LBP2 User Guide
Document No: 50306-001
Rev G 3/12/2020
Page 72
the background starts to look too gray, then the baseline is drifting negative; if too
dark, then the baseline is drifting positive.
Note: These colors apply to the Continuous 128 color palette. The color shading
changes depending upon the palette selection, but the principle remains the same.
Important:
Allow the camera to warm up and reach thermal equilibrium before performing
calibrations. One hour is usually sufficient as a warm-up period. If the ambient
air temperature is changing, then periodically recheck the background energy
levels to make sure they have not been significantly altered.
5.2
Beam Presentation Affects Results
Effective beam presentation is essentially an attempt to improve accuracy by
increasing the signal-to-noise property of the digitized data. Since the camera and the
digitizing process primarily fix the noise level, most efforts concentrate on increasing
the signal content.
Always try to optimize the beam's amplitude into the camera's dynamic operating
range. Whenever possible, use external optical attenuation to bring the beam's peak
signal levels into the upper half of the video signal's dynamic range. If optical
attenuation results in low signal amplitude, use the camera's video gain control to
restore some of the loss.
Important:
Increasing gain also increases noise, so use it sparingly.
To isolate the laser beam profile from unwanted background effects LBP2 has both
Manual Aperture and an Auto Aperture capabilities. Newport recommends always
using the Auto Aperture feature to insure elimination of background noise effects,
which are detrimental when making second moment measurements.
If beam intensity is low and/or covers only a small fraction of the display window, use
a manual aperture to eliminate the background energy noise in the wings. Use
external optical magnification if the beam begins to approach only a few pixels in
width. Widths of at least 10 pixels are required to obtain a reliable beam width
measurement.
5.3
ISO Standards Compliance
The current versions of the International Organization for Standardization (ISO) that
pertains to the measurements of laser beam characteristics have been incorporated
into LBP2. At the same time, other legacy measurement techniques that have found
general favor in the industry have been preserved. Some of these legacy techniques
have been incorporated into ISO standards while others remain outside.
Computational methods that follow the ISO mathematical models are indicated in
LBP2’s results and in other areas by having the suffix
ISO
as part of the results
identifier. However, this marking does not mean that the computed result meets all
the necessary ISO criteria. In particular, an ISO result may
depend upon certain
