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M2 Measurement Systems

Reference: DAT-M2DU-50/200

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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Franz Brandl
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+49 8153 405-71
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Product description

Why care about M-Squared?

  • It is the QA delivery or acceptance criterion on a laser or laser system.
  • You need to understand why a ‘focused’ laser spot diameter is larger than calculation predicted.
  • You are tasked with measuring M2, and/or somebody gave you a copy of the ISO 11146 standard.
  • Because M2 is an invariant property of a laser beam propagating through a perfect* optical system. M2 may therefore be used to describe the beam at any point in that optical system. (*The optical system neither distorts nor truncates the beam.)

M2 or Beam Quality factor

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. 

  • BeamR’2 and WinCamD profiling cameras on linear stages move through the beamwaist to perform ISO 11146 compliant measurements 
  • BeamMap2 gives real-time M2 using a patented multi-planed scanning system.

ISO 11146 Compliant, Single Plane Measurement Systems on a Moving Stage

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:

M2DU-50 and -200 Stages

  • Resolution < 1 μm
  • DataRay software controlled
  • RoHS and CE compliant

Real-time M2

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. 

Downloads - M2 Measurement Systems

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