Optical characteristics of triethylamine in the spectral range of a CO2 laser

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 55, No. 2, pp. 258–260, August, 1991.     

Velocity measurement inside a motored internal combustion engine using three-component laser Doppler anemometry

A three-component laser Doppler anemometry (LDA) system has been employed to investigate the structure of the flow inside the cylinder of a motored internal combustion engine. This model engine was reasonably representative of a typical, single cylinder, spark ignition engine although it did not permit firing. It was equipped with overhead valve gear and optical access was provided in the top and side walls of the cylinder. A principal objective was to study the influence of the inlet port design on the flow within the cylinder during the induction and compression strokes of the engine. Here, it can be noted that results obtained in an unfired engine are believed to be representative of the flow behaviour before combustion occurs in a fired engine (see P.O. Witze, Measurements of the spatial distribution and engine speed dependence of turbulent air motion in an i.c. engine, SAE Paper No. 770220, 1977; Witze, Sandia Laboratory Energy Report, SAND 79-8685, Sandia Laboratories, USA, 1979). Experimental data presented for an inclined inlet port configuration reveal the complex three-dimensional nature of the flow inside the model engine cylinder. Not surprisingly, the results also show that the inclined inlet port created flow conditions more favourable to mixing in the cylinder. Specifically, the inclined inlet flow was found to generate a region with a relatively high shear and strong recirculation zones in the cylinder. Inclining the inlet port also produced a more nearly homogeneous flow structure at top dead centre during the compression stroke. The paper identifies the special difficulties encountered in making the LDA measurements. The experimental findings are examined and the problems that arise in presenting time-varying three-dimensional data of this type are discussed. Finally, the future potential of this experimental approach is explored.     

Spectral photoconductivity of tellurium in the CO2 laser wavelength range

Infrared photoconductivity measurements on tellurium single crystals and evaporated films at 90 K yielded a maximum response at 0.126 ± 0.002 eV using a low power CO₂ laser. The frequency dependence of the response was slow and could not be interpreted as vast intervalence band transitions.     

Pyroelectric detection of a CO2 laser beam using organic copolymers

Pyroelectric detection of a CO₂ laser beam has been investigated by using organic copolymers such as VDF/TrFE- and VDCN/VAc copolymers, and compared with that of PVDF polymer. The voltage responsitiviesR _v are 40 mV/W for VDF/TrFE and 2 mV/W for VDCN/VAc at room temperature and at a chopping frequency of 200 Hz. (For comparison, the value of PVDF is 20 mV/W.) From the frequency dependence of the detected output, the electric time constant _E is evaluated to be about 6.4 ms and 2.6 ms for the former and latter copolymers with the detection area 3×3 mm², respectively. Some theoretical discussion is also given of the responsivity, frequency dependence and temperature dependence obtained.     

High precision materials processing using a novel Q-switched CO2 laser

Holes with diameters of about 400 µm have been laser trepanned in Ti6Al4V and carbon fibre reinforced polymer (CFRP) thin sheets with a thickness of 0.5 mm. A commercial CO₂ laser (SM1500E, FEHA LaserTec, Germany) and a novel Q-switched CO₂ laser (µ-storm, IAI, Netherlands) were used as radiation sources. Optical microscopy, scanning electron microscopy and replicas of the processed holes were used to investigate the influence of the CO₂ laser pulse parameters (e.g. pulse energy, duration and peak power) on the processing quality. It was shown that melt formation and high temperature oxidation reactions of Ti6Al4V during thermal laser processing were reduced significantly by using short and high intense Q-switched CO₂ laser pulses. During trepanning of CFRP heat affected zones resulting from the extremely different thermal properties (melting and vaporisation temperature, heat conduction) of the reinforcing carbon fibres and the polymer matrix were reduced significantly by using the Q-switched CO₂ laser. The results demonstrate that Ti6Al4V and CFRP can be processed very precisely with CO₂ laser radiation and air as processing gas without melt formation and thermal damage.     

管状预电离可调谐TEA CO2激光器.

研制了一种新型的预电离结构--管状预电离器,并将其应用于可调谐TEA CO2激光器.利用光栅选线方案,采用光栅谐振腔,实现了激光的调谐输出.在输出耦合率为50%、气压为40 kPa的条件下,10P(20),10R(20),9P(20),9R(20)四条谱线获得的最高电光转换效率,分别为9.5%,9.7%,9.8%,9....     

An acousto-optic modulator for a CO2 laser rangefinder using heterodyne detection

The ability to superimpose arbitrary modulation waveforms on a CW laser beam makes the acoustooptic modulator suitable for an important task: to apply modern microwave radar electronic signalprocessing and signal-generation techniques to heterodyne CO₂ laser radar systems. The fundamental constraints on modulator design are first presented graphically in a novel treatment. The fabrication of 50–70 MHz germanium-lithium niobate modulators for a CO₂ laser radar is then described. Experimental measurements of efficiency (about 4% per electrical watt transducer input power) and rise time ( 40 ns) are finally presented.     

The laser pulse from a rf waveguide CO2 laser

The behaviour of a rf-excited waveguide CO₂ laser in the pulse regime is studied experimentally. The specific time sections of the pulse have been defined and described in detail. The output pulse evolution versus input power, pressure of the laser mixture, output coupling, repetition frequency and pulse width has been investigated. The spectral content of the pulse has been analysed. A model explaining the effect of laser tuning during the pulse duration is given. The ultrahigh pulse (UHP), defined as the pulse for which the bulge effect occurs, is predicted. Received: 22 October 2002 / Revised version: 13 January 2003 / Published online: 26 March 2003 RID="*" ID="*"Corresponding author. Fax: +48-71/3203-189, E-mail: eda@zr.ita.pwr.wroc.pl     

Localized velocity and turbulence measurement in turbulent swirling flows using laser Doppler anemometry

Turbulent swirling water flow in a pipe has complex velocity distributions with special measurement problems tor experimental work. Some of these problems are described in the introduction to the paper along with comments on the basic characteristics of turbulent swirling flow.The form of laser Doppler anemometer used is briefly noted, with some special optical features developed to suit this class of flow. Experience during some two years of comprehensive experimentation is then outlined, including comment on the data processing system.Results from experiments with tangentially injected water flow in 50 mm bore pipes up to 60 diameters long are reported, with local measurements of mean velocity and turbulence intensity. The variation of mean velocity components and turbulence intensity with radius and distance along the pipe are discussed with a few comparisons of results obtained from other experimental techniques, e.g. pitot-static probe and hot films.For the particular problem examined here it would have been difficult, if not impossible, to obtain the measurements using a technique other than laser anemometry.     

High-frequency pulsed laser diode application in multi-component laser Doppler anemometry

High-frequency pulsed AlGaAs semiconductor lasers with pulse durations in the nanosecond range show a distinctive enhancement of the time-averaged optical output power compared with continuous-wave mode operation. Hence, the signal-to-noise ratio is drastically increased in connection with fast Si-Avalanche photodetectors that show a maximum spectral sensitivity in the emission range of AlGaAs lasers. The emission behaviour and the application of sequential and phase- synchronized pulsed laser diodes in a multi-component laser Doppler anemometer with only one receiver, one signal processing chain and identical wavelength for all components, are outlined.     

Detection of ozone by differential absorption using CO2 laser

The differential absorption method with the conventional CO₂ laser is discussed for the detection and monitoring of ozone in ambient atmosphere. By using the P(14) line in the (00°1 to 02°0) and the R(16) line in the (00°1 to 10°0) band, the measurement of ozone was made in a field. As an experimental result, the minimum detectable concentration of 0.15 ppm was obtained with the system, and the concentration of 0.2 ppm was measured in a photo-chemical smog.     

Stabilization of a CO2 pump laser using external CH3OH stark-cell modulation

In order to stabilize the 118.8 μm CH₃OH laser output, frequency stabilization of the CW 9P(36) CO₂ laser pump is carried out using external CH₃OH Stark-cell modulation without internal frequency modulation. The CO₂ laser output power around the CH₃OH absorption center is stabilized to within ±1.0% for 60 min. The frequency stability of the CO₂ laser is estimated to be within ±1.4 MHz for 60 min, assuming the output fluctuation to be caused by this frequency fluctuation. As a result of the CO₂ pump laser stabilization, an output power stability of about ± 1.0% for 30 min is obtained for the 118.8 μm CH₃OH laser.     

Air-breathing mode a long-pulse laser propulsion with TE CO2 laser

Air-breathing mode laser propulsion experiment with a long-pulse transversely excited （TE） CO2 laser is carried out, and its ignition problem is solved with the ignition needle of lightcraft. Owing to the ignition needle, an order of magnitude reduction in the ignition threshold is demonstrated. The result is compared with previous study. The momentum coupling coefficient is also measured in the experiment and its dependence upon laser pulse energy （6 14 J） and pulse width （20, 32, and 40 μs） is discussed.     

Kinetic modelling of a fast-axial-flow CO2 laser

A six-temperature Boltzmann-equilibrium kinetics model has been developed for simulating the performance of fast-axial-flow, longitudinal-discharge CO₂ lasers. The model includes the effects of electrical excitation, VV and VT collisional relaxation, thermal energy transport, distributed optical losses, and coherent radiation extraction for a CO₂/N₂/He/H₂O mixture. Numerical predictions from the model are compared with experimental results obtained with a 2.5 kW device.