Power Meters FAQ's

Laser Power/Energy Sensors

Using Your Sensor

How should I clean my sensor?

06/09/14

First, clean the absorber surface with a tissue, using Umicore #2 Substrate Cleaner, acetone or methanol. Then dry the surface with another tissue. Please note that a few absorbers (Pyro-BB, 10K-W, 15K-W, 16K-W and 30K-W) cannot be cleaned with this method. Instead, simply blow off the dust with clean air or nitrogen. Don't touch these absorbers. Also, HE sensors (such as the 30(150)A-HE-17) should not be cleaned with acetone.
 
Note: These suggestions are made without guarantee. The cleaning process may result in scratching or staining of the surface in some cases and may also change the calibration.

Must I use a particular sensor only with the meter it was ordered with?

06/03/15

Ophir meters and sensors are calibrated independently. Each meter has the same sensitivity as the other within about 2 tenths of a percent. Each sensor is calibrated independently of a particular meter with its calibration information contained in the DB15 plug. When the sensor is connected to the meter, the meter reads and interprets this information. Since the accuracy of our sensors is typically +/-3%, the extra 0.2% error that could come from plugging into a different meter is negligible and therefore it does not matter which calibrated meter we use with a particular calibrated sensor.

How much power can I put into an Ophir sensor if I only use it for a short time?

05/26/15

There is a rule of thumb about this for sensors made of aluminum. You can use the sensor without cooling for about 1 minute/watt/cm3 of sensor. So if a sensor has a volume of 300cm3 and you put in 100W, you can use it for 3 minutes. The sensor finder program https://www.ophiropt.com/laser-measurement-instruments/laser-power-energ... has an option for intermittent use of an Ophir sensor and will automatically calculate this for you.

I just received my new Ophir Power/Energy equipment. What are some tips I can use to keep this equipment in top performance?

05/26/15

The largest problem we see from equipment that is not working at top performance is contamination on the sensor. Dust or other contamination on the sensor surface can greatly impact the readings the sensor provides. When dust or other contaminations are on the sensor when it is illuminated by laser power/energy it can become "burned onto" the sensor. Simply blowing this contamination off before using the sensor can greatly reduce these problems and make the equipment perform at top performance for a longer period of time. Using canned air or dry nitrogen from a distance of 6 inches or more to lightly blow off the sensors can remove most of the contamination. Turn the sensor upside down so the surface the laser hits on is pointing to the floor. Start a light flow of air while pointed away from the sensor and lightly sweep it across the sensor without increasing the flow. This will lift most of the dust or other contamination from the sensor surface and gravity will continue to pull it to the floor.

Should I measure power in Watts or energy in Joules, and what sensor is best for each method?

09/06/15

This depends on what information you are trying to discover. If your laser is CW, then you will measure the output in Watts (power). To do this you can use a thermopile sensor (for medium and high power) or photodiode sensor (for low power).
 
If you have a pulsed source you can measure the average power using a thermopile sensor. If you would like to measure energy in individual pulses, then a pyroelectric sensor is required. We have pyroelectric sensors that can measure the energy in individual pulses up to 25 kHz pulse repetition rate.

Does measured power depend on distance? I’m measuring power of a laser diode’s beam, and though the beam is parallel and smaller than the sensor’s aperture, the power reading drops with distance.

09/05/16

The basic physics of light tells us that – unless we are dealing with some exotic effect of absorption by the air, such as with extreme UV – a parallel beam contains the same amount of power at long distance as at short distance.

Assuming that the beam really is in fact parallel…The sensor may be measuring something other than just the optical power in the beam. At a close distance, it might be measuring heat coming out of the laser diode as well as light. These laser diodes can produce significant heat; this would explain the decrease in measured power with increasing distance. You can check this by putting a window between the laser diode and the sensor to block the heat (briefly) and seeing if the same effect happens (of course the window will introduce some reflective losses, but this is just to confirm what is happening). It might be a good idea to put the window at a slight angle, so any reflected power won’t go back into the laser diode where it could cause damage.

I was logging data from a power measurement; there were some points when I increased the power of the laser beam, but in the logged data there was a time gap of a few seconds before the sensor responded. Why did this happen?

09/07/20

A gap of a few seconds in the measurement stream is often caused by having the power range set to Auto.
When in Auto Range, no measurements are streamed in the brief period the meter needs to search for a suitable power range when the power level moves out of the present range.
To avoid this, try setting a manual power range.

What is the repeatability of power sensors?

02/02/22

"Repeatability" is the degree to which repeated measurements of a beam's power (assuming the power stays perfectly stable) will give the same results. This is often referred to as "Precision" (as opposed to "Accuracy").
Repeatability of power measurement (assuming the laser power itself is perfectly stable, and also its position, angle, etc.) is limited in the best case– and on the lowest range or scale - by the power noise level of the sensor. (In real life we don’t always achieve the "best case", but still the repeatability is typically better than +/- 1%.) At higher ranges we are limited by simple digitization. For example, let's say we are using a PD300 sensor on its 30mW range; this is displayed as 30.00 mW. The lowest digit is 0.01 mW (i.e. 10 uW); that is in fact the best repeatability we can get on this range.