Dual wavelength light sources.
Boos-RT; Egan-WD; Elliott-RA; Defreeze-RK
Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, H0123031, 1985 Oct; :1-160
This report describes work done to develop a tunable, room- temperature diode laser source for a remote coal mine methanometer. A detailed evaluation showed that a broad area ingaas/inp injection laser operating at approximately 1,650 nm could be suitable for a differential absorption light detection and ranging measurement of methane if the spectral bandwidth could be reduced by a factor of approximately 400. Consequently, an external grating cavity was designed and fabricated to reduce the bandwidth of the injection lasers. The optical design of an off-axis parabolic mirror grating cavity was developed using geometric optics to determine the physical parameters for the external cavity that would produce the desired spectral bandwidth of 0.2 Cm-1. Apart from a smaller than desired methane absorption coefficient, the device met all specifications. The low methane absorption coefficient was attributed to a larger than desired source linewidth, which was measured to be two to three times larger than the design value. The unsatisfactory methane absorption coefficient of the external cavity diode laser source significantly detracts from its suitability for use in an instrument to remotely measure methane in coal mines.
Coal mining; Infrared radiation; Injection lasers; Light sources; Methane; Methanometer
CP; Final Contract Report
NTIS Accession No.
OFR 53-86; Contract-H0123031
Pittsburgh, PA: U.S. Department of the Interior, Bureau of Mines, RI/IC ####
Bethlehem Steel Corp