P4 - Interferometric Heat-Load Sensing of High Power Solid Laser Medium

SENSOR+TEST Conferences 2011
2011-06-07 - 2011-06-09
Proceedings OPTO 2011
OP - Poster Session
M. Baumgart, C. Glassl, A. Tortschanoff, G. Kroupa - CTR Carinthian Tech Research AG, Villach, (Austria)
123 - 126


Compact and reliable high-power lasers for applications in rough environments are increasingly demanded by industry. CTR’s HiPoLas® DPSS laser combines the advantages of high energies per pulse (>40 mJ) and long lasting operation in a compact, temperature and vibration resistant housing. Achieving high energy densities in such a miniaturized layout requires in-depth understanding of the processses occurring during pumping in the laser cavity. A novel, Fabry-Perot-interferometer based, sensing scheme now enables such in-situ measurements in high-energy laser rods.

The core component of the specially adapted interferometric measurement setup is a monolithic Nd:YAG/- Cr:YAG laser rod solely forming the cavity. High power laser diodes situated in the pump chamber around the laser rod deliver the necessary pump energy for laser beam creation. Multiple internal reflections of a coaxially coupled analysis beam occur at the crystal’s highly parallel end faces resulting in an temperature-dependent interference pattern causing laser rod length changes. To follow the highly transient interaction dynamics during one pump pulse, a special temperature modulation method is introduced. Several important characteristics, including laser rod expansion, energy rise inside the laser cavity and absorption-related heat creation per pulse could be calculated from these measurements.

Corresponding optical simulations of the pump light absorption were done including scattering effects at the laser rod’s side surface. The absorption calculations take into account the measured pump diode spectrum and the high resolution Nd:YAG absorption characteristics around pumping wavelength. Both spectra were convoluted by the simulation software. The resulting absorption values correspond nicely with the experimental results.

With the presented interferometric in-situ monitoring method the dynamics of the lasing element can be resolved down to μs pump pulses giving an important insight into the dynamics of the laser pulse transformation. Also, determining the temperature rise in the laser rod, its expansion and the injected heat in real-time is possible. The results are in good agreement with the optical simulations, leading to further optimization of the laser chamber design and cooling layout. Thus, the measurements and according simulations will also lead to a better understanding of thermal lens effects and enable the development of improved, energy efficient cooling of the laser rods.