Ne Laser Light Research Articles

Chemical reactivity of vinyltrimethoxysilane in aerosol particle formation with acrolein under two-photon excitation

Abstract Under irradiation with N 2 laser light, a gaseous mixture of vinyltrimethoxysilane (VTMSi) and acrolein (AC) produced sedimentary aerosol particles with a mean diameter of 1.2 μm. From chemical analysis of the product by XPS and FT-IR spectroscopy, VTMSi was found to be incorporated into the sedimentary particles of polyacrolein as polysiloxane. Gas-phase chemical reaction between VTMSi and AC under irradiation with N 2 laser light was investigated from the analysis of volatile products by GC/MS. Identification of cyclic polysiloxane in the gas phase strongly suggested that VTMSi molecules were cleaved at vinyl–Si bond and at O–CH 3 bond by a two-photon process of N 2 laser light, and produced dimethoxysilanone as an intermediate. The nucleation process of the aerosol particles was studied by measuring monitor (He–Ne laser) light intensity scattered by the aerosol particles as formed under irradiation with N 2 laser light. With increasing partial pressure of VTMSi, the nucleation reaction of aerosol particles was accelerated due to the additional production of reactive species from VTMSi molecules.

In situ high-resolution X-ray photoelectron spectroscopy of light-induced changes in As–Se glasses

To establish the mechanism of reversible photoinduced changes such as in the recently discovered opto-mechanical effect in chalcogenide glasses, we have measured the effect of He–Ne laser light on the electronic structure of As–Se glasses using high-resolution X-ray photoelectron spectroscopy (XPS). We present the first results during in situ irradiation of As–Se bulk glass and amorphous films in the spectrometer, as well as after ex situ exposure in air. The non-reversible light-induced changes are due to the segregation of Se on the surface, increased homogeneity for As, and a greater heterogeneity in the chemical environment of Se. In addition, there are reversible changes in the valence band (VB), indicating transfer of lone-pair states of Se to a new kind of bonding state deeper in the band, which have a smaller population in the absence of light.

Preparation of a 10 nm thick single-crystal silicon membrane self-supporting over a diameter of 1 mm

We report the fabrication of a 10 nm thick, self-supporting, single-crystal silicon membrane. The fabrication process can be broken up into four major stages. First, a buried SiO 2 layer was formed by implantation of oxygen at a depth of 200 nm into a (100) silicon wafer. The size of the membrane was then established by removing the bulk of the silicon over a 1 mm area using a fast acid etch. After this the sample was etched in a hot EDP solution which stops at the buried SiO 2 layer. The sample was then cleaned and the SiO 2 layers removed, after which it was introduced into a plasma-etching chamber. The membrane was thinned down to a final thickness of 10 nm by RF plasma etching in a gas mixture of carbon tetrafluoride and oxygen. The thickness was monitored during plasma etching by measuring the intensity of He–Ne laser light transmitted through the membrane. The electron energy loss spectrum of the membrane has been measured and shows two features due to single and double plasmon excitation. The plasmon energy was 17.05 eV, in good agreement with previous measurements. Membrane thickness has also been estimated from the area of the plasmon energy loss peak. The final sample had good crystalline quality, was of even thickness over the membrane diameter and showed only a small amount of surface contamination due to the plasma etching stage.

Test of Opticlean strip coating material for removing surface contamination

The strip coating material, Opticlean, which has been reformulated, has been shown to remove 1-5-microm-diameter particles as well as contamination remaining from previous drag wipe cleaning on a used silicon wafer. In addition, no residue that produced scattering was found on a fresh silicon wafer when Opticlean was applied and then stripped off. The total integrated scattering technique used for the measurements could measure scattering levels of He-Ne laser light as low as a few ppm (parts in 10(6)), corresponding to a surface roughness of <1 A rms.

Chemical reactivity of allyltrimethylsilane in UV laser induced aerosol particle formation with acrolein

Under irradiation with N 2 laser light, a gaseous mixture of allyltrimethylsilane (ATMeSi) and acrolein (AC) produced sedimentary aerosol particles with a mean diameter of 0.78 μm. From the analysis of FT–IR spectrum measured with the sedimentary particles, 1,1-dimethyl-1-silacyclobutane and trimethylsilyl group were identified in the sedimentary particles, showing that ATMeSi produced 2-methyl-2-silapropene intermediate by a retroene elimination of propene from ATMeSi, in addition to allyl and trimethylsilyl radicals by a homolytic cleavage of ATMeSi. The nucleation process of the aerosol particles was investigated by measuring monitor (He–Ne laser) light intensity scattered by the aerosol particles as formed under N 2 laser light irradiation. From the dependence of scattered light intensity on the partial pressure of ATMeSi, it was found that the reactive intermediates generated from ATMeSi by a two-photon process of N 2 laser light accelerated the nucleation process of the gaseous mixture.

Photoinduced dichroism and its low-temperature characteristics in obliquely deposited amorphous As–Ge–Se–S thin films

The photoinduced dichroism and its low-temperature characteristics in obliquely deposited amorphous As–Ge–Se–S thin films have been studied using a linearly polarized 632.8 nm He–Ne laser light and a control system capable of increasing the film temperature from 77 K. Our experimental results have been discussed on the basis of native valence-alternation pairs depended on the film fabrication. Although the absorption slopes in the extended region (hν&amp;gt;Eop) decrease with increasing deposition angle, the optical energy gap Eop remains the same as for 0° films, i.e., Eop=2.04 eV. A columnar structure with an inclination angle of approximately 70° is formed in 80° deposited films. While the value of saturated dichroism Dsat itself remains constant, independent of the intensity, it depends strongly on the deposition angle θ and the film temperature T, i.e., Dsat(θ,T). For example, Dsat(80°,77 K) is more than four times Dsat(80°,300 K), and the values of Dsat(0°,300 K) and Dsat(80°,300 K) are about 4.2% and 6.0%, respectively. We believe that an enhanced D in a columnar film is attributed to the increase of disorder (boids and dangling bonds). The photoinduced dichroism relaxes during a dark relaxation after its saturation and eventually sustains any value of nonzero, which depends on the inducing light energy and especially the value obtained after a prolonged exposure (∼3.3 h) is evaluated to be about 4.5 for 80° deposited film. However, it is eliminated completely by the exposure of nonpolarized light only for about 3 min.

Phase Behavior and Segmental Mobility in Binary Blends of Polystyrene and Poly(vinyl methyl ether)

The phase behavior and segmental mobility in binary blends of polystyrene (PS) and poly(vinyl methyl ether) (PVME) were investigated. Two nearly monodisperse PSs having weight-average molecular weights (Mw) of 57 000 and 95 000 with polydispersity indexes (PDI) of 1.06 and 1.09, respectively, and PVME having Mw = 99 000 with a PDI of 2.13 were used for this study. Two sets of PS/PVME binary blends with varying compositions were prepared by solvent casting from toluene. Thermograms from differential scanning calorimetry showed that each blend has a single, yet very broad glass transition temperature. Cloud point measurements via He−Ne laser light scattering were taken to determine phase equilibria in each blend, which exhibited lower critical solution temperature (LCST) behavior. Solid-state nuclear magnetic resonance (NMR) spectroscopy was used to examine segmental mobility and component domain sizes. 1H T1ρ experiments were run at temperatures ranging from −40 to 140 °C. We observed only small differences in 1H T1ρ values of PS and PVME at temperatures below 45−80 °C (depending on blend composition) and a large divergence of 1H T1ρ values at higher temperatures. 13C T1ρ and wide-line separation (WISE) experiments were run at room temperature on untreated and heat-treated samples. WISE experiments revealed that heterogeneities from 3.5 nm to greater than 30 nm existed within the blends, depending on the temperature of heat treatment. Since it has been found that 1H T1ρ measurements can give ambiguous domain information, 1H-NOESY NMR was used to examine several blend compositions at 100 °C. We conclude from this study that nanoheterogeneities exist in these PS/PVME blends at temperatures below the binodal curve determined by cloud point measurements and that a broad, single glass transition should not be construed as evidence of miscibility at the molecular level. It has been shown that nanoheterogeneities exist on a segmental level and that there are large changes in mobility at temperatures above 45−80 °C. However, the blend does not phase separate until the critical temperature (LCST), determined by cloud point measurements, is reached.

Laser-induced particle formation and coalescence in a methane discharge

Laser-induced formation of submicrometer dust particles and the subsequent coalescence phenomena in a low-pressure methane radio-frequency plasma have been analyzed. Six distinct phases can be distinguished: (a) nanoparticle synthesis by laser interaction with the plasma species, (b) particle conglomeration and the formation of ordered Coulomb lattices at the plasma–sheath region above the powered electrode, (c) coalescence of grains within the Coulomb lattice and formation of submillimeter strings, (d) condensation of the strings in the discharge and the formation of V-shaped structures, (e) condensation of the V structures into a single network of several centimeters in diameter suspended in the plasma, (f) deposition of the network on the electrode and its subsequent growth on the surface. Large carbon structures as well as nanoparticles have been analyzed in situ by He–Ne laser light scattering and laser ablation and ex situ by an optical and a scanning electron microscope, and by micro-Raman spectroscopy.

Refractive index profiling of a GRIN optical fiber using a modulated speckled sheet of light

A method for calculating the refractive index of GRIN optical fiber from its transverse interference pattern is presented.In this method the transverse interference fringe pattern through an optical fiber using a sheet of light is applied to get the refractive index profile of it. The optical fiber is not immersed in a matching liquid as used in different techniques [Barakat N, El-Hennawi HA, El-Zaiat SY, Hassan R. Pure Appl Opt 1996;5:27]. In this method a sheet of He–Ne laser light is allowed to illuminate the fiber. The light sheet is divided into two parts, the first is refracted through the fiber while the second is used as a reference beam. Interference pattern will be obtained between these two rays displaying the refractive index variation along the fiber radius. The fringe shift of such interference pattern has been measured and used to calculate the deflection angle of light refracted by the fiber and the cladding. An equation is derived to calculate the refractive index profile difference ratio δn at different positions across the fiber cross section in terms of the corresponding deflection angle and is verified experimentally. The optical path difference between these two rays (refracted and reference beam divided by the fiber) has been derived and the fringe shift obtained has been used to calculate the refractive index profile of the fiber. Introducing a ground glass screen on the passage of the two light beams (refracted and reference beam divided by the fiber), two superimposed identical speckle patterns are formed leading to the formation of a third speckle pattern modulated by a grid structure displaying the optical thickness of the fiber.

Scattering of He–Ne laser light by an average-sized red blood cell

The scattering of He-Ne laser light by an average-sized human red blood cell (RBC) is investigated numerically. The RBC is modeled as an axisymmetric, low-contrast dielectric, biconcave disk. The interaction problem is treated numerically by means of a boundary-element methodology. The differential scattering cross sections (DSCS's) corresponding to various cell orientations are calculated. The numerical results obtained for the exact RBC geometry are compared with those corresponding to a scattering problem in which the cell is assumed to be either a volume-equivalent sphere or an oblate spheroid. A parametric study demonstrating the dependence of the DSCS on the wavelength of the incident wave and the cell's refractive index is presented.

In-situ thin film growth/etch measurement and control by laser light reflectance analysis

In this article, I report in-situ thin film growth and etching measurement and control with ultra high precision. A stack of thin film layers of AlAs/Al 0.1Ga 0.9As to form Bragg reflector for the surface emitting semi-conductor laser was grown by gas source molecular beam epitaxy on a rotating wafer and the growth process was monitored with inclined incident polarized He–Ne laser light reflectance measurement. The multiple thin film layers were preferred to increase the visibility of the oscillating intensity variation signal for feasibility experiments. The inferred growth rate from the reflectance analysis was found to be 0.15 nm/s which remained in agreement with set growth parameters. The laser light reflectance analysis method was also employed for in-situ control and measurement of thin film etching process. The inferred etching rate was found to be 0.75 nm/s by the chemical etchant H 3PO 4:H 2O 2:H 2O::3:1:100. Calibrated optical reflectance signal for growth and etching process is proposed for measuring and control their respective thickness and depth with very high accuracy and precision.

Low-frequency modulation of 0.6328 μm He–Ne laser by transverse magnetic field intensity

Effect of transverse magnetic field on 0.6328 μm He–Ne laser light polarized parallel and perpendicular to transverse magnetic field has been studied in this paper. Low-frequency modulation of two kinds of polarized laser light is completed and low-frequency modulation of polarization degree is put forward.

Photochemical fine particle formation in the gas phase from acrolein by a two-photon process

Upon exposure to N 2 laser light, sedimentary aerosol particles of polyacrolein were produced from gaseous acrolein (AC) in the vapor phase. The nucleation process of aerosol particle formation was investigated by measuring He–Ne laser light intensity scattered by growing aerosol particles which were formed under irradiation with N 2 laser light. Scattered light intensity was strongly dependent on N 2 laser light intensity, and the result indicated that a nucleation reaction was initiated through a two-photon process. A gaseous mixture of formaldehyde and AC was used to increase the efficiency of the nucleation process, and a gaseous mixture of an organosilicon compound and AC was used to synthesize a noble material consisting of aerosol particles. Chemical processes of the organosilicon compound which took place at the surface of the aerosol particles are briefly discussed.

Optical switch devices using the magnetic fluid thin films

Two optical switch designs are proposed, with the transmitted intensity of a He–Ne Laser light measured to demonstrate the feasibility of both designs. It was found that the transmitted polarized-light intensity of the magnetic fluid film subjected to a parallel magnetic field is proportional to field strength and tends to saturate at high field. On the other hand, when an unpolarized He–Ne laser light passes through a magnetic fluid film subjected to a perpendicular magnetic field, the magnetic field tends to reduce the transmitted intensity. In both methods, the curves of the intensity versus field strength possess two types of behaviors; one is independent of sweep rate and the other one is sweep rate dependent. This suggests that the structure formation in the magnetic film may play a decisive role in determining the transmittance of light.

Refractive Index Variations for Argon, Nitrogen, and Carbon Dioxide at λ = 632.8 nm (He−Ne Laser Light) in the Range 288.15 K ≤ T ≤ 323.15 K, 0 &lt; p &lt; 110 kPa

Direct measurements of the refractive index n of three gases (Ar, N2, and CO2) near ambient temperature and pressure states have been made by interferometry at the wavelength of the He−Ne laser light. Comparison with data obtained by interpolation of previous data shows good agreement (Δ(n − 1)/(n − 1) < 0.6%), the present data being always slightly higher than those obtained indirectly. Partial derivatives ∂n/∂T, useful in interferogram interpretation, have also been obtained for the three gases.

Formation of polyion-complexed polydiacetylene assembly and its HeNe laser-signal responses on a plastic optical fiber

A novel bilayer-forming polyion complex, consisting of a cationic diacetylene lipid ( 1) and a polyanion (poly(styrene sulfonate), PSS) has been assembled and immobilized on both a quartz plate and the core of a plastic optical fiber (POF), through which a HeNe laser light passes continuously. The complexed cast film ( 1/PSS) shows a crystal-to-liquid crystal phase transition due to an ordered multibilayer structure. Upon UV irradiation, the film can be readily polymerized and gives the blue form of polydiacetylene. It is noteworthy that the polymerized film displays reversible thermochromism. Such polymerization and thermochromic behaviors, observed spectroscopically, are successfully monitored as HeNe laser-signal changes by the use of a POF system. This system seems to have the ability to read out a more subtle molecular rearrangement in polydiacetylene assemblies as well as color changes due to formation of the blue polymer or thermochromism, since the laser light can draw information on refractive index of membrane phases. The pH responsiveness was also examined for a POF coated with the complexed film of a triblock polymer of PSS- block-poly(methacrylic acid)- block-PSS and 1.

Particle size control and optical properties of laser-synthesized silicon nanopowders

Silicon nanoparticles have been synthesized by heating reactant gases with a 500 W CO2 laser. A technique based on scattering of He–Ne laser light by particulates in a reaction flame has been developed for probing the particle size evolution during the process, in order to scale down the particle diameter (under 10 nm). The optical and structural properties of laser-synthesized silicon nanopowders obtained in different runs are reported. © 1998 John Wiley & Sons, Ltd.

Keywords for Solid State Communications

An interferometric method is applied to study piezoelectricity in quartz and electrostriction in SiO2-glass. With the application of an AC-potential at 50 Hz on Au-electrodes, the reflection intensity of polarized HeNe laser light from partially transparent Au/quartz (AT-cut)/Au interfaces is found to oscillate at 50 Hz. The oscillating amplitude is proportional to the amplitude of the applied sinusoidal electric field. The reflection intensity from partially transparent Au/SiO2-glass/Au interfaces oscillates at twice the frequency of the applied AC-potential, i.e. at 100 Hz, with the oscillating amplitude proportional to the square of the amplitude of the applied sinusoidal electric field. The relationships between reflection intensity and applied electric field strength are derived for piezoelectricity and electrostriction, respectively.

Holographic image degradation produced by mechanical stress in the photorefractive crystal

In this work we show the real time holographic image degradation produced by mechanical stress applied to a cubic photorefractive crystal of the sillenite family. The observations were performed in a diffusion only recording mechanisms in the photorefractive crystal Bi 12TiO 20 illuminated by λ=0.633 μm from a He–Ne laser light source. Our results can be easily extended to all BSO-type crystals where the continuous image reconstruction exploits the anisotropic diffraction.

Polarization-dependent, laser-induced anisotropic photocrystallization of some amorphous chalcogenide films

We report the observation of the influence of light polarization on the photocrystallization process and on the properties of crystallized films. Irradiation with linearly polarized He–Ne laser light results in the preparation of polycrystalline films with strong optical anisotropy (dichroism), the sign of which is determined by the direction of the electrical vector of light. The results obtained allow one to select from previously proposed mechanisms of photocrystallization. Large values of photoinduced dichroism in the films studied can be interesting for different applications of photoinduced anisotropy.