Power Meters FAQ's

In general, pyroelectric sensors physically respond only to pulsed sources (the pyroelectric crystal itself responds to the acoustic pulse – essentially a heat pulse – resulting from absorbing a light pulse). The heat from the laser itself is presumably not pulsed, so it shouldn’t directly affect the reading. Note that pyroelectric detectors have a temperature coefficient of sensitivity, on the order of 0.2%/degC. The “PE-C” type sensors (Ophir’s current line of pyroelectric energy sensors) have built in temperature compensation that eliminates most of this variation, but if your laser significantly heats the nearby sensor, then the compensation may not be perfect.

The old pyro sensors and the newer PE-C sensors are almost identical; the differences between them are as follows:

1. More compact
2. User Threshold – minimum energy threshold (below which the sensor will not trigger) can be selected according to users' needs
3. Measures longer pulses (up to 20ms depending on model)
4. Has up to 5 pulse width settings as opposed to only 2 pulse width settings

Disadvantages:
Smaller size and therefore:

• May need a heat sink (P/N 7Z08267) in order to stand up to higher average powers
• May need a mechanical size adapter (P/N 7Z08273) if it must fit into an existing mechanical jig designed for the older models

Meters and Software Support:
StarLite, Juno, Vega, & Nova II fully support the Pyro-C series. Laserstar, Pulsar, USBI, Quasar, and Nova / Orion with adapter* partially support the Pyro-C series:

• Only 2 of the 5 pulse width settings are available
• Lowest measureable energy cannot be selected (no User Threshold).

StarLab software supports both Pyro-C and older pyro series.

*Note: The PE-C series will only operate with Nova / Orion meters with an additional adapter Ophir P/N 7Z08272 (see details in Ophir website).

Wavelength Setting Names:
If you have your own software for communicating with the sensor, it may be important to note that for some models, the names of the wavelength settings are a bit different between the old pyro and the new PE-C, even though they mean exactly the same thing.

For example, with diffuser OUT, the settings in the PE50BB-DIF-V2 are called “<.8u” (i.e. visible, represented by a calibration point at 532nm that covers the full visible range), and “106” (i.e. 1064nm), while in the PE50BB-DIF-C these same settings are called “532” (i.e. 532nm, the calibration point for the visible) and “1064”.

When logging energy measurements on a PC with the StarLab software from a Pyro sensor via either a Nova-II, or Vega, or a USB enabled StarLite meter, the timestamp for each Energy pulse measured in the log is provided entirely by the clock on the PC which has millisecond resolution. (Note: Because a timestamp provided by a multitasking Windows PC is not from a true real time system, there could be instances where the timestamp is not well synced with the actual energy pulse measurement in the log, depending on how ‘burdened’ the computer was at any particular moment.)

When logging energy measurements on a PC with the StarLab software from a Pyro sensor via either a StarBright, Juno or Pulsar, each of these meters provides a precise microsecond resolution timestamp from their on-board clock.

This timestamp is synced to the Energy measurement and the data is written together in the log. The precise on-board clock in the StarBright, Juno or the Pulsar is used here to determine the time differences between measurements - rather than the PC clock which is used here just to set the initial baseline time of the log. This is the best method to log Energy if timing of pulses is critical.

As opposed to Pyro Energy measurements, when logging Power measurements on a PC via StarLab with either Photodiode or Thermopile sensors, where fast measurements are not required anyway, the log timestamp is provided entirely by the millisecond resolution clock on the PC when connected to any of our meters.

If the energy is just a bit over-range, up to 10% above the top of the scale, the meter will give a correct reading of energy and frequency, together with an “Over” warning. If the energy is way above the top of the scale, though, the reading will very likely be nonsensical, but without the “Over” warning. With Ophir’s Pyro-C energy sensors, there is never a “saturation” message on the meter - the output from the sensor can never actually reach saturation. Of course, being “way over” the top of a measurement scale – and not noticing - is not a likely scenario. Common sense is often the best defense.

In theory, if a beam is completely parallel and fits within the aperture of a sensor, then it should make no difference at all what the distance is; it will be the same number of photons (ignoring absorption by the air, which is negligible except in the UV below 250nm). If, nevertheless, you do see such a distance dependence, there could be one of the following effects happening:

• If you are using a thermal type power sensor, you might actually be measuring heat from the laser itself; when very close to the laser, the thermal sensor might be “feeling” the laser’s own heat. That would not, however, continue to have an effect at more than a few cm distance unless the light source is weak and the heat source is strong.
• Beam geometry – The beam may not be parallel and may be diverging. Often, the lower intensity wings of the beam have greater divergence rate than the main portion of the beam. These may be missing the sensor's aperture as the distance increases. To check that you'd need to use a profiler, or perhaps a BeamTrack PPS (Power/Position/Size) sensor.
• If you are measuring pulse energies with a diffuser-based pyroelectric sensor: Some users find that when they start with the sensor right up close to the laser and move it away, the readings drop sharply (typically by some 6%) over the first few cm. This is likely caused by multiple reflections between the diffuser and the laser device, which at the closest distance might be causing an incorrectly high reading. You should back off from the source by at least some 5cm, more if the beam is not too divergent.

Needless to say, it’s also important to be sure to have a steady setup; a sensor held by hand could easily be moved around involuntarily, which could cause partial or complete missing of the sensor’s aperture at increasing distance, particularly for an invisible beam.

Pyroelectric sensors are energy sensors, meaning they measure the energy of pulsed laser sources…not the power of steady-state CW sources. In order for pyroelectric sensors to output a measurement a single shot or repetitively pulsed laser source is required. If you are trying to verify that a pyroelectric sensor is operating and currently do not have a pulsed laser source to direct onto it, they will usually output various measurements when tapping on the mechanical housing indicating that they are operating OK.

See attached

Before using the pyroelectric sensor for power or energy measurement, check that your laser power, energy and energy density do not exceed the head ratings. Use the laser damage test slide that has been sent with your sensor at the laser energy you want to measure to make sure it does not damage. 
Please check the included data sheet or check on the website for the same information; 

https://www.ophiropt.com/laser-measurement-instruments/laser-power-energy-meters/products/energy-sensors/pyroelectric-energy-sensors

With the pyroelectric head, you have been supplied a test slide with the same coating as on your pyroelectric detector. You can also obtain this slide from your dealer. You should use this slide to test the damage threshold with your laser pulses. If the slide is damaged, then either enlarge your beam or lower the laser energy until damage is no longer seen.