Strong exciton-photon coupling with colloidal quantum dots in a tuneable microcavity

Polariton emission from optical cavities integrated with various luminophores has been extensively studied recently due to the wide variety of possible applications in photonics, particularly promising in terms of fabrication of low-threshold sources of coherent emission. Tuneable microcavities allow extensive investigation of the photophysical properties of matter placed inside the cavity by deterministically changing the coupling strength and controllable switching from weak to strong and ultra-strong coupling regimes. Here we demonstrate room temperature strong coupling of exciton transitions in CdSe/ZnS/CdS/ZnS colloidal quantum dots with the optical modes of a tuneable low-mode-volume microcavity. Strong coupling is evidenced by a large Rabi splitting of the photoluminescence spectra depending on the detuning of the microcavity. A coupling strength of 154 meV has been achieved. High quantum yields, excellent photostability, and scalability of fabrication of QDs paves the way to practical applications of coupled systems based on colloidal QDs in photonics, optoelectronics, and sensing.Comment: 14 pages, 3 figure

Compact Source of Electron Beam for Facility of Electron-Beam Welding with the Location of the Electron Gun and the Source of High Voltage in a Single Monoblock. Concept and Bench Tests of the Monoblok Prototype

Представлен прототип компактного источника электронного пучка для установок электронно-лучевой сварки с расположением электронной пушки и источника высоковольтного напряжения в едином моноблоке. Размещение электронной пушки, источника высоковольтного напряжения, электроники управления пучком и питания накала катода источника электронного пучка для электронно-лучевой сварки в едином корпусе-моноблоке снижает вес и стоимость (за счёт уменьшения количества используемых материалов), объём и занимаемые производственные площади. Это существенно расширяет возможности применения представляемого типа источников электронного пучка в разнообразных областях деятельности человека, в том числе в космических технологиях в открытом пространстве космоса. Цель работы – показать целесообразность концепции компоновки источника электронного пучка в едином корпусе-моноблоке на примере стендовых испытаний прототипа источника-моноблока. Спроектирован и изготовлен прототип источника-моноблока. Проведены его предварительные стендовые испытания с лазерным подогревом катода. Обсуждаются возможные применения. Получен электронный ток источника до 70 мА с энергией 90 кэВ. Данный результат демонстрирует возможность практической реализации нового способа компоновки источника электронного пучкаA prototype of an electron beam compact source for electron-beam welding is presented. The electron gun and a high-voltage source are united in a single monoblock. The placement of the electron gun, the high-voltage source, the beam control electronics and the power supply of the cathode heating of the electron beam source for electron beam welding in a single monoblock housing reduces weight and cost by reducing the amount of materials used, volume and occupied production areas. This significantly expands the possibilities of using the presented type of electron beam sources in various fields of human activity, including space technologies in the open space of space. The purpose of the work is to show the expediency of the concept of arranging the electron beam source in the single monoblock housing as the example of bench tests of the source prototype. The prototype of the monoblock was designed and manufactured. Its preliminary bench tests with laser cathode heating were carried out. Its possible applications are discussed. An electron source current up to 70 mA with an energy of 90 keV was obtained. The result obtained demonstrates the possibility of practical implementation of a new method of arranging an electron beam sourc

Dissociation of Trinitrotoluene on the Surface of Porous Silicon Under Laser Irradiation

AbstractDissociation of trinitrotoluene (TNT) sorbed on porous silicon (pSi) surface under UV laser irradiation has been studied. A method based on ion mobility spectrometry (IMS) has been used in this study. Excitation and ionization of TNT molecules has been occurred at atmospheric pressure. A dependence of TNT ion spectrum on standing time of TNT molecules on pSi surface has been demonstrated. The ion type has changed from (TNT-H) – to (TNT-NO2) – which indicates a slow chemical reaction between pSi surface and TNT molecules. The first step of (TNT-NO2) – formation has been found to be a result of laser stimulated surface dissociation and subsequent desorption of a neutral TNT-NO2 fragment. The second step of (TNT-NO2) – formation is a capture of an electron emitted from the pSi surface under laser irradiation. The result of this study could be used in the area of explosive detection

Next-nearest-neighbor coupling with spinor polariton condensates

We report on experimental observation of next-nearest-neighbor coupling between ballistically expanding spinor exciton-polariton condensates in a planar semiconductor microcavity. All-optical control over the coupling strength between neighboring condensates is demonstrated through distance-periodic pseudospin screening of their ballistic particle outflow due to the inherent splitting of the planar cavity transverse-electric and transverse-magnetic modes. By screening the nearest-neighbor coupling we overcome the conventional spatial coupling hierarchy between condensates. This offers a promising route toward creating unconventional nonplanar many-body Hamiltonians using networks of ballistically expanding spinor exciton-polariton condensates

Spectral and spatial characteristics of the electromagnetic modes in a tunable optical microcavity cell for studying hybrid light–matter states

Studies of resonance interaction between matter and localized electromagnetic field in a cavity have recently attracted much interest because they offer the possibility of controllably modifying some of the fundamental material properties. However, despite the large number of such studies, these is no universal approach that would allow investigation of sets of different samples with wide variation of the main experimental parameters of the optical modes. In this work, the main optical parameters of a previously developed universal tunable microcavity cell, i.e., the Q factor and mode volume, as well as their dependence on the characteristics of cavity mirrors and spacing between them, are analyzed. The results obtained will significantly expand the scope of applications of resonance interaction between light and matter, including such effects as the enhancement of Raman scattering, long-range resonance nonradiative energy transfer, and modification of chemical reaction rates.This work was supported by the Ministry of Science and Higher Education of the Russian Federation,contract no. 4.Y26.31.0011

Modulation of quantum dot photoluminescence in porous silicon photonic crystals as a function of the depth of their penetration

International audiencePhotonic crystals doped with fluorescent nanoparticles offer a plenty of interesting applications in photonics, laser physics, and biosensing. Understanding of the mechanisms and effects of modulation of the photoluminescent properties of photonic crystals by varying the depth of nanoparticle penetration should promote targeted development of nanocrystal-doped photonic crystals with desired optical and morphological properties. Here, we have investigated the penetration of semiconductor quantum dots (QDs) into porous silicon photonic crystals and performed experimental analysis and theoretical modeling of the effects of the depth of nanoparticle penetration on the photoluminescent properties of this photonic system. For this purpose, we fabricated porous silicon microcavities with an eigenmode width not exceeding 10 nm at a wavelength of 620 nm. CdSe/CdS/ZnS QDs fluorescing at 617 nm with a quantum yield of about 70% and a width at half-height of about 40 nm were used in the study. Confocal microscopy and scanning electron microscopy were used to estimate the depth of penetration of QDs into the porous silicon structure; the photoluminescence spectra, kinetics, and angular fluorescence distribution were also analyzed. Enhancement of QD photoluminescence at the microcavity eigenmode wavelength was observed. Theoretical modeling of porous silicon photonic crystals doped with QDs was performed using the finite-difference time-domain (FDTD) approach. Theoretical modeling has predicted, and the experiments have confirmed, that even a very limited depth of nanoparticle penetration into photonic crystals, not exceeding the first Bragg mirror of the microcavity, leads to significant changes in the QD luminescence spectrum determined by the modulation of the local density of photonic states in the microcavity. At the same time, complete and uniform filling of a photonic crystal with nanoparticles does not enhance this effect, which is as strong as in the case of a very limited depth of nanoparticle penetration. Our results will help to choose the best technology for fabrication of efficient sensor systems based on porous silicon photonic crystals doped with fluorescent nanoparticles

Enhanced spontaneous emission from two-photon-pumped quantum dots in a porous silicon microcavity

International audience(IN) Received XX Month XXXX; revised XX Month, XXXX; accepted XX Month XXXX; posted XX Month XXXX (Doc. ID XXXXX); published XX Month XXXX Photoluminescence (PL)-based sensing techniques have been significantly developed in practice due to their key advantages in terms of sensitivity and versatility of the approach. Recently, various nanostructured and hybrid materials have been used to improve the PL quantum yield and spectral resolution. The near-infrared (NIR) fluorescence excitation has attracted much attention because it offers deep tissue penetration and avoiding the autofluorescence of the biological samples. In our study, we have shown both spectral and temporal PL modifications under two-photon excitation of quantum dots (QDs) placed in one-dimensional porous silicon photonic crystal (PhC) microcavities. We have demonstrated an up to 4.3-fold Purcell enhancement of the radiative relaxation rate under two-photon excitation. The data show that the use of porous silicon PhC microcavities operating in the weak coupling regime permits the enhancement of the PL quantum yield of QDs under two-photon excitation, thus extending the limits of their biosensing applications in the NIR region of optical spectrum. © 2020 Optical Society of America Light-matter resonance interaction enables control over spontaneous photoluminescence (PL) emission properties of various luminophores, including organic dyes [1,2], rare-earth ions [3], 2D metal dichalcogenides [4], and fluorescent nanocrystals [5,6]. The so-called "weak" coupling regime makes it possible to change the spectral, spatial, and temporal properties of the luminophore PL emission by varying the local electromagnetic environment [7]. The use of photonic crystals (PhCs) is one of the most promising approaches to controlling the electromagnetic field distribution and, hence, to coupling it to the emitters placed inside the PhC microcavities (MCs) [1,3,4,7]. This approach is of special interest in the field of sensing in such emerging areas as the healthcare, environmental monitoring, and food safety [8,9]. Recent studies have demonstrated significant advances of PL-based sensors employing PhC structures in order to improve the critical properties of PL labels [9,10]. Porous silicon (pSi) MCs have been shown to be promising for biosensing applications due to the simplicity and scalability of fabrication and highly developed pore structure making the sensor surface easily accessible for analytes [11-13]. However, the necessity of selective excitation of majority of conventional dyes in the visible region of optical spectrum, low photostability, brightness, and background due to the autofluorescence of biological samples remain the obstacles to wider use of PL-based biosensor techniques. Excitation of the PL probes in the near-infrared (NIR) transparency window of biological samples could resolve some of these problems, allowing one deeper tissue penetration, higher spectral resolution and avoiding the autofluorescence. The nonlinear regime of two-photon excitation is a way to obtain visible-range fluorescence using NIR light sources. Moreover, the use of semiconductor quantum dots (QDs) with uniquely high two-photon absorption cross-sections compared to conventional dyes [14,15] allows one to reach the unprecedentedly high values of fluorescence contrast [16]. In addition, QDs are the excellent probes for sensing due to their wide one-and two-photon absorption [17,18] and narrow PL spectra, high quantum yield [19], and excellent photostability [20,21]. In this study, we have investigated the spontaneous PL emission of CdSe(core)/ZnS/CdS/ZnS(multishell) QDs placed inside a porous silicon MCs under two-photon excitation. We have measured the spectral and temporal characteristics of the spontaneous PL emission of QDs under two-photon pumping, as well as their dependence on the pump power. Significant enhancement of the QD PL at the wavelength corresponding to the MC eigenmode and its suppression within the photonic bandgap were observed. The change in the QD PL spectrum inside the porous silicon microcavity depended on the excitation energy density because the relaxation rates of the PL signal in the spectral regions where it was enhanced or suppressed were different. The increase in the emission rate corresponding to the weak coupling between the exciton transition of QDs and the eigenmode of the MC has been shown, and Purcell factor was determined to be about 4.3