Jochen Speiser

Thin-disk laser - Power scaling to the kW regime in fundamental mode operation

A significant reduction of the influence of the thermal lens in thin-disk lasers in high power laser operation mode could be achieved, using dynamically stable resonators. For designing the resonator, investigations of thermally induced phase distortions of thin-disks as well as numerical simulations of the field distribution in the resonator were performed. This characterization was combined with thermo-mechanical computations. On the basis of these studies, about 500 W output power with an averaged M2 = 1.55 could be demonstrated, using one disk. Almost 1 kW output power with good beam quality could be extracted, using two disks. For the purpose of further power scaling in nearly fundamental mode operation, experiments using more than two disks are in preparation.

Scaling of thin-disk lasers—influence of amplified spontaneous emission

For the thin-disk laser the increased amplification of spontaneous emission for larger disks limits the scalability. An analytical model of the influence of the amplified spontaneous emission on the effective lifetime of the excited ions is developed and with this model optimized parameters for the minimization of the lifetime reduction are found. It is shown that output powers up to the megawatt level are achievable with a single disk, but with disk dimensions far beyond the actual technical limits. The model is also used to evaluate the limits of achievable energy.

Thin disk laser—Energy scaling

A time resolved numerical model of the interaction between pump absorption, excitation and amplified spontaneous emission (ASE) for the Thin Disk laser design was developed. The model accounts for the spectral distribution of the spontaneous emission, the spectral and spatial distribution of emission and absorption and the spectral and angular transmission of surfaces or coatings.

Numerical Modeling of High Power Continuous-Wave Yb:YAG Thin Disk Lasers, Scaling to 14 kW

A numerical model of the thin disk laser, including inversion, absorption, intracavity power density, temperature and ASE is presented. It is combined with FEM analysis to compute deformation, stress and thermal lensing.

Mode Dynamics and Thermal Lens Effects of Thin Disk Lasers

In principle, the thin-disk laser concept opens the possibility to demonstrate high power, high efficiency and good beam quality, simultaneously. For this purpose, a very homogeneous pump power distribution on the disk is necessary as well as very low phase distortions of the disk itself. Spatial mode structure and thermal lens effects in an Yb:YAG thin-disk laser have been investigated as function of the pump power in linear and folded resonators. Whereas thermal lens is shown to be very weak due to the thin disk geometry, a strong correlation of the laser mode with respect to the power density distribution of the pump radiation is exhibited. The experimental results are compared with numerical simulations of the field distribution within the resonator as well as in the far field demonstrating the excellent homogeneity of the disk as laser active medium.

Cr:ZnSe thin disk cw laser

A Thulium fiber laser pumped or InP diode laser stack pumped Cr:ZnSe thin disk cw multimode laser at 2.4 μm with an output power of 5 and 4 W, respectively, and with optical-tooptical efficiencies of 10% will be presented. An experimentally verified and numerically simulated thermal lensing induced and cyclic instability in the laser system will be shown. As a consequence, in order to prevent the lasing conditions in the resonator to be unstable, power scaling of a Cr:ZnSe thin disk laser is possible by enlarging the pump spot and reducing thereby the thermal lensing condition. Therefore, the instability is not initiated. As a conclusion, the investigated instability will show up in any laser active material which has a strong absorption of the pump beam, for instance in transition metal ion laser material systems in connection with any laser concept, like for instance in thin disk, bulk or slab designs.

Comment on "Surface loss limit of the power scaling of a thin-disk laser"

A recent paper [J. Opt. Soc. Am. B23, 1074 (2006)] on power-scaling aspects of thin-disk lasers is based on a wrong assumption concerning the impact of amplified spontaneous emission, which is greatly overestimated. As a consequence of this and two other issues, the evaluated power-scaling limits—which are close to already realized performance values—are substantially too low.

High-power thin disk lasers

In the past decade, the Thin Disk laser design was very successful as a high power laser design for cw lasers with good beam quality and high efficiency. Also pulsed lasers based on Thin Disk amplifiers achieved comparable high average power, but mostly with medium pulse energies. Latest results show that the thin disk still has not reached the scaling limits, neither in cw operation nor in pulsed operation.

Cr:ZnSe Bulk and Cr:ZnSe Thin Disk cw Lasers

A Thulium-fiber-laser pumped Cr:ZnSe bulk cw laser with an output power of 6.5W as well as a Thulium-fiber-laser or diode-laser-stack pumped Cr:ZnSe thin disk cw laser with almost 2W of output powers will be presented.

High power thin disk Ho:YAG laser

The thin disk laser is a successful concept for high output power and/or high pulse energy, high efficiency and good beam quality in the 1 μm range. Holmium-doped materials are a promising approach to transform this success to the 2 μm range. Ho:YAG is especially interesting for high pulse energies due to the long fluorescence lifetime (~ 8 ms) which provides good energy storage capabilities. We have realized a Ho:YAG thin-disk laser with a cw output power of 15 W at 2.09 μm and a maximum optical-to-optical efficiency of 37%. The laser was pumped with a Tm-fiber laser. Numerical simulations are used for further characterization.