P-polarized Reflectance Research Articles

Phonon Characteristics of Gas-Source Molecular Beam Epitaxy-Grown InAs1−xNx/InP (001) with Identification of Si, Mg and C Impurities in InAs and InN

The lattice dynamical properties of dilute InAs1−xNx/InP (001) epilayers (0 ≤ x ≤ 0.03) grown by gas-source molecular beam epitaxy were carefully studied experimentally and theoretically. A high-resolution Brüker IFS 120 v/S spectrometer was employed to measure the room-temperature infrared reflectivity (IRR) spectra at near-normal incidence (θi = 0). The results in the frequency range of 180–500 cm−1 revealed accurate values of the characteristic In-As-like and In-N-like vibrational modes. For InAs1−xNx alloys, a classical “Drude–Lorentz” model was constructed to obtain the dielectric functions ε~ω in the far IR regions by incorporating InAs-like and InN-like transverse optical ωTO modes. Longitudinal optical ωLO phonons were achieved from the imaginary parts of the simulated dielectric loss functions. The theoretical results of IRR spectra for InAs1−xNx/InP (001) epilayers using a multi-layer optics methodology provided a very good agreement with the experimental data. At oblique incidence (θi ≠ 0), our study of s- and p-polarized reflectance (Rs,p(ω)) and transmission (Ts,p(ω)) spectra allowed the simultaneous perception of the ωTO and ωLO phonons of the InAs, InN and InAs0.97N0.03 layers. Based on the average t-matrix Green’s function theory, the results of local vibrational modes for light SiIn+ donors and SiAs−, CAs− acceptors in InAs were found in good agreement with the existing Raman scattering and infrared spectroscopy data. InInN, however, the method predicted an in-band mode for the MgIn− acceptor while projecting an impurity mode of the SiIn+ donor to appear just above the maximum ωmaxInN[≡595 cm−1] phonon frequency region. In InAs1−xNx/InP (001) epifilms, the comparison of reflectivity/transmission spectra with experiments and the predictions of impurity modes for isoelectronic donor and acceptor impurities in InAs and InN can be valuable for appraising the role of defects in other technologically important semiconductors.

Active tuning hBN phonon polaritons and spontaneous emission rates based on VO<sub>2</sub> and graphene

<sec>Active tunability of phonon dispersion and spontaneous emission (SE) are still open problems due to their exciting potential applications. In view of the fact that polaritons are very sensitive to the dielectric environment, in this study, with the help of the differences in optical property between the phase change material vanadium dioxide (VO<sub>2</sub>) during the phase transition from the insulating state to metallic state and the tunable surface plasmon polaritons (SPPs) in graphene, a heterostructure composed of hyperbolic material hexagonal boron nitride (hBN) and graphene and VO<sub>2</sub> is proposed to investigate the active tunability of hBN phonon polaritons (PhPs). In order to illustrate the underlying physical mechanism of the above heterostructures, the dispersion distributions of the above heterostructures are calculated and represented by the imaginary part of the p-polarized Fresnel reflection coefficient of the heterostructure, meanwhile the dispersion relation of the hBN/VO<sub>2</sub> heterostructure in hyperbolic region is verified by the quasi-static approximation method.</sec><sec>Results indicate that the active tunability of hBN PhPs inside type-I and type-II hyperbolic bands can be achieved by controlling VO<sub>2</sub> phase transition in hBN/VO<sub>2</sub> heterostructure. The PhP dispersion change of the hBN/VO<sub>2</sub> heterostructure is mainly caused by the change of the VO<sub>2</sub> dielectric function when VO<sub>2</sub> substrate changes from the insulating state into metallic state, which affects the total Fresnel reflection coefficient of the heterostructure, finally resulting in the PhP dispersion change of hBN/VO<sub>2</sub> heterostructure. When graphene is introduced into the hBN/VO<sub>2</sub> heterostructure, coupled hyperbolic plasmon-phonon polaritons (HPPPs) are obtained within type-I and type-II hyperbolic band of hBN, while the surface plasmon-phonon polaritons (SPPPs) are generated outside its hyperbolic bands. Moreover, comparative analysis of SE rates is presented for a quantum emitter positioned with the hBN/VO<sub>2</sub> and graphene/hBN/VO<sub>2</sub> heterostructure, revealing that the SE rates of these heterostructures can be modulated by the passive means including changing the hBN thickness and distance between the dipole emitter and the proposed heterostructure, and also by the active means including tuning VO<sub>2</sub> phase states and graphene chemical potential without changing structural configurations. This study provides a theoretical guidance in realizing active tunability of both phonon dispersion and SE rate of the natural or artificial anisotropic optical materials by using functional materials including phase change materials and graphene.</sec>

Ultrasensitive broadband photoacoustic microscopy based on common-path interferometric surface plasmon resonance sensing

Ultrafast and sensitive response of surface plasmon polaritons to the ultrasonically-modulated changes in refractive index of the water allows photoacoustic impulses to be measured using surface plasmon resonance (SPR) sensors. However, the sensing modalities always suffer from either low sensitivity or instable signal output, possibly precluding imaging recovery. By exploiting that pressure transients can substantially produce phase shift in p-polarized optical reflection but have no impact on s-polarized component in SPR sensing, we develop a common-path interferometric SPR sensor for photoacoustic measurement, in which time-varying light interference between photoacoustically-perturbed p-polarized beam and its orthogonal s-polarized component of a single interrogation laser is monitored. Such configuration retains optimum photoacoustic measurement with concurrent very stable signal output, high sensitivity (noise-equivalent-pressure sensitivity of ∼95.6 Pa), and broad bandwidth (∼173 MHz). Volumetric microvascular imaging from mouse ear in vivo is obtained, suggesting that the novel sensing approach potentially advances biomedical photoacoustic applications.

Quantum mechanical four-dimensional non-polarizing beamsplitter

Some quantum optics researchers might not realize that classical electromagnetism predicts a mathbf {pi } phase shift between S- and P-polarized reflection and might think the reflection coefficients of the transverse modes are independent, or that such a phase shift has no measurable consequences. In this paper, we discuss theoretical grounds to define elements of a 4x4 matrix to represent the beamsplitter, accurately accounting for transverse polarization modes and phase relations between them. We also provide experimental evidence confirming this matrix representation. From a scientific point of view, the paper addresses a non-trivial equivalence between the classical fields Fresnel formalism and the canonical commutation relations of the quantized photonic fields. That the formalism can be readily verified with a simple experiment provides further benefit. The beamsplitter expression derived can be applied in the field of quantum computing.

Use of interface phonon-polaritons for the alloy determination in ZnO/(Zn,Mg)O multiple quantum wells

A method based on infrared reflectance spectroscopy is presented by which the Mg content in ZnO/(Zn,Mg)O multiple quantum wells with very thin barriers can be determined. The method relies on the observation of interface phonon-polaritons which appear as sharp dips in the p-polarized reflectance spectra at oblique incidence near the longitudinal optical (LO)-phonon frequencies of both QW and barrier materials. By fitting the reflectance spectra to a dielectric function model, the LO phonon frequency of the (Zn,Mg)O barrier layers can be determined. The LO phonon frequency depends on the Mg content. Comparing to Mg content calibration via cathodoluminescence, a linear relationship between the reflectance dip frequency and the Mg content is obtained. The presented method serves as a rapid means to determine the Mg content on final structures with very thin (Zn,Mg)O layers -such as device structures- where alternative, destructive methods cannot be used.

Determination of a grown oxide layer thickness and optical constants of Zn and Cd metals

Optical constants of Zn and Cd polycrystalline metals are measured using both quasi polarizing angle and principal angle of incidence methods at wavelength 633 nm. The quasi polarizing angle is the angle at which the intensity of the p-polarized reflection component reaches its minimum value. It depends only on the rotation of the sample using a rotating stage (with accuracy ± 0.1º) without moving any other parts in the optical setup. This method is considered the most accurate method for determining the optical constants of metal. These two methods are performed to investigate the difference between the quasi polarizing angle and the principal angle of incidence and to determine the optical constants of Zn and Cd metals. To verify the optical constants results of both methods, the same metals are measured by manual null ellipsometer. Very strong correlation is found between all results of optical constants. The thickness of a grown oxide layer, which is naturally formed on the surface of a metal, is measured using PHE-103 spectroscopic ellipsometer. A polishing process is performed to each metal before measuring the thickness of the grown oxide layer with time. It is found that the formed layers grow up faster after polishing and the rate of growth decreases with time. In a period of 144 h, the oxide layer formed on zinc is about three times that formed on cadmium.

The interaction of laser radiation with strongly coupled plasmas

New results of measurements of s- and p-polarized reflectivity of nonideal plasma at the frequency of the external electromagnetic field ν las = 2.83 × 1014 s−1, free-electron number density n e = 3.3 × 1021 cm−3 (Coulomb nonideal plasma parameter Γ = 1.2) and n e = 5.2 × 1021 cm−3 (Γ = 1.4) are presented. These data are the result of the next stage of study of optics of a warm dense matter. We present a microscopic approach to describe the entire set of experimental data on the optics of strongly correlated plasma.

Excitation of Josephson plasma waves in a layered high-temperature superconductor slab embedded in a high refractive index dielectric

The nonlocal optical response of a layered high-temperature superconductor slab embedded in a dielectric medium is theoretically studied. It is assumed that the layers inside the high-temperature superconductor are parallel to the slab surfaces. We calculate its p-polarization optical spectra by using an average permittivity tensor which depends on both the frequency and the wave vector of the electromagnetic wave. Consequently, additional electromagnetic modes just above the characteristic Josephson plasma frequency, being in the terahertz range, are generated. It is shown that the p-polarization reflectivity spectra for a Bi2Sr2CaCu2O8 + δ (Bi2212) superconductor slab, embedded in high refractive index dielectric, exhibit prominent dips breaking the total internal reflection. For very small superconductor slab thicknesses, the optical spectra resonances are associated with Fabry-Perot resonances of the short-wavelength electromagnetic modes. In contrast, the long-wavelength electromagnetic modes, having anomalous dispersion relation, are excited at relatively-large slab thicknesses and manifest themselves as strong resonances in both absorption and transmissivity spectra, suppressing the specular reflectivity.

Study on Mnospectral Peak Identification of Hard Target Based on Brewster Angle

It is difficult to obtain the wide band spectrum of the target in the hard target detection with strong background weak signal by laser. A single spectral peak recognition method based on brewster angle is proposed. By combining the characteristics of pPolarized reflectivity and characteristics of typical target extinction coefficient, the brewster angle solution of hard target is obtained by extremum finding by the second derivative in the hard target detection model. The results show that the brewster angle of nonmetallic hard targets is correlated with inverse triangulation of double index. Therefore, the single spectral peak method can be used to identify the target material by means of the laser which covers the peak spectral segment of the target refractive index.

Berreman effect in bimetallic nanolayered metamaterials

The visible and ultraviolet responses of a binary regular stack, composed of alternating Al and Ag nano-thin layers, are both experimentally and theoretically studied. It is found that the s- and p-polarization reflectivity spectra (Rs and Rp, respectively) of the inherently anisotropic bimetallic system are noticeably different due to the appearance of a prominent dip near the zero of the Ag permittivity. Such an effect is similar to the Berreman one, which is observed in thin polar-crystals films near the longitudinal-optical phonon frequency, as well as in thin metal films near plasma frequency. Using both the effective medium approach and a nonlocal homogenization formalism, being valid even beyond the long wavelength limit, it is demonstrated that the bimetallic multi-layer stack behaves as a uniaxial anisotropic metamaterial. As it is shown, the appearance of the dip in the p-polarization spectrum is associated to the zero of the longitudinal component of the effective permittivity (ϵz). The calculation of 45-degree reflectometry spectrum, namely the difference Rp−Rs2, from experimental and theoretical reflectivity data confirmed that the observed dip in Rp is connected to a plasma resonance of the energy-loss function ℑ(−1∕ϵz).

Nonlocal optical response of a layered high-temperature superconductor slab

We theoretically study the effect of the spatial dispersion on the optical response of a layered high-temperature superconductor slab. The nonlocality of the inherently-anisotropic layered superconductor comes from the wave vector dependence of its average permittivity tensor, and leads to the generation of additional electromagnetic modes just above the characteristic Josephson plasma frequency, that is in the terahertz range. We calculate p-polarization optical spectra for a Bi2Sr2CaCu2O8+δ (Bi2212) superconductor slab, which show very narrow resonances associated with the quantization of the wave vectors of both long-wavelength electromagnetic modes, having negative dispersion, and short-wavelength additional (nonlocal) modes of positive dispersion. The dependence of the frequency position and shape of the resonances on the nonlocality parameter, the slab thickness, and the components of the quasiparticle conductivity is analyzed. We have found that the quantized long-wavelength modes of negative dispersion, which can only be observed at relatively-large slab thicknesses, give rise to prominent resonances in the p-polarization reflectivity spectrum. On the other hand, the resonances associated with quantized additional short-wavelength electromagnetic modes are weak, but they can be clearly observed when the superconductor slab thickness is smaller than the smallest magnetic-field penetration depth.

Polarized reflectivity properties of shock-compressed plasma with strong interaction of particles

New results of s- and p-polarized reflectivity measurements on non-ideal plasma at the frequency of external electromagnetic field νlas = 2.83×1014 s−1, the plasma density ρ = 1.8 g/cm3 and the parameter of Coulomb non-ideality of plasma Γ = 1.4 are presented. Using a Fermi-like density profile along the shock wave front, the reflectivity coefficients of non-ideal plasma were calculated for newly obtained experimental data. As physically expected, a single profile is sufficient to obtain good agreement with the experimental data at all investigated optical laser frequencies.

Spectroscopic ellipsometer study of correlation of out of plane and in-plane plasmons in silver nanoislands with annealing induced growth

In-plane and out of plane plasmons' study in Ag metallic nanoparticles films deposited onto glass substrate using pulsed laser ablation technique and annealed from 100-400 °C temperature range has been presented using spectroscopic ellipsometer (SE). Effective dielectric constants of nanoislands thin films have been obtained by fitting psi and delta measured from SE which contain the information about annealing induced changes in morphological properties. A simultaneous fitting of p-polarized and s-polarized reflection spectra strengths the uniqueness of applied set of oscillators. Behavior of LSPR peak shift has been discussed in the frame of Modified-Yamguchi model. A shape dependent calculation of plasmon linewidth and further comparison with measured linewidth has been made to predict preferred direction of the annealing induced growth of the film. Morphological facts are also confirmed by FESEM images of the films. Both shifts indicate the dewetting of the film and isolation of nanoparticles. Grain boundary diffusion assisted two-dimensional growth of three dimensional particles is confirmed by present analysis.

Femtosecond optical polarization switching using a cadmium oxide-based perfect absorber

Ultrafast control of the polarization state of light may enable a plethora of applications in optics, chemistry and biology. However, conventional polarizing elements, such as polarizers and waveplates, are either static or possess only gigahertz switching speeds. Here, with the aid of high-mobility indium-doped cadmium oxide (CdO) as the gateway plasmonic material, we realize a high-quality factor Berreman-type perfect absorber at a wavelength of 2.08 μm. On sub-bandgap optical pumping, the perfect absorption resonance strongly redshifts because of the transient increase of the ensemble-averaged effective electron mass of CdO, which leads to an absolute change in the p-polarized reflectance from 1.0 to 86.3%. By combining the exceedingly high modulation depth with the polarization selectivity of the perfect absorber, we experimentally demonstrate a reflective polarizer with a polarization extinction ratio of 91 that can be switched on and off within 800 fs. Indium-doped cadmium oxide performs polarization switching on a subpicosecond timescale.

A sensitive reflection method for optical diagnostics of graphene layers

Simple reflection diagnostics possibilities of graphene layers on dielectric and semiconductor substrates at the Brewster angle are analyzed. The analysis is based on a numerical simulation. It is shown that in the vicinity of the Brewster angle optical contrast (differential reflectance) of graphene flakes on bare substrates is strong and significantly different for graphene flakes with different number of graphene layers, which allows for a simple identification of the number of layers in the graphene sheet. Another way to determine the number of graphene layers in a graphene sheet by using the shift of the p-polarized light reflectance minima (quasiBrewster angle) as a function of the number of graphene layers is also proposed.

Dependence of surface plasmon-phonon-polariton in 4 H-SiC on free carrier concentration

In this paper, we present a thorough study of the characteristics of the surface modes that result from coupling between plasmon electronic oscillation modes, phonon modes, and electromagnetic modes. The Fourier transform of p-polarized reflectivity measurements were carried out on different 4 H-SiC epilayers differing in their free carrier concentration. The reflectivity measurements were performed with appropriate care to record reflectivity spectra averaged over a wide range of incidence angles. The complex infrared dielectric functions of the measured samples were determined by correcting the values obtained from the conventional Kramers-Kronig conversion technique with reference to Fresnel equations for reflectivity. The obtained dielectric functions were used to compute the effect of the free carrier concentration and the resulting plasmon electronic oscillation on the dispersion spectrum, lifetime, mean propagation length of the bulk, and surface plasmon-phonon-polariton modes. The effect of the free carrier concentration on the temporal coherence of surface plasmon-phonon-polariton is investigated, showing a potential practical method for enhancing the temporal coherence of SiC based thermal sources.

Simultaneous measurements of s- and p-polarization reflectivity with a cavity ring-down technique employing no polarization optics

The cavity ring-down (CRD) technique is adopted for simultaneously measuring s- and p-polarization reflectivity of highly reflective coatings without employing any polarization optics. As the s- and p-polarized light trapped in the ring-down cavity decay independently, with a randomly polarized light source the ring-down signal recorded by a photodetector presents a double-exponential waveform consisting of ring-down signals of both s- and p-polarized light. The s- and p-polarization reflectivity values of a test mirror are therefore simultaneously determined by fitting the recorded ring-down signal with a double-exponential function. The determined s- and p-polarization reflectivity of 30° and 45° angle of incidence mirrors are in good agreement with the reflectivity values measured with the conventional CRD technique employing a polarizer for polarization control.

Improvement of interface structure and polarization performance of Co/C multilayers by incorporation of nitrogen.

Short-period (~3.5 nm) Co/C multilayer mirrors are fabricated by the direct current magnetron sputtering technique through the addition of a small proportion of nitrogen (4-15% partial pressure) to the working gas (Ar). The addition of nitrogen has been demonstrated to significantly suppress the interdiffusion of neighboring materials due to the nitridation of carbon layers as compared with the Co/C multilayer fabricated with the use of pure Ar. The optimal partial pressure of nitrogen was found to be 6%. At this pressure, nitrogen provides abrupt interfaces and the maximal peak value (19%) of the s-polarized radiation reflectivity at the 251-eV photon energy and 45° angle of incidence. The p-polarized radiation reflectivity proved to be less than 0.3%, demonstrating high potentialities of the nitridated Co/C multilayers as Bragg polarizers in the 4.5-6.5-nm spectral range.

Influence of optical non-uniformity on the reflectance of dense plasmas

We provide theoretical analysis of the reflectance of shock compressed plasmas and warm dense matter for normal incidence of laser radiation as well as for the dependence of s- and p-polarized reflectivity on incidence angle. We use density functional theory approach for the calculation of the dielectric function and reflectivity. The Kohn-Sham set of equations with the projector augmented wave (PAW) potential is solved for valent electrons. Due to the nonlocality of the PAW potentials, the longitudinal expression for the imaginary dielectric function is used. The real part is obtained by the Kramers-Kronig transformation. Quantum molecular dynamics simulation and VASP is used. Comparison with the experimental data for shock compressed xenon is performed. Three wavelengths are considered.

Brewster angle and reflectivity of optically nonuniform dense plasmas.

We provide theoretical analysis of the reflectance of shock-compressed plasmas and warm dense matter for normal incidence of laser radiation as well as for the dependence of s- and p-polarized reflectivity on the incidence angle. The self-consistent approach for the calculation of the optical and electronic properties of warm dense matter and nonideal plasmas developed in our previous works is extended for the description of normal and polarized reflectivity from the broadened optically nonuniform medium. Two methods are applied for the calculation of the reflectivity from spatially broadened optically nonuniform medium. The first one is based on the solution of the Helmholtz equation for the amplitudes of the electromagnetic field. Another one is based on Drude theory of reflection. It allows us to calculate the ratio of the s- and p-polarized reflectivity if dependence of the dielectric function on distance is known. For the case of the polarized reflectivity, the particular attention is concentrated on the Brewster angle. The calculation results for the dielectric function, obtained within the framework of the density-functional theory with the longitudinal expression for the dielectric tensor, are applied for the calculation of the reflectivity. Comparison with the experimental data for shock-compressed xenon is performed.