Polarized Laser Source Research Articles

Ultrahigh-Reflectivity Circularly Polarized Mirrors Based on the High-Contrast Subwavelength Chiral Metasurface

The circularly polarized laser sources are core components for many optical applications such as biomedicine, quantum technology, and AR/VR. However, conventional techniques make it difficult to further diminish the size of circularly polarized lasers. Thus, the high-contrast subwavelength chiral metasurface (HCCM) with a 980 nm operating wavelength is numerically investigated. The HCCM is composed of chiral metasurfaces modulating the circular dichroism of reflectance and 6 pairs of Distributed Bragg Reflectors (DBR) with 55% reflectivity. The reason that the HCCM has an ultra-high reflectivity (99.9%) at the operating wavelength of 980 nm is the combination of the optical refractive index difference between the GaAs metasurface and the AlOx substrate and weak destructive interference in the AlOx support layer. In addition, the circular dichroism of the chiral metasurfaces (2.1%) is mainly caused by the displacement of two square air holes in opposite directions, thus transforming the unit cell of the metasurface from C2 symmetry to chiral symmetry. The reflector has the advantages of a simple structure and miniaturization, which is expected to greatly reduce the fabrication difficulty and cost of the circular polarization VCSELs.

Optical spin hall effect in exciton-polariton condensates in lead halide perovskite microcavities.

An exciton-polariton condensate is a hybrid light-matter state in the quantum fluid phase. The photonic component endows it with characters of spin, as represented by circular polarization. Spin-polarization can form stochastically for quasi-equilibrium exciton-polariton condensates at parallel momentum vector k|| ∼ 0 from bifurcation or deterministically for propagating condensates at k|| > 0 from the optical spin-Hall effect (OSHE). Here, we report deterministic spin-polarization in exciton-polariton condensates at k|| ∼ 0 in microcavities containing methylammonium lead bromide perovskite (CH3NH3PbBr3) single crystals under non-resonant and linearly polarized excitation. We observe two energetically split condensates with opposite circular polarizations and attribute this observation to the presence of strong birefringence, which introduces a large OSHE at k|| ∼ 0 and pins the condensates in a particular spin state. Such spin-polarized exciton-polariton condensates may serve not only as circularly polarized laser sources but also as effective alternatives to ultracold atom Bose-Einstein condensates in quantum simulators of many-body spin-orbit coupling processes.

Metasurface reflector enables room-temperature circularly polarized emission from VCSEL

While most lasers are linearly polarized, circularly polarized laser sources are crucial components for many optical applications such as biosensing, quantum technologies, and AR/VR. However, conventional methods for generating chiral light have limitations in device miniaturization. Vertical-cavity surface-emitting lasers (VCSELs), with their small footprint and surface emission feature, can be integrated with ultrathin metasurfaces for light manipulation, offering an opportunity to realize ultracompact chiral lasers. Here we report, to our knowledge, the first demonstration of chiral lasing from electrically pumped VCSELs at room temperature, without spin injection. This is enabled by incorporating a high-contrast chiral metasurface reflector as the VCSEL top mirror, favoring one specific circular polarization for lasing. Our demonstrated 940 nm VCSELs show stable single-mode chiral lasing and achieve a circular-polarization degree of up to 59%. This study provides a scalable approach for circular-polarization control of VCSELs and holds great promise for applications that desire ultracompact chiral emitters.

Supramolecular Nanohelix Fabricated by Pillararene-Based Host–Guest System for Chirality Amplification, Transfer, and Circularly Polarized Luminescence in Water

Supramolecular Nanohelix Fabricated by Pillararene-Based Host–Guest System for Chirality Amplification, Transfer, and Circularly Polarized Luminescence in Water

Polarimetric LiDAR backscattering contrast of linearly and circularly polarized pulses for ideal depolarizing targets in generic water fogs.

In this paper, we investigate the backscattering depolarization of linearly and circularly polarized laser sources propagating in dense water fogs. We limit our investigation to a simple case where an active LiDAR system is pointed toward a white depolarizing Lambertian solid target. The receiver captures the reflected signal in the orthogonal channel so as to remove most of the backscattering from the water fog. It is shown that in the studied cases, a circularly polarized signal is depolarized faster than a linearly polarized signal and thus produces less contrast. We show that in the cases that can be described by the small angle approximation, the Rubenson degree of polarization (DoP) of a circularly polarized beam can be predicted by the DoP of a linearly polarized beam as DoPcir=2DoPlin-1, even for low-order multiple scattering events. In these conditions, since the linear DoP is always stronger, the contrast is expected to be better in linear polarization for ideal depolarizing targets.

Room-Temperature Lasing in a Low-Loss Tamm Plasmon Cavity

Optical Tamm structures offer great possibilities for the development of new optoelectronic devices ranging from polarized laser sources to plasmon generators. Indeed, thanks to the patterning of a...

Hall effect sensors using polarized electron cloud spin orientation control.

A silicon microring circuit embedded gold film with unique characteristics is proposed for Hall effect, current, and temperature sensing applications. The microring circuit is operated by the input polarized laser sources, in which the space-time distortion control can be employed. A gold film is embedded at the microring center. The whispering gallery mode (WGM) is generated and applied for plasmonic waves, from which the trapped electron cloud oscillation is formed. Through the input port, the input polarized light of 1.55 μm wavelength fed into the space-time control circuit. Spin-up |↑〉(|0〉) and spin-down |↓〉(|1〉) of polarized electrons result when the gold film is illuminated by the WGM. The electric current passing through the gold film generates a magnetic field (B), which is orthogonal to the electric field. Hall voltage is obtained at the output of the circuit, from which the microring space-time circuit can operate for Hall's effect, current, and temperature sensing device. The simulation results obtained have shown that when the input power of 100-500 mW is applied, the optimum Hall effect, current, and temperature sensitivities are 0.12 μVT-1 , 0.9 μVA-1 , and 6.0 × 10-2 μVK-1 , respectively. The Hall effects, current, and temperature sensors have an optimum response time of 1.9 fs.

Real-time modeling of optical orientation in GaAs: Generation and decay of the degree of spin polarization

We present a real-time abinitio description of optical orientation in bulk GaAs due to the coupling with an ultrashort circular polarized laser source. The injection of spin polarized electrons in the conduction band is correctly reproduced, and a non vanishing spin polarization ($\mathbf{P}$) parallel to the direction of propagation of the laser ($z$) emerges. A detailed analysis of the generation and the evolution of $\mathbf{P}(t)$ is discussed. The single $\mathbf{k}$-point dynamics is a motion of precession around a fixed axis with constant $|\mathbf{P}|$ and fixed frequency. Instead, the $\mathbf{k}$-integrated signal shows only a time dependent $P_z(t)$ and decays few pico seconds after the end of the laser pump due to decoherence. Decoherence emerges since the individual contributions activated by the pump give rise to destructive interference. We interpret the results in terms of the \emph{free induction decay} mechanism proposed some years ago. For the first time we are able to reproduce such effect in a full abinitio fashion, giving a quantitative estimate of the associated decay time. Our result also shows a possible explanation to the time decay of spin magnetization observed in many real-time abinitio simulations.

Passive quadrature demodulation of birefringent low-finesse fiber-optic Fabry-Perot interferometric sensors.

We demonstrate a passive quadrature demodulation method using polarized light and a fiber-optic sensor with a birefringent low-finesse Fabry-Perot (FP) cavity. With precisely controlled birefringence in the FP cavity, the fringes probed by light polarized along the two principal axes can have a quadrature phase shift and can be separately detected. We demonstrated the concept for ultrasound detection using a sensor with an FP cavity formed by two low-reflectivity chirped fiber Bragg gratings on a coiled polarization-maintaining (PM) fiber. By controlling the bending radius, bending length, and twist of the coil structure, we obtained an optimized total phase delay of 109° between the fringes of the two polarizations along the principal axes of the PM fiber. Using a linearly polarized laser source and a polarization beam splitter, the signals at the two polarizations were separated and measured by two photodetectors. The experimental results show that the sensor can detect ultrasonic signal when the sensor spectra experience environmental drifts using a laser at a fixed wavelength.

Power scalable 10 W 976 nm single-frequency linearly polarized laser source.

A 10W level 976nm single-frequency linearly polarized laser source was demonstrated with a two-stage all-fiber amplifier configuration. The continuous-wave output power of 10.1W was obtained from the second stage amplifier by using a 20/130μm single-mode, polarization maintaining, 1.5wt.% ytterbium-doped phosphate double-clad fiber. This all-fiber single-frequency laser source is very promising for watt-level deep ultraviolet laser generation via frequency quadrupling.

Dynamically stable Nd:YAG resonators with beam quality beyond the birefringence limit and pumping of a singly resonant optical parametric oscillator.

A simple, reliable, linearly polarized laser source with very high beam quality is demonstrated using standard diode-side-pumped Nd:YAG modules. The laser produced 30W of output power with beam quality factor M2<1.15 over the entire range of input powers and beam quality of 1.02 at the laser operation point. This is, to our knowledge, the highest beam quality for a dynamically stable high-power laser that uses an optically isotropic crystal. The laser was used as a pump source for an optical parametric oscillator based on a periodically poled lithium niobate, producing wavelength in the 1.5-3.8μm range.

Dealloyed Intra-Nanogap Particles with Highly Robust, Quantifiable Surface-Enhanced Raman Scattering Signals for Biosensing and Bioimaging Applications.

Uniformly controlling a large number of metal nanostructures with a plasmonically enhanced signal to generate quantitative optical signals and the widespread use of these structures for surface-enhanced Raman scattering (SERS)-based biosensing and bioimaging applications are of paramount importance but are extremely challenging. Here, we report a highly controllable, facile selective-interdiffusive dealloying chemistry for synthesizing the dealloyed intra-nanogap particles (DIPs) with a ∼2 nm intragap in a high yield (∼95%) without the need for an interlayer. The SERS signals from DIPs are highly quantitative and polarization-independent with polarized laser sources. Remarkably, all the analyzed particles displayed the SERS enhancement factors (EFs) of ≥1.1 × 108 with a very narrow distribution of EFs. Finally, we show that DIPs can be used as ultrasensitive SERS-based DNA detection probes for detecting 10 aM to 1 pM target concentrations and highly robust, quantitative real-time cell imaging probes for long-term imaging with low laser power and short exposure time.

Optimized Spiral Metal-Gallium-Nitride Nanowire Cavity for Ultra-High Circular Dichroism Ultraviolet Lasing at Room Temperature.

Circularly polarized laser sources with small footprints and high efficiencies can possess advanced functionalities in optical communication and biophotonic integrated systems. However, the conventional lasers with additional circular-polarization converters are bulky and hardly compatible with nanophotonic circuits, and most active chiral plasmonic nanostructures nowadays exhibit broadband emission and low circular dichroism. In this work, with spirals of gallium nitride (GaN) nanowires (NWRs) covered by a metal layer, we demonstrated an ultrasmall semiconductor laser capable of emitting circularly-polarized photons. The left- and right-hand spiral metal nanowire cavities with varied periods were designed at ultraviolet wavelengths to achieve the high quality factor circular dichroism metastructures. The dissymmetry factors characterizing the degrees of circular polarizations of the left- and right-hand chiral lasers were 1.4 and −1.6 (±2 if perfectly circular polarized), respectively. The results show that the chiral cavities with only 5 spiral periods can achieve lasing signals with the high degrees of circular polarizations.

Absorption behavior analysis of Carbon Fiber Reinforced Polymer in laser processing

laser machining of CFRP is a potential processing method as an alternative of conventional mechanical machining. This paper studies the absorption behavior of CFRP surface by establishing an optical absorption model based on the interaction of laser and fiber-matrix microstructure in material. In addition to polarization dependence, laser absorptivity is also subjected to the influence of wavelength, fiber volume fraction, and power intensity distribution within the laser spot. It is found that effect of multiple reflections in the microstructure would increase the absorptivity by 30%. Experiments have confirmed that absorption shows little fluctuation along the scanning line due to large laser spot. Short wavelength and arbitrarily polarized laser source are advantageous in achieving an effective and consistent machining process. CFRP sample for validation experiment is obtained through the nanosecond Nd:YVO4 laser milling process. The experiment data are in good agreement with the calculated results.

An electrical injection metallic cavity nanolaser with azimuthal polarization

We demonstrated for the first time an azimuthally polarized laser source from an electrically driven metallic cavity nanolaser with a physical cavity volume of 0.146 λ3 (λ = 1416 nm). Single TE01 mode lasing at 78 K was achieved by taking the advantages of the large free spectral range in such nanoscale lasers and the azimuthal polarization of lasing emission was verified experimentally. Mode shift controlled by device cavity radius was observed over a large wavelength range from 1.37 μm to 1.53 μm. Such metallic cavity nanolaser provides a compact electrically driven laser source for azimuthally polarized beam.

Microstructure Characterization of Simulated Tri‐Isotropic Particles Embedded in Alkaline Borosilicate Glass

A preliminary study of the encapsulation of tri‐isotropic (TRISO) coated particles in alkaline borosilicate glass (ABG) using melting and casting methods is presented. ABG has been developed to encapsulate simulated TRISO fuel particles that are used as nuclear fuel elements in Very High Temperature Reactors. Encapsulation is an alternative to vitrification and it is a process in which radioactive waste is encapsulated within a composite as a first barrier and a glass matrix as a second barrier. This provides two barriers against leaching and diffusion of the radioactive waste once buried in the geological repository. The study investigates the possibility of achieving high densification of glass–graphite composite by sealing the pores of TRISO particles surrogate (28 wt% CeO2, 70 wt% graphite, and 2 wt% poly‐ethylene glycol) with molten ABG at 600°C. This article follows the carbon phases during the encapsulation and highlights the interaction area between the carbon and glass phases before and after melting, using a polarized laser source (Ar, 514 nm). The laser analysis revealed that the graphite no longer was retained in graphene hexagonal structure and that it was linked with the glass network as disordered carbon atoms.

Azo-polymers modified with nucleobases and their interactions with DNA molecules

The photo-fluidization process which is specific for azo-materials opens a new perspective for their use in the field of molecules nano manipulation at the surface of the azo polymer films. This is possible considering that in the case of the UV irradiation from a polarized laser source the azo material has an unidirectional flow. Here, we investigated the structuring phenomena occurring on the surface of the azo-polysiloxanes films modified with nucleobases, upon UV irradiation. Measurements of topography and adhesive forces between polymeric substrates and a hydrophilic probe have been done by atomic force microscopy (AFM). The response of the material upon irradiation has been investigated also by using UV−VIS spectroscopy. This method allowed us to draw the photo-isomerization and relaxation curves. Also, preliminary tests were conducted to determine the capacity of the film surface to immobilize DNA molecules.

Simple technique for generating the partially coherent and partially polarized electromagnetic source

The technique for generating the partially coherent and partially polarized source starting from the completely coherent and completely polarized laser source is proposed and analyzed. This technique differs from the known ones by the simplicity of its physical realization. An original technique for measuring the cross-spectral density matrix is employed. Experimental results of the characterization the coherence and polarization properties of the generated source are shown.

Experimental generating the partially coherent and partially polarized electromagnetic source

The technique for generating the partially coherent and partially polarized source starting from the completely coherent and completely polarized laser source is proposed and analyzed. This technique differs from the known ones by the simplicity of its physical realization. The efficiency of the proposed technique is illustrated with the results of physical experiment in which an original technique for characterizing the coherence and polarization properties of the generated source is employed.

Polarization measurements through a standard single mode fiber for imaging and remote characterization

We report on a polarization imaging device which probes a remote sample through a flexible standard single-mode fiber. Both polarized laser source and polarization analysis system are set on one side of the fiber, the object of interest being probed by the beam exiting at the opposite end. Phase retardation and polarization rotation angle due to either pure linear or pure circular birefringent targets can be measured. In addition, the degree of polarization of partially depolarizing targets is evaluated. The measurement method is based on two key points: (i) the compensation of the fiber birefringence effects over a round trip of the light by means of a miniaturized Faraday rotator set between the output fiber end and the target, (ii) the recording of a set of data operated when the polarization states of the light at the fiber input are varied, followed by a specific processing of these data. An experimental setup based on this process has been implemented. The method was assessed using calibrated birefringent targets, and polarization images of a large variety of targets were obtained.