The LUMOS facility is equipped with ultrafast laser systems covering a broad spectral range that spans the far-infrared to the soft X-ray portion of the electromagnetic spectrum. These systems enable a multitude of ultrafast spectroscopic and imaging experiments, including optical-pump terahertz-probe spectroscopy, high harmonic generation extreme ultraviolet spectroscopies, and scanning probe imaging and spectroscopies. We work closely with the Center for Integrated Nanotechnologies to study and develop novel materials for a wide range of applications.

Our research is focused on the properties and dynamic behavior of complex organic (polymers, molecules) and inorganic (multiferroics, heavy fermions and Kondo systems, topological insulators, and oxide heterostructures) materials. We apply scanning probe microscopies and ultrafast optical spectroscopy to gain an insight into materials functionality at the fundamental spatial and temporal scales. In particular, we rely on broadband coherent electromagnetic probes spanning X-Ray to THz photon energies to investigate how materials properties emerge from strong correlations among spin, lattice, orbital and charge degrees of freedom. We also use scanning tunneling (magnetic, piezoelectric and others) microscopy to reveal the intrinsic connection between these correlations and spatial homogeneity of materials response. Finally, we manipulate the spectral and temporal phases and amplitudes of ultrafast electromagnetic pulses with a goal of controlling the system evolution pathways ensuing coherent photoexcitation.

LUMOS Staff

Abul Azad LUMOS Team Leader

Hou-Tong Chen

Anatoly Efimov

Nicholas Sirica

Dmitry Yarotsky

Prashant Padmanabhan

Antoinette Taylor

 

LUMOS Affiliated Scientists

Rohit Prasankumar

Andrew Cardin

George Rodriguez

Richard Sandberg

Ultrafast Spectroscopy

Contacts: Dmitry Yarotski, George Rodriguez

We are interested in the use of ultrafast optical pulses to study dynamics and phenomena in a variety of complex materials over a broad frequency range (terahertz to x-rays). Some recent examples multiferroics and ferroelectric/ferromagnet oxide heterostructures, ultrafast dynamics in two-dimensional nanosystems (e.g. graphene, topological insulators, transition metal dichalcogenides), and spatiotemporally resolved carrier transport in silicon core/shell nanowires. We further develop new ultrafast optical techniques for interrogating materials over a broad wavelength range with high temporal and spatial resolution (e.g. ultrafast wide-field optical microscopy, infrared pump/optical probe techniques etc.). Finally, we are also interested in combining metamaterial and plasmonic structures with complex materials to control their properties and reveal new phenomena.

^{Time-resolved second harmonic generation measurements on aferroelectric/ferromagnet
oxide heterostructure reveal coupling between magnetic and electric order developing
within tens of picoseconds, limited by spin-lattice relaxation in the ferromagnetic layer.}

Metamaterials and Terahertz

Contacts: Abul Azad and Hou-Tong Chen

Our research interests include fundamental and applied aspects of metamaterials, plasmonics, and electromagnetic phenomena. Recent examples include ultrathin metamaterial terahertz absorber, optically reconfigurable metamaterial, ultrafast surface plasmon polariton, and broadband plasmonic solar absorber. We are also interested in studying strongly coupled metamaterial systems and their interactions with natural/artificial media. We have employed strongly coupled systems to enable electrically small efficient microwave antenna and tunable terahertz modulators. For this research, we extensively use nano/microfabrication facilities and a variety of spectroscopic techniques including time resolved terahertz and optical pump-probe systems. Additionally, we are involved in developing new measurement capabilities including time-resolved terahertz spectroscopy, terahertz ranging system, and microwave anechoic chamber for antenna characterization.

Ultrathin broadband solar light absorber.

X-Ray Imaging and Spectroscopy of Materials Dynamics

Contacts: Richard Sandberg, Dmitry Yarotski, Steve Gilbertson, and George Rodriguez

We are developing x-ray imaging and spectroscopy techniques for studying materials dynamics on a variety of systems. We use various sources from synchrotron and x-ray free electron laser based facilities to tabletop high harmonic generation sources to probe materials' structural, charge, and spin changes on the shortest of time scales (femtosecond to attosecond). We use these x-ray sources to study materials' electronic dynamics with time-resolved angle resolved photoemission, time resolved spectroscopy, and image nanometer-scale structural or magnetic spin dynamics with coherent x-ray imaging.

Diagnostics for Materials in Extremes

Contacts: George Rodriguez and Steve Gilbertson

Our team develops various optical diagnostics to study materials in extreme conditions including shock, detonation, and plasma environments. These diagnostics have taken various forms over time, but include laser velocimetries
(VISAR and photonic Doppler velocimetry [PDV]), time resolved spectroscopies, THz spectroscopy, x-ray imaging,
and optical fiber Bragg grating sensor development. These diagnostics have been used to support a wide array of NNSA and national security missions.

LUMOS Postdocs and Students

2015

1. S. Gilbertson, S. I. Jackson, S. W. Vincent, and G. Rodriguez, “Detection of high explosive detonation across material interfaces with chirped fiber Bragg gratings,” Appl. Opt., vol. 54, no. 13, pp. 3849–3854, 2015.

2. M. A. Subhan, N. Uddin, P. Sarker, A. K. Azad, and K. Begum, “Photoluminescence, photocatalytic and antibacterial activities of CeO₂·CuO·ZnO nanocomposite fabricated by co-precipitation method,” Spectrochim. Acta Part A Mol. Biomol. Spectrosc., vol. 149, pp. 839–850, 2015.

3. T. S. Luk, D. de Ceglia, S. Liu, G. A. Keeler, R. P. Prasankumar, M. A. Vincenti, M. Scalora, M. B. Sinclair, and S. Campione, “Enhanced third harmonic generation from the epsilon-near-zero modes of ultrathin films,” Appl. Phys. Lett., vol. 106, no. 15, p. 151103, 2015.

4. R. V. Aguilar, J. Qi, M. Brahlek, N. Bansal, A. Azad, J. Bowlan, S. Oh, A. J. Taylor, R. P. Prasankumar, and D. A. Yarotski, “Time-resolved terahertz dynamics in thin films of the topological insulator Bi₂Se₃,” Appl. Phys. Lett., vol. 106, no. 1, p. 11901, 2015.

5. N. Kamaraju, W. Pan, U. Ekenberg, D. M. Gvozdić, S. Boubanga-Tombet, P. C. Upadhya, J. Reno, A. J. Taylor, and R. P. Prasankumar, “Terahertz magneto-optical spectroscopy of a two-dimensional hole gas,” Appl. Phys. Lett., vol. 106, no. 3, p. 31902, 2015.

6. A. K. Azad, D. R. Chowdhury, H.-T. Chen, and A. J. Taylor, “Tuning of terahertz metamaterials’ resonances via near field coupling,” in SPIE Sensing Technology + Applications, 2015, p. 94830G.

7. G. Rodriguez, M. Jaime, C. H. Mielke, F. F. Balakirev, A. Azad, R. L. Sandberg, B. Marshall, B. M. La Lone, B. F. Henson, L. Smilowitz, M. Marr-Lyon, and T. D. Sandoval, “Insight into fiber Bragg sensor response at 100-MHz interrogation rates under various dynamic loading conditions,” in SPIE Sensing Technology + Applications, 2015, p. 948004.

2014

1. Sheu, Y. M. et al. "Using ultrashort optical pulses to couple ferroelectric and ferromagnetic order in an oxide heterostructure." Nat. Commun. 5, 5832 (2014).

2. Sandberg, R. L. et al. "Embedded optical probes for simultaneous pressure and temperature measurement of materials in extreme conditions." J. Phys. Conf. Ser.500, 142031 (2014).

3. Rodriguez, G. et al. "Fiber Bragg sensing of high explosive detonation experiments at Los Alamos National Laboratory." J. Phys. Conf. Ser. 500, 142030 (2014).

4. Karl, N. et al. "An electrically driven terahertz metamaterial diffractive modulator with more than 20 dB of dynamic range." Appl. Phys. Lett. 104, 91115 (2014).

5. Sheu, Y. M. et al. "Polaronic Transport Induced by Competing Interfacial Magnetic Order in a La 0.7 Ca 0.3 MnO₃/BiFeO₃ Heterostructure." Phys. Rev. X 4, 21001 (2014).

6. Vanderhoef, L. R. et al. "Charge carrier relaxation processes in TbAs nanoinclusions in GaAs measured by optical-pump THz-probe transient absorption spectroscopy." Phys. Rev. B 89, 45418 (2014).

7. Chowdhury, D. R., O’Hara, J. F., Taylor, A. J. & Azad, A. K. "Orthogonally twisted planar concentric split ring resonators towards strong near field coupled terahertz metamaterials." Appl. Phys. Lett. 104, 101105 (2014).

8. Seo, M. et al. "Ultrafast optical microscopy on single semiconductor nanowires." SPIE OPTO 89840U–89840U (2014).

9. Chen, H.-T. "Semiconductor activated terahertz metamaterials." Optoelectron. 1–17 (2014).

10. Chowdhury, D. R., Azad, A. K., Zhang, W. & Singh, R. "Corrections to 'Near Field Coupling in Passive and Active Terahertz Metamaterial Devices.” Terahertz Sci. Technol. IEEE Trans. 4, 400 (2014).

11. Kaul, A. M. et al. "Damage growth and recollection in aluminum under axisymmetric convergence using a helical flux compression generator." J. Appl. Phys. 115, 23516 (2014).

12. Gilbertson, S. M. et al. "Ultrafast Photoemission Spectroscopy of the Uranium Dioxide UO 2 Mott Insulator: Evidence for a Robust Energy Gap Structure." Phys. Rev. Lett. 112, 87402 (2014).

13. Appavoo, K. et al. "Ultrafast phase transition via catastrophic phonon collapse driven by plasmonic hot-electron injection." Nano Lett. 14, 1127–1133 (2014).

14. Rodriguez, G. et al. "High pressure sensing and dynamics using high speed fiber Bragg grating interrogation systems." in SPIE Sens. Technol. Appl. 90980C–90980C (2014).

15. Barber, J. L., Barnes, C. W., Sandberg, R. L. & Sheffield, R. L. "Diffractive imaging at large Fresnel number: Challenge of dynamic mesoscale imaging with hard x-rays." Phys. Rev. B 89, 184105 (2014).

16. Udd, E., Rodriguez, G. & Sandberg, R. L. "High-speed fiber grating pressure sensors." SPIE Sens. Technol. Appl. 90980B–90980B (2014).

17. Chowdhury, D. R. et al. "Excitation of dark plasmonic modes in symmetry broken terahertz metamaterials." Opt. Express 22, 19401–19410 (2014).

18. Chowdhury, D. R., Singh, R., Taylor, A. J. & Azad, A. K. "Ultrafast Switching in Terahertz Metamaterials using Ion Implanted Silicon on Sapphire." arXiv Prepr. arXiv1407.2715 (2014).

19. Sampat, S. et al. "Tunable Charge Transfer Dynamics at Tetracene/LiF/C60 Interfaces." J. Phys. Chem. C (2014).

20. Heyes, J. E. et al. "Hybrid metasurface for ultra-broadband terahertz modulation." Appl. Phys. Lett. 105, 181108 (2014).

21. Lee, J. & Prasankumar, R. P. Correlation between quantum charge fluctuations and magnetic ordering in multiferroic LuFe₂O₄." Eur. Phys. J. B 87, 1–5 (2014).