I am the manager of a laser ablation lab at Cornell and we have an ESI NWR193HE that was installed Aug 2020. Its only been truly operational for about a year but we are experiencing a high loss of laser energy over time. Fluences of 5-10 J/cm2 are costing more and more of the laser's energy output. At about 6 months, we were already at half of the installation energy output, now at a year we're at a quarter. The service engineer has quoted us for some very expensive optic repairs but has anyone else experienced such a high loss this quickly before?
Sometimes, backreflection or emission from a sample may damage the optics inside the laser resulting in a power drop. Use of an optical isolator is usually recommended to prevent backreflection into the laser.
Although I don't work with ablation laser, with my research scientific laser, even with optimal regular maintenance, most of the optics inside the laser cavity still gradually degrade over time (especially coated optics, as no coating can permanently tolerate the high-dose radiation). Usually, if the power drop starts to happen, it will get worse faster over time. For your case, I think preventive cautions is the most suitable (like suggested by Kim above) as well as make sure you ask the engineer to know all details: which precise optics was damaged, how to prevent this happening next time, what can go wrongs with the daily operations, etc. Make sure to take note all and more careful daily operations should be imposed.
If you do ablation from solids is very easy to reach a critical density of the plasma and reflect a lot of deposited energy back into the laser. This may damage the optical components inside. For this reason, as suggested by Byunggi Kim you should mount an optical isolator ((e.g. Faraday rotator) at the frontend of your laser before focusing onto the sample. Additionally, this is big if but still, maybe some of the material you ablate somehow deposits itself on the optical components? I do not know your system, but ours (10J/1ns, Nd:YAG) needs everyday adjustments (some small tweaks) to sustain the maximum energy output, and still, every year we have major service, when sometimes (not always) we need to replace a polarizer or a mirror... If it is a multistage system (like ours), the beam quality and parameters from the oscillator, seeding subsequently the amplifiers, need to be very good quality and with specific parameters, otherwise, in the end, we will lose the energy.
Hope this helps.
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