Lensing Effect Research Articles

Annular-shaped beam for the mitigation of thermal lensing effects in Nd:YAG solid-state lasers

Annular-shaped beam for the mitigation of thermal lensing effects in Nd:YAG solid-state lasers

2.79-μm high peak power LiNbO3 acousto-optic Q-switched Er,Cr:YSGG laser with thermal lensing effect compensation

A new type of lithium niobate (LiNbO3) acousto-optic Q-switched Er,Cr:YSGG laser with high peak power was designed and the thermal lensing effect compensation was studied. The values of thermal focal length in the gain medium were calculated theoretically and measured experimentally. The experimental results validate the designed plane-convex resonator validity, and the output performance of the 2.79 μm Er,Cr:YSGG laser was obviously improved. When the laser operated at free running region, the maximum values of pulse energy was 160 mJ at 60 Hz, compared with the plane-parallel resonator, the pulse energy was increased by 2 times in the plane-convex resonator. When the LiNbO3 Q-switched laser operated at 60 Hz, the maximum values of pulse energy was 8.5 mJ, and the minimum values of pulse duration was 60.8 ns, and the corresponding peak power approximately was 140 kW, respectively. Compared with the plane-parallel resonator, the pulse energy was increased by 1.6 times in the plane-convex resonator, the corresponding peak power was increased by 2.3 times.

NIR/Visible Light Double Beam Synergistically Enhanced the Emission of Triplet‐Triplet Annihilation Upconversion via Thermal Lensing Effect

AbstractStimuli‐responsive triplet‐triplet annihilation upcoversion (TTA‐UC) systems show additional application potentials in biological and environmental sensing besides the typical applications, such as improving the efficiency of solar‐powered devices. This work presents a double‐beam synergistically controlled TTA‐UC system that can increase the UC emission intensity by more than 6‐fold with the aid of the thermal lensing effect of an near‐infrared (NIR)‐absorbing solution in a double‐beam coupling system of visible/NIR light. The collimation effect of a divergent 532 nm laser beam, achieved through the concave lens effect of a Pdpc(OBu)8 solution under NIR irradiation, significantly increases the excitation power density of the UC system, which is responsible for the increment of UC emission intensity. The ON/OFF ratio of the TTA‐UC switching can be conveniently regulated by the output power of either the 532 nm laser or 721 nm laser, as well as the concentration and compounds of the photothermal lens effect solution. The visible/NIR stimuli‐responsive TTA‐UC system is applied to photolithography to increase both the speed and depth of the photo printing.

Photon motion and weak gravitational lensing in black-bounce spacetime* *Supported by Grant F-FA-2021-510 of the Uzbekistan Ministry for Innovative Development

The effect of spacetime curvature on photon motion may offer an opportunity to propose new tests on gravity theories. In this study, we investigate and focus on the massless (photon) particle motion around black-bounce gravity. We analyze the horizon structure around a gravitational compact object described by black-bounce spacetime. The photon motion and the effect of gravitational weak lensing in vacuum and plasma are discussed, and the shadow radius of the compact object is also studied in black-bounce spacetime. Additionally, the magnification of the image is studied using the deflection angle of light rays.

General polytropic spheres as gravitational lenses

We propose hydrostatic polytropic spheres governed by the Lane-Emden equation (LEE) of index n as a novel set of physical models for axially averaged gravitational lenses anywhere in the Universe, alternative to the familiar singular isothermal sphere (SIS) and the Navarro–Frenk–White (NFW) profile, as such general polytropic spheres are conceptually simple, versatile in representing a series of equations of state, and able to address both the inner core and cusp features. As LEE is nonlinear, there exist several distinct classes of LEE solutions to serve as physical lens models. With a few scaling parameters, the complete problem can be readily reconstructed with full physical dimensions. A given mass density profile satisfying LEE produces lensing effects that are solely determined by a dimensionless parameter q which contains geometric and kinematic information about the source-lens-observer system. The lens mapping and tangential shear or distortion profile are derived, first analytically for special cases and then asymptotically at the outskirts or near the edge of the lens. Numerical procedures for calculating full lensing profiles of a general lens are developed. Our results include the analytical “singular polytropic sphere” (SPS) profile which generalizes the SIS model and may outperform the latter in modeling dark matter halos among others. We further point out that dynamic models of general polytropic spheres in self-similar evolution can serve as several broad classes of gravitational lenses and produce time-dependent lensing effects slow or fast depending on the pertinent time scales. Astrophysical sources that can be lensed include electromagnetic wave sources in the entire frequency band, gravitational wave sources in the entire frequency band, gravitons even possibly with finite masses, neutrino sources of three different types, neutron sources, and ultra high energy cosmic rays (UHECRs) of electrically charged particles which can also interact with magnetic fields. We discuss and elabrate applications to dark matter halos, hypermassive black holes and supermassive black holes in the entire Universe including the early Universe, magnetized supermassive stars, static and dynamically evolving spherical and cylindrical lenses in contexts of astrophysics and cosmology.

Einstein beams and the diffractive aspect of gravitationally-lensed light

The study of light lensed by cosmic matter has yielded much information about astrophysical questions. Observations are explained using geometrical optics following a ray-based description of light. After deflection the lensed light interferes, but observing this diffractive aspect of gravitational lensing has not been possible due to coherency challenges caused by the finite size of the sources or lack of near-perfect alignment. In this article, we report on the observation of these wave effects of gravitational lensing by recreating the lensing conditions in the laboratory via electro-optic deflection of coherent laser light. The lensed light produces a beam containing regularities, caustics, and chromatic modulations of intensity that depend on the symmetry and structure of the lensing object. We were also able to observe previous and new geometric-optical lensing situations that can be compared to astrophysical observations. This platform could be a useful tool for testing numerical/analytical simulations, and for performing analog simulations of lensing situations when they are difficult to obtain otherwise. We found that laboratory lensed beams constitute a new class of beams, with long-range, low expansion, and self-healing properties, opening new possibilities for non-astrophysical applications.

Effects of gravitational lensing by Kaluza-Klein black holes on neutrino oscillations

We study gravitational lensing of neutrinos in a Kaluza-Klein black hole spacetime and compare the oscillation probabilities of neutrinos with the case of lensing by black holes in General Relativity. We show that measuring neutrino oscillations in curved spacetimes may allow us to distinguish the two kinds of black holes even in the weak-field limit, as opposed to what happens for the weak lensing of photons. This promises to become an useful tool for future measurements of the properties of black hole candidates and possibly help to constrain the validity of alternative theories of gravity.

Lensing Reconstruction from the Cosmic Microwave Background Polarization with Machine Learning

The lensing effect of the cosmic microwave background (CMB) is a powerful tool for our study of the distribution of matter in the universe. The quadratic estimator (QE) method, which is widely used to reconstruct lensing potential, has been known to be suboptimal for the low noise level polarization data from next-generation CMB experiments. To improve the performance of the reconstruction, other methods, such as the maximum-likelihood estimator and machine-learning algorithms, have been developed. In this work, we present a deep convolutional neural network model named the Residual Dense Local Feature U-net (RDLFUnet) for reconstructing the CMB lensing convergence field. By simulating lensed CMB data with different noise levels to train and test network models, we find that for noise levels less than 5 μK-arcmin, RDLFUnet can recover the input gravitational potential with a higher signal-to-noise ratio than the previous deep-learning and traditional QE methods at almost the entire observation scale.

Statistical properties and lensing effect on the repeating fast radio burst FRB 180916.J0158+65

ABSTRACT FRB 180916.J0158+65 is a well-known repeating fast radio burst with a period ($16.35~\rm d$) and an active window ($5.0~\rm d$). We give out the statistical results of the dispersion measures and waiting times of bursts of FRB 180916.J0158+65. We find the dispersion measures at the different frequencies show a bimodal distribution. The peaking dispersion measures of the left mode of the bimodal distributions increase with frequency, but the right one is inverse. The waiting times also present the bimodal distribution, peaking at 0.05622 and 1612.91266 s. The peaking time is irrelevant to the properties of bursts, either for the preceding or subsequent burst. By comparing the statistical results with possible theoretical models, we suggest that FRB 180916.J0158+65 suffered from the plasma lensing effects in the propagation path. Moreover, this source may be originated from a highly magnetized neutron star in a high-mass X-ray binary.

Delensing of Cosmic Microwave Background Polarization with Machine Learning

Primordial B-mode detection is one of the main goals of next-generation cosmic microwave background (CMB) experiments. Primordial B-modes are a unique signature of primordial gravitational waves (PGWs). However, the gravitational interaction of CMB photons with large-scale structures will distort the primordial E modes, adding a lensing B-mode component to the primordial B-mode signal. Removing the lensing effect (“delensing”) from observed CMB polarization maps will be necessary to improve the constraint of PGWs and obtain a primordial E-mode signal. Here, we introduce a deep convolutional neural network model named multi-input multi-output U-net (MIMO-UNet) to perform CMB delensing. The networks are trained on simulated CMB maps with size 20° × 20°. We first use MIMO-UNet to reconstruct the unlensing CMB polarization (Q and U) maps from observed CMB maps. The recovered E-mode power spectrum exhibits excellent agreement with the primordial EE power spectrum. The recovery of the primordial B-mode power spectrum for noise levels of 0, 1, and 2 μK-arcmin is greater than 98% at the angular scale of ℓ < 150. We additionally reconstruct the lensing B map from observed CMB maps. The recovery of the lensing B-mode power spectrum is greater than roughly 99% at the scales of ℓ > 200. We delens the observed B-mode power spectrum by subtracting the reconstructed lensing B-mode spectrum. The recovery of tensor B-mode power spectrum for noise levels of 0, 1, and 2 μK-arcmin is greater than 98% at the angular scales of ℓ < 120. Even at ℓ = 160, the recovery of tensor B-mode power spectrum is still around 71%.

Thermo-optic coefficient of chemical vapor deposited graphene multilayers

Observation of strong inelastic light-matter interaction and large thermal conductivity of novel two-dimensional graphene has invigorated the present research. Herein, the thermo-optic coefficient of graphene multilayers is obtained from their nonlinear refraction coefficients calculated from Z-scan experiment in closed aperture geometry. The refractive optical nonlinearity was obtained employing a continuous wave He-Ne laser and occurs due to thermal lensing effect. The graphene multilayers behave as the diverging (concave) lens giving rise to self-defocusing effect leading to negative sign of refractive nonlinearity. Accordingly, a large negative thermo-optic coefficient (-2.43×10-3 K-1) inferred for the graphene multilayers suggests its utility for thermo-optic device applications.&#x0D; Keywords: Graphene, Optical Nonlinearity, Thermal lens, Self-defocusing, Thermo-optic coefficients

DeepGraviLens: a multi-modal architecture for classifying gravitational lensing data

Gravitational lensing is the relativistic effect generated by massive bodies, which bend the space-time surrounding them. It is a deeply investigated topic in astrophysics and allows validating theoretical relativistic results and studying faint astrophysical objects that would not be visible otherwise. In recent years, machine learning methods have been applied to support the analysis of the gravitational lensing phenomena by detecting lensing effects in datasets consisting of images associated with brightness variation time series. However, the state-of-the-art approaches either consider only images and neglect time-series data or achieve relatively low accuracy on the most difficult datasets. This paper introduces DeepGraviLens, a novel multi-modal network that classifies spatio-temporal data belonging to one non-lensed system type and three lensed system types. It surpasses the current state-of-the-art accuracy results by approx 3% to approx 11%, depending on the considered data set. Such an improvement will enable the acceleration of the analysis of lensed objects in upcoming astrophysical surveys, which will exploit the petabytes of data collected, e.g., from the Vera C. Rubin Observatory.

Metasurface-generating high purity narrow linewidth cylindrical vector beams: power scaling and its limitation

1.89 kW cylindrical vector beams (CVBs) at 1,064 nm with the 3 dB linewidth being about 0.08 nm have been generated from a narrow linewidth all-fiber linearly-polarized laser by metasurface extra-cavity conversion. At the maximum output power, the transmission efficiency, mode purity of radially polarized cylindrical vector beams (RP-CVBs) are 97% and 92.7%, respectively. To the best of our knowledge, this is the highest power of narrow linewidth CVBs generated from fiber laser. The temperature of the metasurface is moderate, and the maximum temperature is 75.5°C at 1.89 kW, which means that the system can be further power scaled. The evolution of mode purity has been analyzed numerically, and the influence of high-order modes (HOM) in laser source and thermal effects of metasurface has been calculated, which reveals that the presence of high-order modes and the temperature rise of metasurface degrade the mode purity of the CVBs. Among them, HOM causes a degradation of 1.68%, thermal lensing effect contributes 2.32%, and the microstructure variation of the metasurface contributes the remaining 3.3%.

Thermal Lensing Effect Reduction on High-Power Multi-Mode Diode Lasers

High-power broad-area diode lasers are needed for a variety of applications. However, such lasers suffer from deteriorated beam quality due to multimode behavior in the lateral direction at high power. We propose an approach to reduce the thermal lensing effect by introducing a thermal compensation layer. As a result of reducing the thermal lensing effect, we demonstrated that the lateral divergence angle was reduced by 16.2%, the lateral beam parameter product was reduced by 12.8%, and the lateral brightness was increased by 18.4% for 230 μm wide diode operating at 50 A current while maintaining a good output power.

Testing new massive conformal gravity with the light deflection by black hole

We study the weak gravitational lensing effect of Non-Bocharova-Bronnikov-Melnikov-Bekenstein (BBMB) black hole in new massive conformal gravity. We analyze the deflection angle of light caused by new massive conformal gravity by using the Gauss-Bonnet theorem. As a consequence, we obtain the Gaussian optical curvature and calculate the deflection angle of the new massive conformal gravity for spherically balanced space-time with the Gauss-Bonnet theorem. The resultant deflection angle of light in the weak field limits showing that the bending of light is a global and topological phenomenon. Furthermore, we identify the deflection angle of light in the framework of the plasma medium, we also demonstrate the effect of a plasma medium on the deflection of light by non BBMB. In addition, the behavior of the deflection angle by new massive conformal gravity is explicitly shown in the influence of plasma medium and for the non plasma medium.

Lensing of gravitational waves from tidal disruption events

ABSTRACT In this work, we investigate the effect of gravitational lensing on the gravitational wave (GW) signals of a population of tidal disruption events (TDEs). We estimate the number of lensed-magnified signals that we expect to detect with future space-based GW observatories, in particular LISA and DECIGO. We model the lens distribution using an hybrid approach that combines semi-analytic methods with numerical results from ray tracing simulations. We divide the TDE population in two classes, nuclear TDEs (main sequence stars tidally disrupted by massive black holes in the cores of galaxies) and globular TDEs (white dwarfs tidally disrupted by intermediate mass black holes in globular clusters). We find that, even considering the effect of lensing, LISA will not be able to observe any TDEs, while DECIGO could detect ∼16 strongly lensed (μ &amp;gt; 2) globular TDEs and ∼135 strongly lensed nuclear TDEs, over an observational period of 10 yr. Our results reveal the role that lensing will play in future deci-Hertz GW observatories, indicating exciting multimessenger opportunities with TDEs but at same time signalling the need to develop adequate data analysis techniques to correctly reconstruct the astrophysical properties of the source.

Detecting and Characterizing Young Quasars. III. The Impact of Gravitational Lensing Magnification

We test the impact of gravitational lensing on the lifetime estimates of seven high-redshift quasars at redshift z ≳ 6. The targeted quasars are identified by their small observed proximity zone sizes, which indicate extremely short quasar lifetimes (t Q ≲ 105yr). However, these estimates of quasar lifetimes rely on the assumption that the observed luminosities of the quasars are intrinsic and not magnified by gravitational lensing, which would bias the lifetime estimates toward younger ages. In order to test the possible effects of gravitational lensing, we obtain high-resolution images of the seven quasars with the Hubble Space Telescope and look for signs of strong lensing. We do not find any evidence of strong lensing, i.e., all quasars are well described by point sources, and no foreground lensing galaxy is detected. We estimate that the strong-lensing probabilities for these quasars are extremely small (∼1.4 × 10−5) and show that weak lensing changes the estimated quasar lifetimes by only ≲0.2 dex. We thus confirm that the short lifetimes of these quasars are intrinsic. The existence of young quasars indicates a high obscured fraction, radiatively inefficient accretion, and/or flickering lightcurves for high-redshift quasars. We further discuss the impact of lensing magnification on measurements of black hole masses and Eddington ratios of quasars.

The integrating sphere system plus in-situ absorption monitoring: A new scheme to study absorption enhancement of black carbon in ambient aerosols

Black carbon (BC) is the strongest light-absorbing aerosol in the atmosphere. The coating process causes lensing effects to enhance the BC absorption. The reported BC absorption enhancement values (Eabs) significantly differ partly due to the measurement methods used. The biggest difficulty in measuring the Eabs values is how to denude the coated particles so that the true value of absorption without coatings can be distinguished from lensing effects. In this study, we proposed a new approach based on an integrating sphere (IS) system plus in-situ absorption monitoring instrument to study Eabs in ambient aerosols. This approach is capable of (i) “de-lensing through solvent dissolution and solvent de-refraction”, by which the absorption coefficient of denuded BC is acquired, and (ii) monitoring in-situ absorption with photoacoustic spectroscopy. With the help of the EC concentration measured by a thermal/optical carbon analyser, the Eabs values were calculated as the quotient of in-situ mass absorption efficiency divided by denude mass absorption efficiency. We applied this new approach to measure the Eabs values of four seasons in Beijing and found an annual mean of 1.90 ± 0.41 in 2019. More importantly, a previous assumption that BC absorption efficiency may be progressively enhanced by increased air pollution was validated and quantified using a logarithmic relationship of Eabs = 0.6 ln (PM2.5 ̶ 3.59) ̶ 0.43 (R2 = 0.99). This signals a continued drop of Eabs for future ambient aerosols with the sustained improvement in local air quality in China, meriting serious attention to its influences in climate, air quality, and atmospheric chemistry.

The Significant Contribution of Polycyclic Aromatic Nitrogen Heterocycles to Light Absorption in the Winter North China Plain

By quantifying the absorption of black carbon (BC), brown carbon (BrC) and the lensing effect, we found that BrC dominates the total absorption at 450 nm, and the largest absorption contribution proportion of BrC could reach 78.3% during heavy pollution. The average absorption enhancement (Eabs) at 530 nm was only 1.38, indicating that BC is not coated well here. The average value of the absorption Ångstrom exponent (AAE) between 450 nm and 530 nm was 5.3, suggesting a high concentration of BrC in Wangdu. CHN+ was the greatest contributor to the light absorption of molecules detected in MSOC with a proportion of 12.2–22.4%, in which the polycyclic aromatic nitrogen heterocycles (PANHs) were the dominant compounds. The C6H5NO3 and its homologous series accounted for 3.0–11.3%, and the C15H9N and its homologous series, including one C16H11N and three C17H13N compounds, accounted for 5.1–12.3%. The absorption of these PANHs is comparable to that of nitro–aromatics, which should attract more attention to the impact of climate radiative forcing.

Black hole mirages: Electron lensing and Berry curvature effects in inhomogeneously tilted Weyl semimetals

We study electronic transport in Weyl semimetals with spatially varying nodal tilt profiles. We find that the flow of electrons can be guided precisely by judiciously chosen tilt profiles. In a broad regime of parameters, we show that electron flow is described well by semiclassical equations of motion similar to the ones governing gravitational attraction. This analogy provides a physically transparent tool for designing tiltronic devices like electronic lenses. The analogy to gravity circumvents the notoriously difficult full-fledged description of inhomogeneous solids. A comparison to microscopic lattice simulations shows that it is only valid for trajectories sufficiently far from analogue black holes. We finally comment on the Berry curvature-driven transverse motion and relate the latter to spin precession physics.