Coherent phonon oscillations with a frequency of 2.6 THz observed in optical pump/femtosecond x-ray diffraction probe experiments for different pump fluences of the mid-infrared excitation pulses centered at a wavelength of 5 µm. (IMAGE)
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Fig. 2. (a) Coherent phonon oscillations with a frequency of 2.6 THz observed in optical pump/femtosecond x-ray diffraction probe experiments for different pump fluences of the mid-infrared excitation pulses centered at a wavelength of 5 µm. The phonon wave packets are exclusively observed for strong excitation pulses, i.e., they are absent for pump fluences below 1.9 mJ/cm2. Thus, the reduction of the symmetry of the unit cell via strong optical pumping is necessary to get access to the phonon motion sketched in Fig. 1(d). (b) Spectrum of the phonon oscillation gained by a Fourier transform of the transient at a fluence of 2.9 mJ/cm2 shown in panel (a).
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MBI/M. Runge
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