HAMAR LASER STEALTH Series, General Training Manual

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Appendix D – Coping with Atmospheric Effects
The performance of a laser system is affected by turbulence in the atmosphere. The accuracy of the
system is .0001 in/10 ft between the laser and the target in typical machine shop conditions. This accuracy
can be lessened by a factor of 2 in the winter when the air is cold and dense and can improve by a factor
of 2 in the summer when the air is hot and humid and not very dense.
Turbulence is caused by pockets of air at a slightly higher or lower temperature that act like weak lenses
passing through the laser beam, causing it to fluctuate slightly. This causes an angular effect (the farther
away the target, the greater the effect). This is similar to the “shimmer” that can be seen over a hot tar
road in the summer.
Figure 29 -
Turbulence
Another effect is caused by a vertical temperature gradient, or refraction. In still air the temperature is
warmer nearer the ceiling than at floor level. This condition can bend the line of sight downward as much
as .008 in/40 ft at a 50 degree shop temperature. This same phenomenon occurs with optical tooling or
theodolites. This effect only occurs when the air in a shop is very still and it can be recognized by a
sudden shift in the apparent vertical reading of the target when a door opens or a faint breeze is created.
Usually when vertical gradient errors are present, turbulence will be very light.
Figure 30 - Vertical Temperature Gradient
Note
: Turbulence will average out over a period of 10 to 20 seconds and accurate readings may be taken when it is
present by noting the high limit and low limit of the fluctuations in the readout and splitting the difference.