NikoL, JasonO, RickS

We recently noticed that the output power from our spare Pcal Tx module that is used for Working Standard / Gold Standard responsivity measurements had significantly degraded output power (~0.5 W, down from 2 W) and very poor beam quality.

Today, we adjusted the pump laser temperature (potentiometer W1) and were able to recover most of the power.  The pump laser current (potentiometer W3) seems to be at about the maximum level already.

In the end, we have the following power levels:

• 1.81 W at the laser output aperture
• 1.79 W at the input to the AOM
• 1.75 W total at the AOM output
• 1.28 W in the first order diffracted beam downstream of the wedged beamsplitter

Thus the diffraction efficiency is a bit better than 70%.

The beam quality looks reasonably good.

The maximum OFS PD output is about 7.6 V, so we set the operating setpoint at about 3.5 V.

At this offset, the power downstream of the wedged beamsplitter is about 0,6 W, so we expect about 0.3 W in each beam for the power standard ratio measurements.