At Fraunhofer ILT our experts use a broad portfolio of different amplifier designs based on Yb-doped crystals, including rod, INNOSLAB and Thin-Disk amplifiers. In general, the amplifiers are characterized by a very good beam quality and pulse quality close to bandwidth limit. The institute’s capabilities currently cover average powers of 1 W to kW-class, repetition rates from 10 kHz to 100 MHz and pulse energies of single μJ to 10 mJ. The following examples show the diversity of the ultrafast laser sources developed at Fraunhofer ILT.
- Compact 10 - 150 W Amplifier
For many applications of femtosecond lasers, an average power of 10 W to 150 W is sufficient. In this range, there is a need for inexpensive and compact amplifiers. A novel amplifier design can be used to cover this power range with nearly diffraction-limited beam quality of M² < 1.2 and a round beam profile. The low component count enables a cost-effective, very compact and rugged design.
Without chirped-pulse amplification (CPA), the amplifier allows pulse energies of 5 μJ with pulse durations of 800 fs at pulse repetition rates from 10 kHz to 100 MHz range. With a simple and compact CPA, pulse energies of > 30 μJ can be achieved.
- High-power INNOSLAB Amplifier with Spatial Filtering
Yb:INNOSLAB amplifiers typically provide output powers in the kW range with a beam quality of about M2 = 1.05 x 1.40. For some applications, the lower beam quality in one axis and the resulting ellipticity of the beam profile do not meet the requirements. Both beam quality and ellipticity can be improved in Yb:INNOSLAB amplifiers by a compact high-power spatial filter even at high peak power and kW-class average power. At 600 W average output power, the beam quality could be improved to M² = 1.05 x 1.15 by cutting off less than 10 percent of the power.
- High-power Thin-Disk Amplifier
A multi-pass amplifier was built based on an industrial Thin-Disk module (TRUMPF). This amplifier increases the output power of a Yb:INNOSLAB amplifier from 630 W to 1.5 kW at 710 fs pulse duration. For pulse durations < 1 ps, this sets a new world record (as of May 2015). At 1.5 kW average power, the beam quality is M2 = 1.5 x 2.0. Thanks to the high seed power of the INNOSLAB amplifier, the Thin-Disk amplifier can be kept simple, having 18 reflections on the disk. When the structure is optimized and the number of passes over the disc increased, the design has the potential to reach considerably higher average power and beam quality.