Hello everyone. Recently, I have been building a TIRF microscope based on the objective lens. I found that after adjusting to the TIRF angle, the totally reflected laser converges at the exit of the optical fiber after passing through the lens. I would like to ask everyone if this is a normal situation and whether it will lead to an increase in stray light？
This is normal. It shows that you did a good job of alignment 
. The beam is reflected well and the collimation is good.
I’m not sure I understand the concern about stray light. You are worried about the light scattering off the exit of the optical fiber? Or you are worried about the light coming back through the microscope?
Hi, as Hazen said this shows that you did well ! You may have supplementary background light if the laser reflects again on lenses, it will be sent back to the microscope and sample with improper collimation. But in practice i did not notice this kind of supplementary background.
On the fiber nothing specific will happen.