Incident Laser Polarization Research Articles

Mammalian Cell Surface Imaging with Nitrile-Functionalized Nanoprobes: Biophysical Characterization of Aggregation and Polarization Anisotropy in SERS Imaging

Functionalized silver nanoparticles (NPs) were synthesized with a cyano probe and utilized to label the surface of HeLa cells expressing a recombinant transmembrane domain of the platelet-derived growth factor receptor. Optical imaging, high-resolution Raman imaging, and scanning electron microscopy (SEM) were used to characterize the surface enhanced Raman scattering (SERS) effect at the cell membrane. Different assemblies of NPs resulted in markedly different enhancement. We validated the necessity of NP aggregates and polarization dependency for optimal contrast enhancement in SERS cellular imaging. We demonstrated the ability to image membrane proteins on cells using a cyano-labeled SERS probe. Observed SERS hot-sites correlate well with small aggregated NPs. Furthermore, the strongest SERS signals result from aggregates oriented in the appropriate direction with respect to the incident laser polarization. These observations are critical for designing future molecular imaging agents for SERS imaging o...

Laser Compton back-scattering gamma-ray beamline on NewSUBARU

A laser-Compton scattering system is a unique and useful gamma-ray-beam source. The laser-Compton scattering gamma ray generation was tested on a synchrotron radiation facility, “NewSUBARU” at Lasti/UH. Cw Nd:YVO laser (wavelength: 1.064 μ m , maximum power: 5 W) was used in the experiments. Maximum energies of scattered gamma ray are 17.6 and 39.1 MeV at the operating electron energy of 1 and 1.5 GeV, respectively. Generated gamma-ray was measured and used in the shielding tunnel of 45 cm thickness concrete wall. A scintillation detector (NaI) and Ge detector were used to measure the gamma-ray spectrum and the yield. A measured gamma-ray yield of 5 × 10 3 photons / s / mA / W is in agreement with calculation. A spatial distribution of gamma-ray and its dependence on a polarization of incident laser were measured using imaging plate (IP). Preliminary experiments of gamma-ray application were performed for a nuclear transmutation in the disposal of the radioactive nuclear waste and on a gamma-ray radiography for nondestructive testing of a thick subject. New radiation shielding for the gamma-ray beamline was designed for extracting the higher flux gamma-rays for application. Radiation leakage was calculated by EGS4 and MCNPX. The calculations of neutron transport are important for observation of fast neutron generated from a target sample irradiated by gamma-ray beam.

Anisotropic Properties of GaN Studied by Raman Scattering

The phonon anisotropy property of the GaN wurtzite crystal is studied using angular dependent Raman spectroscopy both theoretically and experimentally. The polarized Raman scattering spectra were recorded from cross-sections of c-axis oriented GaN films as a function of the angle between the incident laser polarization direction and the film normal direction in three different configurations. The Raman intensity of A1(TO) showed a sinusoidal dependence on the rotating angle, as also did the E1(TO) mode, while the E2 mode has a quite different behavior. The theoretical fit takes into account the susceptibility contribution and the phase differential of different vibrating elements.

Imaging colloidal particle induced topological defects in a nematic liquid crystal using third harmonic generation microscopy

The nature of the third-harmonic generation (THG) process in a nematic liquid crystal is investigated for the case of tightly focused, low intensity, laser beams. Colloidal particle induced topological defects in a liquid crystal are visualized in three-dimensions using the dependence of the THG signal on both changes in non-linear susceptibility and the orientation of the liquid crystal director relative to the incident laser polarization state. We have found that the interpretation of THG images in a liquid crystal is complicated not only by the change in polarisation of the electric field as it propagates through the medium but also by anisotropic refractive index mismatch induced aberrations.

Momentum distribution of accelerated ions in ultra-intense laser–plasma interactions via neutron spectroscopy

The dependence of neutron spectra on the incident laser polarization has been studied to elucidate ion acceleration processes in ultra-intense laser–plasma interactions. Obliquely incident, 50–100 TW (450–800 fs) laser pulses irradiated a deuterated plastic solid target at 1019 W/cm2 with both s- and p-polarizations. Neutron spectra from the deuteron–deuteron d(d,n)3He nuclear reactions show the ion acceleration into the target in the direction of the target normal for both polarizations. The experiment and particle-in-cell simulations indicate the ions are accelerated inside the target by an intense electrostatic field created by charge displacement at the laser focus.

Control of supercontinuum generation with polarization of incident laser pulses

Supercontinuum generation is dependent on the polarization state of the incident laser. The polarization of the generated supercontinuum is the same as that of the incident laser. The magnitude of the generated supercontinuum depends on the polarization of the incident laser and increases as the polarization changes from circular to linear, irrespective of the nature of the sample, be it isotropic, anisotropic, or chiral. In all samples, the polarization dependence indicates a preference for the linear component of the incident laser beam. The anisotropic sample shows an additional difference in the generated supercontinuum for the two perpendicular directions of the incident laser polarization.

Increase the storage density of solid immersion lens system by high-pass angular spectrum filter method

In this paper the optical distribution in the near-field region of solid immersion lens (SIL) is investigated from the viewpoint of angular spectrum. Because of the big numeric aperture (NA) of objective in SIL storage system, the polarization of incident laser is also considered. Based on this investigation, a kind of high-pass angular spectrum filter method is proposed to decrease the optical spot size. The effect of filter in SIL system is analyzed in detail. Our theoretical analysis shows that this kind of filter can decrease the spot size by nearly 40% and light intensity loss by around 11%.

Investigations of orientational order for an antiferroelectric liquid crystal by polarized Raman scattering measurements.

The orientational ordering of the antiferroelectric liquid crystal molecules, 4-(1-methyl-heptyloxycarbonyl)phenyl 4(')-octyloxybiphenyl-4-carboxylate was investigated in the series of the successive smectic phases by means of polarized Raman scattering measurement without any external field. An improved equation for the analysis of the polarized Raman intensity was derived as a function of an incident laser polarization and the orientational order parameters. Even in the chiral smectic phases, some apparent orientational order parameters could be defined by the proper corrections for the smectic layer structure and an optical disturbance. An unusual change of the orientational order parameters was observed with decrease in temperature. It was concluded that the irregular variation of the order parameter stemmed from the biaxiality of the molecular orientational distribution, which was attributed to the hindrance of molecular rotation around its long axis.

Suppression of supercontinuum generation with circularly polarized light

Controlling a nonlinear process such as supercontinuum generation (SG) with the polarization-state of laser is an important demonstration of laser selectivity. We show that the threshold for SG and the total amount of supercontinuum generated depends on incident laser polarization for isotropic samples. Irrespective of the nature of the samples chosen, SG efficiency decreases as the incident laser polarization changes from linear to circular and thus, provides the first experimental demonstration of the suppression of SG with circularly polarized light. The ratio of the overall SG between the linear and circular polarization (i.e., measure of suppression) undergoes an intensity dependent decrease from large initial values to asymptotic limits, irrespective of samples.

On the chemical mechanism of surface enhanced Raman scattering: Experiment and theory

We have investigated the chemical mechanism of surface enhanced Raman scattering (SERS) on an atomically smooth metal surface using electron energy loss spectroscopy (EELS) and molecular spectroscopy simulations. The EEL spectra of pyromellitic dianhydride (PMDA) adsorbed on Cu(100) and Cu(111) are reported. Simulations of the surface-enhanced Raman spectra and electron energy loss spectra (EELS) of pyromellitic dianhydride adsorbed on Cu(100) and Cu(111) are reported. The surface enhanced Raman spectra [J. Chem. Soc. Faraday Trans. 92, 4775 (1996)] and the EEL spectra are shown to be sensitive to crystal face. The relevant excited state observed in the EEL spectrum is not intrinsic to molecular PMDA, but results from chemisorption. The Raman spectra are sensitive to the incident laser polarization on both the (100) and (111) surfaces but in different ways. These observations are shown to be a result of the excited state potential energy surface having different shape, and the respective transition dipole moment having a different orientation on the two crystal faces. The nuclear coordinate dependence of the electronic transition dipole moment produces mode selective, polarization dependent Raman scattering cross sections. Based upon this observation we conclude that the transition dipole moment function that couples the ground electronic state to the resonant excited electronic state is also sensitive to the structure of the metal surface.

Determination of unknown stress states in silicon wafers using microlaser Raman spectroscopy

A new technique was developed to predict the unknown in-plane stress state and the magnitude of the stress components in (111) silicon wafers using micro-Raman spectroscopy. The approach is based on analyzing the combined signal from the initially degenerate peaks of the F2g mode in silicon as a function of the angle between the incident laser polarization and the polarization selected from the scattered beam using an analyzer. The peak position of the combined signal when plotted as a function of the angle was found to contain the information required to estimate the magnitude of the individual stress components in the plane-stress condition. The development of this technique is described in this paper for (111) silicon wafers.

On the role of charge-transfer resonances in the chemical mechanism of surface-enhanced Raman scattering

The surface-enhanced Raman spectrum of pyromellitic dianhydride (PMDA) on Cu(100) is reported; it is different from that previously reported for the Cu(111) surface. The spectra are sensitive to the incident laser polarization on both surfaces but in different ways. These observations are shown to be inconsistent with a simple classical picture which considers only the interaction of the surface electromagnetic fields with the anisotropic molecular polarizability. They lend additional support to the hypothesis that the chemical enhancement mechanism involves resonance-Raman scattering via a charge-transfer intermediate state. Simulations suggest that the scattering is primarily Franck–Condon and Jahn–Teller in origin.

Polarization of high-intensity high-harmonic generation.

We have discovered that the polarization of high harmonics generated by intense, short, elliptically polarized laser pulses is rotated with respect to the incident laser polarization. This strong-field effect is a test of models of intense laser-atom processes.

Resonant Raman scattering in Bi 2Sr 2Ca 1−zY zCu 2O 8+δ single crystals

Bi 2Sr 2Ca 1− z Y z Cu 2O 8+ δ single crystals have been investigated by means of Raman scattering as a function of doping (0≤ z≤0.85), incident laser energy, temperature and polarization directions of the incident and scattered light. Compared to pure Bi 2Sr 2CaCu 2O 8+δ, additional phonons are found at 141, 326 and 434 cm −1. At the incident laser energy of 2.6 ± 0.1 eV, the 463 cm −1 “in-phase-out-of-plane” and the 275 cm −1 “out-of-phase-out-of-plane” vibrations of the oxygens situated in the CuO 2 planes as well as the Cu vibration at 165 cm −1 show a resonance. The resonant enhancement for the Cu vibration is larger by a factor of 20 than that for the oxygen modes. While the resonance energy ϵ res is independent of the Y-concentration z, the intensity of all the above resonating phonons at ϵ res is increased with increasing z, i.e., with a decreasing concentration of holes in the CuO 2 layers. The qualitative interpretation of the main resonant Raman-scattering features in Bi 2Sr 2Ca 1− z Y z Cu 2O 8+ δ can be given within the framework of a model, which takes into account the possibility of the creation of additional, “optically pumped” Zhang-Rice singlets formed through the excitation of electrons from the valence (O 2p) band into the upper Hubbard band of Cu.

Raman scattering in Bi 2Sr 2Ca 1−x(Y,Er,Tm) xCu 2O 8+δ single crystals

Bi 2Sr 2Ca 1−x(Y,Er,Tm) xCu 2O 8+δ single crystals have been investigated by Raman spectroscopy as a function of doping (0 ≤ x ≤ 0.85), incident laser wavelength, temperature and polarization directions of the incident and scattered light. Compared to undoped Bi 2Sr 2CaCu 2O 8+δ, additional phonons are found at 136 cm −1, 187 cm −1, 320 cm −1 and 434 cm −1. In contrast to superconducting samples, the B 1g -continuum of electronic scattering is not observed in semiconducting Bi 2Sr 2Ca 1−xY xCu 2O 8+δ (x ≥ 0.5), corroborating the identification of narrow (≈ 60 me V) band-like states near the Fermi energy in superconducting samples. Two-magnon scattering in non-superconducting Bi 2Sr 2Ca 1−x (Y,Er,Tm) xCu 2O 8+δ (x ≥ 0.5) gives rise to a broad peak with its maximum at ≈ 2900 cm −1, becoming more intense with increasing x.

Raman intensities and interference effects for thin films adsorbed on metals

Large oscillations in the vibrational Raman intensity have been observed for thin films adsorbed on a metal substrate as a function of film thickness. The systems studied, N2 and O2 physisorbed on Ag(111) at 14±1 K, have previously been shown to be unenhanced, i.e., the observations are not caused by the surface enhanced Raman (SERS) effect. The observed oscillations are due to multiple beam interference caused by reflections at the film boundaries of the incident laser light, and, to a lesser extent, the Raman scattered light. We extend the two-dimensional theoretical development of Moscovits and co-workers for Raman scattering in thin films to include more general three-dimensional experimental geometries. We derive expressions for the total intensity as a function of film thickness, incident laser polarization and angle, and scattered light polarization and angle. The resultant expressions are applicable to Raman scattering from any dielectric thin film adsorbed on a substrate with known optical parameters. Although complicated, the general expressions have been numerically evaluated for our experimental conditions using a commercial mathematical package on a personal computer. The calculated Raman intensities are in excellent agreement with the experimental results. The observed period of the intensity oscillation relates the film thickness to the exposure allowing the sticking probabilities to be determined. The sticking probabilities of N2 on N2 and O2 on O2 at 14±1 K are 0.84±0.2 and 0.82±0.2, respectively.

Fourier transform Raman optical activity

Raman optical activity (ROA) is conventionally measured by modulating the incident laser polarization between right and left circular polarization states and detecting the difference in the scattered Raman intensities using a dispersive spectrograph attached to a multichannel detector. In this article, a Fourier transform technique using a Martin-Puplett interferometer is shown to be suitable for measuring both the ROA and ordinary Raman intensities in a single measurement. Novel features in this technique include: (a) incident laser radiation is plane polarized; (b) the scattered Raman light is collected without an analyzer.

Spectra and polarization of laser generated plasma second harmonic emission

Spectra of the second harmonic (SH) emission from plasma generated by 35 ps, 1.054 μm laser pulses have been recorded for incident intensities between 10 13 and 10 14 W/cm 2. Blue shifted SH lines are observed throughout, regardless of intensity and polarization (either s or p) of incident ω 0 and emitted 2ω 0 light. The intensity scaling of the blue shift for different incident laser polarization is shown to be consistent with enhanced ponderomotive pressure at oblique incidence due to plasma wave resonance.