Final answer:
The physics behind a non-zero beam waist in a Gaussian beam involves the diffraction of light as it passes through an aperture or optical system. The beam waist size is determined by the wavelength of the light and the focusing properties of the optical system.
Step-by-step explanation:
In Gaussian beam physics, the beam waist refers to the minimum size of the beam. In a non-zero beam waist, the beam is not perfectly focused and has a finite size at some point along its propagation axis.
This is due to the diffraction of light as it passes through an aperture or optical system.
The physics behind a non-zero beam waist in a Gaussian beam can be explained using the principles of wave optics. The beam waist size is determined by the wavelength of the light and the focusing properties of the optical system.
As the beam propagates, it spreads out due to diffraction, causing it to have a finite size at different points along its path.
For example, when a laser beam passes through a lens, the lens focuses the beam to a point called the focus point.
However, due to diffraction, the beam cannot be perfectly focused to a point and instead has a minimum size at the focus point, which is the beam waist.