how to pick the correct size of mirrors?

Knowledge sharing time: how to pick the correct size of mirrors?

For a small laser tube 60W, the beam size looks as small as 4mm while a 130W is 8-9mm when doing a beam test on cardboard. Well, it is wrong but I'm not going to explain it today.

Today, I just want to show you that what an actual dimension of a mirror when it placed in 45 degrees or so. By using trigonometry, it is easy to find out. Remember the SIN and COS?

If a mirror is placed vertical, then the actual work area is the size of the mirror, minus the mirror mount ring which is about 1.5mm. So, a 25mm mirror will provide a 23.5mm workspace. Well, what can you use it for if a mirror is placed in vertical (0 degrees)? For a laser machine, we need to employ 3 mirrors, and each of those needs to be 45 degrees to make a laser beam turning 90 degrees.

Therefore, the actual workspace is: (25mm - 1.5mm)* COS(45') = 16.6mm. See picture below.

I will explain on what size of mirror and lens to be used on a higher power laser system: 130W and up