Beam expander still gets hot

[rob1728]

I have a 2x beam expander. 150 watt laser, RECI tube. I made adjustments from my previous setup and moved the expander to 2.75 inches away from the laser output. When I profile acrylic at 70% power and 28ma the beam expander and mount gets hot.
Also When I make a dot pattern across the width of the table I still get variation in the dot shape and size. I need to have a pattern that does not vary across the table.
So far the beam expander is not doing the job I hoped for or I'm doing something very wrong.
The pattern looks good under a microscope and on a comparator nearest the laser tube.

I am at a loss. Rob

[rob1728]

The beam expander is 1.75 inches away from the laser tube. Not 2.75.

[Tech_Marco]

Just a follow up with this post. I talked to Robert and found that he picked the wrong size beam expaner.
He has a Reci 130W~150W (W6) tube and he grapped a 2.0x beam expander with 15mm object lens, which is wrong

The beam diameter from a 130W Reci tube may be as big as 7~8mm (note: it is hard to tell exact number ). After 2.0x magnification of the beam, the output diameter range from 14 to 16mm. Since the size of the output lens from that 2.0x beam expaner was 15mm. If the angle of attack is just a few degree offset , the reflection angle could be way off and crticical. Therefore, alignment of the intake is very crucial.

Moreover, the reflection area from a reflection mirror is no longer be the same as the mirror specification claimed once it is being setup in 45 degree. In fact, the true usable size is: Mirror actual size * COS(45 degree) = MAS * 0.707

Example: 25mm reflection mirror. The usable area is: 25*0.707 = 17.6mm. Not quite yet. We still need to minus 1mm on each side for the mirror mount. So, the really usage aread is 17.6 - 1mm - 1mm = 15.6mm or 15mm.

So, if you use 2.0x for Reci 130W. Unless the beam spot is 7.5mm or smaller and you have perfect alignment, I'll go for 1.5x instead

Hope this help to assist you guy to pick a proper beam expaner.


Marco