New answers tagged experimental-technique
A way to get long-range interactions in cold atoms is to use polar molecules, which is a rapidly growing field in the cold atoms community.
Both Carl and Johannes (the latter in a comment) have given you good answers. I reproduce Johannes's comment: Shine a laser beam through the system. If exit beam does not diverge, both foci coincide and you have realized an afocal system and you say @Johannes I'm a bit worried that the rail won't be long enough for me to determine if the exit beam ...
Use an auxiliary lens. First run your collimated source beam through the lens and mark the focus location. Then stick your afocal lens assembly in between the source and the auxiliary lens. If the focus location moves, you're not perfectly afocal.
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