Optical Field Intensity Research Articles

Beam quality measurement and image analysis of RF optical emission system

With the development of radio-over-fiber (ROF), beam quality is also an important parameter in evaluating ROF systems. Therefore, this paper selects the low-frequency to very high frequency (VHF) direct modulated optical emission system to verify its feasibility and excellent performance. It then analyzes the beam quality and image processing. In this paper, MATLAB is selected for the theoretical simulation, then CMOS is used to collect light spots, RayCiV2.5 is used to Gaussian fit the light field intensity distribution, and finally the ideal and actual light spot parameters are compared. Due to the influence of noise, this paper also preprocessed the image by brightness adjustment, filtering, edge fitting, etc. It proposed a fast two-sided filtering algorithm, which obtained a high peak signal-to-noise ratio (PSNR) and strong applicability. The results show that the edge-mode rejection ratio is as high as 33.6 dB, the beam quality is good, and it can be well applied in ROF. The M2 factor is 2.75, the optical field intensity Gaussian fit is 99.8 %, and the signal-to-noise ratio (SNR) is as high as 54.7 dB. Moreover, the image is robust after fast bilateral filtering.

Current modulation/optical injection and feedback for semiconductor laser diode based on optical field rate and intensity rate equation model

Current modulation/optical injection and feedback for semiconductor laser diode based on optical field rate and intensity rate equation model

Efficient Time-Dependent Method for Strong-Field Ionization of Atoms with Smoothly Varying Radial Steps

We present an efficient numerical method to solve the time-dependent Schrödinger equation in the single-active electron picture for atoms interacting with intense optical laser fields. Our approach is based on a non-uniform radial grid with smoothly increasing steps for the electron distance from the residual ion. We study the accuracy and efficiency of the method, as well as its applicability to investigate strong-field ionization phenomena, the process of high-order harmonic generation, and the dynamics of highly excited Rydberg states.

Mid-infrared deep subwavelength confinement in graphene plasmonic waveguides

Strong optical field intensity is greatly desired in mid-infrared (MIR) photonics to confine light on miniaturized compact-size chips. However, due to a fundamental trade-off between energy confinement and propagation loss, it has been a challenging task to obtain further deep subwavelength confinement. In this study, we present a simple graphene waveguide that generates image plasmons assisted by metallic cylindrical nanowires operating at a wavelength of 15 μm. Due to high-mobility graphene encapsulated by hexagonal boron nitride (hBN) and ultra-confined image plasmonic mode, the resulting waveguide has two orders of magnitude smaller mode area than the strongest confinement waveguides to date (up to an order of 10−8), in conjunction with comparable loss (a few micrometers of propagation distance). Furthermore, by the tunable graphene locations in the gap, we implement an efficient manipulation of the mode area across an order of magnitude. Such high-performance waveguides may be exploited for deep subwavelength field-enhanced devices, which promise to be unprecedented pathways for nanoscale transmission and manipulation of MIR light.

Strong anapole-plasmon coupling in dielectric-metallic hybrid nanostructures.

The nanoscale ampification of light-matter interactions exhibits profound potential in multiple scientific fields, such as physics, chemistry, surface science, materials science, and nanophotonics. Nonetheless, achieving robust optical mode coupling within cavities faces significant hurdles due to modal dispersion and weak optical field confinement. In this theoretical investigation, we demonstrate the viability of strong coupling between the anapole mode of a slotted silicon nanodisk and the plasmonic modes of an Ag nanodisk dimer at visible light frequencies. By introducing anapole modes, we successfully confine light to subwavelength volumes, suppressing radiative losses and achieving a remarkable Rabi splitting of 468 meV. This substantial coupling is facilitated by the large spatial overlap of intense optical fields. Capitalizing on this strong mode coupling, we generate novel hybrid energy states with significant electromagnetic field enhancement. Our study serves as a valuable blueprint for designing platforms based on strong anapole mode coupling at visible frequencies and paves the way for deeper explorations into nanoscale light-matter interactions.

Performance of laser patterned copper plasmonic photocathodes

We study ultrafast laser surface nanopatterning as an alternative to improve the photo-emissive properties of metallic photocathodes. By tailoring the physical dimensions of these surface nanostructures, one can localize the optical field intensity and exploit plasmonic effects occurring in such nanostructures. As a result, this surface nanopatterning technique can become a great tool for improving metallic photocathodes photoemission behavior enabling their use for next generation high brightness electron sources. Our goal is to investigate such surface-plasmon assisted photoemission processes with a view on simplifying the photocathode production at CERN while extending the lifetime of existing photoinjectors. The performance of two different femtosecond laser nanopatterned plasmonic photocathodes was analyzed by measuring the quantum yield with a 65kV DC electron gun utilizing 266nm laser excitation generated by a nanosecond laser with 5ns pulse duration and 10Hz repetition rate. By comparing the electron emission of the copper surface nanostructured areas with that of a flat area, our results suggest quantum yield enhancements of up to a factor of 5.

Characterization of the Carrier Lensing Effect in a Second Harmonic Generator

This paper presents studies on the carrier lensing effect of a tapered amplifier in a compact cavity-enhanced second harmonic generator. When different injecting currents are applied, carriers in the tapered amplifier are depleted to different levels depending on the local optical field intensity, resulting in a spatial variation of the refractive index and creating an effective convex lens for the amplified laser beam. This can significantly reduce the mode matching between the pump beam and the cavity, leading to a degradation of the second harmonic generator efficiency. To characterize this effect and provide guidance for mode matching, the evolution of optical fields and carriers in the tapered amplifier is simulated numerically with Maxwell-Bloch equations. The effective focal length of the tapered amplifier is calculated theoretically and verified with experimental calibration. Based on these results, the coupling optics of the cavity can be properly designed so as to achieve a high coupling efficiency. Finally, a single-frequency continuous-wave laser at 461 nm is achieved, with an output power exceeding 500 mW and a conversion efficiency of 33%.

Self‐Compression of High Energy Ultrashort Laser Pulses

AbstractNonlinear pulse compression techniques have been applied widely in the pursuit of ultra‐intense laser pulse with extremely high pulse energy (≈mJ) and extremely short pulse duration (≈sub‐10 fs). Although postcompression techniques using dispersive gratings or chirped mirrors have achieved 1 TW few‐cycle pulses, further increasing of the pulse intensity is limited by the damage threshold of dispersive optics, especially when self‐focusing and ionization in the propagation medium are considered. To overcome such limitations, ultrashort pulses self‐compression techniques without vulnerable dispersive optics have been explored in the past two decades. In this paper, the latest advances in these techniques will be reviewed with a discussion on the progress of various experimental approaches as well as their potential applications and roles in generating extremely intense optical fields for strong‐field physics research.

Optical Bullets and Domain Walls with Cross Spatio-Dispersion and Having Kudryashov’s form of Self-Phase Modulation

In this paper, we investigate the retrieval of optical bullets and domain walls in a novel context, considering the interplay of cross spatio-dispersive effects and employing Kudryashov' s proposed form of self-phase modulation. The integration of these two key elements represents a significant advancement in the field of nonlinear optics, enabling the recovery of optical structures with enhanced precision and control. We propose an enhanced Kudryashov’s approach, which overcomes the limitations of conventional methods and facilitates the retrieval of optical bullets and domain walls even in the presence of cross spatio-dispersive effects. Kudryashov' s self-phase modulation mechanism has proven to be a powerful tool in controlling the nonlinear dynamics of optical systems, offering unique opportunities to manipulate light waves through phase variations induced by the medium' s response to intense optical fields. The results presented herein offer new insights into the intricate interplay between self-phase modulation and spatio-dispersive effects in nonlinear optical systems. Moreover, our findings provide a promising avenue for developing novel applications in ultrafast all-optical signal processing, such as the manipulation of light bullets for high-speed data transmission and storage. The enhanced retrieval and control of optical bullets and domain walls are expected to have a profound impact on the advancement of nonlinear optics and its practical implications.

High-Sensitivity Quantum-Enhanced Interferometers

High-sensitivity interferometers are one of the basic tools for precision measurement, and their sensitivity is limited by their shot noise limit (SNL), which is determined by vacuum fluctuations of the probe field. The quantum interferometer with novel structures can break the SNL and measure the weak signals, such as the direct observation of gravity wave signal. Combining classical interferometers and the optical parametric amplifier (OPA) can enhance the signal; meanwhile, the quantum noise is kept at the vacuum level, so that the sensitivity of the nonlinear interferometer beyond the SNL can be achieved. By analyzing in detail the influence of system parameters on the precision of quantum metrology, including the intensity of optical fields for phase sensing, the gain factor of OPA, and the losses inside and outside the interferometers, the application conditions of high-sensitivity nonlinear quantum interferometers are obtained. Quantum interferometer-based OPAs provide the direct references for the practical development of quantum precise measurement.

Improvement of Optical Confinement for Terahertz Vertical-Cavity Surface-Emitting Laser with Square-Lattice Photonic Crystal Structure

A new method proposed to enhance the optical confinement of the terahertz band in a vertical cavity surface emitting laser involves introducing a square-lattice photonic crystal structure. This structure’s filling factor was optimized by computing the energy band structure and optical band values of the photonic crystal. The optimal optical band value is 0.436–0.528 a/λ. At a specific carrier concentration, the real part of dielectric constant of GaAs/AlGaAs materials will gradually increase with the increase of Al elements. By adjusting the length of the resonant cavity, a vertical cavity surface emitting laser with two wavelengths can be created without utilizing current injection. Additionally, the photonic crystal structure’s control effect on the transverse mode of the vertical cavity surface emitting laser and the release effect of the PN junction light confinement were analyzed. Numerical calculations indicated that incorporating a cubic photonic crystal structure in the vertical cavity surface emitting laser resulted in a 2× increase in the difference frequency intensity and a 6.33× increase in the optical field intensity.

Transfer matrix method-based efficiency enhancement of lead-free Cs3Sb2Br9 perovskite solar cell

This work highlights an efficiency enhancement of a lead-free Cs3Sb2Br9-based perovskite solar cell (PSC) by using the transfer matrix method (TMM). This method calculates the optical parameters such as the absorption profile of each layer, and the total reflection profile at the front surface by considering the coherent and incoherent effect in the layers of the Cs3Sb2Br9-based PSC. The calculation of absorption and reflection is done by using the optical electric field (E-field) intensity. The optical E-field intensity profile leads the calculation of the generation of free charge carriers in the absorbing layer and results in the ideal optical current density Jopt of 24.71 mAcm−2. Furthermore, the obtained optical parameters after the TMM-based simulation are used to design two different models; ‘SCAPS model’ and ‘TMM model’, for an electrical simulation using SCAPS-1D software. Finally, the lead-free Cs3Sb2Br9-based PSC using the ‘TMM model’ obtained an effective electrical performance such as JSC of 17.97 mAcm−2, VOC of 1.54 V, FF of 74.61%, and PCE of 20.67%, respectively, which encourage for the understanding of the operational mechanism of the PSC and will contribute further efficiency improvement.

Attosekundnaya interferometriya pri uchastii diskretnykh sostoyaniy

In the paper we theoretically investigate the features of RABBITT (Reconstruction of Attosecond Beating By Interference of Two-photon Transitions) spectroscopy under conditions when transitions through discrete spectrum states play a significant role. Two approaches are applied in the article: the numerical solution of rate equations with continuum discretization and the perturbation theory up to the third order in amplitude. Both approaches use transition matrix elements and photoionization amplitudes obtained by the high-precision R-matrix method. Within the framework of these approaches, photoelectron spectra, the amplitude and phase of RABBITT oscillations were obtained, and the effect of the seed optical field intensity and detuning from a resonance upon excitation of discrete states was studied.

Electronic equivalent of a pump-modulated erbium-doped fiber laser

We built the electronic equivalent circuit based on the model of a pump-modulated erbium-doped fiber laser. The model equations have two state variables, optical field intensity x and population inversion y, and a harmonic modulation applied to the pump parameter. In addition, the model contains two nonlinear terms, xy and ey. The exponential nonlinearity is implemented electronically using a power series expansion. The circuit dynamics is investigated using bifurcation, Lyapunov spectrum, and phase space analyses. Similar to the fiber laser, the equivalent electronic circuit exhibits very rich dynamics, exhibiting chaos and multiple coexisting periodic orbits. The existence of a saddle–node fixed point is demonstrated.

Optical phase singularities: Physical nature, manifestations and applications

Over the past 30 years, physical optics has been enriched by the appearance of singular optics as a new branch approved in scientific classifiers. This review briefly outlines the main concepts of the singular optics, their role in physical research and applications, and prospects of further development. The wave singularities are considered as a sort of structured-light elements and analyzed based on the generic example of screw wavefront dislocation (optical vortex). Their specific topological and mechanical properties associated with the transverse energy circulation are discussed. Peculiar features of the non-linear optical phenomena with singular fields are exhibited, with the special attention to generation of multidimensional entangled quantum states of photons. Optical fields with multiple singularities, especially, the stochastic speckle fields, are discussed in the context of optical diagnostics of random scattering objects. The exact and approximate correspondences between characteristic parameters of the optical-field intensity and phase distributions are analyzed with the aim of recovering phase information from the intensity measurements (“phase problem” solution). Rational singularity-based approaches to informative measurements of the scattered-field distribution are discussed, as well as their employment for the objects’ diagnostics. In particular, the practical instruments are described for the high-precision rough-surface testing. Possible enhancements of the singular-optics ideas and concepts in a wider context, including the transformation optics, near-field optics (surface waves), partially-coherent fields, and wave fields of other physical nature, are briefly exposed.

Subwavelength Quasi-Periodic Array for Infrared Antireflection.

Infrared antireflection of a zinc sulfide (ZnS) surface is important to improve performance of infrared detector systems. In this paper, double-pulse femtosecond laser micro-machining is proposed to fabricate a subwavelength quasi-periodic array (SQA) on ZnS substrate for infrared antireflection. The SQA consisting of approximately 30 million holes within a 2 × 2 cm2 area is uniformly formed in a short time. The double-pulse beam can effectively suppress the surface plasma shielding effect, resulting in obtaining a larger array depth. Further, the SQA depth is tunable by changing pulse energy and pulse delay, and can be used to readily regulate the infrared transmittance spectra as well as hydrophobicity. Additionally, the optical field intensity distributions of the SQA simulated by the rigorous coupled-wave analysis method indicate the modulation effect by the array depth. Finally, the infrared imaging quality captured through an infrared window embedded SQA is evaluated by a self-built infrared detection system.

Study on 1.9 [formula omitted]m structured lasers based on Ince–Gaussian modes superposition with multi-modulation by different directions off-axis dual-end-pump

The double IGp,pe modes multi-modulation superposition evolution structured lasers output is realized, based on the proposed different directions off-axis dual-end-pumping Tm:YLF laser method. Under the modes orthogonal superposition, the theoretical simulation and experimental measurement results have a high degree of agreement, and the orthogonal superposition of double IGp,pe modes within 5 orders is realized, which proves that different order modes and optical field intensity ratio have the capability to modulate the formation of vortex array structured beams. When the low-order IGp,pe modes of the same order are orthogonally superimposed, the phenomenon of superposition of different phase differences occurs, which proves the possibility of modulating the superposition of IGp,pe modes by the phase difference. At the same time, it is found that the regular pattern output of high-order IGp,m modes (odd mode m ≤ 3 or even mode m ≤ 2) can be realized at different angles, which proves the ability of rotation angle to modulate the superposition of double IGp,pe modes. Finally, the 1.9μm Tm:YLF structure laser output with double IGp,pe modes multi-factor composite modulation superposition evolution within 10 orders is realized. When the 10-order double IG10,10e modes are superimposed, the output power exceeds 5.7 W, and the conversion efficiency is higher than 17.5%.

Beyond third-order optical nonlinearities in liquid suspensions of metal-nanoparticles and metal-nanoclusters

Various nonlinear optical (NLO) phenomena observed in liquid suspensions of metal nanoparticles (NPs) and metal nanoclusters (NCs) have received considerable attention in the past few years. For example, multiphoton absorption, modulational instability, optical solitons, and parametric processes, benefit from research on soft-matter systems. Thus, many results are still being published providing support for earlier theoretical predictions and new discoveries. In particular, colloids containing NPs and NCs of noble-metal atoms present outstanding NLO responses and have been exploited to study for studying various phenomena and applications. Indeed, when illuminated with intense optical fields, such colloids can exhibit effective high-order nonlinearities (HONs) with large magnitudes which can dominate their NLO behavior. In this article, we review experiments with liquid suspensions of noble-metal NPs and noble-metal NCs, in which an appropriate methodology has been applied to study effective HONs for different sizes and morphologies of metal-nanostructures. In addition, a nonlinearity management procedure is discussed as a valuable tool to control for controlling the NLO response of metal-colloids through constructive and destructive interference among the nonlinearities of different orders. Because of the strong NLO behavior of metal-colloids, various phenomena associated to effective HONs were investigated such as: self-action effects, saturated multiphoton absorption, NLO scattering, bright and vortex spatial solitons, and operation of Random Lasers. Perspectives for further studies and photonic applications of metal-colloids exploring their effective nonlinearities are also discussed.

Second-harmonic generation in germanium-on-insulator from visible to telecom wavelengths

The second-order χ(2) process underpins many important nonlinear optical applications in the field of classical and quantum optics. Generally, the χ(2) process manifests itself only in a non-centrosymmetric dielectric medium via an anharmonic electron oscillation when driven by an intense optical field. Due to inversion symmetry, group-IV semiconductors, such as silicon (Si) and germanium (Ge), are traditionally not considered as ideal candidates for second-order nonlinear optics applications. Here, we report the experimental observation of the second-harmonic generation (SHG) in a Ge-on-insulator (GOI) sample under femtosecond optical pumping. We especially, report the measurement of the SHG signal from a GOI sample in the telecom S-band by pumping at ∼3000 nm.

Investigation of Quantum Size Effects on the Optical Absorption in Ultrathin Single Quantum Well Solar Cell Embedded as a Nanophotonic Resonator

Subwavelength optical nanocavity using semiconductor nanostructures is a key nanophotonic approach for various optoelectronic devices. In such low-dimensional systems, size-dependent changes can arise due to quantum confinement (QC). In this article, the implications of quantum-size effects on the light harvesting in ultrathin single quantum well solar cell (SQWSC) are analyzed. This device is based on silicon (barrier)/germanium (QW) nanostructures integrated as a deep-subwavelength nanophotonic resonator. Compared with the state-of-the-art, the novelty of this article consists of the investigation of the synergy between photonic and electronic confinements at both functional materials and device levels. It is shown that QC effects enhance the optical absorption efficiency in both low-dimensional germanium single layers and QW structures. However, this is affected by the barrier heights and the interface states. In the SQWSC devices, the changes of the photocurrent output, the resonance condition and the absorption edge as a function of QW thickness are explained based on the optical field and the local absorption distributions. Shorter nanocavity lengths with thinner QW nanoabsorbers result in blue-shifted resonance wavelength, suitable maximum optical field intensity in the visible wavelengths range as well as promoted photonic confinement. This enables an enhancement of the optical absorption efficiency relative to thick counterparts. The nonlinearity in the thickness-related photocurrent implies a drastic reduction in QW thickness while preserving a high photocurrent level. The presented considerations in SQWC could be extended as design rules for the optimization of the photocurrent in derived multiple quantum well systems and for relevant color-neutral semitransparent devices.