Divergence Measurement

Beam divergence is defined in the far-field where the beam divergence is constant, but when measuring beam divergence, it's necessary to determine if the measurements will made in the far-field or near-field. For highly diverging beams, the divergence measurement can be made directly in the far-field, but for lower divergence or collimated beams, the beam waist and far-field may be inaccessible or difficult to define.

Measuring from the Far-field

If measuring from the far-field (greater than four Rayleigh ranges from the beam waist), consider the following solutions:

A BeamMap2 (with appropriate plane spacing) in divergence mode to measure divergence directly in real-time for beam divergences between 1 & 350 mrad (0.02° to 20°). This will work well for CW/quasi-CW beams.
A Beam'R2 or beam profiling camera on a translation stage to measure the beam diameter along several Z-positions to measure divergence directly.
A Beam'R2 or beam profiling camera to measure beam diameter at a known distance Z from the source to measure divergence directly with the assumption of a point source.

Measuring from the Near-field

If measuring from the near-field, consider using a BeamMap2 in M² mode with the beam waist at the zero plane. The first three planes are in the near-field and the last is in the far-field, providing real-time M² and divergence measurements.