Intrapulse quantum cascade laser spectroscopy: pressure induced line broadening and shifting in the ν 6 band of formaldehyde

Abstract

A rapidly swept quantum cascade laser (QCL) has been used to probe a small region of the ν 6 band of formaldehyde around 8 μm by direct absorption spectroscopy. Two of the strongest transitions accessible within the operating region of the QCL are assigned as (1,1,1)←(2,0,2) and (10,1,9)←(9,2,8). In this paper, we report pressure-induced broadening and shift coefficients for these transitions with a variety of gases (He, Ne, Kr, Ar, N2, O2, and CO2). The pressure broadening coefficient measurements are shown (in some cases) to be chirp rate dependent, even under conditions where rapid passage effects are negligible, highlighting the marked difference that can occur between studies with rapidly swept fields and those employing conventional diode laser devices.