Diode end pumped Nd:YAG laser at 946 nm with high pulse energy limited by thermal lensing

• Published in: Applied physics. B, Lasers and optics Lasers and optics, 2009-06, Vol.95 (4), p.721-730
• Main Authors: Wang, S., Eichler, H. J., Wang, X., Kallmeyer, F., Ge, J., Riesbeck, T., Chen, J.
• Format: Article
• Language: English
• Subjects: Beam trapping, self-focusing and defocusing; self-phase modulation; Coefficients; Crystals; Doped-insulator lasers and other solid state lasers; Engineering; Exact sciences and technology; Fundamental areas of phenomenology (including applications); Laser optical systems: design and operation; Lasers; Lenses; Mathematical analysis; Maxima; Nonlinear optics; Optical Devices; Optics; Photonics; Physical Chemistry; Physics; Physics and Astronomy; Pumps; Q-switching; Quantum Optics; Semiconductor lasers; laser diodes; Thermal lensing
• ISSN: 0946-2171; 1432-0649
• DOI: 10.1007/s00340-009-3479-y

Diode lasers with peak powers in the kW range and pulse durations of micro- to milli-seconds have been available since several years. Pumping solid state lasers with such sources yield high output pulse energies in spiking or Q-switched operation. The output energy is limited by the thermal lens effects, which are measured and calculated. The time dependent heat conduction equation in the laser crystal is solved numerically to predict the overall temperature rise and thermal lensing. The thermally induced optical path difference is approximated by a quadratic distribution to obtain the focal length f of the thermal lens. The thermal lens coefficient K =1/( f ⋅ P av ), which depends only weakly on the heat transfer coefficient H of the laser crystal to the heat sink, decreases exponentially with increasing pump frequency until the steady state is reached. Experiments were done with a Nd:YAG crystal at different pump frequencies up to 100 Hz. The thermal lens coefficients obtained by the power maxima of asymmetric flat-flat resonators agree with our calculations.