They're all protected silver mirrors from Thorlabs which have ~97% reflectivity at 1040nm. I have measured ~40% power loss through the delay line and ~60% power loss through the common path to the objective. This is not a big concern as we have enough power at the objective (>600mW for both...
Thanks for the replies!
This has definitely been one of my suspects.
The current setup has the 1040 beam going through a delay line with ~10 silver mirrors, a 2X beam shrinker (to compensate for the divergence of the extra path length), and then joins the tunable beam using a notch filter...
I am trying to align two ~100-140 fs pulsed lasers, one at 1040 nm and one between 750-950 nm through a working custom 2p microscope. The end goal is to do stimulated Raman (CARS and SRS) which requires the two beams to be coincident and the pulses to be perfectly synchronized in time, however...