Showing papers on "Waveplate published in 2021"
01 Mar 2021
Abstract: Metasurfaces with local phase tuning by subwavelength elements promise unprecedented possibilities for ultra-thin and multifunctional optical devices, in which geometric phase design is widely used due to its resonant-free and large tolerance in fabrications. By arranging the orientations of anisotropic nano-antennas, the geometric phase-based metasurfaces can convert the incident spin light to its orthogonal state, and enable flexible wavefront engineering together with the function of a half-wave plate. Here, by incorporating the propagation phase, we realize another important optical device of quarter-wave plate together with the wavefront engineering as well, which is implemented by controlling both the cross- and co-polarized light simultaneously with a singlet metasurface. Highly efficient conversion of the spin light to a variety of linearly polarized light are obtained for meta-holograms, metalens focusing and imaging in blue light region. Our work provides a new strategy for efficient metasurfaces with both phase and polarization control, and enriches the functionalities of metasurface devices for wider application scenarios.
20 citations
TL;DR: In this article, a single-layered terahertz anisotropic metasurface quarter-wave plate consisting of hybrid metallic wire grating arrays is presented, which enables broadband linear to pure circular polarization conversion with an ellipticity over 0.99 and 43% bandwidth of the central wavelength.
18 citations
TL;DR: In this article, the authors proposed a new structure of an ultra-broadband metamaterial absorber by adding an excess dielectric layer on a metammaterial structure with two stacked chromium square resonators.
Abstract: Broadband metamaterial absorbers in the terahertz (THz) range are of great importance because of their applications, especially in the field of THz detection and imaging. Characteristics of an ideal absorber include wide bandwidth and insensitivity to polarization and incidence angle. Here we propose a new structure of an ultra-broadband THz absorber by adding an excess dielectric layer on a metamaterial structure with two stacked chromium square resonators. The excess layer besides protecting chromium resonator from oxidation creates an extra Fabry–Perot cavity that extends the bandwidth of the structure. The relative bandwidth of this structure for 90% absorption exceeds 150% and covers frequencies ranging from 0.52 to 3.66 THz, which is an advantage over the works reported in the literature review. The number of resonating layers is decreased related to the earlier works too. The proposed structure is not sensitive to the polarization of the incident radiation, at the same time its absorption is almost insensitive to the incident angle too. For both TE and TM polarization the absorption stays more than 80% up to 60° of the incident angles. Furthermore, the insensitivity of the proposed device to misalignment between layers is evaluated for misalignment up to $28~\mu \text{m}$ . The results show that the structure is insensitive to misalignment which makes its fabrication easy. We have simulated the proposed structure using the numerical finite element method (FEM). Also, we have extracted a circuit model for the suggested absorber which is in accordance to the numerical model and can be used to reduce the designing process time. Correspondingly, we efficiently explain the absorption mechanism using the circuit model and magnetic field analysis in the structure. We have shown that the broad bandwidth of the structure is the result of coupling between various modes of Fabry–Perot (FP) cavity resonances and surface plasmons (SPs). The FP resonances are coupled through the gap resonators between the different layers. This means absorbers are more compact than the convectional $\text{n}\lambda $ /4 wave plate absorbers.
17 citations
TL;DR: In this paper, the anisotropy of chiral 2D perovskite single crystals is explored and the full-Stokes polarimeter based on pure CHS single crystals was reported, which integrates the polarizer, waveplate and photodetector together and thus can be able to discriminate the polarization states of light.
Abstract: Full-Stokes polarimeters, equipped with the capability of discriminating light polarization states, can find important applications in various optical and optoelectronic devices. Nevertheless, currently most full-Stokes polarimeters require complex and bulky optical elements or optical metasystems integrated with metasurfaces, which can increase the cost and cause energy loss. Here, the anisotropy of chiral 2D perovskite single crystals is explored and the full-Stokes polarimeter based on pure chiral 2D perovskite single crystals is reported. By using optical anisotropy and the ability to distinguish the helicity of the circularly polarized light, chiral 2D perovskite polarimeter integrates the polarizer, waveplate, and photodetector together and thus can be able to discriminate the polarization states of light. The as-fabricated device exhibits a photoresponsivity of 0.136 A W-1 and a detectivity of 1.2 × 1010 Jones. This study provides a paradigm to construct filterless on-chip Stokes polarimeter with great simplicity and low cost.
15 citations
TL;DR: In this article, a direct-view scheme was presented to generate arbitrary cylindrical vector (CV) beams, including CV beams, vortex beams, and CVV beams, by a vortex half-wave plate (VHP).
Abstract: A concise, efficient, and practical direct-view scheme is presented to generate arbitrary cylindrical vector (CV) beams, including CV beams, vortex beams, and cylindrical vector vortex (CVV) beams, by a vortex half-wave plate (VHP). Six kinds of first-order and other high-order CV beams, such as azimuthally polarized (AP) beams, antivortex radial polarization mode beams, and three-order AP beams, are formed by simply rotating a half-wave plate. The Stokes parameters and double-slit interference of multitype CV beams are investigated in detail. The polarization parameters, including degree of polarization, polarization azimuth, and ellipticity, are obtained, which demonstrates the efficient generation of CV beams. In addition, the double-slit interference experiment is introduced in the setup, and fringe misplacement and tilt appear for CVV beams, in which the misplacement number M is 2P+1 for P≤2 and 2P−1 for P≥3, where P is the polarization order number, and the fringe tilt offset is positively related to the topological charge number l of CVV beams. In addition, new types of VHPs can be formed by cascading two or more VHPs when the types of available VHPs are limited, assisting in more flexible generation of multitype CV beams. It is experimentally demonstrated that arbitrary CV beams with high quality are effectively achieved by the proposed setup, and the double-slit interference method can be utilized to determine and analyze CV beams rapidly and concisely by practical performance, which shows the potential to be implemented as a commercial device.
15 citations
TL;DR: In this paper, a bifocal metasurface is designed to focus on one circularly polarized component as a point and spin-opposite components as a vortex under the linearly polarized (LP) incidence.
Abstract: Conventionally, the realization of polarization transformation and wavefront manipulation in metasurfaces relies on the Pancharatnam-Berry (PB) phase together with the dynamic phase. However, the reported polarization transformation and wavefront manipulation were limited to spin-dependent wavefront manipulation for circular polarization (CP). To obtain more abundant functions, we propose a novel technology that relies on the dynamic phase with a spatial interleaving unit arrangement. With the functions of a quarter wave plate, the metasurfaces we designed can achieve multiple wavefront manipulations which are not only for the spin polarization transformation but also for the linear polarization transformation. Specifically, we design a bifocal metasurface, which can focus on one circularly polarized component as a point and spin-opposite component as a vortex under the linearly polarized (LP) incidence. With the further adjustment of the unit arrangement, the left-hand circularly polarized (LCP) and right-hand circularly polarized (RCP) components under the LP incidence can be refocused on the same point and then composited, resulting in a new LP exit wave. Furthermore, we prove theoretically that the desired x-LP component and y-LP component under the arbitrary CP incidence can also be manipulated independently. We believe that the versatility of this method will provide a novel platform for the development of terahertz integrated photonics.
13 citations
11 citations
TL;DR: In this paper, a study on tunable wave plates based on phase-change metasurfaces made of Ge2Sb2Te5 nanopillar structures is presented, which can work as a high-efficiency transmissive half or quarter wave plate depending on their structural parameters.
Abstract: Wave plates based on metasurfaces have attracted intensive attention over the past decade owing to their compactness and design flexibility. Although various wave plates have been designed, their working wavelengths are fixed once they are made. Here we present a study on tunable wave plates based on phase-change metasurfaces made of Ge2Sb2Te5 nanopillar structures. The Ge2Sb2Te5 nanopillars can work as a high-efficiency transmissive half- or quarter-wave plate depending on their structural parameters. The working wavelength of wave plate can be tuned via the phase transition of Ge2Sb2Te5. Moreover, the polarization state of the transmitted light at a fixed wavelength can be modified by changing the crystallinity of Ge2Sb2Te5. The features suggest that tunable wave plates may have applications in optical modulators, molecular detection, and polarimetric imaging.
10 citations
TL;DR: In this article, a simple binary one-dimensional grating is used to achieve independent polarization control around two terahertz frequencies, 0.14 THz and 0.3 THz.
10 citations
20 Nov 2021
TL;DR: In this article, a silica-based metasurface acting almost like a quarter-wave plate in the UV spectral range was designed and fabricated, fulfilling the numerous constraints inherent to high-power laser beamlines, in particular, high LIDT and large sizes.
Abstract: Bringing light–matter interactions into novel standards of high-energy physics is a major scientific challenge that motivated the funding of ambitious international programs to build high-power laser facilities. The major issue to overcome is to avoid laser intensity heterogeneities over the target that weaken the light–matter interaction strength. Laser beam smoothing aims at homogenizing laser intensities by superimposing on the target laser speckle intensities produced by orthogonal left and right circularly polarized beams. Conventional wave plates based on anisotropic crystals cannot support the laser fluences of such lasers, and the challenge is now to design wave plates exhibiting a high laser induced damage threshold (LIDT). Fused silica exhibits high LIDT, but its isotropic dielectric permittivity prevents effects on polarization retardance. Metamaterials have been widely investigated to tailor the phase and polarization of light but with plasmonic or high-refractive-index materials, and applying this approach with silica is highly challenging due to the weak optical contrast between silica and air or vacuum. Here we design and fabricate a silica-based metasurface acting almost like a quarter-wave plate in the UV spectral range, fulfilling the numerous constraints inherent to high-power laser beamlines, in particular, high LIDT and large sizes. We numerically and experimentally demonstrate that fused silica etched by deep grooves with a period shorter than the wavelength at 351 nm operates the linear-to-quasi circular polarization conversion together with a high transmission efficiency and a high LIDT. The high aspect ratio of the grooves due to the short period imposed by the short wavelength and the deepness of the grooves required to overcome the weak optical contrast between silica and air is experimentally obtained through a CMOS compatible process.
8 citations
TL;DR: In this paper, the authors employed the design of the metamaterial half-wave plate by using the multiple layers of the material with some specific rotation angles, which can analyze the rotation angles and can be easily extended to multiple layers.
Abstract: In this paper, we employ the novel design of the metamaterial half-wave plate by using the multiple layers of the metamaterials with some specific rotation angles. The rotation angles are given by composite pulse control which is the well-known quantum control technique. A big advantage of this method can analytically calculate the rotation angles and can be easily extended to the multiple layers. The more layers of the metamaterials can present more bandwidth of half-wave plate. In this paper, we present 1, 3, 5, 7 configurations of layers of a metamaterial half-wave plate and we demonstrate that our device increasingly enhance the bandwidth of performance.
TL;DR: In this paper, the complex refractive indices along the inplane axes and map the birefringence of DyScO3 (DSO) crystals were examined and shown to behave like a QWP over a broad frequency range of 0.50 −0.70 −0.61 µm with a phase tolerance of ± 3%.
Abstract: With growing interest in exploring fundamental phenomena at terahertz (THz) frequencies, the need for controlling the polarization state of THz radiation is indispensable. However, simple optical elements, such as waveplates that allow creating circularly-polarized THz radiation, are scarce. Here, we present THz quarter-wave plates (QWPs) made out of (110)-cut and (001)-cut DyScO3 (DSO) crystals. We examine the complex refractive indices along the in-plane axes and map the birefringence of both DSO crystals. Further, we demonstrate that both 50-μm-thick (110)-cut DSO and 370-μm-thick (001)-cut DSO crystals behave like a QWP over a broad frequency range of 0.50–0.70 THz and 0.50–0.61 THz, respectively, with a phase tolerance of ±3%.
TL;DR: Based on the symmetry of the skylight polarization distribution pattern, Wang et al. as discussed by the authors proposed a novel skyligh orientation sensor consisting of a camera, an S-waveplate, and a linear polarizer.
Abstract: The angle of the polarization (AOP) and the degree of polarization (DOP) of the scattered skylight are symmetrically distributed concerning the solar meridian. Based on the symmetry of the skylight polarization distribution pattern, this paper proposes a novel skylight orientation sensor consisting of a camera, an S-waveplate, and a linear polarizer. The skylight orientation sensor is using the image polarization encoding capability of the S-waveplate and the linear polarizer to convert the skylight polarization information into the image’s symmetry axis extraction, which has the advantages of simple structure, better real-time performance, no resolution loss and instantaneous field of view error. The symmetry axis in the image is consistent with the solar meridian. Therefore, the angle between the solar meridian and the skylight orientation sensor reference axis can be obtained without calculating the polarization information, which shows why the sensor has better real-time performance. The angle measurement accuracy and uncertainty of the skylight orientation sensor are verified by numerical simulation and outdoor experiments. The results demonstrate that the skylight orientation sensor has good application potential in autonomous navigation.
TL;DR: In this paper, a metallic quarter-wave plate with a bandwidth of 600 nm (0.95-1.55 µm) and an average transmittance of more than 70% has been designed and shows excellent potential to be used in miniaturized optical polarization detection systems and as an optical data storage device.
Abstract: A large bandwidth and high-efficiency subwavelength quarter-wave plate (QWP) is an indispensable component of an integrated miniaturized optical system. The bandwidth of existing plasmonic quarter-wave plates with a transmission efficiency of more than 50% is less than 320 nm in the near-infrared band. In this paper, a metallic quarter-wave plate with a bandwidth of 600 nm (0.95–1.55 µm) and an average transmittance of more than 70% has been designed and shows excellent potential to be used in miniaturized optical polarization detection systems and as an optical data storage device. For TE mode incident waves, this miniaturized optical element can be equivalent to a Fabry-Perot (FP) resonator. Meanwhile, for the TM mode incident wave, the transmission characteristics of this structure are controlled by gap surface plasmon polaritons (G-SPPs) existing in the symmetric metal/insulator/metal (MIM) configuration.
TL;DR: In this article, the authors proposed a broadband ultrathin quarter-wave plate to perform circular-to-linear and linear-tocircular polarization conversion using a plasmonic metasurface.
TL;DR: In this article, a potential solution is suggested to account for modulation matrix variation from one cycle to the other, where the number of samples per half rotation is optimized to optimize the data volume.
Abstract: One of the major science goals of the Visible Emission Line Coronagraph (VELC) payload aboard the Aditya-L1 mission is to map the coronal magnetic field topology and the quantitative estimation of longitudinal magnetic field on routine basis. The infrared (IR) channel of VELC is equipped with a polarimeter to carry out full Stokes spectropolarimetric observations in the Fe XIII line at 1074.7~nm. The polarimeter is in dual-beam setup with continuously rotating waveplate as the polarization modulator. Detection of circular polarization due to Zeeman effect and depolarization of linear polarization in the presence of magnetic field due to saturated Hanle effect in the Fe~{\sc xiii} line require high signal-to-noise ratio (SNR). Due to limited number of photons, long integration times are expected to build the required SNR. In other words signal from a large number of modulation cycles are to be averaged to achieve the required SNR. This poses several difficulties. One of them is the increase in data volume and the other one is the change in modulation matrix in successive modulation cycles. The latter effect arises due to a mismatch between the retarder's rotation period and the length of the signal detection time in the case of VELC spectropolarimeter (VELC/SP). It is shown in this paper that by appropriately choosing the number of samples per half rotation the data volume can be optimized. A potential solution is suggested to account for modulation matrix variation from one cycle to the other.
15 Jan 2021
TL;DR: In this article, the authors proposed a new method for small optical rotation measurement based on the use of a half-wave plate and the high-stability common-path heterodyne interferometry.
Abstract: We proposed a new method for small optical rotation measurement. The method is based on the use of a half-wave plate and the high-stability common-path heterodyne interferometry. When the azimuth angle is at 22.5° of a half-wave plate, the phase has a distinct change caused by the small polarization rotation of the test beam. The optical rotation can be obtained from the relationship between the phase and the azimuth angle of the wave plate. The resolution of polarization rotation measurement can achieve 1.6 × 10−5 degree/mm and the detection sensitivity on circular birefringence of glucose-water solution can be up to δ|nr − nl | = 5.6 × 10−11.
TL;DR: This work presents an accurate polarization reconstruction method based on the coherence demodulation technique, which is different from the previous windowing method operating in the optical path difference domain, and shows that the reconstruction technique is robust to misalignment and additional noise.
Abstract: In this work, we present an accurate polarization reconstruction method based on the coherence demodulation technique, which is different from the previous windowing method operating in the optical path difference domain. The proposed method uses a signal multiplier and a low-pass filter to reconstruct Stokes parameters without performing any Fourier transform. Because this method does not require a Fourier transform, the Stokes reconstruction could be finished in the spectral domain. For calibrating the waveplate phase error, coherence demodulation allows for establishing an analytical model to describe the influence of waveplate imperfections on the polarization measurement process. The phase error will result in a channel shift and Fourier broadening, both of which cause serious errors during Stokes reconstruction. With the model, a method based on a linear polarizer was proposed for calibrating the phase deviation of waveplate. After that, the accurate reconstruction of polarization parameters could be achieved. An experiment was performed to check the ability of the proposed method. The experimental result showed that it has the same excellent performance of reconstructing Stokes parameters using the traditional windowing method. Finally, a series of simulations was carried out to verify the robustness of this method, which showed that the reconstruction technique is robust to misalignment and additional noise.
TL;DR: In this article, the authors proposed new designs of the Pancharatnam-based achromatic half-wave plate (AHWP) that eliminate the frequency dependent optic-axis over the bandwidth and maintain high modulation efficiency.
Abstract: Pancharatnam based achromatic half-wave plate (AHWP) achieves high polarization efficiency over broadband. It generally comes with a feature of which the optic-axis of AHWP has dependence of the electromagnetic frequency of the incident radiation. When the AHWP is used to measure the incident polarized radiation with a finite detection bandwidth, this frequency dependence causes an uncertainty in the determination of the polarization angle due to the limited knowledge of a detection band shape and a source spectral shape. To mitigate this problem, we propose new designs of the AHWP that eliminate the frequency dependent optic-axis over the bandwidth and maintain high modulation efficiency. We carried out the optimization by tuning the relative angles among the individual half-wave plates of the five- and nine-layer AHWPs. The optimized set of the relative angles achieves the frequency independent optic-axis over the fractional bandwidth of 1.3 and 1.5 for the five- and nine-layer AHWPs, respectively. We also study the susceptibility of the alignment accuracy to the polarization efficiency and the frequency independent optic-axis, which provides a design guidance for each application.
TL;DR: In this paper, a real-time displacement reconstruction technique based on a phase retardation method is proposed, where the displacement of the external object can be reconstructed by a quadrature demodulation algorithm.
TL;DR: In this article, a theoretical analysis of the performance of an inline Sagnac interferometric optical current sensor with component errors has been completed, showing that rotator assembly errors can cause a ∼10% nonlinear error with current.
Abstract: A full theoretical analysis of the performance of passive inline Sagnac interferometric optical current sensor with component errors has been completed. A mathematical model was developed to show how nonideal components affect the overall performance of the sensor. The Faraday rotator element is a critical component in this passively biased optical current sensor. The analysis indicates that errors in the rotation element in the assembly can cause a ∼10 % / deg nonlinear error with current. Another source of nonlinearity in the response of the sensor is the 45-deg splices to the polarization maintaining fiber (PMF) link between the rotator element and the sensing head assembly. The analysis indicates a ∼0.2 % / deg error for the splice between the rotator and PMF link to the sensing head and a ∼0.1 % / deg error for the splice between the PMF and the quarter waveplate fiber at the sensing head. All quarter waveplate errors in the rotator assembly have linear effects to the sensor response function which can be calibrated out of the final sensor assembly. Temperature response data are presented for an uncompensated sensor over the +40 ° C to −30 ° C temperature range and the sensor shows a ±1.5 % accuracy.
TL;DR: In this paper, a four-pixel photoconductive emitter with an integrated achromatic waveplate was used to achieve full control of the ellipticity of broadband pulses of THz radiation, from linear to left or right-handed circular polarization.
Abstract: Full control of the ellipticity of broadband pulses of THz radiation, from linear to left- or right-handed circular polarization, was demonstrated via a four-pixel photoconductive emitter with an integrated achromatic waveplate. Excellent polarization purity and accuracy were achieved, with Stokes parameters exceeding 97% for linear and circular polarization, via a robust scheme that corrected electrically for polarization changes caused by imperfect optical elements. Furthermore, to assess the speed and precision of measurements of the THz polarization, we introduced a figure of merit, the standard error after one second of measurement, found to be 0.047° for the polarization angle.
TL;DR: A polarizer based on uncoated silicon Brewster plates, an effective, low-cost, high-power compatible tool providing sufficient contrast for signal and idler beam separation of the broadband mid-infrared Type II optical parametric sources is proposed.
Abstract: The availability of optical elements for the mid-infrared wavelength range, such as polarizers and wavelength separators, is limited especially when a broadband wavelength range coverage is required. We propose a polarizer based on uncoated silicon Brewster plates. A detailed analysis of the polarizer’s contrast and the influence of parasitic reflections, its dependence on wavelength, and the angular misalignment is shown. Two different arrangements of the two- and four-plate polarizers are discussed. With contrast including the influence of parasitic reflections of over 103 for the whole transparency range of silicon (1.2–6.5 µm), the four-plate polarizer is an effective, low-cost, high-power compatible tool providing sufficient contrast for signal and idler beam separation of the broadband mid-infrared Type II optical parametric sources. The proposed polarizers can function as an attenuator assembly without any wave plate.
TL;DR: In this paper, a new type of metasurface for multichannel hybrid polarization distribution in near-field is proposed based on the combination of various subwavelength cross-nanofins (CNs).
Abstract: As an inherent characteristic of light, polarization plays important roles in information storage, display and even encryption. Metasurfaces, composed of specifically designed subwavelength units in a two-dimensional plane, offer a great convenience for polarization manipulation, yet improving their integrability and broadband fidelity remain significant challenges. Here, based on the combination of various subwavelength cross-nanofins (CNs), a new type of metasurface for multichannel hybrid polarization distribution in near-field is proposed. Sub-wavelength CN units with various waveplate (WP) functionalities, such as frequency-division multiplexing WP, half-WP and quarter-WP are implemented with high efficiency in broadband. High-resolution grayscale image encryption, multi-image storage and rapid polarization detection are demonstrated by encoding the WP pixels into single, double and four channels, respectively. All these applications possess good fidelity in an ultrabroad wavelength band from 1.2 to 1.9 µm, and the high degree of integrability, easy fabrication and multifunction make the CN-shaped WP pixels a promising candidate in optical device miniaturization, quantum applications and imaging technologies.
TL;DR: In this paper, an equal intensity beam splitter (EIBS) for passive laser speckle reduction is reported, which consists of a segmented half-wave plate (SHWP) with the designed orientation of the fast axis of each segment.
Abstract: An equal-intensity beam splitter (EIBS) for passive laser speckle reduction is reported. The EIBS consists of a segmented half-wave plate (SHWP) with the designed orientation of the fast axis of each segment, a polarization beam splitter, and a mirror. The SHWP is fabricated using patterned photoalignment material and liquid crystal polymer. Ten laser sub-beams are generated by the twenty-one-pixelated EIBS, where the largest intensity ratio among them is 7.6. Laser temporal and spatial coherences are destroyed because of the optical path delays among the laser sub-beams. The EIBS is used to reduce laser speckle passively, and objective speckle contrast is reduced from 0.82 to 0.33 when all 10 laser sub-beams are used.
03 Oct 2021
TL;DR: In this paper, the authors proposed a new type of optical device with variable transmittance based on the incident angle direction, which consist of two liquid crystal devices (LCDs) with a half-wave plate between them.
Abstract: This study proposed a new type of optical device with variable transmittance based on the incident angle direction. These devices consist of two liquid crystal devices (LCDs) with a half-wave plate between them. Hybrid aligned nematic (HAN)-type guest-host (GH) LCDs or GH-LCDs with antiparallel alignment of high pretilt angles were used. The use of a half-wave plate allowed for the control of the p- and s-waves. Using these devices, a wide range of transmittances were obtained because no polarizer was used. The newly proposed LCDs have a wide range of applications, including use on buildings, vehicles, and glasses.
TL;DR: In this article, a rotating anisotropic-mirror-sample-rotating-anisotropic -mirror ellipsometry (RAM-S-RAM-E) was used for the calibration and operation of a Mueller imaging microscope.
Abstract: We demonstrate calibration and operation of a Mueller matrix imaging microscope using dual continuously rotating anisotropic mirrors for polarization state generation and analysis. The mirrors contain highly spatially coherent nanostructure slanted columnar titanium thin films deposited onto optically thick titanium layers on quartz substrates. The first mirror acts as polarization state image generator and the second mirror acts as polarization state image detector. The instrument is calibrated using samples consisting of laterally homogeneous properties such as straight-through-air, a clear aperture linear polarizer, and a clear aperture linear retarder waveplate. Mueller matrix images are determined for spatially varying anisotropic samples consisting of a commercially available (Thorlabs) birefringent resolution target and a spatially patterned titanium slanted columnar thin film deposited onto a glass substrate. Calibration and operation are demonstrated at a single wavelength (530 nm) only, while, in principle, the instrument can operate regardless of wavelength. We refer to this imaging ellipsometry configuration as rotating-anisotropic-mirror-sample-rotating-anisotropic-mirror ellipsometry (RAM-S-RAM-E).
TL;DR: In this article, a left-hand circularly polarized terahertz vortex beam (CPTVB) is generated by utilizing a THz quarter wave plate and a spiral phase plate.
Abstract: A circularly polarized vortex beam possesses similar focusing properties as a radially polarized beam. This type of beam is highly valuable for developing optical manufacturing technology, microscopy, and particle manipulation. In this work, a left-hand circularly polarized terahertz (THz) vortex beam (CPTVB) is generated by utilizing a THz quarter wave plate and a spiral phase plate. Focusing properties of its longitudinal component Ez are detailedly discussed on the simulation and experiment. With reducing the F-number of the THz beam and comparing with a transverse component Ex of a general circularly polarized THz beam, the simulation results show that the focal spot size and intensity of its Ez component can reach 87% and 50% of Ex under a same focusing condition. In addition, the experimental results still demonstrate that the left-hand CPTVB can always maintain fine Ez focusing properties in a broad bandwidth, which manifest the feasibility of this class of THz beams.