Industrial lasers have gained acceptance as effective and reliable production tools. However, up until recent years either power or beam quality limitations have constrained welding focus optics to relatively short focal lengths. Since the advent of CO2 lasers with excellent beam quality (M2 up to 1.2) a few years ago, now both relatively high power and near perfect beam quality are available in the same laser. This has allowed the use of extremely long focal lengths for laser welding, even for keyhole welding, which (for extremely long focal lengths) was something unheard of just a few years ago.
The unusually long focal length, combined with the extraordinarily long depth of focus, has demonstrated equally extraordinary welding results. By comparing the welding results with conventional systems using relatively short focal lengths, some surprising observations have been noted. This topic has been investigated with the use of the remote welding system (RWS), which is a system utilizing an extremely long focal length lens and scanning mirrors to produce a three dimensional (pyramid shaped) work envelope. The results of this work, along with benefits, drawbacks and possible optimizations of long focal length systems, are discussed in the text that follows.