LZH to Push fs Pulse Energies into µJ Range

The first 2-µm femtosecond (fs) laser source with pulse energies in the µJ range is under development and could lead to new applications in medical technology, micromaterial processing and nanotechnology.

The advantages of using ultrashort laser radiation have been known for nearly 20 years. Because the pulse is extremely shortened, very high peak intensities can be reached, even for low pulse energies. These effects are significant: Materials can be precisely cut and removed without thermal damage to the material. Because of this, these lasers have been used for eye surgeries including cornea transplants and cataract treatment, and for the production of more effective solar cells and improved wafers for chip production.

Now, by expanding the emission spectrum of the femtosecond laser into the 2-µm spectral range, while simultaneously keeping the pulse energies high, researchers at the Laser Zentrum Hannover eV (LZH) have opened the door to new fields of application.

The LZH team hopes to construct a compact, regenerative, ultrashort-pulse amplifier that emits in the 2-µm wavelength range, with pulse energies up to 50 µJ and pulse durations below 500 fs. As a seed laser, the scientists used a femtosecond oscillator based on thulium-doped fibers, with an output energy of 1 to 2 nJ, which is then amplified to 25 nJ. Directly after regenerative amplification, nonlinear frequency conversion in the wavelength range of 3 to 6 µm is induced, in an optical parametric generator or amplifier. Gallium arsenide or zinc germanium phosphite was used as a nonlinear crystal.

“Our goal is a 2-µm femtosecond laser system emitting in the mid-infrared range,” said Dr. Dieter Wandt, head of the Ultrafast Photonics Group, which is working on this laser. “These wavelengths have a great growth potential.”

Wandt says that polymer processing is one important field of application. With infrared radiation, polymers can be cut or welded without using additives. For German laser manufacturers, this basic know-how should provide an advantage in the international competition surrounding ultrashort laser pulses.

Femtosecond laser development is part of the project NEXUS (Concepts for ultrashort pulse beam sources of the next generation — Next Generation of Ultrafast Sources). It is funded until 2015 by the “Ultrashort pulse laser for highly precise manufacturing” initiative of the BMBF, or Federal Ministry of Education and Research.

For more information, visit: www.lzh.de/en