Instrumentation for measuring fluorescence cross sections from airborne microsized particles.

An experimental instrument for measuring a laser-induced fluorescence spectrum from a single aerosol particle is described. As a demonstration of instrument capabilities, the results of monodisperse 4.7 microm sodium chloride particles doped with fluorescent riboflavin, produced with an inkjet aerosol generator, are presented. The fluorescence of the aerosol particles is excited in the wide range from 210 to 419 nm using a pulsed, tunable optical parametric oscillator laser. The maximum of the fluorescence emission of separately measured particles is detected at 560 nm. The dependence of the fluorescence on the excitation wavelength is studied and fluorescence cross sections are estimated. Agreement between the measured fluorescence data and the literature data for riboflavin is observed.

Atomic-hydrogen mapping in hot-filament chemical-vapor deposition.

Two-dimensional maps of the atomic-hydrogen concentration distribution were acquired with two-photon laser-induced fluorescence. The environment was a hot-filament chemical-vapor-deposition reactor used for polycrystalline diamond-film deposition. The maps were measured in situ under diamond-deposition conditions with variation of the growth parameters. The parameters investigated were filament temperature, input methane concentration, and total pressure.

Pyrometric sizing of high-temperature particles in flow reactors.

A pyrometric method was developed earlier for the simultaneous in situ measurement of the temperature and the size of combusting fuel particles in entrained flow reactors. The temperature measurement is based on two-color pyrometry and the particle sizing on the proportionality of the measured radiative flux and the cross-sectional area of a particle at a known temperature. This particle-sizing method needs a discrimination procedure to confirm that the detected particle is valid for particle sizing. We report on a novel method for particle discrimination based on coaxial reference optics. The new method has several advantages compared with the method presented earlier, including the measurement in turbulent flow fields.

High-temperature effects in fluorine-doped, fused synthetic silica fibers.

Effects caused by exposure of large-core, fluorine-doped, step-index silica optical fibers to high temperatures were studied experimentally in controlled laboratory conditions. A fiber was located partially inside a temperature-controlled electric tube furnace and irradiated from the end by a light source. The light source was either an incandescent halogen lamp or a blackbody radiator. The influence of fiber temperature on the angular distribution of the radiation in the fiber and the coupling and propagation of thermal radiation in the fiber was studied. With increasing temperature the profile of the angular distribution of the radiation was transformed irreversibly from a Chinese hat profile to a much flatter one. This effect was pronounced at 1000 degrees C and above. Radiation from the furnace was found to propagate in the fiber as an attenuating mode at temperatures above 800 degrees C. Most of the radiation exited the fiber at angles beyond but close to the acceptance angle. Calculations show that thermal self-radiation of the fiber is negligible. The physical explanations for these effects are discussed and practical conclusions are drawn.

Pyrometric measurement of the temperature and size of individual combusting fuel particles.

A two-color pyrometric technique was developed for the in situ simultaneous measurement of individual fuel-particle temperatures and sizes in a pressurized entrained flow reactor (PEFR). A method that requires only a single optical port was developed, and a specially designed optical probe was manufactured for the measurements at the PEFR. The fuel-particle temperature was obtained by applying two-color pyrometry. The particle size was determined from the same pyrometric signals. A discrimination method was developed to confirm that the detected particle was valid for particle sizing. Several series of measurements were made at a PEFR at different process conditions, and some typical results are shown.

Analysis of pollutant chemistry in combustion by in situ pulsed photoacoustic laser diagnostics.

A technique for gas analysis based on pulsed-laser-induced photoacoustic spectroscopy in the UV and the visible is presented. The laser-based technique and the associated analysis probe have been developed for the analysis of pollutant chemistry in fluidized beds and other combustion environments with limited or no optical access. The photoacoustic-absorption spectrum of the analyzed gas is measured in a test cell located at the end of a tubular probe. This test cell is subject to the prevailing temperature and pressure in the combustion process. The instrument response has been calibrated for N(2)O, NO, NO(2), NH(3), SO(2), and H(2)S at atmospheric pressure between 20 and 910 °C. The response of the probe was found to increase with pressure for N(2)O, NO, NH(3), and NO(2) up to 1.2 MPa pressure. The method and the probe have been used for detection and ranging of gas concentrations in a premixed methane flame. Some preliminary tests in a large 12-MW circulating bed boiler have also been done.