Ultrafast Lasers

Brochure Ultrafast Lasers

Brochure Ultrafast Lasers

Ultrafast lasers are becoming increasingly widespread not only in science and research, but also in the industry. The Fraunhofer Institute for Laser Technology ILT has been conducting research on the generation, characterization and application of ultrafast laser pulses for 20 years now. We offer custom solutions for various power ranges from a few watts to 1.5kW and more, as well as for different pulse energies from µJ to mJ at pulse durations of 50 fs to 10 ps.

Femtosecond Amplifiers

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.

 

Pulse Compression

For industrial material processing, ever shorter pulses have been introduced in the past years. They allow for a greater precision and entirely new processes, e.g. by multiphoton absorption or filament formation in glass. High productivity requires, however, high average power of ultrafast lasers. Today, ultrafast lasers employed in the industry reach an average power of up to 150 W with pulse durations between 500 fs and 10 ps. Shorter pulse durations at high average power and peak power are not directly possible because of the basic properties of currently available laser media.

With a new flexible and compact add-on module, the pulse duration can be reduced by a factor of four, and, thus, the pulse peak power increased by approximately the same factor. The additional module is suitable for every ultrafast laser and based on nonlinear spectral broadening with subsequent pulse compression. The process combines a high efficiency of > 90 percent and preserves the beam quality. The unique feature is its ability to compress laser pulses at several 100 W average power and pulse energies of 10 to 200 μJ. This way, the parameter range currently relevant for industrial applications is completely covered.

Simulation

To design and optimize laser sources, Fraunhofer ILT has developed extensive software tools with which the relevant effects of ultrafast and high power lasers can be modeled. These allow a complete three-dimensional analysis of the system being examined:

  • Wave-optical calculation of the propagation of laser radiation and its transformation by means of active and passive optical elements
  • Modeling of 3- and 4-level gain media
  • Consideration of gain, pump light distribution, rate equations, heat conduction, the Kerr effect, self-phase modulation, dispersion and parasitic effects