Thin Disk Laser

Abstract

The principle design ideas of thin disk lasers will be illustrated and the advantages for operating different laser-active materials will be explained in detail. So far, the maximum laser cw-output power demonstrated from one single disk is more than 10 kW with an optical to optical efficiency of more than 50 %. Another way to scale the output power is the use of several disks in one laser resonator. Using this possibility, more than 27 kW output power with ten disks in one resonator and with good beam quality have been demonstrated. In this contribution the scaling laws for cw-operation of thin disk lasers will be laid down showing that more than 100 kW extracted output power from one single disk will also be possible. In conclusion, scaling the power per disk and using several disks in one resonator or using additional disks in a laser-amplifier, may result in MW class laser systems with good beam quality. Due to the large beam size of high power thin disk lasers (> 1 cm diameter) it is challenging to build a resonator for good beam quality or even fundamental mode operation. New resonator designs have been evaluated demonstrating that even for multi-kW output power nearly diffraction limited output power can be demonstrated. Also high power single frequency operation is possible because all non-linear effects are extremely low due to the large mode radii and therefore low power density in all optical components. Besides the outstanding properties of the thin disk laser design for cw-operation it is also well suited for pulsed laser systems, especially if high average output power is demanded. Hence, pulsed thin disk laser systems have been developed and demonstrated for the ns-, ps and fs-pulse duration regime. All systems show excellent beam quality and high efficiency. Since all nonlinear effects are extremely low also narrow line width operation is possible which allows for frequency conversion into the visible and UV spectral regime. So far more than 500 mJ pulse energy has been demonstrated using a master oscillator followed by a regenerative amplifier and a final multi-pass amplifier. In principle, this scheme can be used for any pulse length. Using cavity dumping, pulse durations between 10 ns and more than 1 μs are possible also with several 100 mJ pulse energy. And with adequate laser active materials the generation and amplification of fs-pulses is possible, too. From modelling results it can be shown that more than 10 J extracted pulse energy will be possible from one single disk. This will open a new way to build high energy lasers with high repetition rate and good beam quality. Besides the “classical” materials for solid state lasers also semiconductors can be used in the thin disk laser design. With special quantum well designs much more than 10 W cw-output power has been demonstrated from such lasers. Changing the semiconductor material and the quantum well structure results in different wavelength regimes for these widely tunable lasers. Today, optical pumped semiconductor thin disk lasers have been demonstrated from the UV to the MID-IR (390 nm to 2.8 μm). Because of the outstanding properties of thin disk lasers many companies offer thin disk lasers for many applications e.g. medical applications or materials processing. Today, the power levels are ranging from a few W up to 16 kW for welding applications.