Search

High-order correlated excitonic states in semiconductors, such as trion, biexciton and polaron, etc. hold a great promising platform in contemporary quantum and nonlinear optics. The recently found 2D TMDs further gives such excitonic states additional valley properties, with bound states of excitons in opposite valleys in momentum spaces. Despite great efforts have been made on the emission properties of the excitonic states, their absorption feature, especially the ultrafast absorption dynamics, are rarely reported. Here, we reported the enhanced optical absorption of the charged-excitonic states in monolayer WS2, including singlet and triplet trions, charged biexcitons and semidark trions, by utilizing the interlayer charge transfer-induced photo-doping effect in graphene-WS2 heterostructure. Depending on the recombination rates of the doping electrons, the absorption intensity of the charged complexes exhibits ultrafast decay dynamics, with lifetime of several picoseconds. Due to many-body interaction, both increasing pump intensity and lattice temperature can broaden these fine excitonic absorption peaks and even reverse the shape of the transient absorption spectrum completely.

Integrating metal halide perovskites onto plasmonic nanostructures has recently become a trending method of enabling superior emissive performance of perovskite nanophotonic devices. In this work, we present an in-depth study on the spontaneous emission properties of hybrid systems comprising CsPbBr3 nanocrystals and silver nanostructures. Specifically, a 5.7-fold increment of the photoluminescence (PL) intensity and a 1.65-fold enhancement of the PL relaxation rate is attained when the transition energy of CsPbBr3 is spectrally resonant with the oscillational frequency of Ag nanodisks (NDs), which is attributed to the intense exciton–plasmon coupling-induced Purcell effect. Furthermore, a 540-fs ultrafast energy transfer from the CsPbBr3 excitons to Ag plasmons is revealed by femtosecond pump-probe experiments, suggesting the key mechanism responsible for the Purcell-enhanced radiative emission. Our finding offers a unique understanding of the enhanced emissive behavior in the plasmon-coupled perovskite system and paves the way for further applications.

The extraordinary proliferation of digital coding metasurfaces turns the real-time manipulation of electromagnetic (EM) waves into reality and promotes the programmable operation of multifunctional equipment. However, current studies are mainly involved in the modulation of the transmission process, and little attention has been given to the control of EM wave generation, especially in the terahertz (THz) band. Here, we conceptually propose and experimentally demonstrate coded terahertz emission, which integrates the efficient generation and control of THz waves across a wide frequency band. For validation, two types of stripe-patterned ferromagnetic heterostructures with opposite spin Hall angles were utilized as coding units. The two distinct states in each coding unit (with two polarization or phase states of 0° and 180°) can be characterized as "0" and "1" digits, which can be switched by manipulating the optical field distribution of the pump beam. Such an ability to realize simultaneous terahertz coding and terahertz emission is essential for meeting the increasingly demanding requirements of integration and miniaturization. Our work endows ferromagnetic heterostructures with controllable spatial characteristics and benefits their applications in wireless communications and holographic imaging.

Miniaturized ultrafast switchable optical components with high efficiency and broadband response are in high demand to the development of optical imaging, sensing, and high-speed communication. Sharp Fano-type resonance switched by active materials is one of the key concepts that underpins the control of light in metaoptics with high sensitivity. However, actuating such metasurfaces exhibits a long-standing trade-off between modulation depth and operational bandwidth. Here, the limitations are circumvented by theoretical analysis, numerical simulation, and experimental realization of an achromatic Fano metasurface so that a high contrast of tunability with ultrafast switching rate over a broad range of frequency is achieved. By developing the physics of inter-mode coupling, the Fano metasurface is designed according to a complete phase diagram derived from coupled mode theory. Unlike conventional Fano metasurfaces, the cross-polarized inter-metaatoms coupling is discovered as a superior ability of high-efficiency broadband achromatic polarization conversion. To prove the ultrasensitive nature, a metadevice is constructed by incorporating a thin amorphous Ge layer with a weak photoconductivity perturbation. Transmission modulation over broadband frequency range from 0.6 to 1.1 THz is thus successfully realized, featuring its merits of modulation depth over 90% and On-Off-On switching cycle less than 10 ps.

Dissipative Kerr solitons (DKSs) with mode-locked pulse trains in high- Q optical microresonators possess low-noise and broadband parallelized comb lines, having already found plentiful cutting-edge applications. However, thermal bistability and thermal noise caused by the high microresonator power and large temperature exchange between microresonator and the environment would prevent soliton microcomb formation and deteriorate the phase and frequency noise. Here, a novel method that combines rapid frequency sweep with optical sideband thermal compensation is presented, providing a simple and reliable way to get into the single-soliton state. Meanwhile, it is shown that the phase and frequency noises of the generated soliton are greatly reduced. Moreover, by closing the locking loop, an in-loop repetition rate fractional instability of 5.5 × 10 − 15 at 1 s integration time and a triangular linear repetition rate sweep with 2.5 MHz could be realized. This demonstration provides a means for the generation, locking, and tuning of a soliton microcomb, paving the way for the application of single-soliton microcombs in low-phase-noise microwave generation and laser ranging.

Van der Waals (vdWs) heterostructures based on in-plane isotropic/anisotropic 2D-layered semiconducting materials have recently received wide attention because of their unique interlayer coupling properties and hold a bright future as building blocks for advanced photodetectors. However, a fundamental understanding of charge behavior inside this kind of heterostructure in the photoexcited state remains elusive. In this work, we carry out a systematic investigation into the photoinduced interfacial charge behavior in type-II WS

Broadband, ultrafast and scalable topological insulator Sb2Te3/STO heterostructure photovoltaic detectors were fabricated by molecular beam epitaxy.

Nonlinear plasmons are becoming an appealing and intriguing research area due to their remarkable light concentration and manipulation abilities. In this work, the nonlinear absorption (NLA) phenomena of polarized nanoantenna arrays coupled with the low dimensional topological insulator Bi2Se3 are studied at different excitation wavelengths. Our experimental results indicate that a significant enhancement in the linear absorption coefficient is achieved by localized surface plasmon (LSP) resonance, with enhancement factors that are 10- and 8-fold in magnitude for the cases of 800 nm (y polarization) and 970 nm (x polarization), respectively. Moreover, by polarization sensitive studies under 800 nm laser excitation, this new Bi2Se3-Au nanoantenna hybrid-structure exhibits adverse absorption responses of enhancement and suppression compared to pure Bi2Se3 film, providing excellent potential for applications in information converters. In particular, under 800 nm pump light (10 GW cm-2), the transmittance intensity of 450 nm or 1064 nm continuous wave (CW) probe light alters back and forth when the polarization direction changes by 90°. Thus, "ON" and "OFF" modes of this Bi2Se3-Au nanoantenna hybrid structure-based switch are achieved by using 450 nm and 1064 nm light, respectively, with a corresponding modulation depth of 3.4% and 21.9%, which can be applied in versatile photonic devices.

In this work, we experimentally study the nonlinear absorption enhancement of saturable absorption and two-photon absorption on a hybrid structure comprising a monolayer MoS

Recently, topological insulator based heterostructures (HSs) have attracted tremendous research interest, due to their efficient carrier transfer features at the heterointerface induced by metallic surface states. Here, a novel HS comprising 0D perovskite CsPbBr

The newly raised two-dimensional material MoS

HgCdTe electron avalanche photodiodes (e-APDs) have been widely used for low-flux and high-speed application. To better understand the dark current transport and electron-avalanche mechanism of the devices and optimize the structures, we performed accurate numerical simulations of the current–voltage characteristics and multiplication factor in planar homojunction (p-i-n) HgCdTe APDs. Based on the Okuto–Crowell avalanche model, an efficient physical model has been obtained by concerning the major generation-recombination processes, such as trap-assisted tunneling and band-to-band tunneling (BBT) recombination. Simulated current–voltage characteristics were in good agreement with available data in the literature, which demonstrates the validity of the proposed model. The origins of dark current in high reverse voltages are jointly dominated by BBT and the avalanche mechanism. It is proved to be effective for reducing BBT by improving the uniformity of the electric field distribution across the junction. The electric performance of p-i-n e-APD can be improved by optimizing the APD structure, such as eliminating the sharp corners of junctions, light doping, and the appropriate thickness in multiplication region. Our works provide a good deal of insight into the fundamental carrier transport processes involved in HgCdTe e-APDs.

Investigations in the combination of graphene with noble-metal nanostructures mostly focus on the fabrication of stacked hybrid films or nanoparticle (Au or Ag NPs) decorated graphene sheets, while few are carried out in graphene built-in monodispersed microspheres. Herein, we propose a novel hierarchical composite with a silver-shelled Fe3O4 microsphere as the initial core and graphene oxide (GO) as the multifunctional inserted layer. The flexible GO provides abundant nucleation sites for further in situ growth of Au nanoparticles. Moreover, it introduces considerable chemical enhancement and enhances surface adsorption toward aromatic molecules. Considering the synergistic properties of versatile GO with noble-metal nanostructures, the synthesized Fe3O4@Ag-rGO-Au microspheres were expected to have excellent surface-enhanced Raman scattering (SERS) activity, which was verified by the detection of the sulfhydryl-contained PATP and aromatic DTTC, with respective detection limits of 10−11 M and 10−10 M. The enhancement factor (EF) was calculated to be 2.83 × 106 for totally symmetric (a1) vibrations located at 1077 cm−1 of PATP. Additionally, its fast magnetic response enables rapid separation from solution, which is a key factor for many practical applications. Therefore, the well-dispersed hybrid microspheres have enormous potential in sensing applications as well as in effective immobilization and enrichment of biomolecules and aromatic pollution.

Halide perovskite has attracted significant attention because of excellent optical properties. Here, we study the optical properties of CsPbBr

Correction for 'Broadband ultrafast photovoltaic detectors based on large-scale topological insulator Sb

As a new quantum state of matter, topological insulators offer a new platform for exploring new physics, giving rise to fascinating new phenomena and new devices. Lots of novel physical properties of topological insulators have been studied extensively and are attributed to the unique electron-phonon interactions at the surface. Although electron behavior in topological insulators has been studied in detail, electron-phonon interactions at the surface of topological insulators are less understood. In this work, using optical pump-optical probe technology, we performed transient absorbance measurement on Bi

We propose reducing the threshold of stimulated Brillouin Scattering by enhancing the initial Brillouin ultrasounds, since the high threshold results from the low intensity of the sounds that exist in thermal noises. Theoretical analysis shows that the threshold can be reduced by at least one order through introducing comparatively weak Brillouin ultrasounds. Schemes for enhancing the initial ultrasounds are also proposed, including stimulation by transducers, by electroacoustic media or by direct radiation of microwaves.

International audience; Employing a pump-probe polarization-based two-frame shadowgraphy setup, the formation of filamentary damage induced in bulk fused silica by a nanosecond pulse at 1064 nm is investigated with a picosecond probe. Three different phases are exhibited in the damage experiments. The first phase is the formation of a micrometric plasma channel along the laser direction during the beginning of the pulse likely caused by multi-photon ionization. This channel exhibits growth during similar to 400 ps, and the newly grown plasma is discrete. Then, during the end of the pulse, this channel evolves into a tadpole-like morphology showing an elliptical head upstream the laser flux followed by a thin tail. This observed asymmetry is attributed to shielding effects caused by both the plasma and hot modified silica. Once the damage shows its almost final morphology, a last phase consists in the launch of a pressure wave enlarging it after the laser pulse. The physical mechanisms that might be involved in the formation of plasma channels are discussed. The experimental data are first confronted to the moving breakdown model which overestimates the filamentary damage length. Finally, taking into account the temporal shape of the laser pulses, the coupling between Kerr-induced self-focusing and stimulated Brillouin scattering is discussed to interpret the observations. (C) 2015 AIP Publishing LLC.

This paper reports on the disappearance of photosensitive area extension effect and the novel temperature dependence of junction performance for mid-wavelength HgCdTe detectors. The performances of junction under different temperatures are characterized by laser beam induced current (LBIC) microscope. The physical mechanism of temperature dependence on junction transformation is elaborated and demonstrated using numerical simulations. It is found that Hg-interstitial diffusion and temperature activated defects jointly lead to the p-n junction transformation depended on temperature, and wider band gap compared with the long-wavelength HgCdTe photodiode may correlate with the disappearance of photosensitive area extension effect.

We present a method of threshold reduction of stimulated Brillouin scattering by importing Stokes seeds, which are generated from the light passing through the Brilloun medium via an acousto-optic medium. To realize the scheme, the acousto-optic medium and the Brillouin medium should be of the same material, and the frequency of the transducer must be identical with the Brillouin shift. Essentially, the transducer and the acousto-optic medium constitute a special acousto-optic shifter. Calculations suggest that it is easy to reduce the SBS threshold by at least one magnitude and enhance the reflectivity remarkably by this scheme.

Laser-induced rear surface breakdown process of sodium chloride (NaCl) optical window was investigated based on the time-resolved shadowgraphy and interferometry. Violent particle ejection behavior lasting from tens of nanoseconds to tens of microseconds after the breakdown was observed. Classified by the particle velocity and propagating direction, the ejection process can be divided into three phases: (1) high-speed ejection of liquid particles during the first 100-ns delay; (2) micron-sized material clusters ejection from ∼ 100 - ns to ∼ 1 - μ s delay; (3) larger and slower solid-state particles ejection from ∼ 1 μ s to tens of microseconds delay. The moving directions of particles in the first and third phases are both perpendicular to the sample surface while particles ejected in the second phase exhibits angular ejection and present a V-like particle pattern. Mechanisms include explosive boiling, impact ejection, and shockwave ejection are discussed to explain this multiple phase ejection behavior. Our results highlight the significance of impact ejection induced by recoil pressure and backward propagating internal shockwave for laser-induced rear surface breakdown events of optical materials with low melting point.

In this paper, we report on the disappearance of the photosensitive area extension effect and the unusual temperature dependence of junction transformation for mid-wavelength, n-on-p HgCdTe photovoltaic infrared detector arrays. The n-type region is formed by B+ ion implantation on Hg-vacancy-doped p-type HgCdTe. Junction transformations under different temperatures are visually captured by a laser beam induced current microscope. A physical model of temperature dependence on junction transformation is proposed and demonstrated by using numerical simulations. It is shown that Hg-interstitial diffusion and temperature activated defects jointly lead to the p-n junction transformation dependence on temperature, and the weaker mixed conduction compared with long-wavelength HgCdTe photodiode contributes to the disappearance of the photosensitive area extension effect in mid-wavelength HgCdTe infrared detector arrays.