Researchers at the Laser Zentrum Hannover e.V. (LZH) are developing the world’s first 2 μm femtosecond laser source with pulse energies in the μJ range.
For nearly 20 years, the advantages of using ultrashort laser radiation have been known. Due to fact that the pulsed have been shortened extremely, very high peak intensities can be reached, even for low pulse energies. The effects are significant: materials can be precisely cut and removed, without causing thermal damage to the material. This is already being used for many different applications, for example for eye surgery. Cornea transplants using the fs laser have been common place for years. And since 2011, the systems have been used to treat cataracts. Also, industry has profited from the advantages of ultrashort pulsed laser systems. These systems have been used, for example, to produce significantly more effective solar cells, or for improving expensive wafers used for chip production.
By expanding the emission spectrum of an fs laser into the spectral range of 2 µm, but simultaneously keeping the high pulse energies, the LZH wants to open the door for completely new fields of application, such as in micro-material processing, in medical technology, or in nanotechnology. Economic success is estimated to be high, and this „eye safe“ wavelength also offers a further advantage. Safety measures which are normally expensive and place limitations on production are relatively inexpensive for applications with this laser.
The concrete goal of the work in the Laser Development Department of the LZH is to construct a compact, regenerative, ultrashort pulse amplifier, emitting in the wavelength range around 2 µm, with pulse energies up to 50 µJ and pulse durations below 500 fs. As a seed laser, the scientists use an fs oscillator based on thulium doted fibers, with an output energy of 1-2 nJ, which is then amplified to 25 nJ. Directly following regenerative amplification, non-linear frequency conversion in the wavelength range of 3 to 6 µm is induced, in an optical parametric generator or amplifier (OPG/OPA). Gallium arsenide (GaAs) or zinc germanium phosphite (ZGP) are used as non-linear crystals.
“Our goal is a 2 µm fs laser system emitting in the mid-infrared range,” explains 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. Using IR radiation, polymers can be cut or welded without using additives. For German laser manufacturers, this basic know-how should provide a decisive advantage in the international competition surrounding ultrashort laser pulses.
The activities of the LZH are par of the project „Concepts for ultrashort pulsed beam sources of the next generation – Next Generation of Ultrafast Sources” NEXUS. Funding comes from the initiative “Ultrashort pulse laser for highly precise manufacturing” of the BMBF, until 2015.Apart from the laser institute in Hannover, project partners include the Friedrich Schiller University in Jena, the Leibniz University Hannover and the Ludwig-Maximilians University in Munich.
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