A positive branch unstable-waveguide hybrid resonator has been designed for a RF-excited slab CO2 laser of 100 W level. The output beam mode and the propagation characteristics in the two directions of unstable and waveguide were investigated by numerical and experimental methods. The results show that the output beam was collimated in the unstable direction, and was an approximate fundamental mode in the waveguide direction with a divergence angle of 12 mrad. The output power decreased by 50% with the misaligned angle of the tail mirror of 1.5 mrad, and was close to 0 with the misaligned angle more than 3 mrad.
A numerical model of the folded resonator is founded by using the eigenvector method. The beam characteristics and
relative amplitude distribution of dominant mode of the N-shaped three-folded resonator with different aperture diameter
are obtained by numerical simulation. The experiment of the resonator is done on HUST5000 high power transverse flow
CO2 laser. The results show that the mode volume of the N-shaped three-folded resonator with the aperture diameter of
25mm can match the gain zone of the transverse flow CO2 laser well, the output power and beam mode are fit for
industrial applications. The laser welding system based on this resonator is developed for gas generator of automobile
The output beam characteristics of a toric concave mirror laser resonator are discussed. The experiments of the toric concave mirror laser resonator, the plane-concave stable resonator, and the parallel plane resonator with the same Fresnel number of 17.25 are done on HUST2000 high-power transverse flow CO2 laser. The output laser beam of 1820 W with a doughnutlike distribution, the output laser beam of 1860 W with a Laguerre-Gaussian (LG) transverse electromagnetic modes (TEM)60 distribution and the laser beam of 1000 W with are approximate LG TEM30 distribution are obtained, respectively, at the same discharge current of 5 A. The scanning welding test on 316L stainless steel shows that the output beam of the toric concave mirror laser resonator can used for deep penetration laser welding, the welding depth is >2.4 mm at a velocity of 1 m/min, whereas that of other two resonators cannot be used for deep-penetration laser welding because of low beam quality or low output power. This resonator can be used in the laser with a large transverse gain size to improve beam quality greatly without sacrificing the output power.
By means of the Collins formula and finite-element method, diffraction integral equation of the square resonator with
spherical mirrors is transformed to the finite-element matrix equation, mode-fields of the square aperture resonator is
calculated. Experiment with square aperture resonator is done on HUST2000 high power transverse flow CO2 laser. The
results show that a square multi-mode beam with uniform comparatively intensity appeares in near field distribution.
Laser quenching on 45# steel is done by using the square multi-mode beam and general circle beam. The hardened case
caused by the square multi-mode beam is more uniform than general circle beam.
Rapid calculation methods for both transient temperature fields and steady-state temperature fields of laser heat treatments and their theoretic relation are discussed, with application examples of simulating calculation. The applicable conditions of rapid calculation methods for temperature fields are also investigated. The obtained results show that steady-state temperature fields are the ultimate solution of transient temperature fields, in which the time of laser interaction with matter is infinite, and the rapid calculation of transient temperature fields can describe heat interaction of a real laser much better. A quantitative criterion of the rapid calculation methods is given in the application research.