We generate 52 mW of broadband pulses at 8 μm wavelength by difference frequency generation (DFG) in orientation patterned GaP (OP-GaP). Pumping by fiber lasers is possible because of the wide transparency range of GaP. An Er fiber oscillator at 1.5 μm wavelength and 90 MHz repetition rate provides pulses for direct amplification and shifting to 1.9 μm followed by amplification in Tm doped fiber. The two beams are mixed in OP-GaP with up to 20% photon conversion efficiency. The wavelength is tunable from 5 to 11 μm by changing the crystal period or the degree of wavelength shifting. With coherent broadening, we can also generate midinfrared frequency combs with tunable carrier envelope offset frequencies.
Three-dimensional imaging of molecules in the gas phase has been an important but challenging task, since the randomly oriented molecules only provide one-dimensional structural information. In this work, we show that a three-dimensional structure can be reconstructed from ultrafast electron diffraction from impulsively laser-aligned molecules. The diffraction pattern is taken at the maximum degree of alignment, around two picoseconds after the excitation of the laser. An iterative retrieval algorithm is developed to resolve the problem generated by imperfect alignment and a holographic algorithm is used to reconstruct molecular structure.