DeepLightSeekDefinition:
A beam whose divergence angle reaches the theoretically achievable minimum for a given beam waist radius.
A beam whose divergence angle reaches the theoretically achievable minimum for a given beam waist radius.
For a given wavelength, a laser beam is said to be diffraction-limited if it can be focused to a very small spot, implying its beam quality is ideal. More precisely, for a fixed beam waist radius, the beam divergence after focusing by a curved mirror is minimized.
Its exact meaning also depends on the definitions of beam radius and beam divergence. If the second-order moments are used in these definitions, a Gaussian beam achieves the minimum value for the beam parameter product. This occurs when the intensity profile is Gaussian and the phase front at the beam waist is flat.
Lasers operating in a single transverse resonator mode can produce diffraction-limited output, as "single mode" typically refers to the fundamental mode of the resonator, which generally has a shape close to a Gaussian profile. Beam distortions within the gain medium can deform the fundamental mode or cause multi-mode oscillation, thereby degrading the beam quality.
The beam quality of a laser depends not only on the strength of intra-cavity distortions but also on the details of the resonator design; optimizing the resonator design is crucial for achieving diffraction-limited output.
For a given optical power, a diffraction-limited beam possesses the highest brightness.
