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We report on an experimental study of the statistical effects of optical parametric noise on the signal pulses in a synchronously pumped optical parametric oscillator. We measured a signal pulse that grew from the optical parametric noise using a temporal gating system and found that the time required for the signal growth was remarkably scattered, even if the pump pulses were maintained to be constant. The statistical properties of the signal pulses were not affected by the changes in the pump power but were characterized by the optical parametric noise. We examined these statistical properties numerically using nonlinear coupling equations and found that the measured properties could be reproduced using a simple model in which the optical parametric noise had random phase in the frequency domain.

A theory of lasing in an optically thin layer of active centers disposed at a metal surface is developed from first principles. The approach is based on a rigorous account of the local field in a close vicinity of a reflective surface which provides a feedback for dipole oscillations in active centers. It is demonstrated that the gain medium thickness plays a crucial role in the lasing condition and controls a switching from conventional lasing to lasing without inversion. The numerical calculations are carried out for erbium doped glass bordering a gold surface where radiation at telecom wavelength (1532 nm) can be generated., Comment: 9 pages, 3 figures. arXiv admin note: substantial text overlap with arXiv:2111.11746

Photonic crystals based on graphene plasmons (GPs) are highly tunable and can accurately control photonic transmission at the nanoscales. In this work, the transfer matrix method (TMM) is introduced to study graphene plasmonic crystal (GPC) with periodic surface conductivity in the case of normal incidence. The introduction of TMM after considering the abnormal phase scattering of the abrupt interface gives an idea to accurately manipulate plasmonic crystal structures, and can reduce the calculation workload to a certain extent. The effectiveness of the proposed method is verified with the plane wave expansion method in our model. Furthermore, we study the defect mode and the plasmonic Tamm state in GPC by the transfer matrix method.

In this paper, we discuss the electromagnetic homogenization of graphene-based nanoparticle arrays using the surface impedance approach. For this purpose, we first investigate the contribution of the different harmonics to the equivalent surface impedance of the array. We conclude that the size of the nanoparticles is small compared to the operating wavelength, and the higher-order modes have a negligible impact on the overall response of the array. Then, the accuracy of the homogenization method to describe the macroscopic response of graphene-coated spherical particle arrays is discussed. In particular, it is demonstrated that the surface-impedance modeling provides reliable results when the level of coupling between the nanoparticles is moderate and the model accuracy can be slightly improved by considering the Floquet expansion-based interaction coefficient. Finally, approximate formulas for the array surface impedance, as well as an equivalent circuit model of the metasurface, are extracted.

The interaction between graphene surface plasmons and a semiconductor quantum well has been investigated by means of scattering matrix simulations. Due to the strong confinement factor of the graphene layer, a large Rabi splitting arises from the interaction with intersubband transitions. By varying the Fermi energy in the graphene and the doping in the quantum well, the resulting polariton states show features of strong and ultra-strong coupling. The system has been modeled with the coupled-mode theory to find the highest quality factor for the polariton resonance, reaching a “highly resolved” ultra-strong coupling regime.

International audience; A free-space electro-optic modulator device exploiting graphene's surface plasmon polariton (SPP) at near-infrared frequencies is proposed and theoretically studied. The device is made up of two resonant structures, the first being a metallic SPP displaying broadband absorption, and the second graphene's own SPP, which is shown to frustrate the metallic plasmon when excited, leading to a narrow reflectance peak. Doping of the graphene to achieve Fermi-level tuning is shown to shift the wavelength of the frustration phenomenon, thereby enabling the use of the device as a modulator. A reduction of 20% in the switching energy is expected due to the unique principle of operation which, crucially and contrary to most work in this field, does not rely on electroabsorption but electrorefraction changes in graphene. This coupled SPP resonator geometry also permits efficient channeling of optical energy from free space into graphene's SPP at near-infrared frequencies.

We numerically study a method to increase the photon return flux of continuous-wave laser guide stars using one-dimensional atomic cooling principles. The method relies on chirping the laser towards higher frequencies following the change in velocity of sodium atoms due to recoil, which raises atomic populations available for laser excitation within the Doppler distribution. The efficiency of this effect grows with the average number of atomic excitations between two atomic collisions in the mesosphere. We find the parameters for maximizing the return flux and evaluate the performance of chirping for operation at La Palma. According to our simulations, the optimal chirp rate lies between 0.8 − 1.0 M H z / µ s , and an increase in the fluorescence of the sodium guide star up to 60% can be achieved with current 20-W-class guide star lasers.

Chaos in semiconductor lasers or other optical systems has been intensively studied in the past two decades. However, modulation around threshold has received much less attention, in particular in gain-modulated semiconductor lasers. In this article, we investigate the bifurcation sequence which appears with pump modulation in the threshold region with a large amplitude and different values of modulation frequency. Modulation around threshold necessarily includes ``below-threshold'' dynamics, which can be effectively displayed only through through a nonlinear visualization of the oscillations. The irregular temporal behaviour is examined at various modulation frequencies and amplitudes, highlighting a possible route to chaos for very large amplitude modulation in the near-threshold region. The addition of the (average) spontaneous emission to the lasing mode enables a coupled dynamics between photons and carriers even below threshold, thus extending the pump range in which the modulation actively modifies the laser behaviour. We also report on the existence of a transition between similar attractors characterized by a temporal transient which depends on the amplitude of the modulation driving the pump.

The central theme of this article is the analysis of the usefulness of introducing four-wave mixing or modulation of Kerr nonlinearity in a nonuniform grating structure with gain and loss. To do so, we propose an inhomogeneous system in which the nonlinearity of the $\mathcal{PT}$-symmetric grating is modulated. It is proven that the proposed scheme can be fruitful only if the nonlinearity and its associated modulation terms are assumed to be self-defocusing ones. In order to cut down the intensity required for the steering, the sign of chirping is taken to be negative and the wavelength of operating light is considered to be higher than the Bragg wavelength. Alongside these settings, launching the light from the rear end of the device dramatically reduces the critical intensity to a value of 0.015 (approximately) which must be the lowest switching intensity ever reported in the context of nonlinear $\mathcal{PT}$-symmetric gratings. The ramp-like stable states in the broken $\mathcal{PT}$-symmetric regime prevail even in the company of modulation in the nonlinearity index for both of the light incident directions., Comment: To appear in JOSA B

International audience; Within the frame of a simple, long-wavelength, quasi-static description, we present a theoretical characterization of the optical response of metal nanoparticles doped with active gain elements in a core-shell (metallic core within an active dielectric shell) and nano-shell (active dielectric core within a metallic shell) configurations. The common feature of these structures is that, adding gain to the system produces an increase of the quality of the plasmon resonance, which becomes sharper and sharper until a singular point, after which, the system switches from absorptive to emissive (nanolaser). We use this aforementioned simple model to develop a general method allowing to calculate both the expected singular plasmon frequency and the gain level needed to realize it, and to discuss the spectral deformation occurring before and after this singular point. Finally we propose a way to calculate if the singular behavior is reachable using realistic amounts of gain.

The four-wave mixing (FWM) effect has been systematically studied in an atom–optical cavity coupling system with a second-order nonlinear crystal (SOC), which is formed by coupling an optical cavity with a two-level atom and a SOC. In this research, it is found that the FWM effect largely depends on the SOC, because the SOC can promote a two-photon absorption process. Therefore, a tunable FWM signal can be obtained in this coupling system by controlling the SOC. Moreover, the results also show that the cavity decay rate plays an important role in controlling the FWM signal. By optimizing the cavity decay rate and the SOC, a strong FWM signal can be generated. In addition, by adjusting the cavity–pump detuning, conversion between a single-peak FWM signal and two-peak FWM signal can be easily realized.

A novel, to the best of our knowledge, design of a wavelength-selective solar thermophotovoltaic (STPV) absorber based on a 2D square spiral grating is numerically proposed and analyzed. The suggested STPV absorber is made of tungsten (W) with a spacer of aluminum-doped zinc oxide (AZO). In particular, the AZO is epsilon-near-zero material where its dielectric permittivity can be engineered over a broad wavelength range in the near-infrared. The refractory AZO-W metamaterial exhibits marked radiative optical properties, which control the thermal absorption through an engineered dielectric response function. The geometrical parameters and optical properties of the proposed design are studied using the finite difference time domain method to maximize the absorption through the studied wavelength range. The physical mechanism beyond the geometrical effects is also investigated with the inductor and capacitor model. The 2D square spiral STPV absorber achieves the photon-to-heat conversion efficiency of 75.2% at 1000 K. It is also found that the absorption of the proposed STPV absorber is insensitive to the incident angles from normal incident to 60º for transverse magnetic and transverse electric polarizations. The absorption enhancement is due to the effective coupling among the magnetic polariton, surface plasmon polariton, and intrinsic losses of the tungsten metal.

Ultrabroadband polarization filter based on gold-coated photonic crystal fiber with high birefringence is proposed and analyzed by using the finite-element method. An elliptical central air hole is designed for high birefringence and shifting the wavelength of the loss peak. The gold layers are selectively coated on the inner surface of two elliptical air holes to support the surface plasmon resonance, which contributes to the filtering characteristics. By optimizing the structural parameters, a high extinction ra2tio is obtained of about 290.56 dB at a communication wavelength of 1310 nm when the length of L = 400 µ m , and its bandwidth is ∼ 530 n m . In addition, the birefringence can reach near 0.004 at 1310 nm.

We demonstrate tunable generation of orbital angular momentum (OAM) modes with low loss (0.7 dB) and high efficiency ( > 90 % ) over a 230 nm in the visible and near-infrared spectral range using all-fiber acousto-optic-induced long period gratings. This represents tuning over almost 33% of the carrier frequency, and measured output OAM mode purities are as high as 99%. Our device construction allows accessing any wavelength in the range we probed (591–818 nm) with at most a 55 µs response time. The high-speed tunability, large spectral coverage, and high mode purity can be potentially useful in numerous applications requiring spectrally diverse OAM light.

Using two focused 1064 nm pump beams with an intensity ratio 3:1 and a small crossing angle θ ≈ 3.1 ∘ , two-photon pumped (2PP) tristable lasing behavior has been observed in a dye (AMSPT) solution in dimethyl sulfoxide (DMSO). When each pump beam is incident alone, the measured pump energy threshold for 2PP lasing is ∼ 3.8 m J . However, when the two pump beams are incident together, the energy of the strong pump beam varies from 4 to 10 mJ and the energy of the weak pump beam varies from 1.3 to 3.3 mJ. We then observe two simultaneous output lasing beams. However, when the strong pump beam is blocked, the weak pump beam is unable to create its own lasing output. This observed dual-beam lasing behavior can be well explained by a physical model of energy transfer between these two pump beams via the reflection of an induced Bragg grating. This observed dual-beam and tristable lasing behavior may be useful for future applications in an optical logical circuit or an optical computing system.

We propose a platform that combines the fields of cavity optomagnonics and levitated optomechanics in order to control and probe the coupled spin-mechanics of magnetic dielectric particles. We theoretically study the dynamics of a levitated Faraday-active dielectric microsphere serving as an optomagnonic cavity, placed in an external magnetic field and driven by an external laser. We find that the optically driven magnetization dynamics induces angular oscillations of the particle with low associated damping. Further, we show that the magnetization and angular motion dynamics can be probed via the power spectrum of the outgoing light. Namely, the characteristic frequencies attributed to the angular oscillations and the spin dynamics are imprinted in the light spectrum by two main resonance peaks. Additionally, we demonstrate that a ferromagnetic resonance setup with an oscillatory perpendicular magnetic field can enhance the resonance peak corresponding to the spin oscillations and induce fast rotations of the particle around its anisotropy axis., 22 pages, 13 figures

Negatively charged nitrogen vacancy ( N V − ) centers in diamond are required to be coupled to optical systems for various applications. A slowly varied tapered waveguide displays a near-unity power transfer from an optical fiber to on-chip photonic devices. This physical situation refers to an adiabatic transition of photons from a highly effective confinement mode to a lower effective confinement mode or vice versa. Here, we report tunable bidirectional coupling with enhanced efficiency in a hybrid structure of elliptically faceted (ELFA) diamond nanowire with N V − centers integrated to optical nanowire. Initiating from diabatic transition to adiabatic transition, corresponding to smaller length to longer wire length, respectively, the coupling efficiency oscillates and asymptotically saturates to a maximum value. Our calculations indicate coupling efficiencies of 85% and 84% for azimuthal and radial dipole configurations for the hybrid structure, respectively. The structure with optimum geometry provides similar coupling efficiency of ∼ 81 % for radial and azimuthal dipole configurations. By excitation of one of few dipoles placed strategically at various locations in the cylindrical region of the diamond nanowire will allow one to tune coupling efficiency in the two directions. Tailored size and tunable bidirectional coupling of ELFA diamond nanowire with enhanced efficiency will enable its wide-field applications including multi-scale quantum photonics devices.

We propose a scheme to simulate a one-dimensional Bose–Hubbard model with a coupled cavity optomechanical system. By eliminating the cavity field under the condition of large detuning, an effective Bose–Hubbard model can be achieved. By adiabatically adjusting the classical pumping, we show that the effective Hamiltonian can fully explain transitions from the Mott-insulating phase to the superfluid phase. In addition, we show that the system allows the quantum state transfer after including the dissipation of the oscillators.

In this tutorial, the physical origins and mathematical analyses of laser linewidths are reviewed. The semi-classical model is based on an equation for the light-mode amplitude that includes random source terms, one term for each process that affects the amplitude (stimulated and spontaneous emission, stimulated absorption, and facet and material loss). Although the source terms are classical, their assigned strengths are consistent with the laws of quantum optics. Analysis of this equation shows that the laser linewidth is proportional to the sum of the (positive) source strengths for all gain and loss processes. Three-level and semiconductor lasers have broader linewidths than comparable four-level lasers, because stimulated absorption and the stimulated emission that compensates it both contribute to the linewidth.

Ultrashort laser pulse propagation through few-mode optical fibers is a complex spatiotemporal event: due to mode spatial structures and intermodal delays and dispersions, pulses in such fibers experience spatial patterns and temporal elongations, which are generally considered detrimental for beam quality and pulse shape. However, with careful control of the launched modal contents and their interactions, we demonstrate that, using a single-mode-few-mode (SFe) optical fiber device, ultrashort pulses with various desirable spatiotemporal properties can be achieved. In the SFe device, pulse transformations over space, time, and frequency are related by multimode interference, and in the far field, pulse profile can be obtained by calculating diffraction integrals. We show that, using two example cases (a Bessel-like pulse and an optical bottle pulse), our approach can generate spatiotemporally structured pulses potentially suitable for applications in material science and biological imaging.

Highly coherent visible supercontinuum (SC) sources are demanded for many applications such as bio-sensing and imaging. Either dispersion management on the fiber or optimizing ultrafast pulsed pump parameters can work for achieving broadband coherent fiber SC. Normally, highly coherent SC with medium bandwidth can be obtained in an all-normal-dispersion (ANDi) nonlinear photonic crystal fiber (PCF), which has normal dispersion for all the wavelengths by tailoring the structure parameters of the microstructured cladding to sub-wavelength scale. Hence, such an ANDi fiber requires a submicron core diameter, and it makes precise fabrication challenging. Instead, using a standard anomalous dispersion pumping scheme and an ultrafast pulsed pump source, broadband SC with a high degree of coherence can also be obtained. In this study, we report broadband visible SC with a high degree of coherence approaching unity in a low-index borosilicate glass air-suspended PCF with a micrometer-core diameter, by the anomalous dispersion pumping scheme. The pulse duration of the 800 nm Ti:sapphire femtosecond laser is 29 fs. The experimental results are in good agreement with the numerical simulations, indicating that ultrashort pump pulses are the primary cause for the high degree of the generated visible SC, while the weak Raman effect of the borosilicate glass host plays a non-negligible but secondary role in the procedure of coherent SC generation.

Microring resonators are one of the most sought-after optical components for realizing several on-chip functionalities that include sensing, data routing, new frequency generation, and quantum photonic applications. Many of these applications demand a high quality factor and large notch depth (high extinction ratio), which can be achieved by critical coupling. However, the critical coupling is very sensitive to fabrication accuracies and thermal drift. Geometrical parameters of the resonators are generally swept to attain critical coupling, where a few designs can pass the critical coupling condition criteria. In this work, we propose a methodology to circumvent this vital issue. The proposed technique is based on coupled-resonator systems where two different microrings are embedded into a larger microring, referred to as a nonconcentric nested microring resonator (NN-MRR). The NN-MRR configuration relaxes the requirement of the critical coupling condition by 20% when the strip optical waveguide has either smooth or rough sidewalls. Numerical simulations reveal that, unlike standard MRR, a high Q -factor ( > 1 0 5 ) and a large transmission notch depth > 10 d B can be maintained irrespective of the rings’ coupling conditions for the nested MRRs. Besides the extra degree of freedom of design provided by the inner rings, the other significant advantage of the proposed NN-MRR is its compactness. We believe that the nested MRR arrangement could be highly efficient for biosensing, nonlinear, and quantum applications within a broad ambient temperature range. We have fabricated the NN-MRRs in a silicon-on-insulator platform through electron beam lithography and experimentally demonstrated the theoretical and numerical findings.

In some literature [Prog. Electromagn. Res. 106, 107 (2010)PELREX1043-626X10.2528/PIER10060103], zero-index metamaterials are regarded as non-transformation optics (TO) materials. In this paper, for the first time, to the best of our knowledge, sets of transformation mapping functions are introduced to produce near-zero-index metamaterials using TO. In addition, other than producing near-zero materials, it is shown that the proposed structures can be used in applications like radiators with highly tunable directivity when the parameters of the transformation functions are adjusted. In near-zero-index metamaterials, the refractive index is near zero when either permittivity or permeability, or both, are near zero. The introduced mapping functions are applied to a desired space. Then, using Maxwell’s equations, the wave equation and consequently the wavenumber of the transformed space is obtained. From the wave equation the obtained wavenumber is near zero. Therefore, it is concluded that the transformed space is a near-zero-index material. The mapping is provided for open and enclosed spaces. At the end, a parametric numerical analysis is provided for various sets of obtained parameters for the introduced near-zero-index materials. From the analysis it is shown that the proposed structures can also be used as radiators with tunable directivity.

We perform a theoretical study on the two-photon scattering effect of a single Mie scatterer, and investigate its dependence on the rotation angle of the scatterer, and the wavelength and polarization of incident light. Different regions of the two-photon correlation map are recognized by investigating two parameters, i.e., the visibility of two-photon superposition that represents the path information of different two-photon paths, and the balance factor of the double-side single-photon scattering amplitude that indicates the possibility of the single-photon scattering process. It is shown that the two-photon scattering pattern is a result of two-photon interference from the incoherent to fully coherent regime, together with a contribution from a single-photon-like correlation. In the coherent two-photon interference region, it is found that the transition from destructive to constructive interference emerges by rotating the scatterer, as well as by changing the polarization of incident light. These results demonstrate the rich features of the two-photon scattering effect for a single Mie scatterer, and open new possibilities to explore nano scatterers for controlling two-photon interference, and their applications in communications, sensing, and imaging.

This paper discusses a unified theoretical approach to model the spectral and temporal properties of various quasi-continuous-wave (quasi-CW) fiber lasers. The unified spectral evolution model and temporal evolution model of quasi-CW fiber lasers are established by demonstrating the nonlinear propagation equations with gain coefficient and analyzing the corresponding definite conditions and computation methods for effective simulations. Simulation results based on the two unified models are given to show their capacities and application scope in describing the basic spectral and temporal properties of typical quasi-CW fiber lasers involving single gain mechanism with a simple structure. Furthermore, the two unified models could also be extended to analyze the spectral and temporal properties of quasi-CW fiber lasers involving a hybrid gain mechanism or with a composite structure. Overall, the unified spectral evolution model and temporal evolution model could provide a useful tool to describe and design quasi-CW fiber lasers and quasi-CW fiber amplifiers.

We present a review devoted to hybrid optical fibers, which combine the properties of conventional total internal reflection and antiresonant fibers and enable dispersion control at wavelengths where the material dispersion of the fiber host optical glass is normal. We discuss the main principles of mode propagation in such structures and show the prospects for their practical application.

Recently, high refractive index micro-pillars have been widely used for enhancing the fluorescence of quantum emitters (vacancy/defect centers) embedded within the pillar. However, the maximum observed enhancement from these pillars has been limited to about a factor of 10. Within the dielectric pillars, the Purcell enhancement is restricted to around unity, and the fluorescence enhancement is mainly due to the enhancement of the collection efficiency of the dipole emission from inside the pillar if compared to a bulk substrate. Using multi-polar electromagnetic scattering resonances and near-field plasmonic field enhancement/confinement, here we report a simple metal–dielectric pillar resonator scheme to achieve a close to three orders of magnitude fluorescence enhancement from embedded solid state vacancy centers. The scheme comprises a silver (Ag) cylinder fabricated on top of a silicon-carbide (SiC) dielectric pillar, with both the SiC and Ag cylinders having the same diameter. A selective dipole orientation relative to the metal–dielectric interface for emitters close to the SiC pillar’s top surface leads to a large Purcell enhancement of the dipole’s emission. The Ag cylinder was found to function as an efficient resonator as well as an antenna, enhancing as well as directing a significant fraction of the dipole’s emission into far-field free space.

We characterize a terahertz (THz) source based on plasma in liquid gallium. The dependence of the emitted THz pulse energy on second-order phase, pump pulse energy, and polarization of the short laser pulse is demonstrated. Our study suggests that the THz emission mechanism is due to the ponderomotive force and is aided by a direct-field driven term. The proposed source and accompanying generation mechanism are studied under a non-relativistic regime ( 1 0 15 < I < 1 0 18 W / c m 2 ) for forward directed THz under a single pump excitation scheme.

We address the challenge of finding the optimal laser intensity and wavelength to drive high-energy, strong field rescattering and report the maximum yields of K-shell and L I -shell hole creation. Surprisingly, our results show laser-driven rescattering is able to create inner shell holes in all atoms from lithium to uranium with the interaction spanning from the deep IR to x-ray free electron laser sources. The calculated peak rescattering follows a simple scaling with the atomic number and laser wavelength. The results show it is possible to describe the ideal laser intensity and wavelength for general high-energy laser rescattering processes.

We propose a new method to analyze the adiabaticity of a highly multimode tapered waveguide. The propagation of the optical beam in the multimode fiber taper is calculated using the Monte–Carlo ray tracing technique, and then the corresponding phase space of the optical beam is obtained. By calculating the phase space area, the etendue variation of the light is analyzed, and the quantitative criterion for evaluating the adiabaticity of the multimode fiber taper is given based on the etendue conservation principle.

The incident angle dependences of the diffraction properties of orthogonal-circular polarization gratings (OCPGs) fabricated using a polymer liquid crystal exhibiting biaxial anisotropy have been investigated. The investigations were conducted with the plane orthogonal to the surface of the OCPGs as the plane of incidence. It was found that a specific biaxial anisotropy reduces the incident angle dependence of optically thin OCPGs against the wavelength of the incident light, and is less effective on thick OCPGs. In addition, a method also has been proposed to determine the biaxial anisotropic shape that most reduces the incident angle dependence in thin OCPGs.

One fundamental motivation to know the dispersive or frequency dependent characteristics of localized surface plasmons (LSPs) supported by elliptical shaped particles wrapped with a graphene sheet, as well as their scattering characteristics when these elliptical LSPs are excited, is related to the design of plasmonic structures capable of manipulating light at sub-wavelength scale. The anisotropy imposed by ellipse eccentricity can be used as a geometrical tool for controlling plasmonic resonances. Unlike the metallic case, where multipolar eigenmodes are independent of each other, we find that the induced current on a graphene boundary couples multipolar eigenmodes with the same parity. In the long wavelength limit, a recursive relation equation for LSPs in terms of the ellipse eccentricity parameter is derived, and explicit solutions at lowest order are presented. In this approximation, we obtain analytical expressions for both the anisotropic polarizability tensor elements and the scattered power when LSPs are excited by plane wave incidence.

We propose and experimentally demonstrate a method of spectral measurement of multicomponent radiation emitted by a modulated vertical cavity surface-emitting laser (VCSEL) relying on peculiarities of absorption in alkali metal vapor. The method consists in determination of the radiation spectrum (which is formed due to RF modulation of the injection current of a diode laser) from the dependence of transmittance of rubidium vapor upon the radiation wavelength. We show that the proposed method allows fairly precise measurement of the spectrum of multicomponent radiation used in devices based on the coherent population trapping (CPT) effect when the frequency difference between the radiation components matches that between absorption lines of an alkali metal.

A comprehensive three-dimensional computational fluid dynamics (3D CFD) modeling of flowing-gas Rb diode pumped alkali laser (DPAL) is carried out. The cases of H e / C H 4 and pure He buffer gases are investigated, and the output power and optical efficiency are calculated for various pump powers, mole fractions of methane, buffer gas pressures, and flow velocities. The model considers the processes of excitation of high levels of Rb, ionization, ion-electron recombination, and heating of electrons, which affect the diffusion coefficient of Rb ions. Two types of Rb DPAL were studied: a low-power laboratory-scale device with pump power of several tens of watts and a high-power multi-kilowatt laser. Efficient operation of the Rb laser using pure He as buffer gas can be achieved only in a large-scale laser with a pump beam cross-sectional area of several c m 2 . The calculated results for such a device were compared with those reported by Gavrielides et al. [J. Opt. Soc. Am. B 35, 2202 (2018)JOBPDE0740-322410.1364/JOSAB.35.002202], where a simplified three-level model based on the one-dimensional gas dynamics approach was applied.

A supersonic jet consisting of atomic clusters of noble gases under interaction with high-power femtosecond radiation allows control of the radiation pattern and efficiency of generation of terahertz (THz) radiation. The laser filament formed in this jet is spatially defined by the shape of the jet. The concentration, spatial distribution, and size of the clusters influence the propagation of the femtosecond laser pulse in it and the formation of a THz pulse. We show that a specially formed cluster jet allows the shaping of THz radiation with a high degree of directionality and increase its intensity by more than 10 times.

We propose a method to evaluate the optical propagation properties of a dielectric non-resonant metasurface composed of rectangular nanofins. Our approach is based on a semi-analytical assessment of the effective indices to perform guided vectorial propagation inside the nanostructure. The proposed model is an extension of the commonly used Pancharatnam–Berry model where the effect of the incidence angle can be satisfactorily accounted for. The model shows good agreement with numerical simulations, and it can be inverted to give the nanofin rotation angle for a given output phase function. We show that the far-field distribution of a metalens predicted by our model is in good agreement with data from a simulation code.

Avoided crossings are important in many waveguides and resonators. That is particularly the case in modern-day solid-core and air-core optical fibers that often have a complex geometry. The study of mode coupling at avoided crossings often leads to a complicated analysis. In this tutorial, we aim to explain the basic features of avoided crossings in a simple slab waveguide structure so that the modes can be found analytically with simple sinusoidal and exponential forms. We first review coupled-mode theory for the guided mode in a slab waveguide, which has a higher index in the core. We study the effective index of the guided true mode for a five-layer slab waveguide including two core layers with higher indices compared to the indices in the three cladding layers. Then, we study the same structure by using the overlap between approximate modes confined in the two individual core slabs. When the two individual core slabs are not near each other, the avoided crossing using the true modes within the two-slab waveguide agrees well with the results using the overlap between the two approximate modes. We also study coupled-mode theory and avoided crossings for leaky modes in an antiresonant slab waveguide. We obtain good agreement between the results using the true leaky mode and the results using the overlap between approximate modes. We then discuss examples of avoided crossings in solid-core and air-core optical fibers. We describe the similarities and differences between the optical fibers and simple slab waveguides that we have analyzed in detail.

We show that an interface between two identical metal/dielectric plane-layered ferromagnetic (meta)materials with different directions of magnetization can support electromagnetic surface waves (SWs) of the visible or near-infrared band. We find that such an interface possesses so-called valve action allowing the propagation of SWs only within definite range of angles (including strictly unidirectional propagation), depending on the mutual orientation of magnetizations in the contacted media and filling factor of ferromagnetics in the metamaterial. Furthermore, these SWs can demonstrate unusual properties for conventional surface plasmon-polaritons, namely, a transverse electromagnetic (TEM) structure with zero angular momentum. We also reveal that in a plane-layered metal/dielectric metamaterial the weak optical gyrotropy can be considerably enhanced due to quasi-static LC resonance in this structure.

We present a numerical study on the coherent sideband generation from an incoherently pumped fiber optical parametric oscillator (FOPO). We revisit the fiber dispersion condition in a parametric process that fulfills the convection-induced phase-locking mechanism when pumping incoherently. Particularly, there exist analytical solutions for phase-matching frequencies in a convection-induced phase-locking process when using a parametric gain fiber with two zero dispersion wavelengths. With the optical feedback, we manage to circulate and amplify the convection sideband in a singly resonant FOPO. The autocorrelation shows that the coherence of the oscillating convection sideband can be strongly influenced by the cavity feedback fraction.

In this paper, we propose a simple model to incorporate the spill-out effect of metal nanostructures, which can impact the nanostructure plasmonic properties prominently. Based on Maxwell’s equations, this model divides the smeared-out area into a certain number of thinner layers, and thereby the spatial variable of dielectric function can be adjusted into an integer number. In principle, through the finite element method, the model can be applied to arbitrarily shaped metal nanostructures with spill-out effects. As demonstrative examples, the optical resonance spectra of sodium and potassium metal spheres were computed using the proposed model, and the redshifted plasmon peaks were attained and compared to previous research to support the model. Last, we successfully applied the proposed method to particles with lower symmetry relative to sphere particles, such as prolate spheroids and coned particles, and achieved redshift resonance with the consideration of spill-out layers.

We study the periodic potential of a one-dimensional optical lattice originating from a scalar shift and vector shift by manipulating the lattice polarizations. The ac Stark shift of an optical lattice is measured by Kapitza–Dirac scattering of 87 R b Bose–Einstein condensate, and the characteristics of a spin-dependent optical lattice are presented by scanning the lattice wavelength between the D1 and D2 lines. At the same time, tune-out wavelengths that the ac Stark shift cancels can be probed by the optical lattice. We give the tune-out wavelengths in more general cases of balancing the contributions of both scalar and vector shifts. Our results provide a clear interpretation for a spin-dependent optical lattice and tune-out wavelengths, and help to design it by choosing the appropriate lattice wavelength.

The possibility of using harmonic modulation of the spectral phase to generate multiple replicas of the original short laser pulse or controlled periodic intensity modulation at the terahertz frequency of the stretched chirped laser pulse is shown theoretically and experimentally.

Whispering gallery mode optical resonators have attracted attention due to their simplicity and applicability for sensing. In this paper, analytical formulas are provided that describe resonance conditions in optical resonators. Basic terms (resonance wavelengths and frequencies, free spectral range, Q -factor, summation principle of Q -factors of various processes, finesse, etc.) are introduced. A description of interference of an infinite number of waves of progressively smaller amplitudes and equal phase differences is given. A description of a Fabry–Perot resonator with nonequal reflection coefficients is also given as well as analysis of all-pass and add-drop optical filters. The presented description of resonators will help to analyze the effects of optical resonators, interpret the results of experiments, and guide the development of novel applications of microresonators.

We demonstrate that free-standing multi-walled carbon nanotubes exhibit extraordinary nonlinear terahertz responses upon optical excitation. Terahertz transmission of the photoexcited nanotubes rises in a narrow range of intermediate intensity with increasing intensity, while falling in the regime of low and high intensities. A theoretical analysis shows that the nanotube conductivity drops sharply in the region of intermediate intensity and soars elsewhere. Field-effect mobility and field-induced carrier multiplications are considered to be competing processes governing the rise and fall of the conductivity.

We theoretically investigate the bistable spontaneous emission behavior of a single emitter in the vicinity of a hybrid V O 2 –Au nanoshell. The hybrid nanoshell is illuminated by a continuous wave pump laser. The incident beam generates heat through light absorption and causes the V O 2 to undergo a phase change from semiconductor to metallic mode. Our calculation shows that for certain values, over a range of incident laser intensity [ 0.25 ( G W / m 2 ) < I < 0.84 ( G W / m 2 )], at the resonance wavelength of the V O 2 (semiconductor)–Au nanoshell ( λ = 630 n m ), there is a reasonable bistable contrast for the two spontaneous emission rate values: the radiative and nonradiative decay rates. Our results provide important general guidelines for enabling platforms for optical switching sources and tunable sensors.

In this paper, we have theoretically studied transformations of higher-order modes and angular momentum of light in the optical snake, a coil resonator composed of two evanescently coupled coils of a multimode fiber. To this end, we have developed a full-vectorial theory of normal modes of coupled parallel multimode fibers that allows for the spin–orbit interaction and goes beyond the limits of weak orthogonality approximation. We have studied the evolution of optical vortices and circularly polarized scalar-approximation fiber modes in a two-coil optical snake. We have shown that this system allows a parametric control over the topological charge of the outcoming optical field, as well as its orbital and spin angular momenta.

In this paper, a metamaterial absorber is proposed, which is constructed by graphene rings and a gold film separated by an ultrathin S i O 2 layer. The feature of this absorber is that the absorption bands can be adjusted either by applying external electric fields or by rotating the polarization angles of the incident electromagnetic waves. The calculation results show that the continuous tunable or two- to multi-band absorptions can be realized by the above two methods. Through equivalent medium theory and impedance-matching condition, the anisotropic absorption mechanism of this absorber is explained. Moreover, the simple specific design makes the absorption bands able to be further tuned by adjusting various parameters, such as the geometry sizes and relaxation times of graphene rings. Our results indicate that the absorber has great adjustability and great potential application in filtering, terahertz signal detection, signal parameter estimation, smart sensing, tunable absorbers, and cloaking.

Coherent coupling between two laterally coupled quantum dot semiconductor lasers based on longitudinal modes in the weak coupling regime has been investigated. Considering the effect of homogeneous and inhomogeneous broadenings, the spectral behavior of lasing modes in the coupled lasers depends on the coupling coefficient and the frequency detuning between the lasers. For cavity lengths with a minute difference and specific homogeneous broadening, full phase-locking along with single-mode operation is guaranteed provided that the coupling coefficient reaches a critical value. This result can be generalized for various cavity lengths and homogeneous broadenings covering almost all practical temperatures in the intermediate homogeneous broadening regime. The effect of coherent coupling on the emission spectrum, especially at sufficiently low temperatures at which the lasing spectrum shows broadband emission in the absence of coupling, has also been discussed. For constant cavity lengths and relatively high temperatures, onset of full phase-locking occurs at lower values of the coupling strengths, while longer cavity lengths lead to higher critical coupling strengths at a constant temperature. From a practical view, coherent coupling based on longitudinal modes has been examined in the case of a differential bias condition, which proves the electronically controllable coherent coupling of optical output signals.

We theoretically analyze the transmission characteristics of a magnon–photon coupling system with N cascaded microwave cavities. The influences of the magnon–photon coupling strength and cavity number on the transmission characteristics are the main focus of this research. With an increase in the cascaded cavity number, the slow light effect should be greatly enhanced. By changing the cavity lengths slightly in a staggered way, the group delay could be increased by an order of magnitude with a well guaranteed transmission amplitude. Group delay should be flexibly controlled because of the existence of magnon and the conversion of fast and slow light can be realized. Moreover, by properly adjusting the cavity length, we can control the frequency shifting of the output slow light and narrow the bandwidth of the output slow light, which can aid in the design of high-quality light-storage devices. We believe the results will have applications in the all-optical communications network.

We propose the realization of an on-chip dual identical narrowband Bragg filter at ∼ 1310 and ∼ 1950 n m wavelengths simultaneously based on the silicon-on-insulator (SOI) platform. By taking advantage of subwavelength corrugation behavior at large wavelengths and the difference in the mode areas of the involved modes at the two widely separated wavelengths, undesired diffraction losses are circumvented while achieving Bragg resonances at the two wavelengths simultaneously. A double-corrugation Bragg grating rib waveguide filter is proposed, with two sets of gratings, the inner one close to the rib operating near 1310 nm wavelength, with the outer grating being designed to achieve a transmission dip around 1950 nm. Introducing a proper lateral misalignment to the set of inner grating indents, a dual identical narrowband Bragg filter with ∼ 0.47 n m 3 dB bandwidth at ∼ 1310 n m and ∼ 1950 n m is achieved. The proposed design strategy based on the SOI platform relies on a single-etching fabrication process and presents potential applications in situations where equal-bandwidth filtering is needed in on-chip communications and sensing.