Pump Beam Research Articles

Efficient (∼10%) generation of vacuum ultraviolet femtosecond pulses via four-wave mixing in hollow-core fibers.

We report the generation of the fifth harmonic of Ti:sapphire, at 160 nm, with more than 4 µJ of pulse energy and a pulse length of 37 fs with a 1 kHz repetition rate. The vacuum ultraviolet pulses are produced using four-wave difference frequency mixing in a He-filled stretched hollow-core fiber, driven by a pump at 267 nm and seeded at 800 nm. Guided by simulations using Luna.jl, we are able to optimize the process carefully. The result is a conversion efficiency of ∼10% from the 267 nm pump beam.

Single-frequency orbital angular momentum switchable modes from a microchip laser.

We demonstrate the direct generation of single-frequency switchable orbital angular momentum (OAM) modes in a 1 µm wavelength range using a Nd:YVO4 microchip laser. The 808 nm laser diode pump beam is shaped into annular through an axicon associated with a lens. By adjusting the diameter and power of the annular pump beam, various OAM modes with different mode volumes can oscillate inside the Nd:YVO4 microchip. Moreover, a single-frequency output is also available due to the short cavity of the microchip. In the proof-of-principle experiment, single-frequency twofold multiplexed OAM modes | ± 1> and | ± 2> are generated, with experimentally measured fidelity higher than 96%. This work presents a compact and versatile single-frequency OAM source and will inspire multiple advanced scenarios ranging from classical to quantum photonics.

Dynamically tunable terahertz multi-band perfect absorber based on photosensitive silicon

A tunable narrowband terahertz absorber is proposed based on the photosensitive characteristics of silicon. When silicon is insulating without the pump beam, the absorber realizes three-frequency absorption at 0.731 THz, 1.145 THz, and 1.546 THz with absorptivity of 99.43%, 99.99%, and 99.98%, respectively. When the silicon is excited by the pump beam, it is conducting, and the absorber realizes double-frequency absorption at 0.852 THz, 1.536 THz, with 99.99% and 99.31%. The impedance matching theory explains the perfect absorption, and the electric field and surface current distributions are further discussed to elaborate the physical mechanisms. In addition, the effect of geometric parameters on the absorptivity is discussed. The absorber exhibits wide-angle absorption characteristics when light is polarized along the y-direction, and the absorptivity exhibits weak dependence on the polarization angle. The proposed absorber has promising applications in electromagnetic cloaking, narrow-band thermal radiation, and optoelectronic detection.

Optical bistability at lower photon number via photon and phonon interaction in the presence of Kerr nonlinearity

Optical bistability is theoretically analyzed in a hybrid optomechanical system consisting of an optical cavity including a Kerr medium and an optomechanical cavity coupled by direct tunnel coupling. The dynamics of the system is described by Heisenberg–Langevin equations. It is numerically shown that there is a critical value of the Kerr coefficient to observe the bistability of the intracavity intensity for a given coupling rate, and the changing of the Kerr coefficient will lead to the changing of the critical point to observe the bistability as well. In addition, the first critical value to observe bistability becomes larger with the increasing coupling rate between the two cavities. It is also demonstrated that the pump beam required to realize the bistable behavior in the blue sideband regime is significantly smaller than that in the red sideband regime. And the mean intracavity photon number is relatively larger in the red sideband case than that in the blue sideband case. It is remarkable to observe that the mean intracavity photon numbers in both cavities are much lower than that in ordinary situations.

Infrared imaging with nonlinear silicon resonator governed by high-Q quasi-BIC states

Nonlinear light-matter interactions have emerged as a promising platform for various applications, including imaging, nanolasing, background-free sensing, etc. Subwavelength dielectric resonators offer unique opportunities for manipulating light at the nanoscale and miniturising optical elements. Here, we explore the resonantly enhanced four-wave mixing (FWM) process from individual silicon resonators and propose an innovative FWM-enabled infrared imaging technique that leverages the capabilities of these subwavelength resonators. Specifically, we designed high-Q silicon resonators hosting dual quasi-bound states in the continuum at both the input pump and signal beams, enabling efficient conversion of infrared light to visible radiation. Moreover, by employing a point-scanning imaging technique, we achieve infrared imaging conversion while minimising the dependence on high-power input sources. This combination of resonant enhancement and point-scanning imaging opens up new possibilities for nonlinear imaging using individual resonators and shows potential in advancing infrared imaging techniques for high-resolution imaging, sensing, and optical communications.

Integrated photonic waveguides for on-chip SBS with OAM modes

Stimulated Brillouin Scattering (SBS) is a nonlinear optical process that can provide significant on-chip gain in various materials and platforms. The utilization of chalcogenide and silicon (Si) waveguides has facilitated the advancement of Brillouin lasers and diverse microwave photonic functionalities. The predominant approach has been centered on interactions between conventional guided modes, specifically TE/TM. This study introduces a novel approach that explores diverse guided-wave configurations capable of sustaining SBS with orbital angular momentum modes (OAM). These configurations include a cross-Si waveguide and a silica/chalcogenide waveguide. The simulations examine the forward and backward SBS utilizing OAM modes up to the 4th order in planar on-chip waveguides. A maximum on-chip SBS gain of up to ∼540W−1m−1 has been observed for pump and Stokes OAM mode numbers satisfying the topological charge conservation law. This OAM multiplexing approach can open new avenues for on-chip integrated nonlinear photonics for various applications, especially where pump and signal beam filtering or separation are critical.

Fabry-Pérot photothermal interferometry in a hollow-core antiresonant fiber for gas detection in mid-infrared

Hollow-core antiresonant fiber can simultaneously act as a miniature gas cell and the light guidance with broad wavelength range, introducing an powerful tool to photothermal spectrosocpy and sensitive gas detection. Photothermal interferometry (PTI) is a spectroscopic tehcnique that employs an interferometer to finely measure the photothermal signal of trace gas. By splicing the HC-ARF between solid core fibers, a Fabry-Pérot (F-P) cavity is formed and enables PTI with a brief in-line design. However, the previous structure commonly adopted single-mode solid core fibers and might introduce large optical loss due to mode field mismatch, particularly for MIR pump laser. This could lead to significant decrease in sensitivity. Besides, the gas pressure effect on the HC-ARF-based PTI gas sensor had not been fully studied. In this work, we demonstrated the PTI for 13CO2 detection at 4.35 µm by employing an HC-ARF with a 100-µm core. An InF3 multimode fiber was utilized for the efficient delivery of MIR pump beam and successfully enhanced the pump power by a factor of 6.7. The limit of detection was determined to be 0.4 ppb at the integration time of 240 s. Finally, the relationship between gas pressure and photothermal signal was experimentally studied and compared with theoretical results.

Dual-Criteria Decision Analysis by Multiphotonic Effects in Nanostructured ZnO.

Simultaneous interrogation of pump and probe beams interacting in ZnO nanostructures of a two-wave mixing is proposed for dual-path data processing of optical signals by nonlinear optical effects. An enhancement in third-order nonlinear optical properties was exhibited by Al-doped ZnO thin films. Multiphoton absorption and nonlinear refraction were explored by the z-scan technique at 532 nm with nanosecond pulses. The evolution of the optical Kerr effect in the ZnO thin films was analyzed as a function of the incorporation of Al in the sample by a vectorial two-wave mixing method. Electrical and photoconductive effects were evaluated to further characterize the influence of Al in the ZnO solid samples. Potential applications of nonlinear optical parameters for encoding and encrypting information in light can be envisioned.

Wavelength and polarisation dependence of pump-induced loss in Ti:sapphire

We use pump beam wavelength and polarisation to demonstrate that the phenomenon of pump-induced loss in Ti:sapphire is linked to simultaneous excitation of two separate absorption bands: the Ti3+ pump band and the parasitic 400 nm residual absorption. We find that the degree of pump-induced loss is linked to the relative absorption strengths of the residual absorption band and the Ti3+ pump band at the wavelength(s) of excitation.

Experimental demonstration of complex four-wave mixing processes with pump of orbital-angular-momentum superposition mode

Orbital angular momentum (OAM), characterized by a topological charge ℓ (ℓ integer), serves as a promising vehicle for carrying quantum information. Generating a nonclassical field involving two or more OAM modes can largely enhance the data-carrying capacity of quantum information processing. In this Letter, we present the implementation of a four-wave mixing (FWM) process, featuring a pump beam of a coherent OAM superposition mode and a probe beam of a single OAM mode. We generate twin beams encompassing multiple OAM modes and illustrate their quantum correlation when the pump beam assumes different coherent OAM superposition modes. Furthermore, we analyze the OAM mode components in each output field to deepen our understanding of the nonlinear interaction among different OAM modes. The obtained results show the rich structure of the nonlinear interaction of OAM modes in the FWM process and provide a perspective to study quantum information protocols.

Stable Patterns in the Lugiato–Lefever Equation with a Confined Vortex Pump

We introduce a model of a passive optical cavity based on a novel variety of the two-dimensional Lugiato–Lefever equation, with a localized pump carrying intrinsic vorticity S, and the cubic or cubic–quintic nonlinearity. Up to S=5, stable confined vortex ring states (vortex pixels) are produced by means of a variational approximation and in a numerical form. Surprisingly, vast stability areas of the vortex states are found, for both the self-focusing and defocusing signs of the nonlinearity, in the plane of the pump and loss parameters. When the vortex rings are unstable, they are destroyed by azimuthal perturbations, which break the axial symmetry. The results suggest new possibilities for mode manipulations in passive nonlinear photonic media by means of appropriately designed pump beams.

Robust high-order petal-mode laser with tunable topological charge pumped by an axicon-based annular beam

In this work, we demonstrate a watt-level laser producing high-order, petal-shaped output modes with tunable topological charge, by using an axicon-based divergent annular pump beam. The topological charge of the output beam could be varied in the range of 34–72 by adjusting the position of the Nd:YVO4 crystal relative to the focal plane of the pump beam. The highest order petal-mode beam generated from the system had a topological charge of 72 and a power of 1.3 W. The highest output power up to 2.1 W with a topological charge of 34 was achieved at an absorbed pump power of 5.8 W. The generated output modes were observed to be robust under power scaling and on propagation, with the same spatial profiles being maintained in the near- and far-fields. We anticipate that this system design may find use as a laser source in applications such as 3D optical trapping, fabrication of optical vortex arrays, optical communications, and high-sensitivity spatial measurement.

Kinematic and Dynamic Analysis of Eccentric Balanced Positive Torque Pumping Unit

Beam pumping units have numerous energy transfer links, significant net torque fluctuations and negative net torque in gear boxes, which lead to a high installed power and low system efficiency. In order to improve the efficiency of the pumping unit, in this paper, an eccentric balanced positive torque pump unit was designed based on the principle of eccentric balance that is small in size and adopts a flexible energy transfer system instead of a rigid structure to significantly reduce the energy transfer link. The kinematics and dynamics of the eccentric balanced positive torque pumping unit were analyzed and the ability to operate with positive torque over the entire cycle was verified using theoretical computations. And the results of the theoretical calculation were verified by using the virtual prototype simulation and analysis software ADAMS (Automatic Dynamic Analysis of Mechanical Systems); the pumping unit was optimized for relevant parameters such as the balance crank angle λ and the counterweight center of mass offset angle δ. Indoor testing and comparative field application have demonstrated that the installed power has been reduced by 80%, the weight of the entire prototype has decreased by 25% and the system efficiency has reached 24.3%. Additionally, electricity savings of over 50% have been achieved. These results indicate that the pumping unit has been designed correctly, has high reliability and has significantly improved system efficiency while also providing an obvious energy-saving effect.

Monolayer actively tunable dual-frequency switch based on photosensitive silicon metamaterial

We propose a monolayer actively tunable dual-frequency switch in the terahertz (THz) range based on photosensitive silicon (PSi) metamaterial. The designed unit cell consists of hollow cross-shaped slots and four L-shaped slots made of a perfect electric conductor (PEC), with PSi embedded in both the cross-shaped and four L-shaped slots of identical dimensions. The PEC serves as the dielectric substrate. By varying the intensity of the pump beam to adjust the conductivity of the PSi, tuning of the transmittance at the resonant frequencies of the entire structure is achieved, enabling the switch to function in both ON and OFF states. Under vertical incidence of THz waves in the range of 1 THz to 3 THz, in the absence of pump beam, the PSi is in an insulating state with a conductivity of approximately 1 S/m. The proposed terahertz dual-frequency switch is in the ON state, with transmittances of 97.0% at the first resonance frequency (f1=1.736THz) and 98.3% at the second resonance frequency (f2=2.176THz), and group delays of 4.397 ps and 2.540 ps, respectively. When the pump beam intensity is 294.6 μj/cm2, the PSi is in a metallic state with a conductivity of approximately 1 × 105 S/m. The switch is in the OFF state, with zero transmittance in the range of 1 THz to 3 THz and a group delay of 0.327 ps. The calculated modulation degrees of amplitude at f1 and f2 for this terahertz dual-frequency switch are both 100%, demonstrating a high-performance switch. The two resonant frequencies f1 and f2 of the terahertz dual-frequency switch are generated by weakly coupled superposition between the embedded cross-shaped and four L-shaped PSi resonators (CSPR and FLSPR), exhibiting polarization-insensitive characteristics under vertical incidence of THz waves. We believe that this compact structure of terahertz metamaterial dual-frequency switch holds great application prospects in terahertz filtering, slow light devices, terahertz modulation, and the future 6G communication field.

Quadripartite quantum steering generated by single-pass cascaded nonlinear processes

Quantum steering has become an important resource for quantum information due to its unique asymmetry. In this paper, quadripartite quantum steering generated by single-pass nondegenerate optical parametric amplification cascaded with a sum-frequency process is investigated. Firstly, an idler beam is produced by a different-frequency process between pump and signal. Secondly, a sum-frequency beam is generated by a cascaded sum-frequency process between idler beam and pump in the same optical superlattice. Quadripartite quantum steering among pump, signal, idler and sum-frequency beams is demonstrated based on the criterion for multipartite quantum steering. The influences of nonlinear coupling coefficients κ, dimensionless propagation length ξ, and the initial values of pump and signal on the variation characteristic of the quadripartite steering are also investigated. The results indicate that slightly larger nonlinear coupling coefficients of cascaded nonlinear processes and weaker signals can achieve better quadripartite quantum steering. This simple quadripartite quantum steering preparation scheme does not require a resonant cavity and is easier to implement experimentally, with potential applications in quantum communication and computing.

Stability of vortices in exciton-polariton condensates with spin–orbital-angular-momentum coupling

The existence and dynamics of stable quantized vortices is an important subject of quantum many-body physics. Spin–orbital-angular-momentum coupling (SOAMC), a special type of spin–orbit coupling, has been experimentally achieved to create vortices in atomic Bose–Einstein condensates (BEC). Here, we generalize the concept of SOAMC to a two-component polariton BEC and analyze the emergence and configuration of vortices under a finite-size circular pumping beam. We find that the regular configuration of vortex lattices induced by a finite-size circular pump is significantly distorted by the spatially dependent Raman coupling of SOAMC, even in the presence of a repulsive polariton interaction which can assist the forming of stable vortex configuration. Meanwhile, a pair of vortices induced by SOAMC located at the center of polariton cloud remains stable. When the Raman coupling is sufficiently strong and interaction is weak, the vortices spiraling in from the edge of polariton cloud will disrupt the polariton BEC.

Fourier Transform Thermoreflectance Method Under Front-Heat Front-Detect Configuration

The thermoreflectance method, which can measure thermal diffusivity in the cross-plane direction of thin films, mainly has two possible configurations; rear-heat front-detect (RF) and front-heat front-detect (FF) configuration. FF configuration is applicable to a wide variety of thin films including thin films deposited on opaque substrates, but this configuration has some problems in determination of the thermal diffusivity. One of the main problems is the effect of the penetration of pump beam and probe beam in thin film, which affects the initial temperature distribution near the sample’s surface after pulse heating. Several studies have tried to analyze the effect but there have been no practical analytical solutions which can solve this problem in FF configuration. In this paper, we propose a new analytical solution which considers the penetration of pump beam and probe beam into thin film, and by applying Fourier expansion analysis which we developed in a previous study to thermoreflectance signals, we have determined the thermal diffusivity of thin film in the thermoreflectance method under FF configuration. We measured platinum thin films with different thickness under both FF and RF configuration and obtained consistent thermal diffusivity values from both configurations.

Transient pump-probe analysis of pump-induced lensing in laser amplifiers.

Understanding of pump-induced lensing in laser amplifiers is essential for the optimized design of high-power lasers with high spatial quality, but there is usually incomplete knowledge of the interplay between thermal and population induced lensing mechanisms, lensing under lasing and non-lasing conditions, and transient lensing effects under pulsed operation. This paper provides quantitative insight of pump-induced lensing effects by using experimental transient pump-probe measurements in an alexandrite laser amplifier end-pumped by a short pulse pump beam with Gaussian spatial intensity distribution. Lensing results are presented showing a large difference in lensing under both non-lasing and lasing conditions and distinction of the population lens and thermal lens contributions from their different response time. Different pump beam sizes are used to show the variation of the relative strength of the lensing mechanisms. Comparison of experimental results with the analytical transient theory developed in this paper for the Gaussian pump beam gives excellent agreement and quantitative information on the thermal and population contributions to the amplifier lens. This paper provides a methodology for quantitative investigation of pump-induced lensing in general laser amplifier systems, and potentially other classes of optical materials with residual optical absorption.

Ultrafast random polarization beam smoothing driven by counter-rotating wavefronts via the optical Kerr effect

We propose an ultrafast random polarization smoothing scheme to achieve ultrafast speckle movement and polarization randomization of the focal spot. In the scheme, each beamlet in a laser quad is driven by a rotating petal-like wavefront, giving rise to the ultrafast redistribution of the speckles within the focal spot. The rotating wavefront is induced by an optical Kerr medium pumped by a laser beam with rotating intensity distribution that is generated by the superposition of two Laguerre–Gaussian beams carrying conjugate vortex phase and frequency shift. In addition, by properly selecting the topological charges of the pump beams and polarization states of the beamlets, the beamlets in a quad can be divided into two sets with counter-rotating wavefronts and orthogonal polarizations, which further randomizes the polarization of the focal spot. Results indicate that the proposed scheme can reduce the contrast by more than 70% and the degree of polarization by more than 75% within several picoseconds, by utilizing the rotating phase pumped by two Laguerre-Gaussian beams with a peak intensity of 0.18GW/cm2 and a frequency shift of 1 THz. The ultrafast random polarization smoothing scheme is expected to suppress the growth of Laser Plasma Instabilities (LPIs) including the filamentation and backscatter in indirect-drive inertial confinement fusion (ICF) facilities.

Dispersion‐Engineered Super‐Gain Parametric Amplification in Nanoscale Optical Cavities

The gain factor of the optical parametric amplification (OPA) process is known to be negligible in the small scale due to low‐interaction‐medium length. Hence, in the nanoscale, OPA is deemed as infeasible. Therefore, in small‐scale‐integrated optical devices, stimulated‐emission‐based amplifiers (lasers) are employed instead of OPAs. In contrast, the major advantage of OPAs over lasers is that unlike lasers which only provide amplification over a narrow spectral band, OPAs provide high‐gain amplification over a very large, user‐controlled spectral band. In this article, it is shown that OPA can yield wideband high‐gain amplification over a nanoscale beam propagation distance through dispersion engineering. This is achieved by a proper tuning of the pump (source) wave frequency, which can maximize the effective medium nonlinearity by a few orders of magnitude, while concurrently maximizing the intracavity energy density, thereby compensating for the small co‐propagation distance for the input (signal) and pump beams. In this study, it is shown that an input wave can be amplified by a factor in a nanoscale cavity via precise dispersion engineering. Both empirical and computational formulations are used for the investigation, which display a reasonable agreement.