Probing ultrafast temperature changes of aqueous solutions with coherent terahertz pulses

We introduce an infrared pump–terahertz probe technique to measure the thermalization dynamics of aqueous solutions with a time resolution <200  fs. This technique makes use of the sensitivity of the terahertz absorption to the temperature of the hydrogen bond network. The thermalization dynamics of different aqueous solutions are measured and compared to the dynamics inferred from ultrafast infrared pump–infrared probe measurements on the intramolecular stretch vibration of water. This technique can shed new light on important aspects of energy transfer and heat dynamics and is applicable to a wide range of systems.