Ultrafast functional dynamics in biology, chemistry, and nanotech
The ultraviolet (UVB) damage mechanism of DNA, charge separation in solar cells, and the conformational change to dye molecules that initiates the human vision response; what do these all have in common? The answer: they involve femtosecond-timescale dynamics following photoexcitation that switch on or off the critical function of the system.1-3 Our goal is to capture dynamics like these through stroboscopic methods (think stop-action movies with fleetingly short laser pulses!)
Rapid collective motions pervade matter. Coherent oscillations of local phonon modes at nitrogen vacancy centers, charge density oscillations across a peptide molecule following ionization (think biomolecular plasmons), coherent electronic and vibrational wavepacket motion approaching a conical intersection: these events last just a few femtoseconds.4,5 Collective motions such as these may be harnessed someday for a practical purpose. Our goal is to learn what we can about the most rapid motions for the promise of future applications.
New spectroscopic methods employing ultrashort laser pulses, such as 2D electronic spectroscopy6, and the attosecond streak camera7, have opened up light-matter interaction studies to new domains. Our goal is to expand the reach of ultrafast spectroscopy and metrology methods, with new techniques enabled by a hyperspectral rainbow of light pulses, to allow the detection of ultrafast phenomena of a greater complexity. We are particularly interested in ultrabroadband 2D vibrational spectroscopy and ultrafast photoemission spectroscopy of photoexcited electronic states.
Ultrafast laser technologies
In the Moses Group, our laser research focuses on the development of hyperspectral light-pulse tools that can capture “ultrafast phenomena” (events so brief as to be barely detectable by state-of-the-art technology) in real time. We’re developing a unique instrument, a 10-femtosecond hyperspectral stroboscope, that will span the rainbow and then some! This device will emit 10-fs coherent synchronized light pulses covering the extreme ultraviolet, ultraviolet A/B/C, visible, near-infrared, and mid-infrared portions of the electromagnetic spectrum. We plan to eventually add a sub-femtosecond, i.e., attosecond, duration beam line, as well. This extreme wavelength coverage will allow us to probe multiple degrees of freedoms of a many-body system, such as the vibrational modes of multiple molecular functional groups, excitonic transitions, and electronic transitions in the atomic core.
Many of the technologies we’re incorporating in the stroboscope are new and are being developed in our lab. For example, adiabatic frequency conversion is a brand-new approach to generating coherent mid-infrared light that spans multiple octaves, and allows shaping of the spectral amplitude and phase over the full bandwidth8. As mentioned above, we are interested in applying new optical tools to the investigation of atoms, molecules, and nanostructures. Adiabatic frequency conversion is an example of the converse, as we have found that we can apply a traditional tool used by atomic physicists for controlling atomic populations, rapid adiabatic passage, to the control of nonlinear optics and frequency conversion!
Coherent pulse synthesis9,10 is a method for stitching multiple laser pulses together after they’ve been amplified. These pulses can be used as a coherent multi-color pulse sequence or as a single, extremely broadband probe pulse. High harmonic generation allows coherent conversion of laser light to the extreme ultraviolet. Employing these technologies and other state-of-the-art tools of perturbative and extreme nonlinear optics, a hyperspectral stroboscope covering EUV through mid-IR frequencies is now possible.
1. Bittner, E. R., & Silva, C. (2014). Noise-induced quantum coherence drives photo-carrier generation dynamics at polymeric semiconductor heterojunctions. Nature Communications, 5. doi:doi:10.1038/ncomms4119
2. Polli, D., Altoè, P., Weingart, O., Spillane, K. M., Manzoni, C., Brida, D., et al. (2010). Conical intersection dynamics of the primary photoisomerization event in vision. Nature, 467(7314), 440–443. doi:doi:10.1038/nature09346
3. Schreier, W. J., Schrader, T. E., Koller, F. O., Gilch, P., Crespo-Hernández, C. E., Swaminathan, V. N., et al. (2007). Thymine Dimerization in DNA Is an Ultrafast Photoreaction. Science, 315(5812), 625–629. doi:10.1126/science.1135428
4. Huxter, V. M., Oliver, T. A. A., Budker, D., & Fleming, G. R. (2013). Vibrational and electronic dynamics of nitrogen-vacancy centres in diamond revealed by two-dimensional ultrafast spectroscopy. Nature Physics, 9(11), 744–749. doi:10.1038/nphys2753
5. Remacle, F., & Levine, R. D. (2007). Probing ultrafast purely electronic charge migration in small peptides. Zeitschrift Fur Physikalische Chemie-International Journal of Research in Physical Chemistry & Chemical Physics, 221(5), 647–661. doi:10.1524/zpch.2007.221.5.647
6. Brixner, T., Mančal, T., Stiopkin, I. V., & Fleming, G. R. (2004). Phase-stabilized two-dimensional electronic spectroscopy. The Journal of Chemical Physics, 121(9), 4221–4236. doi:10.1063/1.1776112
7. Itatani, J., Quere, F., Yudin, G., IVANOV, M., Krausz, F., & Corkum, P. (2002). Attosecond streak camera. Physical Review Letters, 88(17), 173903. doi:10.1103/PhysRevLett.88.173903
8. Suchowski, H., Krogen, P. R., Huang, S.-W., Kartner, F. X., & Moses, J. (2013). Octave-spanning coherent mid-IR generation via adiabatic difference frequency conversion. Optics Express, 21(23), 28892–28901. doi:10.1364/OE.21.028892
9. Manzoni, C., Mücke, O. D., Cirmi, G., Fang, S., Moses, J., Huang, S.-W., Hong, K.-H., Cerullo, G. and Kärtner, F. X. (2015), Coherent pulse synthesis: towards sub-cycle optical waveforms. Laser & Photon. Rev., 9: 129–171. doi: 10.1002/lpor.201400181
10. Huang, S.-W., Cirmi, G., Moses, J., Hong, K.-H., Bhardwaj, S., Birge, J. R., et al. (2011). High-energy pulse synthesis with sub-cycle waveform control for strong-field physics. Nature Photonics, 5(8), 475–479. doi:10.1038/nphoton.2011.140