We offer and demonstrate a new type of plasmonic metasurface for sensorics and surface-enhanced Raman spectroscopy (SERS) spectroscopy, characterized by a wide spectral range of sensitivity from 450 nm to 850 nm. The metasurface is formed by Ag nanoparticles of different sizes. The metasurface has clear anisotropy formed by the Ag nanoparticles’ size-dependent plasmonic resonances. The resonant wavelength of the metasurface is linearly changed in one direction on a metasurface realizing a wavelength to space conversion and remains the same in the other direction. The metasurface has advantages for use in different applications of optical microscopy and SERS diagnostics, since it simultaneously provides a strong optical signal amplification of up to 4×107 as well as a wavelength to space conversion with a 10 nm spectral resolution. We show the fabrication of the anisotropic plasmonic metasurface by the use of a robust approach based on Ag nanoparticle self-assembly during a molecular-beam-epitaxy growth process. We demonstrate an application of the metasurface for the fluorescence detection of low concentrations of dye molecules (Cy-7.5) and the surface-enhanced Raman spectroscopy of an organic molecular monolayer (Alq3)
Organic microresonators are highly attractive for numerous applications including biosensing, optical switching and metrology. Adding chiral materials to resonators can enhance their sensing properties due to the appearance of chiroptical effects. Here we study experimentally resonant multiphoton processes in spherical microresonators with the diameter of 2–12 μm made of 1,1’-bi-2-naphthol derivatives by a self-assembly technique. Using nonlinear singleparticle microscopy, we demonstrate that these microspheres provide excitation of whispering gallery modes (WGMs) in two- and three-photon excited luminescence with a Q-factor of up to 300. We also demonstrate that the nonlinear circular dichroism is enhanced due to the WGM excitation and reaches 7.7% and 11% in the two- and three-photon absorption, respectively. Pronounced modulation of the WGMs spectrum due to the mode’s splitting is observed in coupled binol-based microresonators, which opens a path for the control over their resonant response and makes them suitable for nonlinear optical sensing applications.
We describe a compact dual-wavelength (1.047 and 1.053 μm) diode end-pumped Q-switched Nd:YLE laser source which has a number of applications in demand. In order to achieve its dual-wavelength operation it is suggested for the first time to use essentially nonmonotonous dependences of the threshold pump powers at these wavelengths on the cavity length in the region of the cavity semiconfocal configuration under a radius of the pump beam smaller than the radius of the zero Gaussian mode. Here we demonstrate one of the most interesting applications for this laser: difference frequency generation in a GaSe crystal at a frequency of 1.64 THz. A superconducting hot-electron bolometer is used to detect the THz power generated and to measure its pulse characteristics.
We discuss the photon number splitting attack (PNS) in systems of quantum cryptography with phase coding. It is shown that this attack, as well as the structural equations for the PNS attack for phase encoding, differs physically from the analogous attack applied to the polarization coding. As far as we know, in practice, in all works to date processing of experimental data has been done for phase coding, but using formulas for polarization coding. This can lead to inadequate results for the length of the secret key. These calculations are important for the correct interpretation of the results, especially if it concerns the criterion of secrecy in quantum cryptography.
Dielectric-loaded surface plasmon−polariton waveguides (DLSPPWs) are a practically valuable type of plasmonic waveguide. The properties of DLSPPWs at telecommunication wavelengths have been studied in detail. However, the efficient optical excitation of DLSPPWs in the visible spectral range has still not been realized. In this work, we present the results of our experimental investigations of DLSPPWs in the visible spectral range. In addition, a new configuration for the excitation and detection of the DLSPPW mode has been proposed and realized. The propagation of the DLSPPW plasmon mode up to a distance of 45 μm has been demonstrated.
The combination of high operation temperatures and small diode lasers directly grown on silicon substrates is essential for their application in future photonic integrated circuits. In this letter, results are presented for quantum dot III–V-on-Si microdisk diode lasers tested at elevated temperatures. To the best of our knowledge, we have demonstrated the first uncooled microlasers with diameter of 30 µm capable of operating in the continuous wave regime at 60 °C. In the lasing regime, the emission spectra contain one very intense line with a full-width at half-maximum of 30 pm; the side mode suppression ratio reaches 18 dB. Because of self-heating, the actual temperature of the active region is close to 100 °C. Under pulsed excitation, the maximal lasing temperature is 110 °C.
We discuss photonic effects in arrays of frustum-shaped organic microstructures prepared from organic orange dye composed on a solid substrate by self-assembling technique. We demonstrate that such structures reveal strong amplification of second-order nonlinear optical response, including optical second harmonic generation (SHG) and two-photon fluorescence (TPF), as compared to that of a continuous film. This is associated with a strong light localization in microstructures composed of high refractive index material. The TPF and SHG power dependencies show that the observed effects are governed by high second-order nonlinearity of the dye damped by a strong absorption. FDTD calculations confirm that the mechanism of the light localization inside organic frustums can be in the form of whispering gallery modes excitation.
Density matrices of pure multiphoton Fock polarization states and their resultant reduced density matrices of mixed states are expressed in similar ways in terms of matrices of correlators, defined as averaged products of equal numbers of creation and annihilation operators. The degree of entanglement of considered states is evaluated for various combinations of parameters of states and characters of their reduction.
In this letter we present estimates for the distance of secret key transmission through free space for three different protocols of quantum key distribution: for BB84 and phase timecoding protocols in the case of a strictly single-photon source, and for the relativistic quantum key distribution protocol in the case of faint laser pulses.
A new protocol for quantum key distribution through empty space is proposed. Apart from the quantum mechanical restrictions on distinguishability of non-orthogonal states, the protocol employs additional restrictions imposed by special relativity. The protocol ensures generation of a secure key even for the source generating non-strictly single-photon quantum states and for arbitrary losses in quantum communication channel.
A novel method is proposed for highly sensitive surface spectroscopy based on hole burning in the surface plasmon polariton (SPP) quantum generator spectrum due to absorption by analyzed molecules or clusters located inside the SPP cavity. The SPP quantum generator spectrum is calculated with an account of inhomogeneous broadening due to variations of the active medium transition frequency. The influence of an analyzed sample on the generation spectrum is demonstrated. The realization of the SPP generator spectroscopy based on a 2D cavity is proposed. It is shown that a SPP quantum generator with a sufficiently large cavity is qualitatively different from the usual laser. In particular, the SPP generation mode is not identical to the passive cavity mode and it appears only due to the active medium. Thus, such kinds of SPP generation cannot be described by the usual single-mode approach and one needs to solve the corresponding spatial problem. The sensitivity of the proposed plasmonic generator intracavity spectroscopy method is calculated.
The well-known Hong–Ou–Mandel effect is revisited. Two physical reasons are discussed for the effect to be less pronounced or even to disappear: differing polarizations of photons coming to the beamsplitter and delay time of photons in one of two channels. For the latter we use the concepts of biphoton frequency and temporal wave functions depending, correspondingly, on two frequency continuous variables of photons and on two time variables t1 and t2 interpreted as the arrival times of photons to the beamsplitter. Explicit expressions are found for the probability densities and total probabilities for photon pairs to be split between two channels after the beamsplitter and to be unsplit, when two photons appear together in one of two channels.
The concept of the Lorentz-invariant mass of a group of particles is shown to be applicable to biphoton states formed in the process of spontaneous parametric down conversion. The conditions are found when the Lorentz-invariant mass is related directly with (proportional to) the Schmidt parameter determining a high degree of entanglement of a biphoton state with respect to transverse wave vectors of emitted photons.
We show that the density of states and gain spectra of InGaAs/GaAs quantum well-dot (QWD) hybrid nanostructures qualitatively differ from that of quantum wells (QWs) and quantum dots. In QWDs, the density of states does not increase to higher energies and ground-state lasing is maintained up to shorter cavities (higher output loss) as compared to QW lasers emitting in the same optical range. The QWD lasers show lower threshold current densities and better temperature stability than the QW ones.
In the paper by Gleim et al (2016 Opt. Express 24 2619), it was declared that the system of quantum cryptography, exploiting quantum key distribution (QKD) protocol BB84 with the additional reference state and encoding in a sub-carrier, is able to distribute secret keys at a distance of 210 km. The following shows that a simple attack realized with a beam splitter results in a loss of privacy of the keys over substantially smaller distances. It turns out that the actual length of the secret key transmission for the QKD system encoding in the sub-carrier frequency is ten times less than that declared in Gleim et al (2016 Opt. Express 24 2619). Therefore it is impossible to safely use the keys when distributed at a larger length of the communication channel than shown below. The maximum communication distance does not exceed 22 km, even in the most optimistic scenario.
We theoretically investigate a phase-matching (PM) between HE11 and HE13 modes at wavelengths 1596 and 532 nm, respectively, of real germania-silica fiber wave guides, whose perform was made by MCDVD technology. For several measured refractive index profiles of the fiber perform the corresponding waveguide diameters, providing homogeneous PM, both with modal dispersion and power characteristics are calculated. The PM parameters obtained for the real fiber are compared to that calculated for a standard step-index fiber model.
By using the formalism of photon creation operators, we present the simplest description of the effect of quantum teleportation and describe its closest classical analog.
We propose a realization of two remarkable effects of Dicke physics in quantum simulation of light-matter many-body interactions with artificial quantum systems. These effects are a superradiant decay of an ensemble of qubits and the opposite radiation trapping effect. We show that both phenomena coexist in the crossover regime of a ‘moderately bad’ single-mode cavity coupled to the qubit subsystem. Depending on the type of the initial state and on the presence of multipartite entanglement in it, the dynamical features can be opposite resulting either in the superradiance or in the radiation trapping despite of the fact that the initial state contains the same number of excited qubits. The difference originates from the symmetrical or nonsymmetrical character of the initial wave function of the ensemble, which corresponds to indistinguishable or distinguishable emitters. We argue that a coexistence of both effects can be used in dynamical quantum simulators to demonstrate realization of Dicke physics, effects of multipartite quantum entanglement, as well as quantum interference and thus to deeply probe quantum nature of these artificial quantum systems.
The problem of quantum key distribution security in channels with large losses is still open. Quasi-single-photon sources of quantum states with losses in the quantum communication channel open up the possibility of attacking with unambiguous state discrimination (USD) measurements, resulting in a loss of privacy. In this letter, the problem is solved by counting the classic reference pulses. Conservation of the number of counts of intense coherent pulses makes it impossible to conduct USD measurements. Moreover, the losses in the communication channel are considered to be unknown in advance and are subject to change throughout the series parcels. Unlike other protocols, differential phase shift (Inoue et al 2002 Phys. Rev. Lett. 89 037902, Inoue et al 2003 Phys. Rev. A 68 022317, Takesue et al 2007 Nat. Photon. 1 343, Wen et al 2009 Phys. Rev. Lett. 103 170503) and coherent one way (Stucki et al 2005 Appl. Phys. Lett. 87 194108, Branciard et al 2005 Appl. Phys. Lett. 87 194108, Branciard et al 2008 New J. Phys. 10 013031, Stucki et al 2008 Opt. Express 17 13326), the simplicity of the protocol makes it possible to carry out a complete analysis of its security.
In this paper we present measurements and comparison of SPP propagation length at the practically important telecom wavelength (1560 nm) as well as in the near-infrared and visible spectral ranges. The measurements were carried out for plane SPP waves excited on Ag film surface using optical microscopy of SPP waves in the far field. We also demonstrate the possibility of visualization of a SPP waves propagation using multiphoton induced photoluminescence in silver.
We report on the estimation of blood content and vessel volume fraction changes in the microcirculatory bed of human skin under controlled mechanical compression using 3-dimensional optoacoustic (OA) angiography. A consecutive decrease in the fraction of blood vessels and skin blood content as a result of an increase in pressure from 0 to 72 mmHg applied to the imaged area was demonstrated by means of an acoustical-resolution OA microscope with a spatial resolution of 50 μm. Pressures below 32 mmHg were shown to weakly affect the acquired OA angiograms. The loss of OA signal from the blood vessels was observed after a further pressure increase of up to 72 mmHg. The vascular changes observed by OA microscopy were confirmed by infrared (IR) thermometry measurements which revealed similar dynamics of microcirculation interruption in the area under pressure.