MIR-difference-frequency laser spectrometer for CO detection in combustions

Two continuous-wave (cw) single mode diode-lasers (Toshiba TOLD 9150 and Sharp LT024MDO) are applied as pump and signal sources to obtain difference-frequency generation (DFG) in the mid-infrared (MIR) region by using an AgGas, crystal with a length of 30 mm for 90° type I phase-matching. Tuneable MIR laser radiation around 5 um is obtained with an output power in the order of hundred nW while the diode lasers are operated at 20 and 30 mW around their centre wavelengths 789 and 681 nm, respectively. To demonstrate the applicability of this MIR-DFG laser spectrometer we recorded the absorption spectrum of CO for the P(21) rotational line at 2055.4 cm in a 10 cm long cell and in the flame of a McKenna burner in order to estimate the self-broadening coefficient of CO, the collisionalbroadening of CO with CO2, and the CO concentration distribution in the flame