Aug 5 2014
M2value is a parameter used to determine the beam quality of the laser beam. M2 may be derived by dividing the beam parameter product (BPP) of an actual optic beam by the BPP of an ideal Gaussian beam at the same wavelength.
The M2value is also referred to as the beam quality factor, since its value is representative of the deviation of the actual beam from the ideal beam. Since it is a ratio, it is a quantity without any physical units.
Most lasers are operated such that the lasing action occurs in the transverse mode at which it is most intense. In the real scenario, the asymmetries of mirrors and other optical components cause the beam to appear as a minimum spot size. The minimum spot size is a factor “M” times larger than the spot size of a Gaussian beam at the same wavelength. The divergence angle of the real beam will be M times larger than that of a Gaussian beam.
Real laser beams are multi-mode or mixed mode, the multimode beam has M2 times the beam area but 1/M2 less intensity than the Gaussian beam. Determination of the M2value is important for a number of applications and is widely used as an industry specification.
The degree of beam divergence is determined using the M2value. This value is important in the field of fiber optic communications. Most of the laser machine shops operate on the principle that value of M2 increases with the power of laser.
References