You hit the sample with multiple, intense laser pulses (often femtosecond pulses). The fields are so strong that the molecule's response becomes nonproportional (
Shaul Mukamel's work provides a comprehensive framework for understanding nonlinear optical spectroscopy. His approach emphasizes the importance of coherence and the use of Liouville-von Neumann equations to describe the dynamics of molecular systems. You hit the sample with multiple, intense laser
Linear spectroscopy gives you a blurry 1D photo. Nonlinear spectroscopy gives you a . You hit the sample with multiple
In linear spectroscopy, the signal is a simple convolution of the pulse and the molecular response. In nonlinear spectroscopy, the signal is a convolution of the . You hit the sample with multiple, intense laser