Mid-infrared quantum cascade laser spectroscopy probing of the kinetics of an atmospherically significant radical reaction, $$\hbox {CH}_{3}\hbox {O}_{2}+\hbox {NO}_{2}+\hbox {M}\rightarrow \hbox {CH}_{3}\hbox {O}_{2}\hbox {NO}_{2}+\hbox {M}$$ CH 3 O 2 + NO 2 + M → CH 3 O 2 NO 2 + M , in the gas phase

Broadband transient absorption spectroscopy using an incoherent white-light source as probe

Time-resolved spectroscopy and, in particular, transient absorption methods have been widely employed to study the dynamics of materials, usually achieving time resolution down to femtoseconds with measurement windows up to a few nanoseconds. Various techniques have been developed to extend the measurement duration up to milliseconds and beyond to permit probing slower dynamics. However, most of these either demand complicated and expensive equipment or do not provide broadband spectral coverage. This paper proposes a transient absorption technique in which an ultra-short pulse laser and a broadband incoherent continuous-wave light source are employed as pump and probe, respectively. Detection of the transient probe transmission is performed in a time-resolved fashion with a fast photodiode after a monochromator and the data is recorded with an oscilloscope. The time resolution is determined by the electronic bandwidth of the detection and acquisition devices and is ∼1 ns, with a measurement duration window of up to milliseconds and a spectral resolution of <2 nm covering from 0.4 to 2 µm. In addition, the setup can be employed to measure time- and spectrally-resolved photoluminescence.