This photo I took on Wednesday. It shows a Post-it that was attached to the end of our laser tube. The dots are about one millimeter apart.
Is this a TEM01 mode? What is to blame? Imprecise tube length? Thermal expansion?
The tube is pretty new. It was installed at the end of last year and it has rarely been used. In fact, it hasn’t been used at all for the past few months.
I think right after the laser is turned on, it fires in TEM00. This is a bit hard to tell as it’s hard to press the test button just the right amount of time to generate a sharp spot. The picture above was taken after the laser was on for maybe 30 minutes, without doing anything asides from the occasional test firing. The water temperature was probably around 26℃, i.e. room temperature here in Hong Kong at the Dim Sum Labs hacker space.
Replicated test setup (pictures taken today):