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Novel High-Power Femtosecond Oscillators for Mid-Infrared Radiation Generation

Dr. K. Mak, MPQ

Next-generation oscillator technology relies on Yb doped thin-disk technology as one of its main building blocks. A unique combination of high average power, high repetition rate and high peak power is now possible, thanks to this technology. In contrast to laser amplifiers, we explore the power limitations of oscillators which generate femtosecond pulses directly and thus represent the simplest laser systems from this point of view. Oscillators providing over 200 W average power in combination with 10–30 fs pulse duration are highly attractive as driving sources for the generation of the deep ultraviolet (VUV/XUV) and middle infrared (MIR) parts of the optical spectrum.

Pic. 1. The Infrared spectrum (red line) together with the noise floor (gray line) measured using a monochromator.
The infrared spectrum extends from 500 cm−1 to 2250 cm−1 (−30 dB), corresponding to the wavelength range from 4.5 to 20 μm

 

With the aim of generating ever shorter pulses directly from the oscillator, a new mode-locking concept that relies on distributed (cascaded) Kerr lenses (DKLM) has been developed. For the first time, this concept allows the emission bandwidth limit of the gain medium to be overcome by a significant margin, yielding a spectrum that is four times broader (at FWHM) than the fluorescence spectrum of the gain medium. This concept is applicable to any type of gain medium and is expected to open up a new direction in femtosecond oscillator development and be extremely useful for 2 µm laser gain crystals such as Ho: YAG.

Our ultra-broadband, high-power oscillators are uniquely suited for high-sensitivity stimulated Raman scattering and can serve as a primary source for field-resolved spectroscopy. Our close collaboration with several research groups (H. Fattahi, I. Pupeza, M. Zigman) facilitates the immediate application of our techniques and yields very useful user feedback. Finally, our 2 µm based sources will enable efficient generation of much more powerful MIR radiation, making applications such as high-throughput MIR imaging feasible.