We often are asked about measuring the power of widely diverging beams and how to do so.
First of all, Ophir has integrating sphere power meters designed for divergent beams of up to +/-40 degrees divergence. These are the 3A-IS and 3A-IS-IRG power meters. These power meters are primarily for low power beams of under 3W and for the spectral regions 420 – 1100nm and 800 – 1700nm.
In addition to this, our standard broadband thermal power meter coating is quite insensitive to beam angle of incidence. Shown below is a graph of the relative absorption of the coating vs. angle of incidence. From the information below, if a beam of cone angle of up to +/-40 degrees is incident on a thermal power meter with the BB coating, and then the reading will be 2% below that of a parallel beam. Furthermore, Ophir has thermal power meters with apertures of up to 65mm in diameter so all the radiation from a diverging beam can be captured with the appropriate aperture power meter.
You might also like to read: 3 Ways to Keep Track of Your Laser Beam’s Divergence