Power Meters FAQ's

Laser Power/Energy Sensors

Calibration

05/26/15

The Power Accuracy of +/-3% refers to the absolute uncertainty of the measured value. For example, for a 2 Watt reading, the actual "true" value would be between 1.94 W to 2.06 W (with reference to NIST, to which all our calibration is traceable). This assumes the reading is from about 5% of full scale up to full scale. It should be noted that our accuracy specification is in general based on 2 sigma standard deviation.

Repeatability of the measurement (assuming the laser itself is perfectly stable) is limited in the best case by the power noise level of the sensor, and is typically better than  +/- 1%  depending on the thermal stability of the environment. Stability at higher powers from the middle to the top of the range of the sensor head is usually better than the low end. This is due to small temperature variations having less of an effect as they are proportionally a lower percentage of the total power. For more information, refer to our Web tutorial at: https://www.ophiropt.com/laser-measurement-instruments/laser-power-energy-meters/tutorial/calibration-procedure

05/26/15

With normal usage we recommend calibrating every 12 months. To accommodate shelf time and shipping time new manufactured product comes with a calibration sticker that shows a recalibration period of 18 months from manufacturing. However this does not negate the recommended 12 month recalibration interval should you receive the product with more than 12 months remaining on the new manufactured calibration sticker.

05/26/15

If the calibrated wavelength is W1 and I want to measure at wavelength W2 then I look at the relative sensitivities on the curve at W1 and W2 and calculate as follows: Sensitivity at W1: s1 Sensitivity at W2: s2 When instrument is set to W1 and I measure W2, then multiply reading at W2 by s1/s2 to get correct reading at W2.

05/26/15

All absorbers used in power/energy measurement are not entirely flat spectrally, that is, they vary in absorption with wavelength. For this reason, Ophir measuring sensors are usually calibrated at more than one wavelength. If the absorption changes only slightly with wavelength, then we define wavelength regions such as <800nm, >800nm and give a calibration within these regions. In that case, the error in measurement between the wavelength the device was calibrated for and the measurement wavelength is assumed to be within the primary wavelength calibration error.

05/26/15

An explanation of how we can accurately calibrate at a small fraction of the maximum power is given in our catalog introduction and on our website. In addition, in order to be sure of the calibration at higher powers, we have to know if the linearity of our sensors is within specification. For this purpose we have a 1500W sensor calibrated at various powers at a standards lab. Using a beam splitter and a 15,000 Watt laser we periodically check the linearity or our highest power sensors against this secondary standard.