A DFG spectrometer at <f>3 μm</f> for high resolution molecular spectroscopy and trace gas detection

We report the realization and characterization of a spectrometer based on difference frequency generation using a periodically poled lithium niobate crystal. As signal and pump lasers we used a diode-pumped Nd–YAG laser (<f>λ=1.064 μm</f>) and an extended cavity semiconductor diode laser (<f>λ=0.785 μm</f>), respectively. The mid-infrared coherent radiation was produced at <f>3 μm</f> with a maximum power of about <f>160 nW</f> obtained with <f>340 mW</f> of signal and only <f>3.4 mW</f> of pump. That corresponds to an efficiency of <f>0.01%/W cm</f>, which is in good agreement with other data available in literature. The generated radiation around <f>3 μm</f> has allowed us to study fundamental absorption bands of molecules of great atmospheric and physical interest such as water vapor and the hydroxyl free radical. In this work we report preliminary spectroscopic results concerning the <f>ν1 541→652 H2O</f> line at <f>2.968 μm</f>. In particular, for this line we provide the first experimental estimation of self-, <f>N2</f>- and <f>O2</f>-broadening coefficients. [Copyright &y& Elsevier]