More accurate method
Sun recommends using the moving-diode method, which reduces a laser diode Gaussian beam to a geometric beam. Using this method, scientists move the diode in the direction of the fixed-beam axis. Only then can researchers use geometric optics to calculate measurements that are correct in magnitude and arithmetic sign.
Another method, the moving-profiler technique, will yield a measurement that is accurate to within a few percentage points. However, it requires intricate calculations that scientists tend to skip, leading to inaccuracies.
"It's a little surprising that no such research work had been published before [because] the existence and effects of laser diode astigmatism have been well known for many years to many people in the field of manufacturing and application of laser diodes," Sun said.
Experts advise end users to measure astigmatism after the diode is in place with all of its optics.
Users should "concentrate on measuring the beam where they need it. Don't try to back-calculate to the diode. That's where the rat's nest happens," and users get bogged down in calculations, said Lew Brown of Photon Inc., a Santa Clara, Calif.-based maker of measurement instruments.