He-Ne Laser Beam Research Articles

Effect of the ellipticity of an inducing beam on the thermocapillary response

A thermocapillary depression is induced by a He-Ne laser beam in a plane-parallel layer of a transparent liquid on an absorbing substrate. The thermocapillary response is investigated as a function of the laser beam ellipticity, the laser power, and the layer thickness.

ANOMALOUS FIELD-INDUCED DIRECTOR DEFORMATION IN A HOMOGENEOUS THIN NEMATIC LIQUID CRYSTAL CELL

We have investigated the voltage dependence of the light transmittance for homogeneous thin nematic liquid crystal (NLC) cells composed of 4-pentyl-4′-cyanobiphenyl (5CB), which were confined between two glass plates. The substrate surfaces with polyimide layers were rubbed unidirectionally to make a uniform planar director orientation with a strong surface anchoring condition. An NLC cell was set between polarizer and analyzer. The He-Ne laser beam was passed through the NLC slab oriented with its optic axis parallel to the linearly polarized direction of the light beam. The light transmitted through the analyzer, which was crossed with the polarizer, was detected as a function of the applied voltage. In zero electric field it is expected that the director will have a uniform planar alignment and this orientation gives a minimum intensity of the light transmitted. When the voltage is applied to the NLC cell, the director for 5CB with its positive dielectric anisotropy rotates to orient parallel to the electric field. The voltage dependence of the light transmittance showed an anomalous result; that is, light leakage was observed for a certain voltage. This was interpreted by considering the director deformation at the boundaries between rubbed and non-rubbed regions of the polyimide surface.

Laser-light scattering, a new method for continuous monitoring of platelet activation in circulating fluid

We evaluated a novel technique of laser-light scattering (LLS) to detect platelet-volume changes continuously, reflecting platelet aggregation in circulating fluid. Carotid arteries from 20 dogs were mounted in a dual perfusion chamber. Balloon angioplasty (BA) was performed and arteries perfused with platelet-rich plasma (PRP). A He-Ne laser beam was passed through cuvettes connected to tubing draining the arteries. From the angle of incidence, the average volume of aggregates was measured by the ratio of scattering light at 1 to 5 degrees' spread on the diode array of a multichannel analyzer. Platelet volume varied linearly with the scattered light ratio at 1 to 5 degrees (y = −24.2 + 27.6 x [y = particle size, μm3; x = scattered light ratio at 1/5 degrees]). For comparison, we used an electronic particle counter (Coulter counter) to measure platelet volume. P-selectin expression was measured to confirm platelet activation. Comparing 10 uninjured and 10 BA-injured arteries, we found that platelet volume as measured with LLS increased from 21.6 ± 4.1 to 52.1 ± 12.5 μm3 (P <.003); as measured with the Coulter counter, it increased from 29.9 ± 2.4 to 62.3 ± 7.0 μm3 (P <.005). Six BA-injured arteries perfused with PRP and aspirin (0.2 mg/mL) were compared with six arteries treated with BA alone. The aspirin decreased platelet volume as measured with LLS from 56.2 ± 11.8 to 40.2 ± 12.7 μm3 (P <.01); the Coulter counter revealed a decrease from 51.9 ± 18.5 to 38.8 ± 14.2 μm3 (P <.001). Coulter counter and LLS results were correlated: r = 0.74, P <.05. The peak of P-selectin expression coincided with peak platelet volume. These data demonstrate that increases in circulating-platelet size stimulated by endovascular injury can be reliably and continuously monitored with the use of LLS. (J Lab Clin Med 2003;141:50-7)

Instrumental profile of the Debrecen solar spectrograph

The solar spectrograph of the Heliophysical Observatory at Debrecen, Hungary was investigated to determine its instrumental profile. The measurements were made by using a HeNe laser beam. The widths and asymmetries of the profiles decrease toward higher spectral orders, the most advantageous orders being the third and the fourth ones. To eliminate the broadening of solar lines on account of the instrumental profile, the straightforward iteration method of Gurtovenko has been applied. The efficiency of the method is demonstrated by the simulation of the broadened and corrected spectral line profiles.

Characterization of bones by speckle interferometry

Speckle photography interferometry (SPI) is used to evaluate the stress-strain behaviour of animal bones under loads by recording the speckle fields generated on the bone surface and thus finding the relationship between the fractal dimension D s and the compression load P. The procedure consists of application of slow and monotonous compression loads, and recording of the deformation levels and vertical displacements of the specimen. A He-Ne laser beam directed at the surface of bone specimen produces light scattering which generates the speckle. The optical fields show significant differences before and after fracture, due to the changes of the bone surface generated by the strain. Our results support previous suggestions of a relationship between fractal characteristics and parameters related to the mechanical behaviour of materials.

Fabrication of Fresnel zone plate embedded in silica glass by femtosecond laser pulses

We fabricated the Fresnel zone plate by embedding voids in silica glass. We investigated the focusing properties by launching a He-Ne laser beam into the zone plate. The spot size of the primary focal point was 7.0 mum and agreed with the theoretical value of 6.1 mum. The diffraction efficiency was 2.0 %. This technique enables us to make alignment free micro-scale lenses inside bulk materials.

Optical properties of a thermocapillary depression

An axisymmetrical thermocapillary depression is induced by a He-Ne laser beam in a plane-parallel layer of a transparent liquid on an absorbing substrate. The focal length of the central part of this depression in the form of a concave mirror is studied as a function of thickness of the benzyl-alcohol layer and beam power. At a laser power of 3.5–16.5 mW, the focal length increases almost linearly with the layer thickness changing from 200 to 1000 µm. In this range of thicknesses, an increase in the beam power leads to a decrease in the focal length following a power law with an exponent close to −0.8.

Refractive index patterning of tellurite glass surfaces by ultra short pulse laser spot heating

Dot patterns of refractive indices were formed by the laser pulse irradiation on the tellurite glasses. The ternary tellurite glasses of TeO2-Na2O-Al2O3, TeO2-Na2O-GeO2 and TeO2-Na2O-TiO2 doped with 2 mol% of CoO were irradiated by a femtosecond pulse laser beam (800 nm) or by a green light beam (532 nm) from a second harmonic generator of a Q switch pulse YAG laser. The refractive index map of the glass was composed with an He-Ne laser beam by an scanning ellipsometric technique at a resolution of 100 μm × 50 μm, indicating that the spots possessing refractive index lower by about 0.05–0.38 than the surroundings were formed at the region irradiated by the laser beam. The irradiation of the femtosecond laser beam generated the dot patterns roughly equivalent to the beam size. The change of refractive index could be tunable by adjusting laser power, suggesting that the process could be applied to optical recording.

POLARIZATION MEASUREMENT IN NEMATIC LIQUID CRYSTAL BASED ON THE PYROELECTRIC RESPONSE TO LASER IRRADIATION

The polarization measurement of a nematic liquid crystal has been performed by a pyroelectric technique using short pulse of a Nd:YAG laser to create temperature increment. The temperature increment has been evaluated independently by monitoring temperature dependent birefringence for a He-Ne laser beam. The sign and absolute magnitude of surface polarization have been evaluated for both the planar and homeotropic orientation of the nematic liquid crystal at a solid substrate. The flexoelectric polarization in a hybrid cells has also been measured using the same pyroelectric technique. The value of the sum of the flexoelectric coefficients (e 1 +e 3 ) for 5CB is negative and about—13pC/m at room temperature.

Amorphous-Si Transmission Gratings Prepared by Ga+-Focused-Ion-Beam Milling and Their Polarization Characteristics

Amorphous-Si (a-Si) transmission gratings of ∼ 0.1 µm thickness with four-type periods (Λ= 0.4 µm and 0.6 µm for sub-wavelength and Λ=1.0 µ and 1.4 µm for above-wavelength) have been fabricated on quartz substrates using 50 keV Ga+-focused-ion-beam (FIB) milling and CF4-reactive-ion etching (RIE) methods. Some optical properties of the fabricated gratings have been investigated using a linear polarized HeNe laser beam (λ=632.8 nm). Maximum diffraction efficiencies (ηMAX), measured at an incident angle (θB) to satisfy Bragg's condition with an effective index Neff=1.803–1.853, were very high. In particular, for gratings with Λ=0.6 µm (linewidth=0.25 µm, linespace=0.35 µm), the ηMAX at θB=17.0° is estimated to be about 96%. In addition, transmittance for two polarizations (TE and TM) was measured using a simple optical system, and the total phase difference (ΔΨTE-TM) and birefringence (Δn) were approximately calculated. The transmittance difference between TE and TM polarizations is the largest in the case of gratings with Λ=0.4 µm (approximately∼λ/2) among the gratings fabricated by us. That is, the TM/TE ratio is about 10.38, and both ΔΨTE-TM and Δn exhibit maximum values in the case of Λ=0.6 µm, which are about -76.7° and -1.35, respectively. The a-Si transmission gratings with a relatively high refractive index (∼ 2.9 at 632.8 nm) are successfully fabricated by FIB milling. In addition, we believe that this technique is one of the potential candidates for use in various optical devices and elements and, in particular, compatible with other optoelectronic devices for monolithic planar integration.

Acousto-optic collinear diffraction of a strongly divergent optical beam

Collinear diffraction of a strongly divergent optical beam by a monochromatic acoustic wave is investigated theoretically and experimentally. Three-dimensional patterns of acousto-optic (AO) phase matching are calculated and their transformation with varying acoustic frequency and ultrasound propagation direction is analysed. Two effects are discussed which appear at spectral collinear filtration of optical images, namely distortion of filtered image structure and spectral resolution deterioration. It is shown that the effects result in contradictory requirements on AO cell parameters. However, a compromise is possible which allows filtering of high-spatial-resolution images with an acceptable reduction in spectral resolution. Experimental results on diffraction of a strongly divergent He-Ne laser beam in a CaMoO4 AO cell are also presented in this paper.

LASER BEAM SCATTERING FROM CONDUCTING CIRCULAR CYLINDER COATED BY NEW SYNTHETIC ORGANIC POLYMERIC MATERIALS BASED ON POLYIANILINE)

ABSTRACTThe problem of laser beam scattering from circular cylinder coated by organic dielectric polymeric material based on polyaniline is investigated. In this study, polyaniline is prepared in laboratory, it was chemically synthesized, via the chemical oxidation of aniline by persulfate anion in aqueous solution. It showed good yield and intermediate electrical conductivity (a =5 S/cm). This conductivity assigns it as a semiconductor material. Polyaniline was characterized by different methods of analysis such as: thermogravimetric analysis, electric conductivity, infrared and UV—visible absorption spectroscopy. The prepared polymer was formulated for laser beam scattering studies. The Gaussian beam scattering from an infinitely long conducting circular cylinder with large size parameter and located in the far zone from the source of excitation and coated by polyaniline dielectric material is investigated. This problem had been solved via modal expansion technique. The Gaussian beam is expanded in teens of continuous plane waves with amplitudes and phases given by a Gaussian weighting functions. The continuous plane wave spectrum of the Gaussian beam is obtained. Thus, the evaluation of the Gaussian beam scattering from the conducting circular cylinder reduces to evaluating the inverse Fourier transform to the scattered plane waves. Numerical results using a code developed under MATLAB environment is obtained. The obtained solution is compared with the previously published solutions that are based on modal expansion technique and good agreement is achieved. Experimental measurements are worked out for He-Ne laser beam of wave length ( A, = 0.6328 gm) incident on conducting circular cylinder coated by different thickness of polyaniline material. The attenuation of the scattered field due to this dielectric material is computed and compared by the measured results.

LASER BEAM SCATTERING FROM CONDUCTING CIRCULAR CYLINDER COATED BY NEW SYNTHETIC ORGANIC POLYMERIC MATERIALS BASED ON POLY(ANILINE)

ABSTRACTThe problem of laser beam scattering from circular cylinder coated by organic dielectric polymeric material based on polyaniline is investigated. In this study, polyaniline is prepared in laboratory, it was chemically synthesized, via the chemical oxidation of aniline by persulfate anion in aqueous solution. It showed good yield and intermediate electrical conductivity (a =5 S/cm). This conductivity assigns it as a semiconductor material. Polyaniline was characterized by different methods of analysis such as: thermogravimetric analysis, electric conductivity, infrared and UV—visible absorption spectroscopy. The prepared polymer was formulated for laser beam scattering studies. The Gaussian beam scattering from an infinitely long conducting circular cylinder with large size parameter and located in the far zone from the source of excitation and coated by polyaniline dielectric material is investigated. This problem had been solved via modal expansion technique. The Gaussian beam is expanded in teens of continuous plane waves with amplitudes and phases given by a Gaussian weighting functions. The continuous plane wave spectrum of the Gaussian beam is obtained. Thus, the evaluation of the Gaussian beam scattering from the conducting circular cylinder reduces to evaluating the inverse Fourier transform to the scattered plane waves. Numerical results using a code developed under MATLAB environment is obtained. The obtained solution is compared with the previously published solutions that are based on modal expansion technique and good agreement is achieved. Experimental measurements are worked out for He-Ne laser beam of wave length ( A, = 0.6328 gm) incident on conducting circular cylinder coated by different thickness of polyaniline material. The attenuation of the scattered field due to this dielectric material is computed and compared by the measured results.

Laboratory determination of beam-shape coefficients for use in generalized Lorenz–Mie theory

The use of the generalized Lorenz-Mie theory (GLMT) requires knowledge of beam-shape coefficients (BSC's) that describe the beam illuminating a spherical scatterer. We theoretically demonstrated that these BSC's can be determined from an actual beam in the laboratory. We demonstrate the effectiveness of our theoretical proposal by determining BSC's for a He-Ne laser beam focused to a diameter of a few micrometers. Once these BSC's are determined, the electromagnetic fields of the illuminating beam may be evaluated. By relying on the GLMT, we can also determine all properties of the interaction between beam and scatterer, including mechanical effects (radiation pressures and torques).

The refractive index profile of highly-oriented fibres

A new method is suggested for measuring the refractive index profileof homogeneous highly-oriented fibres. This method depends on the principle ofthe variable wavelength interferometric technique. A numerical fitting is usedto determine the fringe shift profile at a certain wavelength. The refractionof the light beam by the fibre is taken into consideration in the mathematicaltreatment. Poly(ethylene terephthalate) and poly(ethylene2,6-naphthalene-dicarboxylate) fibres are used as examples of thesehighly-oriented fibres. The diffraction of a He-Ne laser beam is used todetermine the diameter and the cross sectional shape of these fibres. Also, atwo-beam interference microscope (Pluta microscope) is used for measuringthe refractive index profile of these fibres, at the same wavelength, forlight vibrating perpendicular to the fibre axes to confirm the results of thenew method. Microinterferograms are given for illustration.

近接Ｘ線露光におけるセクタフレネルゾーンプレートによるアライメント計測

Fresnel zone plate patterns have been widely applied to mask to wafer alignment because the fresnel beam spots are unaffected by poor edge definition or by rough surfaces arising from variation in processing. This paper describes a video-based alignment using a sector fresnel zone plate (SFZP) which is unique among the zone plates in having an oblique line focus. SFZPs printed on both X-ray mask and wafers are illuminated with collimated He-Ne laser beam. The bright image formed on an oblique line focus shows high contrast better than 11-15dB in signal to background ratio. With SFZPs, position sensing repeatability better than 9 nm (3σ) has been obtained in four processed wafer types.

Laser-based thermal pulse measurement of liquid thermophysical properties

In this work, a laser-based thermal pulse technique is presented that simultaneously measures thermal conductivity and thermal diffusivity for liquids, from which the volumetric specific heat can be determined as well. The measurement is based on photothermal deflection of a HeNe laser beam that passes through the test liquid next to a thin heating wire. Liquid thermophysical properties are determined by fitting a numerical simulation of the heat conduction and probe beam deflection to the measured time-dependent probe beam deflection. Results are presented for five liquids: glycerol, 1-propanol, 2-propanol, methanol, and ethanol, and are found to be in very good agreement with values reported in the literature. The experimental setup is small, inexpensive and reliable. The temperature dependence of the liquid refractive index is also determined during the measurement process, and the same experimental technique is capable of measuring the thermal conductivity and thermal diffusivity of thin conducting wires.

A laser-based 2-dimesional angular deflection measurement system for tilting microplates

A laser-based system that is capable of measuring the angular deflection of the microplate in two-dimension is developed. The system consists of a HeNe laser, lenses, beamsplitters, objective lens, CCD camera and position sensitive photodiode. The operation of the system is based on the measurement of the displacement of a HeNe laser beam reflecting off the surface of the microplate using position sensitive photodiode. The angular resolution is estimated at 0.2° and the response time of the system is as short as 4 μs. This system can measure the static and dynamic angular response and resonance frequency of microplates, such as spatial light modulators and micromirrors, in two orthogonal directions.

Photoinduced alignment of polymer liquid crystals containing azobenzene moieties in the side group VII. On He-Ne laser beam irradiation

Photoinduced alignment in a polymer liquid crystal prepared from 6-{1-[4-(2-cyano-4-nitrophenylazo)phenyl]piperazino}hexyl acrylate and 4'-[6-(methacryloyloxy)hexyloxy]-4-cyanobiphenyl was investigated for the first time on irradiation with a polarized He-Ne laser beam at 633 nm. The azobenzene moieties as well as the inert cyanobiphenyl mesogenic units were aligned with the molecular long axis perpendicular to the polarization direction of the irradiation light. Alignment induced on short irradiation was reversible, while that induced under prolonged irradiation was irreversible due to the occurrence of crosslinking which might be caused by photoinduced decomposition of the azobenzene moieties during the photoirradiation process.

Laser observation of flying ink jet electrostatically extracted: main results and application to tone reproduction of images

At present, there are several methods for measuring the diameter of droplets of ink jets. The authors have conceived a method by which not only the droplet diameter but also the state of ink jet flight can be determined using the same optical system by changing the light source only. The electrostatically extracted ink jet method using dielectric ink was used for the experiment. In the case of electrostatically extracted ink jet, a liquid thread of continuous flow is generated from the nozzle tip and disperses in corpuscles from the leading edge of the liquid thread. Observation of dispersing ink flight is difficult by any of the conventional methods. In their study, the state of ink from the liquid thread to corpuscles was observed by controlling applied voltage and ink pressure and with the use of an He-Ne laser beam or dye pulse laser beam depending on the observation objectives. Interesting results obtained are reported in this paper. In designing commercial models of printers using ink jets, their observation method presents new aspects for examining the state of flying ink.