DeepLightSeekdefinition:
The position with the smallest beam radius.
The waist of a laser beam refers to the point where the beam radius is the smallest in the direction of propagation. The beam radius at this location is called the waist radius.
The waist of Figure 1 refers to the area where the beam radius is the smallest.
Focusing through a lens with a larger numerical aperture can achieve a smaller waist radius. For non circular beams, the position of the beam waist varies for different tangential directions, which is called the astigmatic effect.
