A Thulium fiber laser pumped or InP diode laser stack pumped Cr:ZnSe thin disk cw multimode laser at 2.4 mu m with an output power of 5 and 4 W, respectively, and with optical-to-optical 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.

We present a concept for power scaling of high brightness solid state lasers, which introduces so called gain modules containing the laser active media. These modules can be inserted as relay imaging optical systems in any type of laser resonators. The gain modules are optically neutral; hence, power scaling can be provided inserting several modules. Here, we provide the basic functional units of gain modules as well as an exemplary experimental implementation in thin-disk lasers with dynamically stable resonators. On the basis of these studies, more than 1 kW output power with an averaged M 2=2.6 could be demonstrated using two disks. Experiments with four disks are in preparation.

A Thulium fiber laser pumped Ho:YAG thin disk laser with 15W (cw) or several mJ (pulsed) operation will be presented. Additionally, a narrow (<0.5nm), tunable (30nm) cw operation near 2.09 µm, will be shown.

Experimental investigations concerning the operation characteristics of a coherent fiber laser MOPA array are presented. The experimental set up consists of a single frequency fiber coupled 35 mW DBR diode laser at 1063 nm as master oscillator and two polarization maintaining two stage 2 W Yb doped commercial fiber amplifiers. Phase control is accomplished by fiber coupled acousto-optic frequency shifters prior to the amplifiers and an opto-electric phase locked loop operating at 100 MHz. Phase measurement at the amplifier output is achieved by a combination of a free space and fiberoptic interferometer in combination with RF photodiodes. A heterodyne signal of the amplifier output signal is generated with respect to a reference signal derived from the master oscillator and works as input signal for the phase control. Phase coupling of the array is demonstrated and the degree of coherence is determined from the contrast of the far field diffraction pattern of the output beam as well as from analysis of the RF photodiode signals. The characteristics of the phase control and phase stability are investigated and residual phase disturbances resulting from thermal and acoustic effects as well as depolarization are identified. Achievable beam quality as a function of fill factor is compared to theoretical computations. Finally, perspectives concerning a coherent 4x15 W MOPA array with three stage amplifying systems are outlined.

In this paper, we report on our development of new concepts for power scaling of Yb:YAG thin-disk lasers with high brightness. Thin-disk laser resonators can be considered as resonators with variable internal lenses. Usually, there are dynamically stable configurations of this type of laser resonators with maximum insensitivity of the mode radius in the laser active medium to variations of the refractive power of the internal lens (thin-disk).

A significant reduction of the influence of the thermal lens for high power laser operation could be achieved in a thin-disk laser by systematic characterization of the thin-disk laser medium and the utilization of a dynamically stable resonator. Furthermore, the power scalability of the thin-disk laser concept could be demonstrated with two disks in one resonator and with large pump spot radii, realizing an output power of approximately 1 kW with nearly diffraction limited beam quality.

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 M-2 = 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.

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.

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.

25.4 W continuous-wave power of quasi-three-level transitions was achieved with a diode-pumped Nd:YAG thin disk laser. With an etalon in the resonator laser powers of 14 W at 946 nm and 6 W at 938.5 nm are obtained.

Experimental results and numerical simulations for the power scalability of an Yb:YAG thin disk laser in fundamental mode operation are presented. So far, an output power of 225 W with an M/sup 2/<1.1 is demonstrated.

For the construction of thin-disc lasers, active media with high RE-dopant concentrations and high thermal conductivity are required. YAG is well known for its excellent thermal properties, which are surpassed only by the sesquioxides Sc2O3, Y2O3, and Lu2O3. Among these, Lu2O3 is the most promising oxide because of its high Yb-doping capability at nearly no drop of the heat conductivity. Another important parameter is the quantum efficiency, which in the case of high Yb concentrations may decrease strongly due to energy migration between the Yb ions and finally deexcitation at certain impurities. To overcome this drawback either crystals of extreme purity have to be grown or crystals with structures have to be used, where for reduced energy migration the minimum Yb–Yb separation is quite large like in KY(WO4)2 (KYW) and LaSc3(BO3)4 (LSB). Both routes have been investigated and successfully applied in thin-disc lasers.

Yb-doped sesquioxides (Sc2O3, Lu2O3) grown by the Bridgman-method produced an output power of 124W cw in the thin-disk-laser-setup. Crystals of improved optical quality can be grown by the heat-exchanger-method (HEM).

Summary from only given. We present the first thin disk Nd:YVO/sub 4/ laser at 914 nm. A maximum output power of nearly 6 W has been reached at a cooling fluid temperature of -35 C with the 0.3 at. % doped sample.