axion star formation rate and correspondingly the enhanced axion field value near supermassive black holes. Then, we present the range of axion-photon couplings within the axion mass range 10−21–10−16 eV that can be probed by the Event Horizon Telescope. The axion parameter space probed by black hole polarimetry will expand with the improvement in sensitivity on the polarization measurement and more black hole polarimetry targets with determined black hole masses. Published by the American Physical Society 2024

Plug-and-play four-state modulation continuous-variable quantum key distribution

In this paper, a novel and highly efficient secure communication scheme is proposed through the integration of four-state modulation quantum key distribution and plug-and-play technology. This scheme serves the purpose of transmitting information reliably while preserving data confidentiality between two communicating parties. The most important advantage of the proposed continuous-variable QKD system is that the birefringence effect in fiber can be compensated automatically. Notably, simulation experimental evaluations are conducted, unveiling the performance of the plug-and-play four-state QKD which is as good as the four-state protocol when having small Rayleigh scattering noise. Furthermore, we conduct a comprehensive analysis of potential security threats targeted at the proposed protocol, thereby substantiating its robustness against such attacks. Moreover, theoretical justifications are provided to validate the security of the proposed scheme.

X-ray Polarimetry of X-ray Pulsars

Radiation from X-ray pulsars (XRPs) was expected to be strongly linearly polarized owing to a large difference in their ordinary and extraordinary mode opacities. The launch of IXPE allowed us to check this prediction. IXPE observed a dozen X-ray pulsars, discovering pulse-phase dependent variation of the polarization degree (PD) and polarization angle (PA). Although the PD showed rather erratic profiles resembling flux pulse dependence, the PA in most cases showed smooth variations consistent with the rotating vector model (RVM), which can be interpreted as a combined effect of vacuum birefringence and dipole magnetic field structure at a polarization-limiting (adiabatic) radius. Application of the RVM allowed us to determine XRP geometry and to confirm the free precession of the NS in Her X-1. Deviations from RVM in two bright transients led to the discovery of an unpulsed polarized emission likely produced by scattering off the accretion disk wind.

Effects of Birefringence and Dichroism in Magnetic Fluids with Different Degrees of Aggregative Stability

Effects of Birefringence and Dichroism in Magnetic Fluids with Different Degrees of Aggregative Stability

Efficient Manipulation of Near‐Field Terahertz Waves: Individually Addressable Transmissive Meta‐Device

AbstractDue to the powerful capability in manipulating electromagnetic (EM) waves, digital coding and programmable metasurfaces have found vast application prospects across numerous areas such as next‐generation wireless communications and digital holography. Liquid crystals (LCs), as dielectric materials with significant birefringence effect over a wide frequency range, provide a cost‐effective solution for achieving the programmable metasurfaces and flexible EM manipulations, especially in the terahertz (THz) band. Different from the conventional 1D control and single functionality of transmissive LC‐based devices, here, a 16 × 16 addressable amplitude‐phase coding meta‐device is proposed to support for frequency multiplexing by using the film on glass (FOG) technology. Both numerical simulations and experimental results demonstrate that the meta‐atom exhibits an amplitude modulation depth over 90% and a phase tuning range ≈180° at two distinct frequencies, and hence the single meta‐device can provide multifunctional EM applications, including near‐field printing imaging, 3D THz energy convergence, and zero‐order Bessel beam generation. The proposed strategy paves a way for constructing highly integrated and high‐performance THz multifunctional information processing systems.

Tunable and switchable multi-wavelength mode-locked fiber lasers induced by an optimized hybrid mode-locked composite filtering effect.

A multi-wavelength mode-locked fiber laser can generate different wavelengths from a single laser cavity, offering potential as a dual-frequency comb and serving as an ideal light source for terahertz wave generation. We present an optimized hybrid mode-locked Er-doped fiber laser with flexible outputs: switchable and tunable dual-wavelength mode-locking, along with stable tri-wavelength mode-locking, which is achieved by introducing 0.69 m polarization-maintaining fiber and bent 200 m single-mode fiber to enhance intra-cavity birefringence and nonlinear effect to optimize the hybrid mode-locking effect, that is, build the composite filter effect. The dual-wavelength mode-locking not only covers a tunable wavelength range of 5 nm but also provides tunable wavelength intervals of 4-26 nm due to the composite filter effect. The formation dynamics of the tri-wavelength mode-locking can be switched either pair-by-pair or one-by-one. This approach enables the realization of wavelength interval tunable dual-wavelength mode-locking in mode-locked fiber lasers simply by introducing fiber without additional actions. Such a simple, compact fiber laser with tunable wavelength capabilities holds significant potential for diverse applications.

Power scaling of intra-cavity Nd:YAG/LBO laser at 532 nm by birefringence compensation

We report an effective method to reduce the impact of polarization state changes caused by thermal birefringence in intra-cavity frequency-doubled laser. The laser consists of a diode side pumped Nd:YAG module, an acousto-optic modulator Q-switch, and an LBO crystal used for SHG generation in 532 nm laser. The effect of thermal birefringence originated by the Nd:YAG rod with concave-shape end surfaces on SHG efficiency is compensated by the insertion of a λ/8 plate into the cavity. At the repetition frequency of 9 kHz, the 532 nm laser achieves a maximum output power of 23.8 W, a pulse duration of 60 ns (FWHM), and a beam quality factor of Mx 2 × My 2 = 1.52 × 1.43. Compared with the λ/4 plate and without plate, the maximum average power of the laser with the λ/8 plate has increased by 22.7% and 66.4%, respectively, the beam quality factor has also been greatly improved correspondingly. This method provides a new solution for lasers to compensate thermally induced birefringence.

β-Pb3P2S8: A new optical crystal with exceptional birefringence effect

Birefringent crystals play an irreplaceable role in optical systems by adjusting the polarization state of light in optical devices. This work successfully synthesized a new thiophosphate phase of β-Pb3P2S8 through the high-temperature solid-state spontaneous crystallization method. Different from the cubic α-Pb3P2S8, the β-Pb3P2S8 crystallizes in the orthorhombic Pbcn space group. Notably, β-Pb3P2S8 shows a large band gap of 2.37 eV in lead-based chalcogenides, wide infrared transparent window (2.5−15 μm), and excellent thermal stability. Importantly, the experimental birefringence shows the largest value of 0.26@550 nm in chalcogenides, even larger than the commercialized oxide materials. The Barder charge analysis result indicates that the exceptional birefringence effect is mainly from the Pb2+ and S2− in the [PbSn] polyhedrons. Meanwhile, the parallelly arranged polyhedral layers could improve the structural anisotropic. Therefore, this work supports a new method for designing chalcogenides with exceptional birefringence effect in the infrared region.

Improved modeling of in-ice particle showers for IceCube event reconstruction

The IceCube Neutrino Observatory relies on an array of photomultiplier tubes to detect Cherenkov light produced by charged particles in the South Pole ice. IceCube data analyses depend on an in-depth characterization of the glacial ice, and on novel approaches in event reconstruction that utilize fast approximations of photoelectron yields. Here, a more accurate model is derived for event reconstruction that better captures our current knowledge of ice optical properties. When evaluated on a Monte Carlo simulation set, the median angular resolution for in-ice particle showers improves by over a factor of three compared to a reconstruction based on a simplified model of the ice. The most substantial improvement is obtained when including effects of birefringence due to the polycrystalline structure of the ice. When evaluated on data classified as particle showers in the high-energy starting events sample, a significantly improved description of the events is observed.

Homoatomic Polychalcogenide Nonlinear Optical Anionic Groups with Ultra-Large Optical Anisotropy.

Functional assembly of nonlinear optical (NLO) motifs with a large optical anisotropy is vital to the development of advanced NLO and birefringent materials. In this work, we highlight that, in addition to heteroatomic NLO motifs, homoatomic anionic clusters formed by aggregated anions (S, Se, Te) exhibit diverse chain-, ring-, and cage-like chemical structures as well as one-, two-, and three-dimensional motif alignments. The rich structural chemistry enables homoatomic polychalcogenides (HAPCs) to exhibit asymmetric structural features and anisotropic optical properties, with great potential for NLO and birefringent performance. Focusing on totally 55 binary HAPCs A2Qn (n = 2, 3, 4, 5; A = Na, K, Rb, Cs; Q = S, Se, Te) and their ternary analogues, we employ the state-of-the-art first-principles approach to systematically investigate the modulation evolution of their NLO and birefringent properties. Remarkably, Rb2Te3 and Na2TeSe2 exhibit rarely colossal birefringence (>1.0@10 μm) and NLO effects (>20 × AgGaS2), much larger than conventional NLO chalcogenides. Na2Te3 presents the largest birefringence to date (∼3.48@1, 2.72@2, 2.34@10 μm), indicating the unique structural superiority of HAPC in terms of ultra-large birefringence. By mining the intrinsic mechanism, the HAPC anionic groups are identified as novel mid-infrared NLO "material genes", furnishing unique NLO and birefringent performance for the design of novel optoelectronic materials.