Beam profiling quantifies light sources

Applications ranging from optical telecommunications to bar-code scanning require precise characterization of light beams. Ideally, you could characterize a beam with a single number that defined its width or diameter. Unfortunately, beams—even laser beams—don't have sharp edges, and

For the Gaussian power distribution that beams typically exhibit, you can specify the "1/e2 " diameter—the points at which beam power density measures 13.5% of maximum. Or, you can specify the full-width half-maximum (FWHM) level—at which power density is one-half the maximum level. By measuring beam diameter as a function of displacement from the beam's waist—or point of minimum diameter—you can calculate divergence and the beam width at any point.

Traditionally, engineers have used phosphors, Plexiglas blocks, burn papers, or photographic film to measure beam widths, but such approaches require subjective evaluation. In contrast, beam profilers that combine scanning apertures with photodetectors or that employ CCD array cameras provide numerical outputs. So, too, do goniometric radiometers, which make measurements by rotating detectors through the divergent beams from components such as edge-emitting laser diodes and some vertical-cavity surface-emitting lasers (VCSELs).

Beam profilers such as the NanoScan from Photon (San Jose) can help automate applications such as the collimation of fiber-lens pairs in optical communications equipment. A multiaxis positioning stage in an automated collimation fixture can manipulate lens-to-fiber alignment while monitoring beam-profiler output; epoxy curing can complete the assembly process when the fixture achieves optimum alignment. To learn more about beam profiling, visit www.photon-inc.com/BeamProfiling.pdf .