The usual procedure to align the beam for a best absorption signal is:

- to make the 2 beams pass through the pinhole
- maximize the DC centering the probe on the detector
- maximize the AC aligning the pump.

Adding the second probe beam makes things a bit more difficult because if we move the pump, we lose the alignment with the other probe. So, the maximization of the 1310nm probe AC signal have to be done without moving the pump. 

Since the 1310nm probe turns out to be difficult, we decided to follow the usual procedure for the 1310nm laser, moving the pump to maximize it. Then try to recover the alignment on the red probe without moving the pump.

38.85mm is the position of the maximum of the scan with the red probe. Then we move the pump to find the maximum with the 1310nm probe.

filename:
Mon, Jan 22, 2018 3-01-33 PM.txt ; pd distance 83mm. Stage pos: 9mm
Mon, Jan 22, 2018 3-53-55 PM.txt ; pd distance 95mm (not better)
Mon, Jan 22, 2018 3-59-17 PM.txt ; pd distance 65mm

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After trying the alignment many times, I noticed that the 1310nm probe is not focused properly, so we decided to measure the beam profile.
We discovered that the waist position is about 6 cm after the crossing point.
So we decided to change the focusing lens from f200mm to f300mm and to move the lens backward.