J. Kissel, R. Short, J. Oberling

This is the first installment of aLOGs documenting the setup of a new stand-alone 1064 nm NPRO laser system whose current "end game" intent is to provide ~100 [mW] of fiber-coupled p-pol light to the SPI laser prep chassis.

Step 1: Gathering materials, find what optics / mounts we had vs. what would be need, and physically layout the plan.

Jason lets Ryan and I know that there are three NPROs in the optics lab, two of which are PSL spares that cannot be used. 
The remaining laser is S/N 1661, the laser used in the PSL during O3 which is *functional* but was briefly installed during O4 circa Fall/Winter 2024 then removed from use in the PSL because of reported glitching / incompatibility with the frequency stabilization servo (FSS) issues -- see the bottom of LHO:81391 for a nice summary, and LHO:81409 for record of its removal.

Inspired by the setup at Stanford Sina shared with us, we're looking to build up the following system to accomplish the goal:
    - NPRO (presumed to be elliptically polarized with Is / Ip = 5:1)
    - QWP (to linearize the polarization)
    - HWP1 (to rotate the polarization into horizontal)
    - FI (accepts horizontal linear polarization, to ensure back-reflections from down-stream components don't seed the NPRO causing glitches/mode hopes/frequency noise)
    - HWP2 (to rotate the FI output polarization into the desired amount of vertical polarization -- aka the desired amount p-polarization)
    - PBS (to filter out and dump the unneeded horizontal / s-pol light, and transmit the desired power of p-pol)
    - SM1 (one of two steering mirrors to align the beam into the fiber collimator)
    - L1 (the single-lens mode-matching solution to convert the NPRO beam into what the fiber collimator needs)
    - SM2 (two of two steering mirrors for alignment into the fiber collimator)
    - 50:50 PWR BS (45 [deg] AOI, optimized for p-pol; to provide a pick-off port for live power measurement)
    - Fiber Collimator

Ryan started with a 24" by 12" breadboard that was lying around in the optics lab. He build up a makeshift stand from three posts and dogs in the lower left corner such that the S/N 1661 NPRO projects the beam at 4" height. The 0.5" thick breadboard has a 1 inch hole pattern offset by 0.5" from the edges. I'll refer to this grid as having axes "m" and "n" where the m-axis are the "row" holes running from 0 to 23, and the "column" n-axis holes run from 0 to 11. I chose (m,n) breadboard coordinates so as to not confuse them with traditional beam profile coordinates of (z [propagation distance], x (transverse horizontal), y (transverse vertical)). 

Thus, the NPRO being in the "lower left" means it projects the beam along the m = 3 row, and the front face of the NPRO is sitting at n = 8. We'll call this beam position z = 0.

We then proceeded to gather as much as we could of optical components from the optics lab drawers, and ended up with this pictured preliminary version of the setup.

Step 2. Power up the NPRO.
Here's were we ran into our first snag. Normally, NPROs are paired/tuned with specific controller boxes. However, when Ryan turned on the S/N 1661 laser with the S/N 1661 control box, the crystal temperature readback reported the temperature was quickly, linearly rising well beyond the desired temperature of 24.7 [deg C]. At ~42 [deg C], (but still below the internal automatic watchdog threshold of 50 [deg C]), Ryan knew something was wrong and turned it all off. He repeated the turn on just in case, and it did the same.

After conversing with Jason, we figure it's good enough to run with one of the other controllers for now, and in the mean time figure out how what's wrong and repair the S/N 1661 controller.

So, we're running with the S/N 7974, and things seem fine. 
    Laser Diode Temp Setup:
        Diode 1 33.7 [deg C]
        Diode 2: 33.1 [deg C]
        Laser diode injection current readback 2.08 [A] (for both diodes)
    Crystal Temp setting is 24.7 [deg C]

We measured the output power*** with no optical elements at all as 1.820 +/- 0.005 W (not noisey, but a slow drift around).
Good enough! Onward and upward!

*** Power measured by ThorLabs power meter
	Model S302C
	SN 111149
	Sensing factor of 316.25 [mV/W]
	(last calibrated Feb 3 2012).

FAMIS 31126

Not much to report this week. FSS has been on and off due to JAC installation and commissioning.

Closes FAMIS#39752, last checked 89164

Laser Status:
    NPRO output power is 1.841W
    AMP1 output power is 70.47W
    AMP2 output power is 138.8W
    NPRO watchdog is GREEN
    AMP1 watchdog is GREEN
    AMP2 watchdog is GREEN
    PDWD watchdog is GREEN

PMC:
    It has been locked 0 days, 2 hr 51 minutes
    Reflected power = 26.95W
    Transmitted power = 104.0W
    PowerSum = 131.0W

FSS:
    It has been locked for 0 days 0 hr and 0 min
    TPD[V] = 0.4856V

ISS:
    The diffracted power is around 3.8%
    Last saturation event was 0 days 2 hours and 9 minutes ago

Possible Issues:
    PMC reflected power is high

FAMIS 31125

Since the FSS and ISS were re-enabled last week, things have generally been stable in the PSL. The RefCav could probably use some alignment touchup, but it's not too bad for now.

FAMIS 39751

Laser Status:
    NPRO output power is 1.834W
    AMP1 output power is 70.51W
    AMP2 output power is 138.8W
    NPRO watchdog is GREEN
    AMP1 watchdog is GREEN
    AMP2 watchdog is GREEN
    PDWD watchdog is GREEN

PMC:
    It has been locked 3 days, 19 hr 53 minutes
    Reflected power = 26.72W
    Transmitted power = 103.9W
    PowerSum = 130.6W

FSS:
    It has been locked for 3 days 15 hr and 53 min
    TPD[V] = 0.4774V

ISS:
    The diffracted power is around 4.0%
    Last saturation event was 3 days 19 hours and 53 minutes ago

Possible Issues:
    PMC reflected power is high

We replaced the failed +/-12V Kepco supplies in VDD-C6 U34 which power the PSL dome cameras
U34_LHS: +12V supply S1201947 removed due to failed fan, replaced with upgraded supply S1202017
U34_RHS: -12V supply S1201992 removed due to failed fan, replaced with upgraded supply S1300289

F. Clara, M. Pirello

FAMIS 31124

FSS has been on and off over the past week and the PZT has been swept several times for JAC install work, but otherwise not much to report this week.

FAMIS 28229

pH of PSL chiller water was measured to be between 10.0 and 10.5 according to the color of the test strip.

This is for FAMIS #39750.

Laser Status:
    NPRO output power is 1.841W
    AMP1 output power is 70.43W
    AMP2 output power is 139.4W
    NPRO watchdog is GREEN
    AMP1 watchdog is GREEN
    AMP2 watchdog is GREEN
    PDWD watchdog is GREEN

PMC:
    It has been locked 0 days, 21 hr 23 minutes
    Reflected power = 27.19W
    Transmitted power = 103.9W
    PowerSum = 131.1W

FSS:
    It has been locked for 0 days 18 hr and 54 min
    TPD[V] = 0.4791V

ISS:
    The diffracted power is around 4.0%
    Last saturation event was 0 days 0 hours and 0 minutes ago

Possible Issues:
    PMC reflected power is high

Jennie W, Jason O, Masayuki N, Keita K, Jim W,

Summary: To check the function of the new EOM in chamber we made a measurement of the modulation indexes by locking the IMC and aligning the beam to AS_C with SR2. We couldn't get a good measurement of the sideband heights but this is probably due to the RF power being down by a factor of 100 from nominal. Will check with EE/Daniel on Monday.

First order of business was checking for stray beams at 100mW input power. Jason moved the BD we already placed for JM2 as we had moced this mirror position yesterday. We also put a new beam dump right after unused JAC port (output side there is tranismission through the curced mirror).

After this we turned the power up to 1W.

Lastly we found a stray beam exiting the table in the -Y direction, this was traced to the JAC REFL path. The REFL beam was hitting the side of a beam dump (near the -X side/PSL of the table) which is meant to cath a beam reflecting off the SEPTUM plate. This beam reflected off the beam dump causing a stray beam. We re-aligned the REFL path so the beam does not do this and instead bounces off the three REFL path steering mirrors and heads into a previously placed beam dump for this purpose on the -Y side of the table. This path will have to be re-aligned in order for the beam to get onto the IOT1 table.

No further stray beams were found so Jason de-energised the waveplate.

Photos to come.

After realising that the beam did not reach the AS_C,A and B QPDs yet we came to the control room to re-align to the output port. This is with the ITMY, PRM and SRM mirrors mis-aligned to allow us to mode scan the OMC in the 'single bounce' IFO configuration.

After Jim re-isolated HAM4,5 and 6 and BSC2 for us we were able to use SR2 to bring back the alignment to AS_C and then turn on the DC centering loops for AS_A and AS_B.

The OMC ASC did not work at first as the suspensions were railed. I cleared the ASC history, this did not help. We cleared the locking filter banks for OM1-3 and this unrailed the outputs and allowed us to turn on the OMC ASC.

We took an OMC scan at 1W input power, shown here. Roughly calibrated into MHz with the known FSR.

We cannot identify the 45MHz or 9MHz peaks, but after checking we realied that these RF driver powers were lowered 15 days ago. See image.

We will come back to this Monday.

Jason put back the rotation stage, locked it out and closed the light pipe.

Modulation depth measurement work has been completed for the day, so I have returned the PSL power in HAM1 to 0.1 mW and de-energized and locked out the PSL rotation stage.  The PSL shutter has also been closed and locked out for the weekend.

We will need to revisit the modulation depth measurement on Monday, so I am leaving WP 13006 open and extending its date.

Jennie W, Jason O

Jason and I added four beam dumps - two before we turned the power up, two after.

There were no beams leaving the table at 100mW but we dumped two beams going towards the PSL septum plate (one was transmission through JM1).

Jason saw one leaving the table after we were at one watt so this and the transmission throuhg JM3 + JM2 are now dumped.

FAMIS 31122

I touched up RefCav alignment this morning (alog88891) and turned on the ISS. PMC alignment may be drifting slightly, but I left that alone so as not to significantly change the output power and potentially disturb the JAC installation team. Not much else to report this week.

This morning, I finally got around to realigning the RefCav after having watched its transmitted power drop significantly over the past several weeks, which doesn't surprise me with the changing weather. Using the picomotors upstream of the RefCav, and with the ISS enabled, I was able to greatly improve the signal on the TPD from 250mV to 500mV. This isn't quite as high as we've seen it after a good on-table alignment, so perhaps sometime in the future we will go into the enclosure and touch up the alignment there.

Attaching a picture of the quad video display post-alignment for posterity; before I started the RefCav reflected spot looked like two distinct lobes vertically next to each other, showing a very obvious misalignment in pitch (which I found to be the area of most improvement when using the picos).

FAMIS 39748

Laser Status:
    NPRO output power is 1.835W
    AMP1 output power is 70.39W
    AMP2 output power is 139.0W
    NPRO watchdog is GREEN
    AMP1 watchdog is GREEN
    AMP2 watchdog is GREEN
    PDWD watchdog is GREEN

PMC:
    It has been locked 14 days, 20 hr 48 minutes
    Reflected power = 26.68W
    Transmitted power = 104.1W
    PowerSum = 130.8W

FSS:
    It has been locked for 8 days 2 hr and 16 min
    TPD[V] = 0.3187V

ISS:
    The diffracted power is around 4.0%
    Last saturation event was 0 days 0 hours and 0 minutes ago

Possible Issues:
    PMC reflected power is high
    FSS TPD is low

FAMIS 31121

Things are looking very stable over the past week; makes sense since very little has been asked of the PSL recently. The PMC and RefCav could still use an alignment touch-up, which I'll get to hopefully this week.

FAMIS 31120

Starting last Thursday, the NPRO temperature is a bit more unstable than usual, but I'm not exactly sure why. There was a brief incursion into the anteroom last Friday, which is seen in the usual places, but everything appears to have come back as expected. The RefCav still looks to need some alignment, which I will likely get to next week. Otherwise, the PSL is looking good.

Closes FAMIS#39747, last checked 88725

Laser Status:
    NPRO output power is 1.845W
    AMP1 output power is 70.39W
    AMP2 output power is 139.1W
    NPRO watchdog is GREEN
    AMP1 watchdog is GREEN
    AMP2 watchdog is GREEN
    PDWD watchdog is GREEN

PMC:
    It has been locked 6 days, 18 hr 2 minutes
    Reflected power = 26.47W
    Transmitted power = 104.5W
    PowerSum = 131.0W

FSS:
    It has been locked for 2 days 23 hr and 18 min
    TPD[V] = 0.4029V

ISS:
    The diffracted power is around 4.0%
    Last saturation event was 0 days 0 hours and 0 minutes ago

Possible Issues:
    PMC reflected power is high