Beam Shift Research Articles

Goos–Hänchen and Imbert–Fedorov shifts for rotational elliptical Gaussian beams impinging on graphene–substrate surfaces

This paper derives the analytical solution of Goos–Hänchen and Imbert–Fedorov shifts of rotational elliptical Gaussian beams (REGBs). Furthermore, we find that near the Brewster angle incidence at near-p incident paraxial beam polarization, the values of the beam shifts and the widths of the corresponding resonance shift curves become dependent on the beam waist. By introducing the effective beam waist and rotational phase factor, the causes of the beam shift variation phenomenon are analyzed from the viewpoints of analytical solutions and Fourier optics. Meanwhile, by adjusting the Fermi energy level of graphene, it is found that the direction of GH shift of the elliptical rotating Gaussian beam depends on the reflecting material, and the direction of IF shift depends on the rotational phase of the beam.

Current-induced switching of photonic spin Hall effect in a magnetic insulator based on spin–orbit torques

The photonic spin Hall effect (PSHE) is analogous to the electronic spin Hall effect, which has substantial potential for optoelectronic applications. However, PSHE-based devices are rarely studied, and manipulating the PSHE by charge current has remained elusive thus far. In this paper, we demonstrate current-induced switching of PSHE in the Ce1Dy2Al0.42Fe4.58O12 thin film capping with Pt electrodes, which is mediated by spin–orbit torques at the Pt/Ce1Dy2Al0.42Fe4.58O12 interface. The results show that the transverse beam shifts related to the PSHE can be reversed by applying a small order of magnitude charge current (∼108 A·m−2) to the Pt layer in opposite directions, which predicts low dissipation in our proposed heterostructure. In addition, by applying an in-plane magnetic field, the saturation beam shifts can be increased, which can significantly enhance the switching ratio.

Analysis of Laser Cell Response Characteristics under Different Irradiation Conditions

Although the application of laser wireless energy transmission technology in many fields such as UAV power supply is increasing, the laser incidence angle and beam shift remain the key factors limiting the efficiency of long-range laser wireless energy transmission. In this study, a laser cell response test platform was built to measure and analyze the response characteristics of a laser cell under different laser incidence angles and beam shifts. The results show that the increase in the incident angle intensifies the reflection on the irradiated surface, resulting in a linear decrease in the power density received by the laser cell, which eventually leads to a significant decrease in the output power, and the output power tends to be close to 0 when the incident angle exceeds 75°. The increase in the beam offset distance increases the reverse bias of the cell, which is the main reason for the significant decrease in the output power. The local irradiation also leads to an increase in the heat generation power; when the beam coverage is below 50%, the overall output power tends to be close to 0. This study provides a reference for improving the laser wireless energy transmission efficiency and laser cell optimization.

Goos–Hänchen and Imbert–Fedorov shifts of the Airy beam in dirac metamaterials

We theoretically derive the expression for the Goos–Hänchen (GH) and Imbert–Fedorov (IF) shifts of the Airy beam in Dirac metamaterial. In this work, the large GH and IF shifts can be found when the Airy beam is reflected near the Dirac and Brewster angles. Compared to the Gaussian beam, the GH shifts of the Airy beam are more obvious in the vicinity of the Brewster angle. Interestingly, it is found that the ability to produce an Airy vortex beam at the Dirac point. In addition, the magnitude and the direction of the GH shifts can be controlled by the rotation angles of the Airy beam. We take advantage of this property to design a reflective optical switch based on the rotation angle-controlled GH shifts of the Dirac metamaterial. Our solutions provide the possibility to implement light-tuned optical switches. Moreover, our model can also be used to describe the GH and IF shifts generated by novel beams in other similar photonic systems.

Diverse lateral shifts of beams in non-Hermitian waveguide arrays.

Non-Hermitian systems have attracted considerable attention in optics due to the rich physics introduced by the existence of real spectra and exceptional points (EPs), which is exploited in lasers, optical sensors and on-chip manipulations of light. Here, focusing on the dynamics of beams in non-Hermitian waveguide arrays supporting a ring of EPs (exceptional ring) and 3rd-order EPs, we theoretically demonstrate that the center of energy of a beam prepared around an eigenstate of the waveguide array near EPs could exhibit non-zero shifts in the lateral direction during its propagation. When the initial state of the beam prepared around an eigenstate inside (outside) the exceptional ring with the imaginary (real) eigenvalue, the lateral shifts of the beams are manifested by the non-oscillating (Zitterbewegung-like) motions, which are robust to the perturbations of coupling coefficients between waveguides. Remarkably, the amplitude of the non-oscillating shift is dependent on a non-Hermitian Berry connection (U(1) gauge invariance). It contradicts the conventional wisdom that the Berry connection cannot induce the dynamic effect. Furthermore, near the high-order EPs, the initial-state-dependent lateral shifts of the beams present diversity, such as multifrequencies and destructive interferences. The counterintuitive lateral shifts of the beams stem from the non-orthogonal nature of eigenstate of the non-Hermitian systems, which may open a gateway towards the non-Hermitian beam dynamics and manipulations of beams.

Spatial shifts of reflected light beam on black phosphorus/hexagonal boron nitride structure

We examined Goos-Hänchen (GH) and Imbert-Fedorov (IF) shifts of the reflective beam from the hexagonal boron nitride (hBN) covered by black phosphorus (BP) layers, where the BP layers are rotated by an angle with respect to the incident plane. The interaction of phonon polaritons in hBN and plasmon polaritons in BP, as well as the structure surface and interface between the two media determines the two shifts. In the common frequency–response range of the BP and hBN, the GH- and IF-shifts can be very large in the vicinity of epsilon-near-zero (ENZ) for a linearly-polarized incidence. The GH-shift can be continuously tuned from positive to negative or even to zero at a fixed frequency by adjusting the electron density and anisotropic axis-orientation of the BP. Another fascinating phenomenon is that the IF-shift can be not only excited by the linearly-polarized incidence but also greatly improved, even up to -156λ0. These conclusions are applicable to the other 2D anisotropic materials, which will become a guidance of new polarization-dependent, anisotropic optoelectronics devices.

Ultrafast optical phase-sensitive ultrasonic detection via dual-comb multiheterodyne interferometry

Highly sensitive and broadband ultrasound detection is important for photoacoustic imaging, biomedical ultrasound, and ultrasonic nondestructive testing. The elasto-optical refractive index modulation induced by ultrasound arouses a transient phase shift of a probe beam. Highly sensitive phase detection with a high Q factor resonator is desirable to visualize the ultraweak transient ultrasonic field. However, current phase-sensitive ultrasonic detectors suffer from limited bandwidth, mutual interference between intensity and phase, and significant phase noise, which become key to limiting further improvement of detection performance. We report a phase-sensitive detector with a bandwidth of up to 100 MHz based on dual-comb multiheterodyne interferometry (DCMHI). By sensing the phase shift induced by the ultrasound without any resonators in the medium, the DCMHI boosted the phase sensitivity by coherent accumulation without any magnitude averaging and extra radio frequency amplification. DCMHI offers high sensitivity and broad bandwidth as the noise-equivalent pressure reaches 31 mPa / √Hz under 70 MHz acoustic responses. With a large repetition rate difference of up to 200 MHz of dual comb, DCMHI can achieve broadband acoustic responses up to 100 MHz and a maximum possible imaging acquisition rate of 200 MHz. It is expected that DCMHI can offer a new perspective on the new generation of optical ultrasound detectors.

Exotic Photonic Spin Hall Effect from a Chiral Interface

AbstractThe photonic spin Hall effect provides a quantitative way to characterize the spin–orbit interaction of light and enables many applications, such as the precise metrology, since this effect is featured with a spin‐dependent transverse shift of the light beam. This transverse shift is generally nonzero during the reflection/transmission process, and it is sensitive to the polarization and the incident angle of the light beam. By contrast, here it is revealed that for the transmitted light, the transverse shift can be always zero and polarization‐independent, irrespective of the incident angle. The underlying mechanism is that the conversion between the spin and orbit angular momenta of light is fully suppressed during the transmission process. Such an exotic photonic spin Hall effect occurs, if , , and , where t stands for the transmission coefficient and its first (second) superscript represents the polarization of the transmitted (incident) light, and () is the transmitted (incident) angle. These transmission conditions are achievable, e.g., by exploiting an interface only with a chiral surface conductivity. Similarly, a polarization‐independent photonic spin Hall effect is revealed for the reflected light.

Spin Hall Effect of Light via Momentum-Space Topological Vortices around Bound States in the Continuum.

Optical bound states in the continuum (BICs) are exotic topological defects in photonic crystal slabs, carrying polarization topological vortices in momentum space. The topological vortex configurations not only topologically protect the infinite radiation lifetime of BICs, but also intrinsically contain many unexploited degrees of freedom for light manipulation originating from BICs. Here, we theoretically propose and experimentally demonstrate the spin Hall effect of light in photonic crystal slabs via momentum-space topological vortices around BICs. The strong spin-orbit interactions of light are induced by using the topological vortices around BICs, introducing both wave-vector-dependent Pancharatnam-Berry phase gradients and cross-polarized resonant phase gradients to the spinning light beam, which lead to spin-dependent in-plane-oblique lateral light beam shifts. Our work reveals intriguing spin-related topological effects around BICs, opening an avenue toward applications of BICs in integrated spin-optical devices and information processing.

Revisiting the photonic orbital Hall effect with the vortex mode decomposition

The photonic orbital Hall effect (POHE) refers to the vortex-dependent beam shifts, which is generally believed to result from the conversion of intrinsic orbital angular momentum (IOAM) to extrinsic orbital angular momentum (EOAM). However, the physical mechanism of the POHE, such as how the IOAM is converted to the EOAM, remains further elucidation. In this paper, we re-examine the POHE of a vortex beam with additional IOAM illuminating at an optically thin slab by means of vortex mode decomposition. By considering the competition and coupling between the radial and azimuthal vortex harmonics of the abnormal mode in the transmitted beam, it is found that the underlying mechanism of the POHE is in fact a spin-to-orbital angular momentum (OAM) conversion process. And the IOAM carried by the incident beam is directly superimposed on the OAM obtained during the conversion. Our findings not only offer an alternative perspective for understanding the POHE, but also exhibit application potential in orbit–orbit and spin–orbit optical components.

Plasmonic Biosensing with Nano-Engineered Van der Waals Interfaces.

Observing a Goos-Hänchen (GH) shift of the incident light beam provides a simple and convenient method of detecting fast phase variations without the need for cumbersome direct phase measurements. Here, we show that few-monolayers-thick van der Waals structures (WS₂ , MoSe₂ and graphene) nano-engineered onto a plasmonic surface can enhance the phase variation sensitivity to analyte presence, leading to more than 3 orders of magnitude increase in the Goos-Hänchen shift (ca. 886 mm/RIU for a WS₂ /graphene/Au multilayer). The detection limit is evaluated to be as low as 0.1 aM (6.7 pg/mL) for bovine serum albumin protein with molecular weight of 67 kDa and 1 fM (24.4 ng/mL) for biotin (244 Da) molecules.

Robust Secure Resource Allocation for RIS-Aided SWIPT Communication Systems.

Aiming at the influence of channel uncertainty, user information leakage and harvested energy improvement, this paper proposes a robust resource allocation algorithm for reconfigurable intelligent reflector (RIS) multiple-input single-output systems based on imperfect channel state information. First, considering the legal user minimum secret rate constraint, the base station maximum transmit power constraint and the RIS phase shift constraint with the bounded channel uncertainty, a joint optimization of the base station active beam, energy beam and RIS phase shift is established. A multivariate coupled nonlinear resource allocation problem for matrices is addressed. Then, using S-procedure and alternating optimization methods, the original non-convex problem is transformed into a deterministic convex optimization problem and an alternating optimization algorithm based on continuous convex approximation is proposed. The simulation results show that the proposed algorithm has better fairness harvested energy compared with the traditional robust algorithm.

On anomalous optical beam shifts at near-normal incidence

We develop the theory of optical beam shifts (both Goos–Hänchen and Imbert–Fedorov) for the case of near-normal incidence, when the incident angle becomes comparable with the angular beam divergence. The developed theory uncovers the unified origin of the anomalous beam shift enhancement via the geometric Berry phase singularity. Particularly, we predict the large Goos–Hänchen shift occurring for small incidence angles. We also propose a simple experimental scheme involving a quarter-wave q-plate that allows us to observe the giant transverse and longitudinal, spatial and angular beam shifts simultaneously. Finally, we analyze the relevant beam parameters, polarization structure, and intensity profiles of the shifted transmitted beam. Our results can find applications in spin–orbit photonics, polarization optics, sensing applications, and quantum weak measurements.

Effect of frequency stabilization on beam shift of total reflection prism laser gyro

For the phenomenon of degradation of the performance of total reflection prism laser gyro before and after reset jump, this paper investigates the effect of frequency stabilization on the beam shift of total reflection prism laser gyro using a matrix optics method, and proposes a method to calculate the beam shift with frequency stabilization. The numerical simulation and experimental results show that, unlike the beam shift characteristics caused by the prism temperature, the frequency stabilization additionally causes an approximately equal beam shift at each prism interface, and the shift is proportional to the frequency stabilization control amount. It is pointed out that the large abrupt change of beam propagation path before and after reset jump is the main reason for the degradation of total reflection prism laser gyro performance, and the frequency stabilization control method of reset jump once for each optical wavelength adjustment can effectively reduce the beam shift caused by frequency stabilization.

Characteristics of an Airy beam at a dielectric interface

A full analytical theory for the reflection and transmission of an Airy beam impinging on a dielectric surface is presented. Based on the plane-wave angular spectrum expansion, the analytical expressions for the reflected and transmitted fields comprising beam modes are derived. To improve the calculation accuracy, the actual beam field retains up to the second-order terms. The influences of decay factor and beam width on the intensity distributions of the incident, reflected, and transmitted beams are studied. In addition, we investigate the effects of decay factor and beam width on the beam shift of the reflected beam near the Brewster angle. There is a giant negative lateral shift near the Brewster angle. Results show that the beam shift decreases and increases with increasing decay factor and beam width, respectively. A comparison with the beam shifts of Airy beams incident on the interface and dielectric slab at the Brewster angle is also discussed. The beam shift of the dielectric slab exists an abrupt increase. Finally, an Airy beam incident from air to the left-handed material (LHM) is considered. Results indicate that the imaging position of the incident Airy beam in the LHM is affected by the incident angle and negative refractive index. Our results may provide some theoretical support for the applications of Airy beams in detection and imaging.

Spin Hall effect of transversely spinning light.

Light carries spin angular momentum, which, in the free space, is aligned to the direction of propagation and leads to intriguing spin Hall phenomena at an interface. Recently, it was shown that a transverse-spin (T-spin) state could exist for surface waves at an interface or for bulk waves inside a judiciously engineered metamaterial, with the spin oriented perpendicular to the propagation direction. Here, we demonstrate the spin Hall effect for transversely spinning light—a T-spin–induced beam shift at the interface of a metamaterial. It is found that the beam shift takes place in the plane of incidence, in contrast to the well-known Imbert-Fedorov shifts. The observed T-spin–induced beam shift is of geometrodynamical nature, which can be rendered positive or negative controlled by the orientation of T-spin of the photons. The unconventional spin Hall effect of light found here provides a previously unexplored mechanism for manipulating light-matter interactions at interfaces.

Controllable Peculiar Spin‐Dependent Transverse and In‐Plane Shifts of Airy Beam

AbstractGenerally, most of the photonic spin Hall effect (SHE) are investigated based on the Gaussian beam, and the research of the photonic SHE in novel beams with non‐Gaussian distribution is relatively rare. The Airy beam is one of the novel beams whose initial field distribution is asymmetric and tunable. Thus, it is necessary to explore the photonic SHE in the Airy beam. Here analytical solutions for the transverse and in‐plane shifts of the Airy beam are derived, and the peculiar photonic SHE of the Airy beam is systematically researched. The theoretical research results show that the transverse shifts of the left‐ and right‐handed circularly polarized beams are asymmetric, and the in‐plane shifts of the left‐ and right‐handed circularly beams are identical. More importantly, the variation rules of the transverse and in‐plane shifts with the incident centroid position are obtained, and the incident centroid position is regulated by the decay factor of the Airy beam. That is, the spin‐dependent transverse and in‐plane shift can be manipulated flexibly and purposefully by adjusting the beam parameter. It is believed these findings will provide more ideas for exploring the application of the photonic SHE based on novel beams.

Continuous Goos-Hänchen Shift of Vortex Beam via Symmetric Metal-Cladding Waveguide.

Goos-Hänchen shift provides a way to manipulate the transverse shift of an optical beam with sub-wavelength accuracy. Among various enhancement schemes, millimeter-scale shift at near-infrared range has been realized by a simple symmetrical metal-cladding waveguide structure owing to its unique ultrahigh-order modes. However, the interpretation of the shift depends crucially on its definition. This paper shows that the shift of a Gaussian beam is discrete if we follow the light peak based on the stationary phase approach, where the M-lines are fixed to specific directions and the beam profile is separated near resonance. On the contrary, continuous shift can be obtained if the waveguide is illuminated by a vortex beam, and the physical cause can be attributed to the position-dependent phase-match condition of the ultrahigh-order modes due to the spatial phase distribution.

Challenges in double-beam laser interferometry measurements of fully released piezoelectric films

When utilizing double-beam laser interferometry to assess the piezoelectric coefficient of a film on a substrate, probing both top and bottom sample surfaces is expected to correct the erroneous bending contribution by canceling the additional path length from the sample height change. However, when the bending deformation becomes extensive and uncontrolled, as in the case of membranes or fully released piezoelectric films, the double-beam setup can no longer account for the artifacts, thus resulting in inflated film displacement data and implausibly large piezoelectric coefficient values. This work serves to identify these challenges by demonstrating d33,f measurements of fully released PZT films using a commercial double-beam laser interferometer. For a 1 μm thick randomly oriented PZT film on a 10 μm thick polyimide substrate, a large apparent d33,f of 9500 pm/V was measured. The source of error was presumably a distorted interference pattern due to the erroneous phase shift of the measurement laser beam caused by extensive deformation of the released sample structure. This effect has unfortunately been mistaken as enhanced piezoelectric responses by some reports in the literature. Finite element models demonstrate that bending, laser beam alignment, and the offset between the support structure and the electrode under test have a strong influence on the apparent film d33,f.

Focal shift and focal switch of broadband hollow Gaussian beams passing through an aperture-lens system

Focal shift and focal switch of broadband hollow Gaussian beams passing through an aperture-lens system