Nonlinear spectroscopy.
Although nonlinear spectroscopy evolved slowly in its initial stages, it is now becoming an important new branch of atomic and molecular spectroscopy. A variety of phenomena are being observed for the first time, either in steady state or in transient behavior. In a sense, the methods of microwave and nuclear magnetic resonance spectroscopy are now being reproduced in the optical region, and with the same precision and detail.
D007834:Lasers; D009682:Magnetic Resonance Spectroscopy; D008433:Mathematics; D008697:Methane / Q000032:analysis; D013057:Spectrum Analysis
D008697:Methane