Quantifying The Quality Of A Laser Beam With The Beam Parameter Product And The M2 Factor

All laser beams diverge. Their rays slowly spread out as they travel, diluting the laser’s power. This happens because of diffraction, a fundamental – and unavoidable – property of light.

We cannot completely eliminate divergence. The best we can hope for is a beam with the smallest divergence allowed by the laws of diffraction. Such a beam is said to be diffraction-limited. Beams with a Gaussian beam profile are diffraction-limited. Beam quality quantifies how close a laser is to this ideal diffraction-limited Gaussian beam.