ATP: continuously variable attenuator for true laser profiles

摘要

Abstract: ment of the beam profile and/or beam width of a laser source is complicated by the fact that most detectors available are just too sensitive. Typical lasers measured in millijoules/cm$+2$/ must be attenuated to a few 10s of nanojoules/cm$+2$/. To maximize the photoreceptor's digitizer range and operate at a maximum signal-to-noise ratio, it is preferred that the input energy is controlled to just below the detector saturation point. The most common attenuation methods are either discrete in increment, narrow in wavelength range, or operate on a polarization principle that can produce erroneous results for many mixed-mode lasers. Metalized gradient pair attenuators suffer from nonlinear attenuation across the beam and/or multiple interference fringes. What is described here is a novel technique to continuously attenuate an incident laser beam over a ratio of 6300:1 or more (3.8 orders of magnitude). It can be adjusted to the nearest incremental transmission value of 0.005 (0.5 percent). It achieves this at near normal incidence, which is very important if the source contains polarization- dependent laser mode components. Photon, Inc.'s ATP attenuator package achieves this performance without interference fringes, bubbles, or stria and with a minimum of deflection or redirection. A broad wavelength performance also is achieved that ranges from 360 to 2,500-plus nanometers. ATP's primary application is with very sensitive CCD or vidicon array detectors that are capable of measuring beam sizes of a few hundred microns. ATP does this with virtually no root mean square wavefront errors. This device coupled with a high accuracy beam profiler will produce true accurate profiles and beam widths. !3