Transient absorption spectroscopy is one the most popular methods to study photochemistry and photophysics. This technique allows observation of dynamics in electronic excited states after photoexcitation over a wide range timescales, from femtosecond millisecond timescales. The probed relaxation involve multiple channels competition, such as internal conversion, intersystem crossing, fluoresce...

A recently developed distributed feedback quantum cascade laser (QCL) capable of thermoelectric-cooled (TEC) continuous-wave (cw) operation and emitting at ∼ 9 μm is used to perform laser chemical sensing by tunable infrared spectroscopy. A quasi-continuous-wave mode of operation relying on long current pulses (∼ 5 Hz, ∼ 50% duty cycle) is utilized rather than pure cw operation in order to exte...