Interesting recent problem with Filters
Below is a picture of what happens to an excitation filter if you do a lot of reasonably high power reflection imaging. Note that a hole has actually been burned into the filter. The symptoms were that we started to get really BAD reflection imaging, however the problem was not an obvious one to solve. We realized that it might be related to filters, but because the filters are so difficult to see, it took a while before we diagnosed the problem. We solved it for the mean time by rotating the filter. Obviously filter replacement is necessary. Yes - filters do have a limited lifepan!

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