We run 3kW / 3.2kW Trumpfs. They use compressed air in the laser beam guards not costly nitrogen. The size of both reflective and transmissive optics on a Trumpf laser is the same whether you have 3kW or 6kW. With an output coupler the beam is not fully developed and is potentially more prone to thermal damage of all the optics. Lenses are prone to damage since they are all Ø38mm and more difficult dissipating 6kW than 3kW. I have always taken the attitude that unless we need more than 3kW, we stick with 3kW. The hourly running costs are lower and if we only have for example 5% of our work at the thicker end of the machine capability then why use a 6kW machine. If your customers are wanting 15mm stainless and 25mm mild steel all day, everyday then you need 5kW minimum but you will have a higher hourly running cost.

For Trumpf read Bystronic, I am fairly certain they both use the same size optics for all their power range.