Ultrafast dynamics of photoexcited materials

In order to understand and tailor the properties of materials for specific applications, it is important to investigate the fundamental electronic and structural behavior of matter in equilibrium and in transient physical states. The relevant timescales, which govern the redistribution of electrons and the rearrangement of atoms in a solid after excitation to a non-equilibrium state, lie in the range of a few femtoseconds (10-15 s) up to several microseconds (10-6 s). Electronic measuring devices are not capable of resolving such ultrashort timescales. One alternative probe for the study of electron and lattice dynamics in solids is electromagnetic radiation in the form of ultrashort pulses. Femtosecond lasers can be employed successfully for exciting and probing electron and lattice dynamics in solids with a time resolution 1.000 to 10.000 times shorter than the resolution of other experimental techniques. Furthermore, intense ultrashort laser pulses prepare material systems in extreme physical states, serving as handles that produce novel states of matter.

A laser pulse is absorbed at the surface of a solid, initiating electronic and structural changes in the photoexcited volume.

In collaboration with Professor Eric Mazur at Harvard University, we employed an optical pump-probe technique, with which we are able to initiate and monitor changes in the dielectric function of solids in a broad range of optical frequencies, extending from the infrared to the ultraviolet part of the electromagnetic spectrum, with femtosecond time resolution. Our results include the response of semiconductors, metals, and polymers, bulk and thin films, to excited electronic populations which are 3 to 4 orders of magnitude larger compared to weak excitation studies. We were able to coherently control large amplitude lattice vibrations in tellurium, elucidate the solid-to-liquid phase transition mechanism in aluminum, and demonstrate enhanced optical nonlinearities in bis (n-butylimido) perylene thin films containing gold nanoparticles.  

In collaboration with Professor Keith Nelson at MIT, we employed a single-shot femtosecond pump-probe technique for the study of materials which are photoexcited above the threshold for permanent damage. So far, very few studies have looked into photoinduced phase transitions involving permanent structural changes. Single-shot measurements, which are able to capture all the time-dependent electronic and structural dynamics with a single laser pulse, are advantageous for investigating irreversible phase transitions. Our work focuses on coherent phonon spectroscopy of highly excited semimetals above the threshold for irreversible structural changes.  

Modulation of the dielectric function of tellurium by the excitation of coherent optical phonons.

Beyond its immediate scientific contribution, our work relates to technology and industry. The materials and processes being studied have important applications in semiconductor device technology, optical data storage, and materials processing.  

Single-shot femtosecond spectroscopy

Broadband dielectric function spectroscopy

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Related publications

Ultrafast dynamics of bis (n-butylimido) perylene thin films excited by two-photon absorptionhttp://dx.doi.org/10.1007/s00339-009-5197-zhttp://dx.doi.org/10.1007/s00339-009-5197-zshapeimage_2_link_0

C. R. Mendonca, M. Kandyla, T. Shih, R. F. Aroca, C. J. L. Constantino, and E. Mazur

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Optical control of coherent lattice vibrations in telluriumhttp://dx.doi.org/10.1103/PhysRevB.70.212302http://dx.doi.org/10.1103/PhysRevB.70.212302shapeimage_10_link_0

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Physical Review B 70, 212302 (2004)

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T. Shin, J.W. Wolfson, S.W. Teitelbaum, M. Kandyla, and K.A. Nelson

Review of Scientific Instruments 85, 083115 (2014)

T. Shin, S.W. Teitelbaum, J.W. Wolfson, M. Kandyla, and K.A. Nelson

The Journal of Chemical Physics 143, 194705 (2015)

T. Shin, J.W. Wolfson, S.W. Teitelbaum, M. Kandyla, and K.A. Nelson

Physical Review B 92, 184302 (2015)

open access

S.W. Teitelbaum, T. Shin, J.W. Wolfson, Y.-H. Cheng, I.J. Porter, M. Kandyla, and K.A. Nelson

Physical Review X 8, 031081 (2018)