He-Ne Laser Beam Research Articles

Control of self-pumped phase conjugate reflectivity in a photorefractive crystal by another laser beam

When a photorefractive Ce:BaTiO 3 crystal is suddenly irradiated by an Ar + laser beam, the self-pumped phase conjugate reflectivity of a He-Ne laser beam in the crystal drops to a minimum and then recovers to a steady state value. When the Ar + laser beam is then blocked, a similar time dependence of the phase conjugate reflectivity is observed. The laser beams do not overlap in the crystal.

Effect of Dyeing Process on Optical Anisotropy of Polyester Fibres

A two beam interferometric technique using a pluta polarizing interference microscope has been used for the determination of the refractive index profiles and the birefringence of undyed and dyed polyester fibres with single and mixture colorants. Diameters and cross-sectional shapes of these fibres were determined from the diffraction pattern of a He-Ne laser beam, incident perpendicular to the fibre axis.

Effect of Dyeing Process on Optical Anisotropy of Polyester Fibres

A two beam interferometric technique using a pluta polarizing interference microscope has been used for the determination of the refractive index profiles and the birefringence of undyed and dyed polyester fibres with single and mixture colorants. Diameters and cross-sectional shapes of these fibres were determined from the diffraction pattern of a He-Ne laser beam, incident perpendicular to the fibre axis.

Intensity fluctuations in a laser beam due to propagation through a plane turbulent jet

A planar heated air jet was constructed. Its flow properties were characterized and shown to be both reproducible and in good agreement with the results of turbulence theory. The optical properties of the jet were studied with the help of a 632.8 nm HeNe laser beam. Measurements of the random phase modulations imposed on the wavefront of the beam traversing the jet were made and the results reported in a previous paper. The intensity fluctuations arising in the beam were also measured and their spectra and variance determined at various distances from the jet. The spectra behave like power laws with a slope of −1 at low temporal frequencies and a slope of −8/3 at higher frequencies. This dual power-law behaviour is attributed to the differential velocities within the planar jet.

Two-grating diffraction and Lau effect under laser illumination

We first describe an unconventional Lau experiment that is performed with a collimated He-Ne laser beam. We then describe an elegant experimental arrangement in which a collimated He-Ne laser beam is gradually rendered spatially incoherent; this demonstrates the evolution of the Lau fringes from the Fraunhofer diffraction pattern of the two gratings in the Lau setup.

Structural and optical characteristics of SiO2 thin film containing GaAs microcrystallites

Structure of GaAs-SiO2 composite thin films prepared by magnetron rf co-sputtering technique were investigated by transmission electron microscopy, x-ray diffraction, and x-ray photoelectron microscopy. The results show that GaAs microcrystallites with an average size of 10 nm were uniformly dispersed in SiO2 thin film. Quantum confinement effect was observed in the film by the measurement of absorption spectrum, and the blueshift of absorption edge was measured to be 0.5 eV. Nonlinear optical absorption and nonlinear optical refraction were studied by Z-scan technique using single Gaussian beam of He-Ne laser (632 nm). An enhanced third-order nonlinear optical absorption coefficient and nonlinear optical refractive index were achieved in the thin film, and measured to be 2×10−1 and 4×10−6 cm2/W, respectively.

Unidirectional laser oblique illumination (ULOI): a comparison with partial dark field illumination (PDFI) in the optical microscopy of metals

Some metallographic observations of the surface of polycrystalline specimens in an optical microscope illuminated with a HeNe laser beam; at oblique incidence; are compared with observations with white light also at oblique incidence. It is shown that similar effects are obtained in both cases; however; the width of the maximum in the dispersed intensity is narrower in the case of illumination with the laser beam. In addition; this kind of illumination permits us to distinguish distinct angular directions of the surface roughness.

Measuring the thickness and refractive index of a thick transparent plate by an unexpanded laser beam

The thickness and refractive index of a thick transparent plate are measured by using an unexpanded HeNe laser beam. The laser beam is incident at different angles onto the plate; and then two reflected beams; from the front and back surfaces; are received on a distant screen: the corresponding separations between them are measured. A theoretical relation between the refractive index; thickness; angle of incidence and separation is derived. This relation is experimentally verified and shows good agreement. The errors in the measured thickness and refractive index are analysed. The method is non-contact; non-destructive and low cost.

Light-Induced Periodic Lattice of Defects in Smectic A and C Liquid Crystals: Structural and Dynamical Aspects

Structural and dynamical studies of Optically-induced effects in SmA and SmC* liquid crystals are presented. The smectic materials are doped with photosensitive molecules capable of trans-cis isomerization under light illumination. Laser irradiation leads to the formation of strongly scattering textures with periodical array of parabolic focal conic domains (PFCD's). What is most surprising is that the effect is caused by a low-power (≤ 10 mW) He-Ne laser beam; its efficiency is highest in the visible part of the spectrum. The written information can be erased by another beam with shorter wavelength, such as from an Ar laser or a UV source. The PFCD's lattice can be stabilized by a polymeric network. The most plausible mechanism of the light-induced effect is compression/dilation of smectic layers caused by phototransformation of the molecules.

He-Ne Laser Propagation in Silica Fiber after Delivery of KrF Excimer Laser.

He-Ne laser propagation in silica fiber after delivery of KrF excimer laser was experimentally investigated. The intensity at the outer part of deliveried He-Ne laser beam after delivery of KrF excimer laser was observed to be extremely reduced in comparison with that before delivery of KrF laser. We consider that this reduction results from the absorption of skew rays and/or the refractive index change at the outer part of core silica. It is supposed that these changes of optical property originate from the KrF-laser-induced defects located at the outer part of core layer.

Optical Trappings of ThO2and UO2Particles Using Radiation Pressure of a Visible Laser Light

Optical trappings of ThO2 and UO2 particles have been first demonstrated in water using the radiation pressure of a TEM00-mode He-Ne laser beam of λ=633 nm. It was observed that a ThO2 particle was successfully trapped three-dimensionally in the focus region and transferred by moving the focus. On the other hand, for a UO2 particle of which a refractive index and an extinction coefficient are relatively large in the visible region, only two-dimensional trapping was observed when the beam focus was located near the bottom of the particle. One of the main difficulties in the optical trapping of nuclear fuel particles is attributed to their relatively large absorption coefficients in the visible region. Computational studies on three-dimensional optical trapping performances of absorbing particles were, therefore, perfomed with a simulation code based on geometrical optics. The present calculation can well predict the experimental results on the optical trapping characteristics for ThO2 and UO2 particles.

Excimer laser ablation of Ba 2NaNb 5O 15 optical waveguide films on MgO(001) substrates

Polycrystalline Ba 2NaNb 5O 15 (BNN) optical waveguide films were grown on MgO (001) substrates by excimer laser ablation for the first time. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were applied to characterize the as-grown BNN film, which showed that single-phase nearly stoichiometric BNN films, with flat surface and uniform thickness were obtained. The favorable optical waveguide properties were evaluated by m-line observation and measurement of the propagation loss of the He-Ne laser beam confined in the waveguide film of TE and TM mode.

Laser Metallography of Zinc — Analysis of the Dispersed Intensity / Lasermetallographie von Zink - Analyse der Streulichtintensität

Light metallographic observations of the surface of zinc crystals using oblique illumination with a He-Ne laser beam were reported. It was shown that the intensity of the dispersed laser light presents maxima, as a function of the angle of rotation of the specimen with respect to an axis perpendicular to its surface. The angular differences between these maxima were related to the orientations of the different twins present which, in turn, were related to the crystallographic orientations. As the degree of chemical etching was increased, a crystallographically facetted surface was produced, which was associated with a maximum in the dispersed intensity.

Optical probing of laser-induced shock waves in air

Shock Waves (SW) were produced in air by focusing the (0.25 J, 6 ns) second-harmonic (λ = 532 nm) Nd : YAG laser light into a stainless-steel cylindrical cell at a pressure from 200 to 760 Torr. The laser fluence at the focal point is > 5 GW/cm2. The spatial variation and consequently the time evolution of the radial propagation velocityU of the generated shock waves were measured via a simple optical system utilizing a HeNe laser beam triply intersecting the propagating shock wave at three successive positions. Using a reflector, we were able to probe the traveling SW in six consecutive positions during its round trip. Good agreement was obtained between the experimental results and the predictions of the point strong explosion theory. It is shown that this method is simple with a fairly good precision. It therefore appears to be useful for the determination of the SW dynamic parameters, namely its Mach number, the pressure at the SW front, the thickness of the compressed air layer and the energy consumed in producing this layer.

Time-resolved detection of laser-ablated particles based on intensity decrease of cw probe laser beam

A prototype system was constructed for the detection of laser-ablated particles. The second harmonic of a picosecond Nd:YAG laser was used for the ablation of a polycrystalline copper target in vacuum. The typical laser intensity was 10 11 W cm −2. A probe HeNe laser beam which passed through the ablation plume was scattered by the ablated particles. The intensity of the probe beam was measured as a function of the elapsed time from the ablation laser pulse, and its dip was observed to exhibit a Maxwell-Boltzmann-like distribution. The delay time of the dip depended linearly on the distance between the target and the probe beam. The velocity of the expansion at the peak of the dip was derived as8.3 × 10 3cm s −1, and this reflected the expansion velocity of the plume. When helium, neon, argon, and nitrogen gases up to 40 kPa were introduced, the expansion velocity decreased and a long tail of the dip was observed.

Opto-thermal properties of fibres: 3-effect of anisotropic optical parameters in polypropylene fibres as a function of annealing process

This study deals with the changes in the optical properties of polypropylene fibres (4:1 draw ratio 515 tex polypropylene, Bolton, UK) due to the effect of thermal annealing on its structural characteristics. Changes in the structure of annealed polypropylene fibres at a constant time of 2 h and different temperatures (60–140 °C) were studied interferometrically. The diffraction of a He-Ne laser beam was used to measure the dimensional parameters transverse sectional shape and the area of the polypropylene fibres sections. An optical microscope was used to confirm the geometrical parameters of the cross-sections. The diffraction technique was utilized to study the effect of annealing on swelling factors of these fibres for some different liquids at room temperature 19 ± 1 °C. Two methods were applied for the measurement of the refractive indices and birefringence of the polypropylene annealed and unannealed fibres. The first was concerned with the application of the Becke-line method for determining the refractive indices and the birefringence of the skin layer. The second method used multiple-beam Fizeau fringes in transmission to observe the changes in the values of the refractive indices due to the annealing process in the skin and core layers. Also, the mean refractive indices and their profiles were determined, taking the refraction and different temperatures into consideration. The resulting data were used to calculate the polarizabilities per unit volume and the isotropic refractive index.

Numerical Analysis of Radiative Energy Transmission through a Fibrous Layer and Its Experimental Verification. Large-Size-Parameter Case.

An analytical model developed to calculate the radiative energy transmission through a fibrous layer is verified by the experimental results obtained via measurement of the transmittance of a He-Ne laser beam through nickel-fiber sheets with a large size parameter. The model is used to calculate the radiative energy transmission by the Monte Carlo method and the optical characteristics of a fiber with large size parameter are estimated by the method developed by Yamada et al. Which considers the diffraction and reflection by the fiber. The following results are obtained. The results of the analysis agree very well with the experimental ones. The directional profile of the transmitted energy becomes flatter when the thickness of the fibrous layer is increased. When the number of fibers with orientations other than parallel to the fibrous layer is increased, the transmittance is increased. Even when fibers have varying diameters in the range of 20∼28μm, the transmittance is the same as in the case of the fibrous layer with uniform average diameter of 24μm.

Optical Trappings of ThO2 and UO2 Particles Using Radiation Pressure of a Visible Laser Light.

Optical trappings of ThO 2 and UO 2 particles have been first demonstrated in water using the radiation pressure of a TEM oo -mode He-Ne laser beam of λ=633 nm. It was observed that a ThO 2 particle was successfully trapped three-dimensionally in the focus region and transferred by moving the focus. On the other hand, for a UO 2 particle of which a refractive index and an extinction coefficient are relatively large in the visible region, only two-dimensional trapping was observed when the beam focus was located near the bottom of the particle. One of the main difficulties in the optical trapping of nuclear fuel particles is attributed to their relatively large absorption coefficients in the visible region. Computational studies on three-dimensional optical trapping performances of absorbing particles were, therefore, perfomed with a simulation code based on geometrical optics. The present calculation can well predict the experimental results on the optical trapping characteristics for ThO 2 and UO 2 particles.

PYROELECTRIC AFFECTION ON THE READOUT OF PHOTO-REFRACTIVE HOLOGRAPHIC GRATING

The photorefractive holographic grating in a Mn doped K1-yNayBa2-xSrxNb5O15 (KNSBN) is written with two 0.27mW He-Ne laser beams (632.6nm) and is read with one quasicontinuous dye laser beam (621.8nm, 1.6mW or less). It is found that the Bragg diffracton suddenly reaches its maximum at the beginning and then decays to its minimum with a time constant of about 0.6s. The ratio of the maximum to the minimum can be higher than 7.5. A theory including pyroelectric effect has been developed and it fits the experiment well.

Laboratory Measurements of Light Scattering by Dust Particles

AbstractWe have set up an experimental device to optically study the scattering properties of dust particles. Measurements over the 8 — 174° interval of scattering angles are performed on a continuously flowing dust loaded jet illuminated by a polarized red HeNe laser beam. The scattering is averaged over the population of the dust particles in the jet, which can be determined independently, and give the “volume scattering function” for the two directions of polarization directly. While results for spherical particles are in good agreement with Mie theory, those for arbitrary particles show conspicuous deviations.