J. Oberling, E. Merilh

Short Version

The new NPRO is now aligned through the 35W FE, with a final output power of 39.0 W.  We will change the pump diode currents for the NPRO and MOPA so the output power is closer to 35 W (this will increase the lifetime of both the NPRO and the FE diode box).  The final steps for tomorrow are:

• Measure beam profile of FE, adjust mode matching if necessary.
• Check FE alignment through HPO, adjusting as necessary.
• Injection lock HPO to FE.
• Recover PSL subsystems (PMC, FSS, ISS).

Long Version

We began the day by aligning the new NPRO to the EOM, AOM, and FI; the NPRO diode current remained at 0.900 A through this process.  The beam height of this NPRO was not too dissimilar to the old one, but the elevation angle was different, to the point that the beam, when centered on the EOM and AOM, would not pass the lens in front of the FI (FE_L2).  To get the beam through the FI, we had to adjust the lens after the initial polarization optics (it has no designation on the PSL table drawing, so I'll call it FE_L0 for the purposes of this alog), at the same time adjusting the EOM and AOM to follow the beam.  Once we got the beam through the FI we started aligning to the new irises we placed on Tuesday using mirrors FE_M2 and FE_M3.  Most of the adjustment was done vertically (adjusting the beam up), with very little horizontal adjustment needed (adjusting left if looking in the direction of propagation).  At one point we had to adjust lens FE_L0 again as we were clipping on the FI, but needed to continue to move the beam up to get through the irises; this then required another adjustment of the EOM to prevent clipping.  Once the beam was through the irises, we measured the NPRO power after FE_L0 and at the entrance to the MOPA:

• After FE_L0: 66.8 mW
• MOPA entrance: 48.0 mW

The NPRO diode current was then turned up to it's nominal value of 2.35 A and the same measurements were taken; we also measured the power at the MOPA exit (all measurements done with an Ophir 10W power meter):

• After FE_L0: 1.94 W
• MOPA entrance: 1.72 W
• MOPA exit: 0.129 W

I adjusted mirrors FE_M4 and FE_M5 to get the beam through the MOPA; the final power meter reading was 1.40 W.  We then installed the 30W power meter as the next step would finish with a FE output power > 10 W.  We turned the MOPA pump diodes on at 10 A and measured the output power, and stepped them up to a final value of 30 A:

• 0 A: 1.32 W
• 10 A: 1.32 W
• 15 A: 1.82 W
• 20 A: 2.76 W
• 30 A: 6.12 W

Ed then aligned the NPRO beam through the MOPA using mirrors FE_M4 and FE_M5; at the end of this alignment the output power was 16.35 W.  We then had to install the 200 W power meter (this is what happens when you don't think ahead, we should have used the same power meter for these measurements).  The FE diode currents were increased to their nominal operating values of 46.3 A for D1 and D2 and 49.7 A for D3 and D4 (the pump diodes are chained in pairs), with a stop at 40 A along the way.  The output power of the FE was measured at each point:

• 30 A: 17.3 W
  • This is why we should have used the same power meter, simply changing the meter gave us a 1 W "increase" in the output power of the FE...
• 40 A: 29.9 W
• Operating currents: 36.3 W

Ed then aligned the NPRO beam through the MOPA using the same mirrors; after this alignment the FE is outputting 39.0 W (Go Ed!).  We can decrease the operating current of both the NPRO and the MOPA so the output power is closer to 35 W; this is beneficial as it will extend the lifetime of both the NPRO and the MOPA diode box.  At this point we called it a day, as we were both starting to get tired.  The final steps for tomorrow are:

• Measure the beam profile of the FE and adjust the mode matching if necessary.
• Check FE alignment through HPO, adjusting as necessary.
• Injection lock HPO to FE.
• Recover PSL subsystems (PMC, ISS, FSS).