on two-stage fourth-harmonic generation in beta barium borate (BBO). The beam quality is
close to being diffraction limited with an M^ 2 value of 1.3× 1.6. The pulse duration is 150 fs,
which, potentially, is compressible down to 40 fs. A plain BBO and a sapphire-BBO
compound are compared with respect to the achievable beam quality in the conversion
process. This laser is applicable in scientific and industrial fields. Further scaling to higher …