Hi, We do time resolved ARPES, which involves a mid-IR pump (6-20 um) and a UV probe (195 nm). I would like to confidently and quickly find t=0 and spatial overlap of these beams inside of a UHV chamber. We have methods that work, but they are quite slow and difficult; so I am curious if there are better approaches. Our pulses are
You can find the temporal overlap of the beams in the laser table using a fast oscilloscope. There will be broadening of the peaks but this is possible even if you are using laser pulses of 100 fs duration or below. It is nevertheless recommended that you calculate the beam paths so that time zero is in the center of the delay stage. For the spatial overlap, you might add a little bit of phosphorus powder in the sample holder itself, at least once. You can then scan a reference sample. Once time zero is found, it will nearly not change as soon as the configuration of the optics in the laser table remains unchanged. To further check the spatial overlap, you might add two flipping mirrors outside and right in front of the chamber windows, so that the overlap can be checked at the long distance, i.e. at the focal distance corresponding to the distance between windows and and sample if possible.
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