Lidar thermometry using two-line atomic fluorescence

In this work, Scheimpflug lidar has been combined with the thermometric technique two-line atomic fluorescence, to carry out stand-off, spatially resolved temperature measurements. Indium atoms were seeded into a modified Perkin-Elmer-burner and two tunable single-mode diode lasers with their wavelengths tuned to 410.17 and 451.12 nm were used to excite the seeded atoms. The fluorescence signal was collected using both a line-scan detector and a two-dimensional intensified CCD camera. One-dimensional flame temperature profiles were measured at different heights above a porous-plug burner, located at a distance of 1.5 m from the lidar system. The technique was also used to demonstrate two-dimensional temperature measurements in the same flame. The accuracy of the measured temperature was found to be limited mainly by uncertainty in the spectral overlap between the laser emission and the indium atom absorption spectrum as well as uncertainty in laser power measurements. With the constraint that indium can be introduced into the measurement volume, it is anticipated that the developed measurement concept could constitute a valuable tool, allowing in situ spatially resolved thermometry in intractable industrial applications, sufferings from limited optical access, thus requiring remote single-optical-port sensing.

Vapor phase tri-methyl-indium seeding system suitable for high temperature spectroscopy and thermometry

Tri-methyl-indium (TMI) is used as an indium transport molecule to introduce indium atoms to reactive hot gas flows/combustion environments for spectroscopic diagnostics. A seeding system was constructed to allow the addition of an inert TMI laden carrier gas into an air/fuel mixture burning consequently on a burner. The amount of the seeded TMI in the carrier gas can be readily varied by controlling the vapor pressure through the temperature of the container. The seeding process was calibrated using the fluorescent emission intensity from the indium 6(2)S1/2 → 5(2)P1/2 and 6(2)S1/2 → 5(2)P3/2 transitions as a function of the calculated TMI seeding concentration over a range of 2-45 ppm. The response was found to be linear over the range 3-22.5 ppm; at concentrations above 25 ppm there is a loss of linearity attributable to self-absorption or loss of saturation of TMI vapor pressure in the carrier gas flow. When TMI was introduced into a post-combustion environment via an inert carrier gas, molecular transition from InH and InOH radicals were observed in the flame emission spectrum. Combined laser-induced fluorescence and absorption spectroscopy were applied to detect indium atoms in the TMI seeded flame and the measured atomic indium concentration was found to be at the ppm level. This method of seeding organometallic vapor like TMI to a reactive gas flow demonstrates the feasibility for quantitative spectroscopic investigations that may be applicable in various fields, e.g., chemical vapor deposition applications or temperature measurement in flames with two-line atomic fluorescence.