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2 µm room-temperature diode lasers for Co(2)-detection
2 µm raumtemperaturbetriebene Diodenlaser für die CO(2)-Detektion
We report on the detection of CO2 using diode lasers grown by low-pressure MOCVD on InP-substrate. Employing the InP substrate based GaInAsP material system and technology, well developed and established for fabrication of 1.3 mu m and 1.55 mu u semiconductor lasers for optical fiber communication, the long wavelength limit of this material system is explored. In order to match the CO2 absorption line around 2 mu m - detection limit at 2.004 mu m: 6.1 mu g/m3 (approx. 5 ppb) - the active region of the laser consists of compressively strained GaInAs quantum wells (QWs) and tensile strained GaInAs barriers. The CO2 absorption at 2 mu m can be covered by these devices which are manufactured using standard process technology and operate at room temperature. Increasing the heat sink temperature up to 310 K the emission wavelength of these devices can be tuned up to 2.04 mu m. Replacing the ternary barriers by quaternary GaInAsP the emission wavelength extends up to 2.09 mu m at aheat sink temperature of 330 K. In a first demonstration laser diodes with ternary barriers were applied to tunable diode laser absorption spectroscopy (TDLAS) of CO2 25 per cent CO2 in N2 was measured operating the devices at 287 K.