EA-1 User Manual
25
Measuring Average Power for Low Frequency Pulsed Lasers - “Low Freq. Power Mode”:
Starting from app & firmware v1.17 (Jan. 2019), a second method to measure average power on photodiode sensors
is to use the “Low Freq. Power Mode”. This method is useful when measuring average power for pulsed lasers with
frequency in the region of ~5Hz to ~100Hz. Using the regular power mode with such a laser source can cause beating
effects and saturation of the electronics, which causes unstable or incorrect readings in many cases. The “Low Freq.
Power Mode” solves these problems using a special measurement technique in the firmware that synchronizes to
the laser frequency (as supplied by the user). This mode is supported only using Photodiode sensors (PD300-xx), but
not when using Thermopile sensors (which normally do not exhibit such problems, as their response time is much
slower than photodiodes).
To start measurements using the Low Freq. Power mode, click on the “Low Freq. Power” button:
Choose the laser frequency either using the provided drop-down or entering the value manually in the edit box. The
value entered can contain several digits after the decimal point if required, such as 33.123Hz.
Some care needs to be taken when choosing the correct frequency value. If the frequency setting is slightly different
from the actual laser frequency, the power readings may show beating effects. If the frequency setting is too low,
this may result in periodic positive “spikes” of power above the average power level being measured. If the
frequency is too high, the spikes will be negative, below the average power level. As the frequency is adjusted closer
to the correct laser frequency, the spikes will become smaller and further apart, until they disappear altogether
when the frequency is adjusted perfectly. Note that due to slight errors in the nominal internal clock frequency of
the EA-1, or of the laser pulse frequency, the exact frequency setting required for perfect measurements may not be
exactly as expected.
After setting the frequency, choose the correct power range. As a rough guide, the power range should
approximately match the expected AVERAGE power to be measured. The correct range to use is usually the most
sensitive range available that does not show “OVER” or “over” on the screen - meaning the average power is too