As a mid-infrared laser with large magnification and high beam quality, carbon dioxide lasers are often used as intermediate amplifiers in picosecond terawatt laser systems. With the combination of gas discharge and optical pump, the gain spectrum in 10μm can be greatly improved. In this paper, a numerical model is set up to describe the laser amplification and kinetic processes, based on six-temperature level structure, in hybrid pump CO2 laser amplifier system. The influences of the pump power and its amplification results compared with conventional CO2 laser are simulated and discussed. Such a hybrid pump CO2 laser amplifier is very promising in improving output pulse quality by reducing the pulse split.
A Nd : YAG / Cr4 + : YAG composite crystal passively Q-switched laser with high-output pulse energy is studied both theoretically and experimentally. According to the characteristics of flash lamp pump, the rate equations of nonuniform pump are established. The pulse interval, pulse energy, and pulse width of the output pulse train are analyzed accurately by nonuniform pump. The experimental parameters are optimized by numerical simulation, with Cr4 + : YAG saturable absorber initial transmittance of 14%, output coupling mirror reflectivity of 30%, and cavity length of 9.7 cm. Under the same conditions, the maximum static energy is 954.34 mJ without Q-switch. An output pulse train with four pulses can be obtained at the same pump condition in experimental study. The four pulses energy are 156.5, 151, 149.74, and 145.76 mJ in turn with corresponding intervals of 20.81, 24.16, and 46.03 μs. The average pulse width is 5.72 ns. The Q-switch efficiency is 63.2%. The energy of the four pulses decreases, the pulse interval increases, and the pulse width is basically unchanged. The nonuniform pump theoretical and experimental results are in good agreement.
Ultrafast fiber laser has been widely used for spreading the extensive industrial applications and exploring the optics nonlinear dynamics. Here, we report a bidirectional fiber laser passively mode-locked by nonlinear polarization rotation (NPR) technique, supporting the emission of multi-state solitons. For the first time to the best of our knowledge, a Φ-shape auxiliary cavity based on chirped fiber Bragg grating (CFBG) is proposed to simultaneously introduce large anomalous and normal dispersion into the lasing oscillator. As a result, different dispersion distributions are achieved intra-cavity, respectively corresponding to counter propagating directions. Thus, conventional soliton (CS) and dissipative soliton (DS) are respectively generated in clockwise and counter-clockwise propagating directions. The results could benefit multifunctional ultrafast fiber laser system, which is potentially set for many practical applications as well as the study of soliton dynamics.
As a novel cw hybrid laser, the lasing wavelengths lie in the near-IR range and for in the transparency window of the terrestrial atmosphere, diode pumped metastable rare gas lasers (DPRGLs) can be considered as a beam conversion system that produces a high-quality laser beam by passing a diode laser with poor beam quality through the rare gases medium at room temperature. In this paper, a numerical model is set up to describe the kinetic processes and the laser amplification, based the five-level structure, in DPRGL amplifier (DPRGA) system. Influences of the pump power and the cell length on the output laser are simulated and discussed. Such a master oscillator power amplifier (MOPA) system is very promising in achieving high output power for low power DPRGL radiation.
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.