Time resolved spectroscopy of dynamics in mid infrared quantum cascade lasers below and above threshold

The spectral gain profile and modal gain coefficient can be measured by coupling a broadband mid infrared pulses generated by phase matched difference frequency mixing in a 30 mum thick GaSe crystal . This enables us to detect the transmitted light by coherent detection facilitating the electro optic effect in a crystal. The advantage of time resolved spectroscopy enables easy access to dynamic parameters of a InGaAs/AlInAs/InP QCL during operation even above threshold.