Μm He-Ne Laser Research Articles

Two-chord interferometry using 3.39 μm He–Ne laser on a flux-coil-generated FRC

A two-chord λ(IR)∼3.39 μm He-Ne laser interferometer system was developed for a flux-coil-generated field-reversed configuration to estimate the electron density and the total temperature of the field-reversed configuration (FRC) plasma. This two-chord heterodyne interferometer system consists of a single ∼2 mW infrared He-Ne laser, a visible (λ(vis)∼632.8 nm) He-Ne laser for the alignment, a 40 MHz acousto-optic modulator, photodetectors, and quadrature phase detectors. Initial measurement was performed and the measured average electron densities were 2-10×10(19) m(-3) at two different radial positions in the midplane. A time shift in density was observed as the FRC expands radially. The time evolution of the line-averaged density agrees with the density estimated from the in situ internal magnetic probes, based on a rigid-rotor profile model.

In situ Measurement of Fuel Concentration of Hydrocarbon near Spark Plug in an Engine Cylinder by 3.392.MU.m Infrared Laser Absorption Method (Application to Actual Engine)

An infrared absorption method was used to determine the fuel concentration with a 3.392μm He-Ne laser. The effects of pressure and temperature on the molar absorption coefficients of hydrocarbon fuels were clarified, so that it increased with increasing temperature and decreased with increasing pressure. Molar absorption coefficient of multi component fuel like gasoline can be estimated using molar absorption coefficient of each component and considering mass balance. By exchanging an ordinary spark-plug for a spark plug with a developed sensor in which light can pass through mixture in the combustion chamber, successive measurement of fuel concentration was performed in a spark-ignition engine. The effects of liquid droplets, mechanical vibration, and other gas like H2O on measurement accuracy were discussed.

In situ measurement of hydrocarbon fuel concentration near a sparkplug in an engine cylinder using the 3.392 µminfrared laser absorption method: application to an actual engine

An infrared absorption method with a 3.392 µmHe–Ne laser was used to determine the hydrocarbon fuel concentration near thespark plug in a spark-ignition engine. Iso-octane was used for the fuel. Thepressure and temperature dependence of the molar absorption coefficient wasclarified. The molar absorption coefficients of a multi-component fuel such asgasoline were estimated by using the coefficient of each component andconsidering the mass balance. A sensor was developed and installed in a sparkplug, which was substituted in place of an ordinary spark plug in a spark-ignitionengine. Light can pass from the sensor through the engine cylinder tomeasure the fuel concentration. The effects of liquid droplets inside theengine cylinder, mechanical vibrations and other gases such as H2O andCO2on the measurement accuracy were considered. Four main conclusions were drawnfrom this study. First, the pressure and temperature effects on the molarabsorption coefficient of liquid fuel vapour were determined independently inadvance using a constant-volume vessel. The pressure and temperaturedependence of the molar absorption coefficient was determined underengine firing conditions. Second, the molar absorption coefficients of amulti-component hydrocarbon fuel such as gasoline were estimated by consideringthe molar fraction of each component. Third, in situ measurements of thehydrocarbon fuel concentration in an actual engine were obtained usingthe spark plug sensor and the molar absorption coefficient of iso-octane.The concentration near the spark plug just before ignition was almost inagreement with the mean value that was obtained from the measurement ofthe flow rate made with a burette, which represented the mean valueaveraged over many cycles. And fourth, no liquid droplets were observed atnear-idling conditions. The effects of other gases, such as CO, CO2 andH2O,can be neglected.

Flame propagation through concentration gradient

The experiment was carried out in homogeneous propane-air mixture and in several concentration gradient of mixture. Igniter is put on the upper side of the combustion chamber. In concentration gradient experiment, mixture was ignited from lean side. An experimental study was conducted in a combustion chamber. The combustion chamber has glass windows for optical measurements at any side. For the measurement of distribution of fuel concentration, infrared absorption method using 3.39µm He-Ne laser was used, and for the observation of propagating flame, Schlieren method was employed. As a measurement result of flame propagation velocity and flammable limit, for a mixture of an identical local equivalence ratio, flame propagation velocity in concentration gradient is faster than that in homogeneous mixture, and rich flammable limit in concentration gradient shows a tendency to be higher than that in homogeneous mixture.

A quantitative study of the polarization states of a quasi-isotropic 3.39 μm He-Ne laser subject to weak optical feedback

We present an extensive experimental study of the polarization behaviour of a quasi-isotropic HenNe gas laser operating in a single-transverse, single-longitudinal mode at 3.39 μm, and subject to weak polarized optical feedback. We make a quantitative comparison of the experimental results with a vector extension of Lambis single-mode laser theory. We concern ourselves with both the qualitative and quantitative aspects of instabilities and the resulting hysteresis loops in the polarization state. In particular, the location of the instabilities and the width of the hysteresis loops within the emission line are examined as a function of the experimental control parameters. The relationship between these instability scenarios and how the system moves catastrophically from one kind of hysteresis loop to another is illustrated. Specifically, we show that the polarization behaviour of the laser is controllable by means of the weak polarized feedback from optical components external to the cavity. The importance of the strength, orientation and phase of the feedback is clearly demonstrated. Resume : Nous prOsentons les rOsultats de liOtude expOrimentale complte diun laser HenNe quasi-isotropique opOrant en mode transversalement et longitudinalement simple ‡ 3,39 μ me t soumis ‡ une faible contre-rOaction optique polarisOe. Nous comparons quantitativement les rOsultats expOrimentaux avec ceux diune extension vectorielle de la thOorie de Lamb pour un laser opOrant en mode simple. Nous nous concentrons sur les aspects qualitatifs et quantitatifs des instabilitOs et sur les boucles dihystOrOsis qui en rOsultent dans liOtat de polarisation. Nous examinons en particulier la localisation des instabilitOs et la largeur des boucles dihystOrOsis dans la raie diOmission en fonction des paramtres expOrimentaux de contrUle. Nous illustrons la relation entre les intabilitOs et les sauts catastrophiques diun type de boucle dihystOrOsis ‡ liautre. SpOcifiquement, nous montrons que la polarisation du laser peut Œtre controlOe par une faible contre-rOaction polarisOe provenant des composantes ‡ liextOrieur de la cavitO. Les facteurs comme liamplitude, liorientation et la phase de la contre-rOaction sont clairement mis en Ovidence. (Traduit par la rOdaction)

A quantitative study of the polarization states of a quasi-isotropic 3.39 μm He-Ne laser subject to weak optical feedback

A quantitative study of the polarization states of a quasi-isotropic 3.39 μm He-Ne laser subject to weak optical feedback

Further Study on Temperature, Density, and Perturber Dependences of Absorption of 3.39 µm He-Ne Laser by Methane

In order to supplement the information on the perturber dependence of absorption at 3.39 µm of the He–Ne laser by methane, the decadic molar extinction coefficients of methane diluted with helium, hydrogen and carbon dioxide have been measured. The broadening data S γl( CH4–X)/ S γl( CH4–Air) and βl( CH4–X) for He, H2 and CO2, which are available in a wide range of temperature (300–1000 K), are proposed.

Measurement of the spontaneous emission factor of a 3.39 μm HeNe laser

The spontaneous emission factor N sp = N 2 (N 2 − N 1) of a 3.39 μm HeNe laser is determined from spontaneous emission light radiated from the side of the gain tube. N sp is shown to depend linearly on the intra-cavity optical intensity. This linear power dependence of N sp will give rise to a power-independent contribution to the quantum-limited spectral linewidth of the laser. We predict that at an output power of 190 μW this contribution will already make up half of the fundamental laser linewidth.

Short wavelength interferometer for ITER

There is a need for a real time, reliable density measurement compatible with the restricted access and radiation environment on International Thermonuclear Experimental Reactor (ITER). Due to the large plasma path length, high density and field, refraction, and Faraday rotation effects makes the use of contemporary long wavelength (≳50 μm) interferometers impractical. In this paper we consider the design of a short wavelength vibration compensated interferometer which allows operation without a prohibitively large vibration isolated structure and permits the optics to be conveniently mounted directly in or on the tokamak. A density interferometer design for ITER incorporating a 10.6 μm CO2 interferometer with vibration compensation provided by a 3.39 μm HeNe laser is discussed. The proposed interferometer design requires only a small intrusion into the ITER tokamak without a large support structure, refraction and Faraday rotation problems are avoided, and it provides a density resolution of at least 0.5%. Results are presented from an interferometer installed on the DIII-D tokamak incorporating essential elements of the proposed ITER design including 10.6 and 3.39 μm lasers, a retroreflector mounted on the vacuum wall of the DIII-D tokamak and real-time density feedback control. In this paper we consider a short wavelength interferometer design that incorporates vibration compensation for use on ITER. Our primary concern is to develop an interferometer design that will produce a reliable real time density monitor. We use the ITER conceptual design activity report as the basis of the design.

A Study on Concentration Field of Unsteady Gaseous Fuel Jet. Axisymmetric Turbulent Free Methane Jet.

Fuel gas injection is used for gas diesel engines. It is very important to investigate the behaviour of the unsteady jet. In this study, the concentration field of a suddenly started cold methane gas jet into still air was nonintrusively measured by the infrared absorption method with a 3.39μm He-Ne laser. Furthermome, the equations of mass, momentum, energy, species (methane and air) and the k-ε turbulence model were solved numerically. The concentration field was obtained and compared with the experimental results. As a result, it was found that the global trends of the jet, that is to say, penetration and averaged concentration, are predicted well, though the unsteady concentration near the jet axis is not predicted because the turbulence model is based on the time-averaged one.

Verification of Revised Water Vapour Correction to the Index of Refraction of Air

The Edlén equation has become the standard method of relating the index of refraction of air to the air temperature, pressure and humidity. The recent suggestion for improvements in the humidity dependence by Birch and Downs has been verified at the 0,633 μm He-Ne laser wavelength using the line scale interferometer at the National Institute of Standards and Technology (NIST).

High temperature absorption of the 3.39 μm He-Ne Laser line by Methane

The absorptivity of methane diluted in N 2 for the 3.39 μm laser line has been measured in the 290–800 K temperature range. Line-by-line calculations are in good agreement with the experimental data. Tabulations of the temperature dependence of the absorption are given for the 300–2000 K range.

Polarization four-wave mixing in the long 3.39 μm HeNe laser

We study experimentally and theoretically a special kind of the DFWM process: polarization mixing occurring in the interaction of collinearly propagating waves inside the long lasing medium of the HeNe laser on the 3.39 μm line under low-quality cavity conditions. The propagation of all waves and the competition between them are taken into account in our description.

Study of intracavity absorption and laser behavior for C2H4, C2H6, CH3F, CH3Cl, and CH4/N2 by photoacoustic resonance spectroscopy

The first radial mode of a cylindrical resonator was excited in extracavity and intracavity configurations employing a modulated 3.39 μm HeNe laser. The resonance curves were measured as a function of pressure by a computer-controlled method and fitted to Lorentzian profiles. Measurements were performed for C2H4, CH3Cl, CH3F, C2H6, and CH4, where the optical absorption coefficient determined by transmission experiments increases from C2 H4 to CH4 . From the signal strengths and the Q factors of the resonances the so-called photoacoustic signal (PAS) was determined and compared with theory. Good agreement between theory and experiment was observed for all extracavity measurements and in the case of intracavity experiments with low optical losses in the laser resonator. In order to describe the large discrepancies between the experimentally determined PAS and the existing theory for high losses, improved models were developed, which are based on an inhomogeneous distribution of laser power in the optical cavity. Deviations from these models were found near threshold. The PAS observed above threshold is attributed to amplified spontaneous emission.

Optical probing of magnetostatic forward volume waves in thin film yttrium-iron-garnet

An optical probe system has been developed that uses magneto-optic effects to examine the microwave magnetization of microwave magnetostatic waves propagating in thin ferrite films. The optical probe uses light from a 45 mW, 1.15 μm He-Ne laser which is focused upon a ferrite for localized probing. An effective spatial resolution of 100 μm was achieved with the optical probe. Experiments to examine linear and nonlinear magnetostatic forward volume waves (MSFVW) were conducted with the probe. MSFVW, with microwave frequency from 1 to 2 GHz, were launched in the [21̄1̄] direction of a thin film of liquid-phase-epitaxy (LPE) yttrium-iron-garnet (YIG). The LPE-YIG thin film was 47.4 μm thick, and deposited on a 1-in. disk of gadolinium-gallium-garnet with the [111] direction perpendicular to the surface of the disk. The nonlinear microwave MSFVW effects were characterized by a MSFVW power saturation and then a decline as input power to the MSFVW was increased. Localized optical probing of nonlinear effects, along the propagation path of the MSFVW, showed that a monotonic increase in MSFVW modulation of light with increasing microwave input power does not always occur. Optical probing of linear MSFVW examined the evolution of a MSFVW profile, transverse to the phase-propagation direction, as the MSFVW traveled from its launching antenna.

Intracavity photoacoustic resonance spectroscopy of C2H4

Intracavity and extracavity photoacoustic resonance experiments have been performed for C2H4, using a cylindrical acoustic resonator and a 3.39 μm HeNe laser as a light source. The pressure dependence of the photoacoustic signal of the first radial mode excited in the acoustic resonator was studied as a function of C2H4 pressure. It is shown that theory yields a reasonable description of the experimental results taking into account the effective laser power.

Examination of magnetostatic waves by new optical and induction probes

New optical and induction probes have been developed and used to investigate microwave (1–4 GHz) magnetostatic waves (MSW) propagating in yttrium iron garnet (YIG) thin films (5–50 μm). The optical probe uses the magnetooptic properties of YIG, and light from a 45 mW, 1.15 μm HeNe laser, to examine rfmagnetization of MSW. Focused light for localized probing has achieved a spatial resolution of 100 μm. The induction probe senses the rf magnetic field, which fringes from the surface of YIG thin films, with metal loops of either gold wire wrapped around a plastic support or aluminum photolithographically fabricated on glass. The highest spatial resolution was attained with 45μm aluminum loops. The optical probe has been used to examine the amplitude of linear and nonlinear forward volume waves (MSFVW). Nonlinear effects are characterized by MSFVW saturation and then a decline as input power to the wave increased. Localized probing of nonlinear properties showed, that over small regions, a monotonic increase of light modulation with increasing microwave input power to MSFVW does not always occur. MSFVW in the linear regime were studied for evolution of the amplitude profile as it propagated from the launching antenna. Magnetostatic surface (MSSW) and backward volume (MSBVW) waves have been explored with the induction probe for amplitude and dispersion relation. In a uniform bias field, an apparent form of spatial focusing was exhibited by MSSW. Direct measure of wavelengths of MSSW and MSBVW gave the dispersion relations.

The refractivities of water vapour for CO 2 laser lines

The refractivities of water vapour in the 10 μm region at temperatures near 20°C are measured with an accuracy of 1% using a 10.6 μm CO 2/0.63 μm He-Ne laser interferometer with a 2 m long vacuum cell. The measured refractivities are 30% less than the value calculated by extrapolating the dispersion equation for water vapour in the visible region. From this result, the CO 2 laser is found to be useful as a light source for a three-wavelength laser ranging system of correcting for the air refractivity in the path.

Study of relaxation and dissipation processes by photoacoustic detection of laser-excited acoustic modes

Abstract Photoacoustic resonance experiments have been performed for CH 4 and CH 3 F. The first radial mode of a cylindrical cavity was excited using the chopped beam of a 3.39 μm He-Ne laser. The pressure dependence of the resonance frequency and half-width of the acoustic resonances was determined. The frequency dispersion and peak broadening due to vibrational relaxation were obtained by calculating the contribution of other dissipation processes and intermolecular forces. The agreement between theory and experiment indicates an accuracy of a few percent in the description of the resonator processes.

FM eliminated CH<inf>4</inf>locked frequency stabilization of 3.39 µm He-Ne laser in dual feedback control

The frequency of the 3.39 μm He-Ne laser was locked to the CH <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> saturated absorption line by means of integral-proportional feedback control, i.e., dual feedback control. The frequency modulation was applied by a vibrating mirror placed outside a laser cavity, obtaining a modulation-free laser beam with a stabilized frequency. The long-term stability achieved under integral feedback control was about <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\pm1.1 \times 10^{-11}</tex> , which was further improved to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\pm 1.35 \times 10^{-12}</tex> under dual feedback control. The Allan variance measured by the photomixing technique was <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.77 \times 10^{-12}</tex> at an average time 100 s.