Participants: Yuhang, Yuefan, Matteo

Today we tried again to couple the laser beam into the fiber.

But first, we moved the two steering mirrors and collimator closer to each other. Since the further the distance, every time the movement on the collimator input is larger.

Then by adjusting the two steering mirrors and the x, y screws of the collimator, we are able to reach 10V(maximum) on the photodiode which corresponds to 5.5mW which is even larger than the input laser power.

We found out this is because the oscilloscope has a high impedance which will amplify the power. So we add a 50ohm resistor and we could get 10% beam power coupled into the fiber and after that, it became difficult to improve more.

According to Thorlab website, this collimator should have 2.09mm at the output, but now with a 200mm focal length just after the laser output, we have a beam at the collimator around 400um in radius.

So we did a bit simulation, in order to get the right size of the beam we should combine one -100mm and one 200mm lens. We will try to change the setup tomorrow.