R. Short, J. Oberling, F. Clara

Continuing from yesterday, this morning Ryan and I looked at mode matching solutions and found one we liked, see attached.  It seems pretty robust, in that we can have the lenses several mm off and still get >99.9% mode overlap (not easily seen in the picture as the other lens positions are off screen).  Once the LVEA was transitioned to Laser Safe we went out to do the readback adjustments on the new NPRO.  All of the adjustments were going well until we got to the Laser On/Off Monitor adjustment.  For information on this particular adjustment see the file 'Some further information needed... .docx' in T1900456.  No matter how we adjusted the potentiometer we could not get the PSL Beckhoff software to recognize that the laser was on.  We installed a 25-pin breakout board and looked at the voltage, all we saw was 0.032 V.  No matter how the pot was adjusted this value never moved, but very occasionally jump up to a higher voltage (1.5 V to 2.5 V range).  This looked like a connection problem, so we took the power supply to the EE shop and enlisted Fil's help in figuring this out.  We referenced what little wiring diagram info we had to carefully trace the signal path, check the proper resistor was installed in R33 (4.7k, it was correct), and made sure all the wiring had been done properly (it was).  Fill cleaned some excess flux from around where the remote board picks off the signal it needs to detect if the laser is on or off (for future reference, this is the top side of power supply resistor R1 for the ON signal and the left side (when looking at the vertically mounted circuit board from the inside) of component T11 for the OFF signal).  He also didn't like the way the solder around remote board resistor R33 looked so he reflowed it.  At this point he wanted to power it up, so we plugged it in.  Unfortunately the power supply interlocks itself if no laser is attached (as expected), so we took the power supply back out to the PSL racks and hooked it up to the laser (but not the Beckhoff system).  A breakout board was hooked to Diagnostics port 2 and we turned on the power supply.  With the laser off the pin read 0V (as it should), and with the laser on the pin read ~7V (yay!).  So apparently either cleaning the flux or reflowing the solder fixed the connection problem.  We then wired the power supply to the PSL Beckhoff system and tuned the correct potentiometer so the voltage was at the ~10V it should be.  The software correctly detects when the laser is on, when it is off, and is capable of turning the laser on and off, and all of the diagnostic readbacks are reading the correct values.  At this point it was after 1pm, so we broke for some lunch.

After lunch we went in to the enclosure to begin recovering Amp1.  With all of the lenses between the NPRO and Amp1 removed, and the NPRO power turned down to ~85mW (using WP14), we roughly aligned the beam through Amp1.  We had ~53mW incident on Amp1 and were able to get 2.38 mW in transmission.  While this doesn't seem like much, there are no lenses installed so the beam is overfilling the amp's entrance aperture and every optical element inside the amp, so this is expected.  When I had removed lens L02 it was a little stuck in its mount, and when it came out I inadvertently put my thumb right on the surface.  So time was spent getting the lens cleaned before storage.  This done, we then grabbed the lenses needed for our mode matching solution.  Back in 2021 we had stored them with First Contact on them, so we removed it.  It left behind a large amount of residue on every surface, so the lenses require cleaning again.  As we do not have First Contact in the PSL enclosure, we contacted Camilla about the location of more.  Since neither Ryan nor I have worked with First Contact much, Camilla offered to clean the lenses in the morning; since it was already 4pm we took her up on that offer (Thank You!!!).  We then began building the component stack needed to mount the third lens of the mode matching solution.  Turns out when we installed this PSL confiuration back in 2021 we used all of the spacer blocks designed to put the lens at our 4" beam height, so all we had left were the old spacer blocks designed for a 100mm beam height.  What we do have, however, is small 1.6mm spacers that could be used to get the height correct, but they needed modified so they work with our larger spacer block.  I contacted Tyler about doing this quick mod in the morning, and he agreed (Thank You!!!).

So on deck for tomorrow:

• Lens cleaning (Camilla)
• 1.6mm spacer mods (Tyler)
• Install mode matching solution, align lenses, take beam propagation measurements and do Gaussian fit to ensure mode matching is doing what we expect, modify if it isn't
• Begin aligning through Amp1 and powering it up