Joerg Koerner

High-efficiency, room-temperature nanosecond Yb:YAG laser

Yb(3+)-doped gain media offer favorable properties for diode-pumped laser amplifiers for high-energy ns-pulses. To reach high optical-to-optical conversion efficiencies at room temperature however, very high and often impractical fluences are required both for pumping and extraction. Low temperature operation offers a solution, but the required cryogenic cooling systems add considerable complexity, bulkiness and cost. Multi-passing both pump and extraction beams through the gain medium is an alternative approach to overcome efficiency limitations at room temperature. In this article we present numerical and experimental results to this effect.We demonstrated ns-pulse output from a diode-pumped Yb:YAG amplifier at an energy of 566 mJ and an optical-to-optical efficiency of 20%, which is almost a doubling of the efficiency achieved with ns-lasers employing Yb(3+)-doped gain media at this energy level.

Spectroscopic characterization of various Yb3+ doped laser materials at cryogenic temperatures for the development of high energy class diode pumped solid state lasers

Precise values of absorption, emission and gain cross-sections of Yb:YAG, Yb:LuAG, Yb:CaF2 and Yb:FP15-glass at cryogenic temperatures are presented. To obtain the emission cross-sections two theoretical approaches were used. The first is the McCumber or reciprocity method (RM) which is based on the absorption spectra. The second is the Fuchtbauer-Ladenburg (FL) method using fluorescence spectra. From the results of cross-sections one can expect significant impact on laser performance on these materials especially in the case of high energy class diode pumped solid state lasers.

HiLASE cryogenically-cooled diode-pumped laser prototype for inertial fusion energy

We present the design parameters of a diode-pumped 100J-class multi-slab Yb:YAG laser at 10 Hz scalable to the kJ regime. Results of detailed energetics and thermo-optical modeling confirm the viability of cryogenic helium-gas cooling approach to drastically reduce thermally-induced distortions in the laser slabs. In addition, a comparison of spectral measurements from laser-diode stacks and Yb:YAG crystals validates the feasibility of highly efficient diode-pumped solid-state lasers at cryogenic temperatures.

Diode-pumped ytterbium-based chirped-pulse amplifier

This paper will describe a comparative study on four different Yb-doped laser materials in a diode-pumped femtosecond chirped-pulse amplifier. Broadband multi-pass amplification using single crystalline Yb:CaF2, Yb:KGW, and Yb:YAG as well as Yb-doped fluoride phosphate glass was demonstrated. The seed pulses as short as 85 fs were generated in a Ti:Sapphire oscillator tuned to a center-wavelength of 1030nm and then boosted to the 100 μJ-level in a diode-pumped Yb:glass regenerative amplifier. Furthermore, the amplifier performance at nanosecond and microsecond time-scales was analyzed. With regard to the 10-nm line-width of the emission cross section the gain narrowing in Yb:YAG was investigated in particular. The pulse spectrum was narrowed to 1.9nm at a total gain of 103 in an Yb:YAG multi-pass amplifier. This corresponds to a compressed pulse duration of 0.85 ps. When seeding with nanosecond pulses of a Q-switched oscillator a maximum pulse energy of 220mJ at a repetition rate of 10Hz has been achieved.

Temperature dependent emission and absorption cross section of Yb 3+ doped yttrium lanthanum oxide (YLO) ceramic and its application in diode pumped amplifier

Temperature dependent absorption and emission cross-sections of 5 at% Yb(3+) doped yttrium lanthanum oxide (Yb:YLO) ceramic between 80K and 300 K are presented. In addition, we report on the first demonstration of ns pulse amplification in Yb:YLO ceramic. A pulse energy of 102 mJ was extracted from a multi-pass amplifier setup. The amplification bandwidth at room temperature confirms the potential of Yb:YLO ceramic for broad bandwidth amplification at cryogenic temperatures.

Efficiency, Energy, and Power Scaling of Diode-Pumped, Short-Pulse Laser Amplifiers Using Yb-Doped Gain Media

We present a novel approach to overcome efficiency limitations of nanosecond lasers based on Yb-doped materials. Furthermore, we introduce a combination of bulk and thin-disk design for power scaling of diode-pumped lasers.

Comparative damage study on ytterbium-doped materials for diode-pumped high energy lasers

We report on a comparative study of the damage threshold of ytterbium-doped laser materials which are important for diode-pumped, high-energy class short pulse lasers. Both surface and bulk damage thresholds at the lasing wavelength of 1030 nm were investigated. A pulse duration of 6.4 ns was chosen which allows a scaling of the damage threshold for gain media in q-switched lasers as well as chirped-pulse amplifiers. In order to achieve comparability and repeatability of the damage measurements the surface preparation of the used samples was kept constant. Furthermore, the correlation of the bulk damage threshold and the UV absorption spectra was analyzed.

High-energy Laser Amplifiers using Ultra-broad Emitting Yb-doped Materials

High-energy laser amplifiers using Yb-doped gain media often show reduced efficiencies especially when operating at ultra-short pulses. We summarize techniques to improve storage and extraction efficiencies of Yb-based laser amplifiers.

High-Energy, Diode-Pumped Laser Amplification in Yb:CaF 2 and Yb:SrF 2

We present nanosecond pulse amplification to the Joule-level based on diode-pumped Yb:CaF2and Yb:SrF2. When seeding with microsecond pulses a maximum pulse energy of 1.54 J at a repetition rate of 1 Hz was achieved.