Laser beam quality

The beam quality, and beam quality, called Strahlpropagations or K - factor is a dimensionless figure of merit of laser radiation.

Basically, it says something about how well a laser beam can be focused and how fast he is in the spread relative to its diameter widens ( divergence, beam parameter product ).

K is the beam quality of the reciprocal value of the beam quality factor M2 and is thus at the angle of divergence of an ideal Gaussian beam in comparison to the angle of divergence of a real laser beam of the same diameter at the beam waist:

• Applies for an ideal laser beam ( fundamental mode TEM 00)
• In a real laser beam

A real laser beam is so bad by a lens or focusing optics (eg a concave mirror ) focusable laser beam as an ideal. This is reflected by the fact that in real rays only one area ( focal spot ) forms of a specific size in a certain distance can not be less. That the cross-section of an actual laser beam - and a focused - is always greater than zero. This is due to the finite wavelength of the radiation and the fact that most real laser beams do not have the ideal power distribution, ie their performance does not take the edge of the beam on all sides evenly. This is due to transverse oscillation modes in the laser cavity, which leads to power peaks and troughs in the jet, which are also directional deviations.

The divergence of a laser beam, i.e. the divergence of the beam during its propagation ( beam propagation ) can be described by the numerical aperture or angle information. Due to the resonator, the angle may be different in the two spatial directions, resulting in that the height and diameter or width of the focal spot are different. This is especially the case with laser diodes and diode lasers.

For example, to return them in a processing machine, a large beam path in air with no great divergence of a laser beam must have a low divergence.

Both the divergence and the focusing ability can be improved by a beam expander (see telescope ) having an arrangement composed of two lenses or mirrors the cross-section of the beam is increased in favor of its parallelism. However, then larger and more accurate focusing lenses and mirrors are required.