He-Ne Laser Beam Research Articles

Three-Dimensional Electric Field Vector Measurements in Nitrobenzene Using Kerr Effect

We have been investigating a nonuniform electric field measurement method in dielectric liquids using the Kerr electrooptic effect. Three-dimensional electric field vectors were measured as the first step in determining the three-dimensional nonuniform electric field distributions. The electric field vector to be measured was produced in a pair of inclined parallel-plane electrodes. Negative high-voltage pulses were applied to the electrode system. Nitrobenzene with large Kerr constant was used in the experiments. A He-Ne laser beam passed through nitrobenzene between the electrodes along two different orthogonal directions. The magnitude and the direction of the electric field vector were calculated from the light intensity measured by a photodiode. Maximum errors of measured electric field strength and direction were 9.3% and 4.3°, respectively.

Fiber-optic proton beam intensity monitor

The thermally induced change of the birefringence of a high-birefringence fused-silica optical fiber, when exposed to a proton beam (2 MeV, 0.5–44 nA, 5-mm spot diameter), was measured with a fiber-optic polarimetric sensor. A short length (5 cm) of 125-μ-diam, single-mode, polarization-maintaining optical fiber was put orthogonally to the beam in vacuo and the linear polarization of a HeNe laser beam launched into the fiber was analyzed by a polarizer and recorded by a photodetector. The response of the sensor both to a continuous and to a modulated proton beam was studied. The photodetector output, which varies with the cosine of the induced relative phase retardance between the fiber eigenmodes, provides a dc or an ac (10 Hz test modulation frequency) measurement of the beam current. This device acts as a proton beam intensity monitor, with minimum beam perturbation and a sensitivity of 0.1 nA. Its possible use also as a beam position monitor or as a wire-scanner beam profiler is suggested.

Interferometric method for the observation in real time of some infrared photothermal effects

We present here an original experimental method utilising the interference between two He-Ne laser beams for the detection of photothermal phenomenon on semiconductor at 10,6 µm. A JAMIN interferometer splits the beam of one He-Ne laser in two parallel beams. The first one undergoes a transverse photothermal deflection due to its passage in a zone disturbed by a pump laser (the CO2 laser emits in the vicinity of 10 µm), the second beam serves as a reference. The experimental setup is very stable and is also extremely accurate. It allowed us to observe in real time the change of the temperature both during and after a pulse of the pump laser on a sample of silicon. We present here the description of the experimental setup, the conditions of measurements and the first results.

Transmittance of a laser beam through a pair of crossed polarizers

The transmission of a cw He-Ne laser beam through a pair of imperfect linear polarizers was measured. It was found that the transmittance is not minimum if the polarization plane of the beam and polarizer axes are mutually crossed, as commonly expected. Mutual angles (at which the transmittance is minimum) depend on the polarization degree of the beam and on the imperfection of both the polarizers.

Spatial solitons in photorefractive Bi12TiO20 with drift mechanism of nonlinearity

The analysis performed shows that in cubic photorefractive crystals (of Bi12SiO20 and GaAs type in particular) with drift (‘‘quasilocal’’) mechanism of optical nonlinearity spatial soliton propagation can be observed for reasonable external dc electric fields 10–15 kV/cm. These photorefractive solitons which can be excited at very low cw laser power are stable in a broad region of signal(soliton)/incoherent(spatially uniform) intensity ratio, and allow easy switching from bright to dark type. Original experimental results of self-channeling of submicrowatt HeNe laser beam in a cubic Bi12TiO20 sample under external dc field are presented.

Fuel Drop Size Measurement in a Carburetted Induction System with Two Throttling Methods

A new throttling system far SI engines is examined. The SMD of the fuel droplets in the induction system is measured to evaluate the performance of the new device with respect to the conventional throttle plate arrangement. The measurements are conducted at steady now conditions. A forward angular scattering technique with a He-Ne laser beam is used for droplet size measurement. The experiments are carried out with different mixture strength, stream velocity and throttle positions. It is observed that A/F ratio has no effect on SMD. However, stream velocity and throttle position have a significant influence on SMD. The new throttling method is found to be more effective in reducing the SMD, particularly at low throttle opening and high stream velocity compared to the conventional throttle plate.

Non-Contact Temperature Measurement with Infrared Interferometry

ABSTRACTWe have successfully utilized the temperature dependence of the refractive indices of various substrates (GaAs and InP) in detecting their temperature variations. The detectionwas accomplished by injecting a beam of HeNe laser (1.15 μm) toward a double-sidepolished substrate. An interference pattern developed among the reflected laser beams, and the actual temperature increment/decrement could be deduced from the interference maxima and minima. The method was first calibrated inside a diffusion furnace from room temperature up to 200ºC, and the detection resolution was found to reach as high as ±0.7ºC. The same measurement setup was later used on the temperature calibration of a substrate heater in a molecular beam epitaxy (MBE) growth chamber, and was finally used to detect surface temperature change during Ar+ laser assisted metalorganic MBE (MOMBE) growth. Because a direct contact is unnecessary and only the relative signal intensity is needed, this low-cost method can be applied to any otherexperiments in a fairly straightforward manner.

Effect of the oxidative power of iodination on the optical properties of Alpaca fibres

This study deals with the changes in the optical properties of Alpaca fibres due to the effect of the oxidative power of iodine on the structural characteristics of Alpaca fibres. The diffraction of a He-Ne laser beam was used to measure the dimensional parameters, transverse sectional shape and area of the Alpaca fibre sections. Optical and scanning electron microscopes were used to confirm the geometrical parameters of the cross-sections. Two methods were applied for the measurement of the refractive indices and birefringence of the Alpaca wool fibres. The first was concerned with the application of multiple-beam Fizeau fringes in transmission before treating the fibre with iodine. The second method made use of a double refracting interference microscope (the Pluta polarizing interference microscope). The double beam technique was considered the most suitable in determining the mean refractive indices and the double refraction of the samples after the iodine treatment. Large changes were observed in the values of the refractive indices due to the iodination process, while the birefringence exhibited no appreciable change. Examination of the Alpaca fibres by X-ray diffractometry showed that the crystalline parts had been completely decomposed and degraded due to the effect of I 2, which causes oxidative scission of the intermolecular disulphide bonds of the keratins.

Experiments and numerical simulations on beam bending and transverse beam encoding by spatial self- and cross-phase modulation in ruby

Experiments and numerical simulations are performed on the nonlinear beam evolution of simultaneously propagating cw argon-ion and HeNe laser beams through a ruby rod. The HeNe probe beam exhibits a deflection of nearly 12 mrad when a 1.5 W, 514.5 nm laser beam is injected into the ruby rod at an angle to the probe. The copropagating geometry is also studied where the azimuthally symmetric transverse beam encoding leads to complex ring structures in both the HeNe and argon-ion laser beams. The numerical simulations are compared with the experimental data to obtain the cross-phase modulation term. Using previously reported values for the saturable nonlinear index of ruby and a nonlinear index for cross-phase modulation n c = 1.35Re( n 2), the nonlinear wave equation in two transverse dimensions is numerically solved to predict the bending angles and emerging beam profiles. These findings are discussed in light of previous experiments in ruby as well as the possibility of using these effects for producing nanosecond optical switching systems.

Automated spatially scanning ellipsometer for retardation measurements of transparent materials

A highly sensitive and automated technique has been developed for measuring the birefringence in transparent optical materials. The spatially scanning modulated transmission ellipsometer maps the birefringence of a transparent material by probing it with a polarization-modulated He-Ne laser beam. Computer-controlled voltage biasing of a Pockels cell permits self-calibration and background subtraction of the system retardance. The technique is capable of resolving differential retardances as small as 0.1 nm (λ/6328) through a range of ±λ/2, where λ = 632.8 nm. Samples typically range in size from 50 µm to 10 cm in diameter within the sample plane and as much as 400 mm along the optical axis.

Study of polarization of laser radiation scattered 90 deg

A qualitative experimental study was undertaken of the effects of spherical particle scattering on the polarization of linearly polarized He-Ne laser beams. Four concentrations of particles (either 0.22- or 0.494-^im diam) were suspended in filtered, distilled water to serve as the scattering centers. Data representing the effects of volumetric particle concentration, detector acceptance angle, cylindrical scattering volume container diameter, and detector depth are investigated. In general, large diameter particles and high particle concentrations depolarize the incident beam the most. Also, increasing the length of the path traversed by the scattered beam greatly increases the depolarization of the beam.

Investigations of solar radiation detectors using a laboratory test facility for solar radiation meteorological instruments

A laboratory test facility for solar radiation detectors has been built and is in operation at the Aerological Station of the Swiss Meteorological Institute (SAP/SMI). This installation is conceived as a universal test bed for solar radiation exposed meteorological instruments, and consists of a commercially available solar simulator, a laser alignment system, a translation mechanism with instrument mounts, and an adjustable projection mirror. The solar simulator produces a well characterized radiation beam which can be filtered to match the terrestrial or outer space solar spectrum with an irradiance of up to one solar constant (1367 Wm −2). The instrument mounts and a HeNe laser beam provide a precise and easy alignment of the reference and the test instruments in the radiation beam, allowing for incident angles in the range of 15°–75°. The measurement is based on a comparison of the response of an active cavity absolute radiometer PMO6 with the signal of the test instrument. Detailed investigations of the Haenni Solar 111B type heliometer have revealed important irregularities in the sunshine threshold irradiance angular distribution. Measurements performed with and without the protection glass cover prove the exceedingly high threshold values at large declination angles to be a consequence of enhanced reflections due to the incident angle and inhomogeneities in the glass cover. Very satisfactory results have also been obtained on characterization measurements of pyranometers showing the mean values of the responsivity to be within 0.8% of the calibration values measured at the world radiation center (WRC) at Davos.

Refractive index of salt water: effect of temperature

Abstract The Fraunhofer's method used to measure the refractive index of liquids has been modified. The modification includes an electric circuit containing a sensitive photodiode in order to measure accurately the deviation angle of a HeNe laser beam. The refractive index of pure water and four different concentrations of NaCl solution is measured at temperature range 5–90°C. Four mathematical equations relating the refractive index to the temperature and concentration are obtained using the least squares method. The effect of temperature and concentration on refractive index are explained using Lorentz-Lorenz formula.

Holographic Lithography with Endpoint Detection of Resist Development

Grating patterns with a period of about 0.4 µm are fabricated by means of holographic lithography with a He-Cd laser (λ=441.6 nm). In the fabrication process to develop a resist film sample a He-Ne laser beam irradiates the sample and its reflection intensity is observed. The reflection intensity of the He-Ne laser does not change periodically during the development. We calculate the He-Ne laser reflection intensity from the resist grating during the development assuming either the rectangular or the triangular resist grating profiles. The calculated reflection intensity with the triangular profile shows good agreement with the experimental one. The reflection intensity can be applied to the endpoint detection of the development. We have fabricated resist gratings with vertical profiles whose lines and spaces are approximately 0.1 µm and 0.3 µm in width, respectively. Very fine lines of 0.06 µm in width with vertical walls have also been fabricated by controlling the development time. Au gratings with 10 nm thickness can be made directly using the lift-off technique.

Optical monitoring of nucleation and growth of diamond films

Early stages of diamond film deposition on molybdenum substrates using dc arc discharge in CH4/H2 gas mixtures were studied by in situ measurements of optical reflectivity of growing film. Ultrafine diamond grit of ≊200 Å size was used for seeding to increase nucleation density up to 2×109 cm−2 and to produce smooth thin films. Evolution of He-Ne laser beam reflection at 0.63 μm wavelength is described in terms of Mie scattering by nonabsorbing dielectric spheres in the case of nucleated film and of light interference in the system of continuous diamond film on a metal substrate. During the deposition process the growth rate passes through a minimum at the moment when a minimum roughness is supposed to be achieved.

Photoacoustic studies on multilayer dielectric coatings

Non-destructive testing of multilayer dielectric coatings (SiO2/TiO2 structure) has been carried out using the photoacoustic technique. This technique makes use of a 10 mW He-Ne laser, a photoacoustic cell and a lock-in amplifier. The chopped He-Ne laser beam is allowed to fall on the sample placed in a photoacoustic cell. The acoustic signals thus generated are detected using a microphone and the resulting output is processed by a lock-in amplifier. The amplitude and phase of the signals were measured as a function of the chopping frequency. Striking step-like variations are observed in the phase against frequency plot which clearly reveals the different layers present in the multilayer structure.

Transient response of a photorefractive grating produced in a BSO crystal by a short light pulse

The transient photorefractive properties of a BSO crystal after illumination by two coherent light pulses were studied by monitoring the diffracted beam intensity of a HeNe laser beam. The previously observed peculiar response curve, having a dip between the first fast rise and second slower rise, can be explained by a newly developed “four-level” model with two shallow acceptor levels, an inactive ionized acceptor level, and a donor level. The temperature dependences of transient photorefractive properties and transient photocurrent, which were measured for the first time, also support the present model.

Determination of the laser-induced damage threshold of bulk polymer samples at 1.06 mu m using the pulsed photothermal deflection technique

A pulsed Nd-YAG laser beam is used to produce a transient refractive index gradient in air adjoining the plane surface of the sample material. This refractive index gradient is probed by a continuous He-Ne laser beam propagating parallel to the sample surface. The observed deflection signals produced by the probe beam exhibit drastic variations when the pump laser energy density crosses the damage threshold for the sample. The measurements are used to estimate the damage threshold for a few polymer samples. The present values are found to be in good agreement with those determined by other methods.

Creation of long-living ordered electron-hole structures in a disordered system: Slow nonlinear response and formation of a beam channel by weak pumping.

Experimental and theoretical studies of an amorphous As 2 S 5 semiconductor show the appearance of a nonlinear variation of the refractive index Δn e produced by a weak He-Ne laser beam. The refractive-index variation needs long-time exposure (hours) and survives for a long time (a few days) after the laser is switched off. The main feature of the theoretical model proposed here is the existence of electron and hole trapped states resulting in slow relaxation and recombination, and the dependence of generation and recombination rates in a given trap on the space distribution of electron-hole ordering

Laser reflective interferometry for in situ monitoring of diamond film growth by chemical vapor deposition

A simple laser reflective interferometer has been employed for in situ monitoring of diamond film growth in a hot-filament chemical vapor deposition reactor. This method uses a low power HeNe laser beam reflected at normal incident from the substrate. The high refractive index of the diamond film and the relatively high reflectivity of the Si substrate result in pronounced and easily detected interference oscillations in the reflected beam intensity. The oscillation period provides an accurate and immediate measure of the growth rate. In addition, the variations of the extrema of the oscillations provide an estimate of the quality and surface texture of the diamond films. Significant improvement in research productivity has been realized by using this technique.