Comparison of high-order harmonic generation in uracil and thymine ablation plumes

Abstract

We present studies of high-order harmonic generation (HHG) in laser ablation plumes of the ribonucleic acid nucleobase uracil and its deoxyribonucleic acid counterpart thymine. Harmonics were generated using 780 nm, 30 fs and 1300 nm, 40 fs radiation upon ablation with 1064 nm, 10 ns or 780 nm, 160 ps pulses. Strong HHG signals were observed from uracil plumes with harmonics emitted with photon energies >55 eV. Results obtained in uracil plumes were compared with those from thymine, which did not yield signs of harmonic generation. The ablation plumes of the two compounds were examined by collection of the ablation debris on a silicon substrate placed in close proximity to the target and by time-of-flight mass spectrometry. From this evidence we conclude that the differences in HHG signal are due to the different fragmentation dynamics of the molecules in the plasma plume. These studies constitute the first attempt to analyse differences in structural properties of complex molecules through plasma ablation-induced HHG spectroscopy.

Probing the molecular frame of uracil and thymine with high-harmonic generation spectroscopy

“…But only only one experimental attempt to measure HHG in uracil and thymine is present in literature, by Hutchinson et al. 47 Authors used a laser ablation technique to produce weakly ionized plasma plumes from solid samples of uracil and thymine. Only the uracil HHG signal has been observed.…”

Why plasma harmonics?

“…Finally, the developed method has already allowed the analysis of the structural properties of complex systems, such as DNA components (thymine and uracil, Fig. 10) [121,122].…”

“…Among other possible developments in the application of plasma HHG technique one may anticipate such areas as seeding of plasma resonance harmonics in the XUV free-electron lasers, application and analysis of endohedral fullerenes using plasma HHG, analysis of molecular structures through the study of harmonic spectra from oriented molecules in plasmas using the gating and pump-probe techniques [121,123,124].…”

“…units) Figure 10. XUV spectra from uracil, thymine and a target made of a 50 : 50 mixture of uracil and thymine in the case of 1300 nm probe pulses and 780 nm, 160 ps ablating pulses (I = 2 × 10 10 W cm -2 ) (reproduced from [121] with permission from the PCCP Owners Society). ent-day plasma harmonic studies motivate for further development of this technique.…”

Full-dimensional treatment of short-time vibronic dynamics in a molecular high-order-harmonic-generation process in methane

“…In methane, CH 4 , the key dynamics occur in the vicinity of a symmetry-required triple electronic surface intersection in a transiently prepared CH 4 + cation. In larger, more electronically complex systems, which are beginning to be explored with HHS [53][54][55][56][57][58][59][60] (see Ref. [61] for a review), conical intersections and nonseparable vibronic dynamics are expected to become ubiquitous [62,63].…”