Three key measurements were made: 1) a baseline measurement of the source beam using the 1/e2 measurement value, 2) a measurement calculation of the beam’s ellipticity (roundness), and 3) a calculation as to the laser source’s Gaussian, or Goodness of Fit value.
The analysis of this laser source was first conducted with the SP300 camera positioned at 1m from the source, without optics, splitters, or other optical interference between the source and the CCD array. The camera was only installed with an ND2 attenuator to avoid the camera saturating, a condition that can, if allowed to persist, damage the array and produce meaningless measurement values.
The first beam analysis was conducted on the raw beam from the laser source to establish a baseline of the size and shape of the beam, the orientation of the beam (round or oval), and, if oval, the direction of the minor and major axis positions. Due to the critical nature of the quality of the laser source, having a beam that possesses an ellipticity value of 92% or better is essential (a perfectly round beam has an ellipticity of 100%). Most high quality laser sources demonstrate an ellipticity value of 90% or better. In most high reliability applications, any measurement that is within 10% of an absolutely perfectly round beam meets specification.
The beam size, measured using the 1/e2 (13.5% of Peak) technique as specified by the manufacturer of the source, was validated by the BeamGage measurement when imaged at a short distance from the source. The overall shape of the beam and the distribution of the intensity internal to the beam was another issue that had yet to be diagnosed.
Once the overall beam size had been validated and determined to be within specification, the next analysis required the measurement of the ellipticity (or roundness) of the beam. BeamGage Professional software offers this quantitative measurement and graphic validation of this condition by activating the ellipticity measurement, which is a ratio of the major and minor axes. The quantitative measurement of ellipticity was determined to be 97%. Figure 1 shows the major crosshair (from lower left to upper right) and the minor crosshair (from lower right to upper left). The actual difference in the beam diameter measurement vs the same measurement when the ellipticity measurement is activated is only a difference of 197um.