Using the FL250A-LP1-DIF-33 at "None of the Above" wavelengths

The FL250A-LP1-DIF-33 is specified over the range 0.4um – 3um. However, as the spec points out, it is only calibrated at 3 specific wavelengths (532nm, 755nm, 1064nm); what if your laser is "none of the above", say, Erbium at 2940nm?

The FL250A-LP1-DIF-33 uses the LP1 absorber, whose spectral response is not flat, and also has an alumina diffuser – whose spectral response is also not flat. Although we do have the full measured curve as part of the regular calibration process for LP1 sensors, doing so for a sensor with a diffuser is for various reasons technically problematic.

As stated in the spec, then, we calibrate this sensor at the 3 wavelengths 532nm, 75nm and 1064nm. The sensor responds, however, at all wavelengths in the specified spectral range.

If you need to measure at a wavelength other than one of the 3 calibration points, the practical solution would be as follows:

  • set the meter's wavelength to one of the calibrated wavelengths, say 1064nm (or whichever is closest to your wavelength);
  • take the reading of the laser


calculate a correction factor for your wavelength using the following graph:

Using the FL250A-LP1-DIF-33 at None of the Above wavelengths

  • Apply the correction factor to your reading as follows:
    • Say the calibrated wavelength is W1; find its relative sensitivity ("absorption") on the graph, which we'll call S1.
    • Say you want to measure at wavelength W2; find its relative sensitivity ("absorption") on the graph, which we'll call S2.
    • With the instrument is set to W1, measure at W2; then multiply the reading at W2 by S1/S2 to get the correct reading at W2.


If for whatever reason your application cannot get by with using a calculated correction factor, but rather you need to have an actual calibration at your wavelength, we are in many cases able to do this as a special calibration. If that is the case please contact us.