chapter  24
22 Pages


Diode-laser sensors, based on absorption spectroscopy, oer new capabilities for

fast and accurate measurements of a variety of important parameters. These in-

clude gas temperature, velocity, species concentrations, mass ux, and thrust in

combustion systems. The sensors utilize tunable, narrow-linewidth, semiconduc-

tor diode-lasers as light sources. These lasers, which are presently available in the

wavelength range from 600 to 2000 nm, are robust, reasonably economical, and

are readily compatible with optical bers to facilitate measurements in remote

locations. Moreover, the semiconductor lasers have inherently high bandwidths

and thus may be rapidly tuned in wavelength over absorption features by simply

modulating the laser injection current, typically yielding complete measurements

in less than 1 ms. In addition, the outputs of multiple lasers can be easily com-

bined into a single ber (multiplexing) using o-the-shelf ber-optic components

to enable simultaneous absorption measurements at multiple wavelengths along

at Stanford University for measurements of important parameters in laboratory-

and industrial-scale gaseous owelds. For example, a mass ux sensor was

developed based on rapid measurements of O

absorption near 760 nm in super-

sonic owelds [1]; and a multiplexed sensor was developed for the simultaneous

measurement of various pollutants representing unburned hydrocarbons (CH



Cl) near 1.65 m [2].