M2 or Beam Quality factor is a dimensionless parameter that characterizes the degree of imperfection of a real-world laser beam. The lower the value of M2 , the more tightly the beam can be focused to a small spot.
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Availability date: 08/25/2016
M2 or Beam Quality factor is a dimensionless parameter that characterizes the degree of imperfection of a real-world laser beam. The lower the value of M2 , the more tightly the beam can be focused to a small spot. A perfect TEM00 beam has M2 = 1. No laser beams are ‘perfect’. Limitations of the laser cavity, the lasing medium, and/or the output/ancillary optics, means that most beams are not the diffraction-limited, Gaussian profile, pure TEM00 mode described in textbooks. Complex beams contain multiple mode contributions that increase M2. Even a ‘good’ laboratory HeNe laser has an M2 of around 1.05 to 1.2, rather than the 1.0 of a ‘perfect’ TEM00 beam.
At its simplest M2 may defined as: The ratio of the divergence of the actual beam, to that of a theoretical, diffraction-limited beam with the same waist diameter M2 = (Θ/θ) where Θ is the measured, far-field, full-angle divergence of the actual beam, and θ is the theoretical far-field divergence of a ‘perfect’ TEM00 Gaussian beam which has the same waist diameter as the measured beam.
DataRay offers both imaging camera and slit scanning systems to measure M2, divergence, beam profile, beam position, Raleigh range, etc.
The ISO 11146 standard requires measurement of the second moment beam diameter in multiple planes (≥5) about the beamwaist and multiple planes (≥5) in the far field. In most circumstances this requires a single plane beam profiler moved along the propagation axis by a z stage. DataRay’s modular based systems offers users the ultimate flexibility in M2 measurement. A spreadsheet supports selection of the optimal M2 measurement configuration: Camera based or slit scan based system, lens selection, 50 or 200 mm long translation stage: http://www.dataray.com/assets/xls/Lens_choice_for_M2_measurement2.xlsm
M2DU-50 and -200 Stages
The BeamMap2™ is a high resolution (0.1 µm) patented, multiple z plane XYZΘθ measurement system that gives realtime measurement of M2, alignment, divergence, and beamwaist position and dimensions. BeamMap2 has two versions covers focused beams with slit plane separation d options of 50, 100, 250, 500 or 750 µm. The ColliMate™ version covers close-to-collimated beams and has a plane spacing of 5 mm.