Pulse Rate and Pulse Width: Pyroelectric sensors have some pulse rate dependence. Since Ophir sensors are always calibrated with the beam centered on the absorber, if the measurement is made with the beam centered and the beam is not larger than 1/4 the aperture, this error can in most cases be ignored. Uniformity: The uniformity of Ophir sensors is in general not given in the specification but in most cases it is ☒% maximum variation for beam position anywhere within the central 50% of the area of the aperture and is better than this in many cases. If the power level is less than 70% of maximum power for photodiode sensors, then the linearity will be within ☐.5%. For photodiode sensors, the linearity error is not published but it is always less than ☑% except very close to maximum power. Note that for thermal sensors, the linearity error is in general +/-1% or whatever is in the specification for that particular sensor. Linearity: The linearity of Ophir sensors is always given in the published specification for thermal and pyroelectric sensors and the expected error due to nonlinearity is to be added to the basic calibration error as discussed below. If the absorption difference between the nearest calibration wavelength and the measurement wavelength is larger than 1-2% and cannot be accommodated in the total error, then we define a continuous calibration curve covering the variations at all wavelengths in the region. In that case, the error in measurement between the wavelength the device was calibrated at and the various other wavelengths in the defined wavelength region is taken into account in the total error budget. If the absorption difference between the nearest calibration wavelength and the measurement wavelength is larger than 1-2%, then either we add to the specification an error with wavelength in that region or calibrate over a continuous calibration curve covering all wavelengths in the region. 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. If the absorption changes only slightly with wavelength, then we define wavelength regions such as 600nm and give a calibration within these regions. For this reason, Ophir measuring sensors are usually calibrated at more than one wavelength. Wavelength: All absorbers used in power/energy measurement are not entirely flat spectrally, that is, they vary in absorption with wavelength. The calibration uncertainty of the display unit.īefore focusing on (1) and (2), the primary subject of this document, we will go over the other factors in measurement accuracy. how much does the reading vary depending on what is the pulse rate of the laser.ħ. The pulse rate dependence in the case of pyroelectric sensors, i.e. if the sensor is calibrated with a small laser beam in the center of the absorber, how much will this change if the beam is not centered or is large sized?Ħ. The uniformity of reading over the surface, i.e. if we increase the input power or energy by a factor of say 2, do we get twice the reading.ĥ. if it was calibrated at one wavelength and the measurement is with a laser of a different wavelength, how much this affects the accuracy of the measurement.Ĥ. The wavelength dependence of the sensor, i.e. This is of concern only for thermal sensors, not for pyroelectric energy sensors.ģ. the extra error that is due to the extra calibration step necessary to calibrate energy. The calibration¹ uncertainty of the measuring sensor at the power level, energy level and wavelength at which it was calibrated.Ģ. The total accuracy of measurement of a laser power/energy meter is affected by the following factors:ġ. This document discusses the interpretation and basis for stated measurement accuracy of Ophir Laser Power/Energy meters. Detailed Analysis of Power and Energy Calibration Errors Analysis of Power and Energy Calibration ErrorsĤ.
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