engraving rubber stams

[ecoworld]

Hello friends
I have chineese laser which i have been using for quite some time, it was originally a 60 watts co2 machine.I upgraded the laser tube to 100 watts and changed the appropriate power supply. I had been using it for about one after the upgrade without any problem but now the engraving is not satisfactory. It uses Lasercut software and recntly the engraving is not uniform. See attached picture. I'm getting wavy background and the depth is not uniform.
Any idea what can be the problem. This problem is more noticable on rubber stamps. Its seems also there is a loss of power, however while cutting it seems ok.
Any help will be very much appreciated.

Thanks in advance