The Transient Grating (TG) is a type of Four Wave mixing technique, on which two high power laser pulses, interfere inside the sample producing a periodic spatial modulation of the index of refraction. This modulation can be probed with a third pulse, continuous or pulsed, which is diffracted by the pump induced grating. The measurements of the scattered beam intensity gives information on the relaxation of the grating, and so on the relaxation of the excited mode. Depending on the type of probe, a dynamical range from 300 fs to hundreds of µs can be covered, allowing measurements on acoustic, magnetic, structural and thermal degrees of freedom.

More information about the technique HERE.