This results in the polarization response of the crystal to be shifted back in phase with the pump beam by reversing the nonlinear susceptibility.

The power for this comes from the two pump beams, which are depleted by the process.

Although, there is some indication of quantized vortices when the pump beam has orbital angular momentum.

Also, due to the conservation of energy, the two photons are always symmetrically located within the cones, relative to the pump beam.

A laser with a relatively high intensity is sent through the atomic vapor, known as the pump beam.

The stronger the pump beam, the wider and deeper the dips in the Gaussian Doppler-broadened absorption feature become.

The probe beam can be made of a reflection of the pump beam passed through neutral density filter to reduce its intensity.

The pump beam excites the molecule to a virtual state.

By increasing the probe path length, it becomes delayed with respect to the pump beam and arrives at a later time on the sample surface.

The pump beam heats the material and the probe beam is deflected.