Quantum-cascade laser – time-resolved IR spectroscopy
In this pump-probe technique a quantum-cascade laser (QCL) is used as a monochromatic measuring light. The sample is probed by the mid IR beam output either in transmission or an ATR configuration. After pulsed laser excitation the absorption changes of the sample are measured by sampling the signal of a high speed mercury cadmium telluride (MCT) detector. Because of the high brilliance of the QCL, an outstanding signal to noise ratio is achieved with only a few averages taken. Due to the direct approach of the technique, a single wavenumber kinetic can be measured over a broad time range of up to 10 decades, enabling the access to even very slow cyclic samples.