About a month ago,I built a light path that can be used to research ultrafast demagnetization on ferromagnetic film.But later,for some reason,I have to cleam my optical platform.And I recovered it these days.The light travel a totally same path, which means the order of optical element are unchanged.Of course,I can't promise all the element are in the same position as before.But I think that doesn't matter.
What bothers me now is that I can't find any usefule signal from the test data.It looks confusing.
I wonder what might have gone wrong with my experiment.
What's more, I found my light spot from laser is a little wierd.Something must be wrong.Does it affect the experiment?
Your question is very vague and not clear. What do you mean by weird? You are showing a laser spot on white paper, what is its location in the experimental setup? You must be aware that you cannot derive any information on laser spot by showing it on the paper except it can give a very superficial information about any obstruction in the path etc. As far as laser beam shown in paper is concerned, Is that the actual laser beam used in experiment? if so Spot looks deformed circle and it is fine. What is the laser and its characteristics? Post some reference paper relevant to your experiment so that it can give better understanding of the experimental setup of your problem to the readers. Elaborate little more on your problem.
if you use lens in your project in my book check the focal lens, that your next instrument(after lens) should not be in focal distance of your lens it means you must increase your distance
or the best way is using OSLO program that can help you to solve your problem.
break a leg!
Have you checked the polarisation direction of your laser beams for both light path configurations? This can affect your demagnetization on your ferromagnetic films according to the reference below
Spin Dynamics and Damping in Ferromagnetic Thin Films and Nanostructures作者：Anjan Barman， Jaivardhan Sinha
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