S-polarized Radiation Research Articles

Study of s-polarized photonic bandgap structure in three component optical fibonacci multilayers composed of nanoscale materials

In this communication dispersion relation, reflection and transmission coefficient for quasiperiodic optical multilayers arranged according to the three-component Fibonacci rule is derived using transfer matrix method. In this work Fibonacci multilayers using three different photonic band gap (PBG) materials is designed and its photonic band gap structure is presented. Also, a detailed calculation for allowed and forbidden frequency bands for s-polarized radiation of light incident on these structures at various angles is presented. It is demonstrated that in case of s-polarized mode of radiation, widening in the band gap and frequency shifts occur as one moves towards the higher frequency region, which shows that such a multilayer can be used as an efficient polarizer. The effect of an imaginary value for the propagation vector Q on the existence of forbidden photonic bands in these lattices is also studied.

Application of Thin Titanium/Titanium Oxide Layers Deposited on Gold for Infrared Reflection Absorption Spectroscopy: Structural Studies of Lipid Bilayers

Ultrathin titanium layers when deposited on the surface of gold can be successfully applied for infrared reflection absorption spectroscopy (IRRAS) investigations. It was shown that the reflectivity, the phase shift, and the mean square electric field of the p- and s-polarized IR radiation in up to 20 nm thick titanium layers covered with a 3-4 nm thick layer of native oxide are comparable to those of the air/gold interface. The surface selection rule is fulfilled. Thus, qualitative and quantitative analysis of 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) bilayers transferred in liquid expanded (LE) and liquid condensed (LC) states can be performed. Differences are found in the hydration state and molecular arrangement of the two investigated bilayers. In the DMPC bilayer in the LE state, the C-N bond in the positively charged choline moiety is inclined by approximately 70 degrees toward the surface of the negatively charged titanium substrate. In the phosphate moiety, the in-plane vector of the O-P-O group makes a small angle of approximately 15 degrees to the surface normal. This open structure of the lipid molecule corresponds to the B crystal structure of the DMPC molecule and provides space for strong hydration of the polar headgroup. In the DMPC bilayer in the LC state, the intermolecular distances are reduced; the C-N bond of the choline group makes a smaller angle to the surface normal, and the in-plane vector of the O-P-O group in the phosphate moiety displays a larger tilt. The degree of hydration is reduced. The arrangement of the polar headgroup region corresponds to the A crystal structure of the DMPC molecule.

ATR FT-IR Absorption Enhancement of a Thin Film under the Photon-Tunneling Condition

A simple, yet very powerful technique for the spectral acquisition of an extremely thin film with enhanced absorption was explored. An infrared absorption of an extremely thin film confined between media of high refractive indices was greater than that of its bulk when the spectrum was acquired under the attenuated total reflection (ATR) condition with parallel (p) polarized radiation. The absorption enhancement was not observed under perpendicular (s) polarized radiation. Theoretical investigations indicated that the absorption enhancement was proportional to the integration of the mean square evanescent field within the film. The field integration under p-polarized radiation increased, while that under s-polarized radiation decreased as the thickness of the confined film became thinner. The maximum enhancement was observed when the film was sufficiently thinner than the penetration depth. The phenomena were experimentally investigated, and the results agreed very well with theoretical predictions.

Intraband light absorption in InAs/GaAs quantum dots covered with InGaAs quantum wells

The spectral and polarization dependences of intraband light absorption in n- and p-doped structures with InAs/GaAs quantum dots covered by InGaAs layers were studied experimentally and theoretically. The transmittance of p- and s-polarized mid-infrared radiation was studied in a multi-pass sample geometry. Elastic strain, piezoelectric fields and a complex valence band structure were taken into account in calculations of the energy spectrum, the carrier wavefunctions and intraband optical matrix elements. The experimentally determined value of the absorption cross section corresponding to |0 0 0⟩→|0 0 1⟩ intraband electron transitions is 4.1 × 10−15 cm2. Light absorption related to intraband hole transitions was found to be significantly smaller. The dispersion of the dot sizes was evaluated using the experimentally determined spectral widths of intraband absorption peaks.

Aligned Silver Nanorod Arrays as Substrates for Surface-Enhanced Infrared Absorption Spectroscopy

Preferentially aligned silver nanorod arrays prepared by oblique angle vapor deposition were evaluated as substrates for surface-enhanced infrared absorption (SEIRA) spectroscopy. These nanorod arrays have an irregular surface lattice and are composed of tilted, cylindrically shaped nanorods that have an average length of 868 nm +/- 95 nm and an average diameter of 99 nm +/- 29 nm. The overall enhancement factor for chemisorbed organic films of para-nitrobenzoic acid (PNBA) deposited onto the Ag nanorod arrays analyzed by external reflection SEIRA was calculated to be 31 +/- 9 compared to infrared reflection-absorption spectroscopy (IRRAS) obtained from a 500 nm Ag film substrate. This enhancement is attributed to the unique optical properties of the nanorod arrays as well as the increased surface area provided by the nanorod substrate. SEIRA reflection-absorbance intensity was observed with both p- and s-polarized incident radiation with angles of incidence ranging from 25 degrees to 80 degrees . The largest intensity was achieved with p-polarization and incident angles larger than 75 degrees . Polarization-dependent ultraviolet/visible/near-infrared (UV/Vis/NIR) spectra of the nanorod arrays demonstrate that the red-shifted surface plasmon peaks of the elongated nanorods may be partially responsible for the observed SEIRA response. The SEIRA detection limit for the Ag nanorod arrays was estimated to be 0.08 ng/cm(2). Surface-enhanced Raman scattering (SERS) and SEIRA analysis of chemisorbed PNBA utilizing the same nanorod substrate is demonstrated.

Azimuthal dependence of X-ray reflectivity in the vicinity of the S K-edge in hexagonal CdS crystal

Reflection spectra for an hexagonal CdS crystal are measured near the S K-absorption edge at the grazing angle θ = 0.8° with the help of s-polarised radiation for a surface cut parallel to the crystallographic c-axis for various Azimuthal orientations with respect to the electric field vector E. The experimental confirmation of the theoretically predicted strong focusing effect for the polarisation E⊥ c is obtained for the first time.

External Reflection FTIR Spectroscopy of the Cationic Surfactant Hexadecyltrimethylammonium Bromide (CTAB) on an Overflowing Cylinder

External reflection Fourier transform infrared spectroscopy (ER-FTIRS) has been used to study the adsorption of the cationic surfactant hexadecyltrimethylammonium bromide (CTAB) at the air-water interface under nonequilibrium conditions. An overflowing cylinder (OFC) was used to generate a continually expanding liquid surface with a surface age of 0.1-1 s. ER-FTIR spectra were acquired by a single bounce of p- or s-polarized radiation from the flowing surface of the OFC. The C-H stretching region of CTAB spectra was analyzed both by subtraction of a reference spectrum of pure water and by a chemometric technique known as target factor analysis (TFA). The TFA method is shown to give lower scatter in the weight of the component assignable to the adsorbed CTAB monolayer and to permit analysis of spectra at lower bulk surfactant concentrations. The surface sensitivity of ER-FTIRS is demonstrated both experimentally and by theoretical modeling. Modeling shows that surfactant adsorbed at the surface and dissolved in the bulk solution can be distinguished by reflection spectroscopy but also highlights potential errors that can arise from the neglect of the bulk surfactant contribution to the ER-FTIR spectra. Polarized spectra are consistent with an isotropic distribution of transition dipole moments of the hydrocarbon chains in CTAB. Component weights of the CTAB monolayer determined by TFA are compared with an independent determination of values of the dynamic surface excess, Gammadyn, by neutron reflection and ellipsometry. The relationship between the component weights and Gammadyn shows a small but significant deviation from linearity. Possible explanations for this deviation are discussed. The feasibility of using TFA to deconvolute ER-FTIR spectra of mixtures of hydrocarbon surfactants is demonstrated.

Mo/B_4C/Si multilayer-coated photodiode with polarization sensitivity at an extreme-ultraviolet wavelength of 135 nm

A silicon photodiode coated with an interface-engineered Mo/Si multilayer was developed as a polarization sensitive detector. The Mo/B4C/Si multilayer was designed to reflect 13.5-nm extreme-ultraviolet (EUV) radiation at an incident angle of 45 degrees, at which the maximum polarization sensitivity occurs. The sensitivity of this specially coated photodiode and its polarization responses were determined by measurement of the reflectance and transmittance of the multilayer coating with synchrotron radiation. The Mo/B4C/Si multilayer was found to reflect 69.9% of the s-polarized radiation and only 2.4% of the p-polarized radiation, thus transmitting approximately 0.2% s-polarized radiation and 8.4% p-polarized radiation at a 13.5-nm wavelength and a 45 degrees angle of incidence. A polarization ratio, (Tp - Ts)/(Tp + Ts), of 95% was achieved with sufficiently high sensitivity from this photodiode. This result demonstrates the high polarization sensitivity and the usefulness of multilayer-coated photodiodes as novel EUV polarimeters.

Anisotropy of x-ray reflectivity: chemical and structural effects on K-shellexcitations in hexagonal BN crystal

The experimental investigation of the B and N K-reflection spectra usingboth s-polarized synchrotron radiation and unpolarized radiation fordifferent crystal orientations with respect to the electric field vector Ewas carried out. The absorption spectra calculated from the reflection spectrausing Kramers–Kronig analysis are presented. A strong orientation dependence ofboth reflection and absorption spectra is exhibited. Analysis of the orientationdependences of the x-ray reflection and absorption spectra near both edgesstrongly supports a possibility of tracing the role of each excitation canal in theformation of fine structure. The high sensitivity of the reflection spectra finestructure to the vibronic interaction connected with Jahn–Teller distortions aswell to the core-hole relaxation is discussed. A very strong dependence of theabsolute values of the reflectivity on planar crystal anisotropy was discovered.

Volume and surface photoemission from a niobium target by polarized ultraviolet radiation

This work reports on the experimental results of a Nb photocathode stimulated by two different lasers, of wavelengths 308 and 222 nm. A fast current detector, Rogowski coil, recorded the high output currents, while the beam angular distributions were measured by an array of small Faraday cups placed along the propagation axis of the beam. With p-polarized light, we found quantum efficiencies (QEs) of 1.6×10−5 and 1.0×10−6 for λ=222 nm and λ=308 nm, respectively. The efficiency of the photocathode was measured to be higher for s-polarized laser beams than for the p-polarized ones. They resulted in QEs of 5.3×10−5 and 2.1×10−6 for λ=222 nm and λ=308 nm, respectively. From the electron-beam angular divergence values, we determined the upper limit emittance. The lowest upper limit normalized emittance value found was 7 (π mm mrad), achieved by the s-polarized radiation of 308 nm. In both cases the s-polarized light generated electron beams of lower emittance.

Polarisation characteristics of the harmonics and reflected radiation upon the interaction of 100-GW picosecond pulses with aluminium films

The generation of harmonics from a solid surface irradiated by 27-ps pulses (I≤1.5×1015 W cm-2) from a neodymium laser is studied. The conversion efficiency of p-polarised laser radiation was more than ten times greater than that of the s-polarised radiation for the second harmonic generation and more than one hundred times greater for the third harmonic generation. The optical rotation of the second harmonic generated by s- and p-polarised laser radiation is studied. The efficiencies of the second, third, and fourth harmonic generation were 2×10-8, 2×10-10, and 5×10-12, respectively. The intensities of the second, third, and fourth harmonics exhibit a power dependence on the laser radiation intensity with exponents equal to 1.5, 1.8, and 3.8, respectively.

Coupling of near-grazing microwave photons to surface plasmon polaritons via a dielectric grating

A dielectric grating on top of a planar metal substrate is shown to couple near-grazing microwave photons to surface plasmon polaritons (SPPs). It is shown that when the grating grooves are oriented such that they are parallel to the plane of incidence (phi = 90 degrees), coupling to SPPs with both s- and p-polarized photons is possible at three different energies. It is demonstrated that one mode is coupled via p-polarized radiation and the other two modes are both coupled via s-polarized radiation. A multilayer, multishape differential grating theory allows the identities of each of the modes to be confirmed by modeling the electromagnetic fields above the metal substrate. In addition, a comparison between the experimentally derived reflectivity scans and the theoretical model is made.

Hyper-Rayleigh scattering in Gd-containing Langmuir–Blodgett superstructures

Incoherent optical second harmonic (SH) generation, or hyper-Rayleigh scattering (HRS), is used to study the structure and properties of Gd/C18H36O2 multilayer Langmuir–Blodgett (LB) films. SH reflection spectra (in combination with linear absorption spectra), HRS indicatrices, thickness dependence, and wave polarization diagrams are measured for s-polarized fundamental radiation. The SH radiation is entirely diffuse but predominantly s polarized, with the maximum of the HRS indicatrix shifted by 8° relative to the specular direction, which is interpreted as being due to the contribution of a fluctuating quadrupole to the nonlinear-optical response of the films. The estimated correlation length of spatial fluctuations of the nonlinear-optical polarization in the film is ∼400 nm. These properties are associated with an islandlike structure formed by Gd ions inside LB structural units.

A SNIFTIRS study of the adsorption of pyridine at the Au(111) electrode–solution interface

Subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS) has been applied to study coordination of the pyridine molecules to the Au(111) electrode surface. The IR spectra have been recorded using both p- and s-polarized radiation. The ratio of the integrated band intensities for the spectra recorded with p- and s-polarized light was then used to study changes in the surface coordination of pyridine molecules. We have derived an expression describing the dependence of this ratio on the tilt angle. We have described the orientation of the adsorbed molecule in terms of angles formed between the surface, and: (i) C 2 v axis of the pyridine molecule, (ii) the direction in plane of the molecule and normal to the C 2 v axis. We were able to demonstrate that both angles increase by moving from negative to positive potentials. This result indicates that the pyridine molecule not only stands up at positive potentials but also its plane rotates somewhat with respect to the electrode surface.

Investigation of the Formation and Structure of Self-assembled Alkylsiloxane Monolayers on Silicon Using In Situ Attenuated Total Reflection Infrared Spectroscopy

The formation of alkylsiloxane monolayers OxSi−(CH2)n−Y with different hydrocarbon chain lengths (n = 10, 16, 17) and different terminal substituents (Y = CH3, COOCH3, CN, Br) on native silicon (Si/SiO2) was studied by means of in situ internal reflection IR spectroscopy (ATR) at the interface between a Si ATR crystal and the precursor solution. The growth of the ν(CH2) stretching absorptions of the monolayer films, monitored with s-polarized and p-polarized radiation, provided information on the monolayer formation rates and on structural changes in the course of the growth process. The film molecules adsorb initially in a random, disordered configuration. With increasing coverage, the hydrocarbon chains gradually align and stand up on the surface. Their final orientation in the complete monolayer films depends both on the chain length and on the type of terminal substitution, whereby chain tilt angles between 7° for OxSi−(CH2)17−CH3 and 21° for OxSi−(CH2)16−CN and OxSi−(CH2)16−Br were found. The film gr...

Origin of the infrared reflectance increase produced by the adsorption of CO on particulate metals deposited on moderately reflecting substrates

Potential-difference IR spectra of CO chemisorbed on noble metal electrodes have, if the two potentials are within the stability range of chemisorbed CO, a bipolar shape, since the frequency of the absorption maximum of the CO stretching band increases with increasing electrode potential. Therefore, in an IR spectrum with the reference at the lower potential the higher frequency lobe of the bipolar band is negative. An anomalous bipolar band with the opposite shape was first reported in 1994 for CO chemisorbed on Pt particles deposited on a basal plane graphite disc, and the anomaly was attributed to a reversible potential-induced migration of the chemisorbed CO molecules from Pt terraces to edge or kink sites. Anomalous bipolar bands were later found for other metals deposited on glassy carbon, and it was observed that the anomalous shape was due to the fact that the adsorbed CO produced an increase, instead of a decrease, of the IR reflectance at the frequency of the absorption maximum. On the basis of our observation of the band also with s-polarized radiation, which shows that the metals surface selection rule cannot be applied to glassy carbon, it is shown that this reflectance increase is due simply to the use of a glassy carbon substrate, which absorbs moderately, and therefore reflects IR radiation only moderately. Consequently, adsorption of a strong IR absorber, such as CO, will increase the reflectivity of glassy carbon.

Carbon/titanium multilayers as soft-x-ray mirrors for the water window

C/Ti multilayers with a period thickness of 2.1-2.7 nm were produced by electron-beam evaporation in ultrahigh vacuum as soft-x-ray mirrors in the water window (lambda = 2.3-4.4 nm). For smoothing the individual interfaces and thus enhancing the total reflectance, each layer was ion polished with an Ar(+) ion beam after deposition. For a multilayer of 85 bilayers, a reflectance of approximately 11% at an angle of incidence of 59 degrees (with respect to the surface normal) by use of s-polarized radiation at a wavelength of 2.77 nm was achieved.

Immunoassays based on surface-enhanced infrared absorption spectroscopy.

A new type of biosensor for pathogens has been developed. The sensor produces spectral fingerprints of biological systems by using surface-enhanced infrared absorption (SEIRA) spectroscopy. Antibodies were immobilized onto a 10-nm-thick film of gold which had been previously deposited on a Si wafer. SEIRA spectra of the antibodies measured in the external reflection mode exhibited two new bands at 1085 and 990 cm-1. These new bands were observed with p-polarized radiation but were absent with s-polarized radiation. The spectrum of water on the surface of the sensor was observed under both directions of polarization. The sensor was first tested with a model system consisting of glucose oxidase (GOX) and the antibodies for glucose oxidase (anti-GOX). In addition to the bands due to the anti-GOX at 1085 and 990 cm-1, new bands were observed at 1397, 1275, and 930 cm-1 when the GOX antigens were present. The same type of sensor was prepared for Salmonella (SAL) by immobilizing antibodies for Salmonella (anti-SAL) on a gold-surfaced Si water. The SEIRA spectra for anti-SAL antibodies were very similar to those for anti-GOX, with bands at 1085 and 990 cm-1; however, a sharp new band was observed at 1045 cm-1 after the sensor was exposed to the SAL antigens. In addition to specific new bands due to antigens, both GOX and SAL sensors exhibited changes in the regions of water absorptions at approximately 3500 and 850 cm-1 when the antigens were present.

Extracting polarizabilities of organic molecules at their optical absorption regions from the enhanced reflection of a submonolayer of organic molecules at air-quartz interface

It has been demonstrated in this paper that polarizabilities of organic molecules at their optical absorption regions can be extracted from the experimental data of the enhanced reflection for s-polarized electromagnetic radiation caused by a submonolayer of organic molecules physisorbed on quartz surface. Experiments have been carried out with Rhodamine-6G and D289 molecules. For each molecule, the polarizability increases dramatically in the wavelength region where the electronic transition takes place. For Rhodamine-6G, the polarizability is about 980 Å3 at its peak absorption wavelength 530 nm, and for D289, the value is about 392 Å3 at its peak absorption wavelength 470 nm. The perfect match between the reflection and transmission spectra of Rhodamine-6G indicates that the polarizability of a molecule at its absorptive region is proportional to its molar absorptivity.

Emission of x rays from a plasma formed by a train of picosecond laser pulses

Experimental and theoretical investigations were made of the characteristics of the interaction between solid targets and picosecond laser pulses with a complex profile. A prepulse preceding the main picosecond pulse increased the absorption of the s-polarised radiation and reduced the absorption of p-polarised radiation. Moreover, the prepulse made it possible to control the intensity of various components of the x-ray radiation emitted by the laser plasma. A satisfactory agreement between the experimental results and numerical calculations was obtained and a theoretical optimisation of the efficiency of x-ray generation was made.