Power Meters FAQ's

BeamTrack Power/Position/Size Sensors


The Vega, Nova II, StarLite. StarBright and Juno support the BeamTrack (PPS) sensors. All other instruments can display power and single-shot energy of a BeamTrack sensor, but do not display beam position and size.


Yes StarLab can log beam position. The BeamTrack sensors are thermal sensors. The power measurements for all Ophir power sensors are logged at 15 times a second. When a BeamTrack sensor is connected to StarLab via a Juno, the position / size measurements are also logged 15 times a second. When a BeamTrack sensor is connected to StarLab via a Vega/ Nova II, the position / size measurements are logged once a second. This is because in the Vega / Nova II we sample these parameters slower.


The Ophir BeamTrack series of Power/Position/Size meters may be just the thing. In addition to all the things an ordinary power/energy meter does, the BeamTrack will measure the beam position and size as well to a precision of ~0.1mm. For a gaussian beam it will give you the actual beam waist diameter and for other beams it will give a relative number that changes with beam size. See http://www.youtube.com/watch?v=U2oliO-Cz8M for a demo of the BeamTrack.


The specified response time is only for the power and not for the size or position; response time is intentionally given in the Power section of the spec.
We haven't defined a position and size measurement response time because it depends on too many different parameters. For example:

  • Small changes in size or position will respond quickly, large changes are much slower.
  • Going from a large spot size to a smaller one is faster than going the other way.
  • Position and size can change at the same time.
  • If the power also changes it is even more complicated.

So the response time for size and position cannot be meaningfully specified by a single number. Having said all that, however: 
In general, unlike the power reading which is accelerated by the predictive “speedup” function, the size and position measurements can't use the speedup so they are a bit slower.
The rise time for Position and Size is typically 5x – 10x the specified power response time.
Fall times for a decrease in power density (i.e. increase in size relative to power, as above) can be longer.


The answer to this is, of course, it depends. It depends on the pulse frequency and it depends on which sensor you want to use. Thermopile detectors do not have very fast response times, so frequencies above 100Hz are effectively the same as CW to them and all BeamTrack functions will perform as expected. Below 100 Hz the response time of the detectors becomes relevant. Low power sensors generally have faster response times so they will be more susceptible to fluctuating readings when used with a pulsed laser. The position measurement function uses the same thermopile detector as the power reading. If the laser frequency is high enough for the sensor to provide a stable power reading without fluctuations then the position measurement function will perform well too. All of our BeamTrack sensors will provide reliable position measurements for pulse frequencies down to below 10 Hz. The beam size function employs a detector that has a faster response time. At low frequencies the size measurement reading will fluctuate. We don't recommend relying on the size reading for laser pulse frequencies below 100 Hz. In any event, you can always try the sensor with your laser. If the readings are stable, without significant fluctuations, then they will be reliable.