New project targets generation of mid-IR ultrashort laserpulses

Extremely short laser pulses help us understand and control matter on the tiniest scale. A challenge is to shift commercial laser technology from its preferred near-infrared wavelength range towards longer wavelengths: in particular in the mid-infrared ultrashort laser pulses can be used to probe and control dynamics of important chemical bonds, and they are also key tools in current extreme optical experiments.

Ultra-short laser pulses are indispensable components for a broad range of research fields, and among the applications are time-resolved spectroscopy in chemistry, biology, physics and materials science. In particular ultra-short pulses in the mid-infrared range (mid-IR, wavelength 2-10 microns) is currently a hot topic since they can be used for probing and even manipulating the ultra-fast vibrational dynamics of chemical bonds, such as the important C-H, O-H and N-H bonds. In order to temporally resolve the ultra-fast vibration and provide strong coherent excitations energetic few-cycle mid-IR pulses are needed.

 

Another major driver for maturing mid-IR ultrafast laser technology is the quest for the shortest pulses ever with wavelengths in the deep UV regime (10-200 nm) and X-ray regime (below 10 nm). In particular wavelength as lows as 3-4 nm are sought, because this spectral range contains the so-called water window of organic material, where water absorption is small and organic bonds absorb well. Few-cycle coherent pulses in the water window could be used for time-resolved X-ray microscopy of living specimens, which would give an unprecedented temporal and spatial resolution. Paradoxically, using longer wavelength mid-IR pulses (3-5 microns wavelength) instead of conventional near-IR laser pulses (0.8-1 microns wavelength) for pumping harmonic generation gives access to convert to much shorter wavelengths: with current near-IR technology as front end the deep UV is accessible, but with a mid-IR front end coherent few-cycle X-ray pulses in the water window can be generated.

 

A current obstacle is that today’s ultrafast laser technology is almost exclusively located in the near-infrared regime, and while parametric amplification is standard it always comes at a price of generating pulses with multi-cycle duration. The motivation behind the new project is to bridge the conventional ultrafast laser technology in the near-IR and the demand of ultrashort few-cycle energetic pulses in the mid-IR. One possible method relies on ultra-fast cascaded frequency conversion, which potentially can generate energetic mid-infrared pulses having a duration of only a few oscillation cycles of the electromagnetic field (i.e. 10-20 femtoseconds). This method compresses energetic, longer near-infrared laser pulses towards few-cycle duration using solitons.  While this occurs a broad-band few-cycle pulse can be observed in the mid-IR. Another possible method is to exploit ultrashort solitons generated with the simpler method of cascaded second-harmonic generation. When this happens, an ultrashort dispersive wave may form in the mid-IR.

 

The project title is Femto-midIR: Femtosecond few-cycle mid-infrared laser pulses, and it is a 3-year Research Project funded by the Danish Council Independent Research | Technology and Production Sciences. The project will start in the summer 2012.

 

Contact the scientist in charge, associate professor  Morten Bache, DTU Fotonik, for more details. Read more about the Ultrafast Nonlinear Optics group’s activities here.