Changing from 150mm to 300mm lens, can't repeat 150mm ablation

30w MOPA with 150mm lens, lasering a thin plastic film to obtain a slight color change in the polymer. These settings work for what I’m after and no melting.
line interval-0.06
dot width 0.08.

Changed to a 300mm lens because I want to laser the same image but larger. I understand I can’t use the same settings as the 150 and the power is exponentially reduced–but I can’t replicate the 150 results no matter what settings/combinations/# of passes/etc. I make. Lasering either does nothing to the substrate, or I can melt it–nothing in-between or that matches the 150 results. I don’t mind continuing down a learning path to eventually find the right settings but want to ask the question…are there time where a 300 lens just won’t replicate a 150 Lens no matter the changes in settings, passes, time, etc? Thanks in advance!

I would review the steps for changing a lens if you haven’t already and double check if you’ve missed something, while we wait for someone with a fiber laser to reply :slight_smile:

A rule of light, double the distance will give you 1/4 the intensity. In other words, at double the distance, you will be scanning 4 times the area. Maybe this will help you zero in on the magic settings.

Did you compensate for spot size?

A 150mm lens has an approximate spot size of about 60.808 microns (0.0608mm) a 300mm is about 121.615 microns (0.1216mm)

There is the same power, but it’s size being twice as large will reduce apparent power into the material. Remember these are pulses/mm machines.

It’s twice the size, so your interval would have to be adjusted along with your speed/power/frequency to compensate.


Yes on spot size but this might be a setting I a) haven’t found the right number yet or b) am making an error in my LB settings. Will recheck, thanks for input.