Matthias C. Hoffmann

All Publications

• The 2023 terahertz science and technology roadmap JOURNAL OF PHYSICS D-APPLIED PHYSICS Leitenstorfer, A., Moskalenko, A. S., Kampfrath, T., Kono, J., Castro-Camus, E., Peng, K., Qureshi, N., Turchinovich, D., Tanaka, K., Markelz, A. G., Havenith, M., Hough, C., Joyce, H. J., Padilla, W. J., Zhou, B., Kim, K., Zhang, X., Jepsen, P., Dhillon, S., Vitiello, M., Linfield, E., Davies, A., Hoffmann, M. C., Lewis, R., Tonouchi, M., Klarskov, P., Seifert, T. S., Gerasimenko, Y. A., Mihailovic, D., Huber, R., Boland, J. L., Mitrofanov, O., Dean, P., Ellison, B. N., Huggard, P. G., Rea, S. P., Walker, C., Leisawitz, D. T., Gao, J., Li, C., Chen, Q., Valusis, G., Wallace, V. P., Pickwell-MacPherson, E., Shang, X., Hesler, J., Ridler, N., Renaud, C. C., Kallfass, I., Nagatsuma, T., Zeitler, J., Arnone, D., Johnston, M. B., Cunningham, J. 2023; 56 (22)

  View details for DOI 10.1088/1361-6463/acbe4c

  View details for Web of Science ID 000968966700001

• Measurement of femtosecond dynamics of ultrafast electron beams through terahertz compression and time-stamping APPLIED PHYSICS LETTERS Othman, M. K., Gabriel, A. E., Snively, E. C., Kozina, M. E., Shen, X., Ji, F., Lewis, S., Weathersby, S., Vasireddy, P., Luo, D., Wang, X., Hoffmann, M. C., Nanni, E. A. 2023; 122 (14)

  View details for DOI 10.1063/5.0134733

  View details for Web of Science ID 000964331000010

• Terahertz-Driven Local Dipolar Correlation in a Quantum Paraelectric. Physical review letters Cheng, B., Kramer, P. L., Shen, Z. X., Hoffmann, M. C. 2023; 130 (12): 126902

  Abstract

  Light-induced ferroelectricity in quantum paraelectrics is a new avenue of achieving dynamic stabilization of hidden orders in quantum materials. In this Letter, we explore the possibility of driving a transient ferroelectric phase in the quantum paraelectric KTaO_{3} via intense terahertz excitation of the soft mode. We observe a long-lived relaxation in the terahertz-driven second harmonic generation (SHG) signal that lasts up to 20 ps at 10 K, which may be attributed to light-induced ferroelectricity. Through analyzing the terahertz-induced coherent soft-mode oscillation and finding its hardening with fluence well described by a single-well potential, we demonstrate that intense terahertz pulses up to 500  kV/cm cannot drive a global ferroelectric phase in KTaO_{3}. Instead, we find the unusual long-lived relaxation of the SHG signal comes from a terahertz-driven moderate dipolar correlation between the defect-induced local polar structures. We discuss the impact of our findings on current investigations of the terahertz-induced ferroelectric phase in quantum paraelectrics.

  View details for DOI 10.1103/PhysRevLett.130.126902

  View details for PubMedID 37027861

• Ultrafast Optomechanical Strain in Layered GeS. Nano letters Luo, D., Zhang, B., Sie, E. J., Nyby, C. M., Fan, Q., Shen, X., Reid, A. H., Hoffmann, M. C., Weathersby, S., Wen, J., Qian, X., Wang, X., Lindenberg, A. M. 2023

  Abstract

  Strong coupling between light and mechanical strain forms the foundation for next-generation optical micro- and nano-electromechanical systems. Such optomechanical responses in two-dimensional materials present novel types of functionalities arising from the weak van der Waals bond between atomic layers. Here, by using structure-sensitive megaelectronvolt ultrafast electron diffraction, we report the experimental observation of optically driven ultrafast in-plane strain in the layered group IV monochalcogenide germanium sulfide (GeS). Surprisingly, the photoinduced structural deformation exhibits strain amplitudes of order 0.1% with a 10 ps fast response time and a significant in-plane anisotropy between zigzag and armchair crystallographic directions. Rather than arising due to heating, experimental and theoretical investigations suggest deformation potentials caused by electronic density redistribution and converse piezoelectric effects generated by photoinduced electric fields are the dominant contributors to the observed dynamic anisotropic strains. Our observations define new avenues for ultrafast optomechanical control and strain engineering within functional devices.

  View details for DOI 10.1021/acs.nanolett.2c05048

  View details for PubMedID 36898060

• Lightwave-driven electron emission for polarity-sensitive terahertz beam profiling APL PHOTONICS Lange, S., Hoffmann, M. C., Jepsen, P. 2023; 8 (1)

  View details for DOI 10.1063/5.0125947

  View details for Web of Science ID 000923543500001

• Ultrafast modification of the electronic structure of a correlated insulator PHYSICAL REVIEW RESEARCH Granaes, O., Vaskivskyi, I., Wang, X., Thunstroem, P., Ghimire, S., Knut, R., Soederstroem, J., Kjellsson, L., Turenne, D., Engel, R. Y., Beye, M., Lu, J., Higley, D. J., Reid, A. H., Schlotter, W., Coslovich, G., Hoffmann, M., Kolesov, G., Schissler-Langeheine, C., Styervoyedov, A., Tancogne-Dejean, N., Sentef, M. A., Reis, D. A., Rubio, A., Parkin, S. P., Karis, O., Rubensson, J., Eriksson, O., Dirr, H. A. 2022; 4 (3)

  View details for DOI 10.1103/PhysRevResearch.4.L032030

  View details for Web of Science ID 000856584000004

• Observation of photo-induced plasmon-phonon coupling in PbTe via ultrafast x-ray scattering. Structural dynamics (Melville, N.Y.) Jiang, M. P., Fahy, S., Hauber, A., Murray, E. D., Savic, I., Bray, C., Clark, J. N., Henighan, T., Kozina, M., Lindenberg, A. M., Zalden, P., Chollet, M., Glownia, J. M., Hoffmann, M. C., Sato, T., Zhu, D., Delaire, O., May, A. F., Sales, B. C., Merlin, R., Trigo, M., Reis, D. A. 2022; 9 (2): 024301

  Abstract

  We report the observation of photo-induced plasmon-phonon coupled modes in the group IV-VI semiconductor PbTe using ultrafast x-ray diffuse scattering at the Linac Coherent Light Source. We measure the near-zone-center excited-state dispersion of the heavily screened longitudinal optical (LO) phonon branch as extracted from differential changes in x-ray diffuse scattering intensity following above bandgap photoexcitation. We suggest that upon photoexcitation, the LO phonon-plasmon coupled (LOPC) modes themselves become coupled to longitudinal acoustic modes that drive electron band shifts via acoustic deformation potentials and possibly to low-energy single-particle excitations within the plasma and that these couplings give rise to displacement-correlations that oscillate in time with a period given effectively by the heavily screened LOPC frequency.

  View details for DOI 10.1063/4.0000133

  View details for PubMedID 35311000

• Ultrafast electron dynamics in platinum and gold thin films driven by optical and terahertz fields APPLIED PHYSICS LETTERS Unikandanunni, V., Rigoni, F., Hoffmann, M. C., Vavassori, P., Urazhdin, S., Bonetti, S. 2022; 120 (2)

  View details for DOI 10.1063/5.0068086

  View details for Web of Science ID 000791375600005

• Spatiotemporal Measurement of THz Near-Fields Using Electro-Optic Sampling Gabriel, A. E., Othman, M. K., Hoffmann, M. C., Nanni, E. A., IEEE IEEE. 2022

  View details for DOI 10.1109/IRMMW-THz50927.2022.9895825

  View details for Web of Science ID 000865953000311

• Subterahertz collective dynamics of polar vortices. Nature Li, Q., Stoica, V. A., Pasciak, M., Zhu, Y., Yuan, Y., Yang, T., McCarter, M. R., Das, S., Yadav, A. K., Park, S., Dai, C., Lee, H. J., Ahn, Y., Marks, S. D., Yu, S., Kadlec, C., Sato, T., Hoffmann, M. C., Chollet, M., Kozina, M. E., Nelson, S., Zhu, D., Walko, D. A., Lindenberg, A. M., Evans, P. G., Chen, L., Ramesh, R., Martin, L. W., Gopalan, V., Freeland, J. W., Hlinka, J., Wen, H. 2021; 592 (7854): 376–80

  Abstract

  The collective dynamics of topological structures1-6 are of interest from both fundamental and applied perspectives. For example, studies of dynamical properties of magnetic vortices and skyrmions3,4 have not only deepened our understanding of many-body physics but also offered potential applications in data processing and storage7. Topological structures constructed from electrical polarization, rather than electron spin, have recently been realized in ferroelectric superlattices5,6, and these are promising for ultrafast electric-field control of topological orders. However, little is known about the dynamics underlying the functionality of such complex extended nanostructures. Here, using terahertz-field excitation and femtosecond X-ray diffraction measurements, we observe ultrafast collective polarization dynamics that are unique to polar vortices, with orders-of-magnitude higher frequencies and smaller lateral size than those of experimentally realized magnetic vortices3. A previously unseen tunable mode, hereafter referred to as a vortexon, emerges in the form of transient arrays of nanoscale circular patterns of atomic displacements, which reverse their vorticity on picosecond timescales. Its frequency is considerably reduced (softened) at a critical strain, indicating a condensation (freezing) of structural dynamics. We use first-principles-based atomistic calculations and phase-field modelling to reveal the microscopic atomic arrangements and corroborate the frequencies of the vortex modes. The discovery of subterahertz collective dynamics in polar vortices opens opportunities for electric-field-driven data processing in topological structures with ultrahigh speed and density.

  View details for DOI 10.1038/s41586-021-03342-4

  View details for PubMedID 33854251

• Ultrafast structural dynamics of strongly-THz-driven materials Hoffmann, M. C., IEEE IEEE. 2021

  View details for DOI 10.1109/CLEO/Europe-EQEC52157.2021.9542729

  View details for Web of Science ID 000728078301051

• Enabling high repetition rate nonlinear THz science with a kilowatt-class sub-100 fs laser source OPTICS EXPRESS Kramer, P. L., Windeler, M. R., Mecseki, K., Champenois, E. G., Hoffmann, M. C., Tavella, F. 2020; 28 (11): 16951–67

  Abstract

  Manipulating the atomic and electronic structure of matter with strong terahertz (THz) fields while probing the response with ultrafast pulses at x-ray free electron lasers (FELs) has offered unique insights into a multitude of physical phenomena in solid state and atomic physics. Recent upgrades of x-ray FEL facilities are pushing to much higher repetition rates, enabling unprecedented signal-to-noise ratio for pump probe experiments. This requires the development of suitable THz pump sources that are able to deliver intense pulses at compatible repetition rates. Here we present a high-power laser-driven THz source based on optical rectification in LiNbO3 using tilted pulse front pumping. Our source is driven by a kilowatt-level Yb:YAG amplifier system operating at 100 kHz repetition rate and employing nonlinear spectral broadening and recompression to achieve sub-100 fs pulses with pulse energies up to 7 mJ that are necessary for high THz conversion efficiency and peak field strength. We demonstrate a maximum of 144 mW average THz power (1.44 μJ pulse energy), consisting of single-cycle pulses centered at 0.6 THz with a peak electric field strength exceeding 150 kV/cm. These high field pulses open up a range of possibilities for nonlinear time-resolved THz experiments at unprecedented rates.

  View details for DOI 10.1364/OE.389653

  View details for Web of Science ID 000542303000096

  View details for PubMedID 32549507

• Ultrafast Dynamics of a Terahertz Dual-Fed Relativistic Electron Bunch Compressor Othman, M. K., Snively, E. C., Kozina, M. E., Kramer, P. L., Shen, X., Ji, F., Weathersby, S., Wang, X. J., Hoffmann, M. C., Nanni, E. A., IEEE IEEE. 2020

  View details for Web of Science ID 000612090000481

• THz-driven bunch compression for varying electron beam energy Snively, E., Othman, M. K., Kozina, M., Ofori-Okai, B., Weathersby, S., Park, S., Shen, X., Wang, X., Hoffmann, M., Li, R., Nanni, E., IEEE IEEE. 2020

  View details for DOI 10.1109/IRMMW-THZ46771.2020.9370507

  View details for Web of Science ID 000662887600118

• Generation of high-field single-cycle terahertz pulses at 100 kHz Kramer, P. L., Hoffmann, M. C., Tavella, F., IEEE IEEE. 2020

  View details for Web of Science ID 000612090001010

• Nonlinear Magnetization Dynamics Driven by Strong Terahertz Fields. Physical review letters Hudl, M., d'Aquino, M., Pancaldi, M., Yang, S., Samant, M. G., Parkin, S. S., Durr, H. A., Serpico, C., Hoffmann, M. C., Bonetti, S. 2019; 123 (19): 197204

  Abstract

  We present a comprehensive experimental and numerical study of magnetization dynamics in a thin metallic film triggered by single-cycle terahertz pulses of 20MV/m electric field amplitude and 1ps duration. The experimental dynamics is probed using the femtosecond magneto-optical Kerr effect, and it is reproduced numerically using macrospin simulations. The magnetization dynamics can be decomposed in three distinct processes: a coherent precession of the magnetization around the terahertz magnetic field, an ultrafast demagnetization that suddenly changes the anisotropy of the film, and a uniform precession around the equilibrium effective field that is relaxed on the nanosecond time scale, consistent with a Gilbert damping process. Macrospin simulations quantitatively reproduce the observed dynamics, and allow us to predict that novel nonlinear magnetization dynamics regimes can be attained with existing tabletop terahertz sources.

  View details for DOI 10.1103/PhysRevLett.123.197204

  View details for PubMedID 31765192

• Dynamical Slowing-Down in an Ultrafast Photoinduced Phase Transition. Physical review letters Zong, A., Dolgirev, P. E., Kogar, A., Ergeçen, E., Yilmaz, M. B., Bie, Y. Q., Rohwer, T., Tung, I. C., Straquadine, J., Wang, X., Yang, Y., Shen, X., Li, R., Yang, J., Park, S., Hoffmann, M. C., Ofori-Okai, B. K., Kozina, M. E., Wen, H., Wang, X., Fisher, I. R., Jarillo-Herrero, P., Gedik, N. 2019; 123 (9): 097601

  Abstract

  Complex systems, which consist of a large number of interacting constituents, often exhibit universal behavior near a phase transition. A slowdown of certain dynamical observables is one such recurring feature found in a vast array of contexts. This phenomenon, known as critical slowing-down, is well studied mostly in thermodynamic phase transitions. However, it is less understood in highly nonequilibrium settings, where the time it takes to traverse the phase boundary becomes comparable to the timescale of dynamical fluctuations. Using transient optical spectroscopy and femtosecond electron diffraction, we studied a photoinduced transition of a model charge-density-wave (CDW) compound LaTe_{3}. We observed that it takes the longest time to suppress the order parameter at the threshold photoexcitation density, where the CDW transiently vanishes. This finding can be captured by generalizing the time-dependent Landau theory to a system far from equilibrium. The experimental observation and theoretical understanding of dynamical slowing-down may offer insight into other general principles behind nonequilibrium phase transitions in many-body systems.

  View details for DOI 10.1103/PhysRevLett.123.097601

  View details for PubMedID 31524450

• Dynamical Slowing-Down in an Ultrafast Photoinduced Phase Transition PHYSICAL REVIEW LETTERS Zong, A., Dolgirev, P. E., Kogar, A., Ergecen, E., Yilmaz, M. B., Bie, Y., Rohwer, T., Tung, I., Straquadine, J., Wang, X., Yang, Y., Shen, X., Li, R., Yang, J., Park, S., Hoffmann, M. C., Ofori-Okai, B. K., Kozina, M. E., Wen, H., Wang, X., Fisher, I. R., Jarillo-Herrero, P., Gedik, N. 2019; 123 (9)

  View details for DOI 10.1103/PhysRevLett.123.097601

  View details for Web of Science ID 000483048500015

• Parallel-plate waveguides for terahertz-driven MeV electron bunch compression OPTICS EXPRESS Othman, M. K., Hoffmann, M. C., Kozina, M. E., Wang, X. J., Li, R. K., Nanni, E. A. 2019; 27 (17): 23791–800

  View details for DOI 10.1364/OE.27.023791

  View details for Web of Science ID 000482098300013

• Terahertz-pump Experiments On Complex Solids at X-ray FELs Hoffmann, M. C., Kozina, M. E., Razeghi, M., Baranov, A. N. SPIE-INT SOC OPTICAL ENGINEERING. 2019

  View details for DOI 10.1117/12.2322169

  View details for Web of Science ID 000461341400004

• An Ultrafast Symmetry Switch in a Weyl Semimetal Nature Sie, E. J., et al 2019; 565, 61

  View details for DOI 10.1038/s41586-018-0809-4

• THz-driven bunch compression and timing stabilization of a relativistic electron beam Snively, E., Othman, M., Kozinal, M., Ofori-Okai, B., Weathersby, S., Park, S., Shen, X., Wang, X., Hoffmann, M., Li, R., Nanni, E., IEEE IEEE. 2019

  View details for Web of Science ID 000591783800140

• Parallel-Plate THz Waveguides for Relativistic Electron Bunch Compression Othman, M. K., Hoffmann, M. C., Li, R., Nanni, E. A., Wang, X. J., IEEE IEEE. 2019

  View details for Web of Science ID 000482226303003

• Terahertz Kerr Effect in beta-Alumina Ion Conductors Poletayev, A. D., Hoffmann, M. C., Teitelbaum, S. W., Trigo, M., Chueh, W. C., Lindenberg, A. M., IEEE IEEE. 2019

  View details for Web of Science ID 000482226301054

• THz-Pump UED-Probe on a Topological Weyl Semimetal Sie, E. J., Nyby, C. M., Pemmaraju, C. D., Park, S., Shen, X., Yang, J., Hoffmann, M. C., Ofori-Okai, B. K., Li, R., Reid, A. H., Weathersby, S., Mannebach, E., Finney, N., Rhodes, D., Chenet, D., Antony, A., Balicas, L., Hone, J., Devereaux, T. P., Heinz, T. F., Wang, X., Lindenberg, A. M., IEEE IEEE. 2019

  View details for Web of Science ID 000482226301297

• Phonon-Suppressed Auger Scattering of Charge Carriers in Defective Two-Dimensional Transition Metal Dichalcogenides. Nano letters Li, L. n., Lin, M. F., Zhang, X. n., Britz, A. n., Krishnamoorthy, A. n., Ma, R. n., Kalia, R. K., Nakano, A. n., Vashishta, P. n., Ajayan, P. n., Hoffmann, M. C., Fritz, D. M., Bergmann, U. n., Prezhdo, O. V. 2019

  Abstract

  Two-dimensional transition metal dichalcogenides (TMDs) draw strong interest in materials science, with applications in optoelectronics and many other fields. Good performance requires high carrier concentrations and long lifetimes. However, high concentrations accelerate energy exchange between charged particles by Auger-type processes, especially in TMDs where many-body interactions are strong, thus facilitating carrier trapping. We report time-resolved optical pump-THz probe measurements of carrier lifetimes as a function of carrier density. Surprisingly, the lifetime reduction with increased density is very weak. It decreases only by 20% when we increase the pump fluence 100 times. This unexpected feature of the Auger process is rationalized by our time-domain ab initio simulations. The simulations show that phonon-driven trapping competes successfully with the Auger process. On the one hand, trap states are relatively close to band edges, and phonons accommodate efficiently the electronic energy during the trapping. On the other hand, trap states localize around defects, and the overlap of trapped and free carriers is small, decreasing carrier-carrier interactions. At low carrier densities, phonons provide the main charge trapping mechanism, decreasing carrier lifetimes compared to defect-free samples. At high carrier densities, phonons suppress Auger processes and lower the dependence of the trapping rate on carrier density. Our results provide theoretical insights into the diverse roles played by phonons and Auger processes in TMDs and generate guidelines for defect engineering to improve device performance at high carrier densities.

  View details for DOI 10.1021/acs.nanolett.9b02005

  View details for PubMedID 31434484

• An ultrafast symmetry switch in a Weyl semimetal. Nature Sie, E. J., Nyby, C. M., Pemmaraju, C. D., Park, S. J., Shen, X. n., Yang, J. n., Hoffmann, M. C., Ofori-Okai, B. K., Li, R. n., Reid, A. H., Weathersby, S. n., Mannebach, E. n., Finney, N. n., Rhodes, D. n., Chenet, D. n., Antony, A. n., Balicas, L. n., Hone, J. n., Devereaux, T. P., Heinz, T. F., Wang, X. n., Lindenberg, A. M. 2019; 565 (7737): 61–66

  Abstract

  Topological quantum materials exhibit fascinating properties1-3, with important applications for dissipationless electronics and fault-tolerant quantum computers4,5. Manipulating the topological invariants in these materials would allow the development of topological switching applications analogous to switching of transistors6. Lattice strain provides the most natural means of tuning these topological invariants because it directly modifies the electron-ion interactions and potentially alters the underlying crystalline symmetry on which the topological properties depend7-9. However, conventional means of applying strain through heteroepitaxial lattice mismatch10 and dislocations11 are not extendable to controllable time-varying protocols, which are required in transistors. Integration into a functional device requires the ability to go beyond the robust, topologically protected properties of materials and to manipulate the topology at high speeds. Here we use crystallographic measurements by relativistic electron diffraction to demonstrate that terahertz light pulses can be used to induce terahertz-frequency interlayer shear strain with large strain amplitude in the Weyl semimetal WTe2, leading to a topologically distinct metastable phase. Separate nonlinear optical measurements indicate that this transition is associated with a symmetry change to a centrosymmetric, topologically trivial phase. We further show that such shear strain provides an ultrafast, energy-efficient way of inducing robust, well separated Weyl points or of annihilating all Weyl points of opposite chirality. This work demonstrates possibilities for ultrafast manipulation of the topological properties of solids and for the development of a topological switch operating at terahertz frequencies.

  View details for PubMedID 30602749

• Disentangling Transient Charge Density and Metal-Ligand Covalency in Photoexcited Ferricyanide with Femtosecond Resonant Inelastic Soft X-ray Scattering JOURNAL OF PHYSICAL CHEMISTRY LETTERS Jay, R. M., Norell, J., Eckert, S., Hantschmann, M., Beye, M., Kennedy, B., Quevedo, W., Schlotter, W. F., Dakovski, G. L., Minitti, M. P., Hoffmann, M. C., Mitra, A., Moeller, S. P., Nordlund, D., Zhang, W., Liang, H. W., Kunnus, K., Kubicek, K., Techert, S. A., Lundberg, M., Wernet, P., Gaffney, K., Odelius, M., Foehlisch, A. 2018; 9 (12): 3538–43

  Abstract

  Soft X-ray spectroscopies are ideal probes of the local valence electronic structure of photocatalytically active metal sites. Here, we apply the selectivity of time-resolved resonant inelastic X-ray scattering at the iron L-edge to the transient charge distribution of an optically excited charge-transfer state in aqueous ferricyanide. Through comparison to steady-state spectra and quantum chemical calculations, the coupled effects of valence-shell closing and ligand-hole creation are experimentally and theoretically disentangled and described in terms of orbital occupancy, metal-ligand covalency, and ligand field splitting, thereby extending established steady-state concepts to the excited-state domain. π-Back-donation is found to be mainly determined by the metal site occupation, whereas the ligand hole instead influences σ-donation. Our results demonstrate how ultrafast resonant inelastic X-ray scattering can help characterize local charge distributions around catalytic metal centers in short-lived charge-transfer excited states, as a step toward future rationalization and tailoring of photocatalytic capabilities of transition-metal complexes.

  View details for PubMedID 29888918

• Anti-reflection coating design for metallic terahertz meta-materials OPTICS EXPRESS Pancaldi, M., Freeman, R., Hudl, M., Hoffmann, M. C., Urazhdin, S., Vavassori, P., Bonetti, S. 2018; 26 (3): 2917–27

  Abstract

  We demonstrate a silicon-based, single-layer anti-reflection coating that suppresses the reflectivity of metals at near-infrared frequencies, enabling optical probing of nano-scale structures embedded in highly reflective surroundings. Our design does not affect the interaction of terahertz radiation with metallic structures that can be used to achieve terahertz near-field enhancement. We have verified the functionality of the design by calculating and measuring the reflectivity of both infrared and terahertz radiation from a silicon/gold double layer as a function of the silicon thickness. We have also fabricated the unit cell of a terahertz meta-material, a dipole antenna comprising two 20-nm thick extended gold plates separated by a 2 μm gap, where the terahertz field is locally enhanced. We used the time-domain finite element method to demonstrate that such near-field enhancement is preserved in the presence of the anti-reflection coating. Finally, we performed magneto-optical Kerr effect measurements on a single 3-nm thick, 1-μm wide magnetic wire placed in the gap of such a dipole antenna. The wire only occupies 2% of the area probed by the laser beam, but its magneto-optical response can be clearly detected. Our design paves the way for ultrafast time-resolved studies, using table-top femtosecond near-infrared lasers, of dynamics in nano-structures driven by strong terahertz radiation.

  View details for DOI 10.1364/OE.26.002917

  View details for Web of Science ID 000425365900069

  View details for PubMedID 29401825

• Development of a THz Pump MeV Ultrafast Electron Diffraction Probe Apparatus Ofori-Okai, B. K., Hoffmann, M. C., Reid, A. H., Li, R., Shen, X., Yang, J., Zheng, Q., Park, S., Mannenbach, E. M., Weathersby, S. P., Edstrom, S., Polzin, W., Lindenberg, A. M., Glenzer, S. H., Wang, X., IEEE IEEE. 2018

  View details for Web of Science ID 000526031002462

• Single-Shot Electro-Optic Measurement of Mid-Infrared Pulses Kozina, M. E., Hoffmann, M. C., IEEE IEEE. 2018

  View details for Web of Science ID 000526031003024

• Anti-reflection coating design for metallic terahertz meta-materials Pancaldi, M., Freeman, R., Hudl, M., Hoffmann, M. C., Urazhdin, S., Vavassori, P., Bonetti, S., IEEE IEEE. 2018

  View details for Web of Science ID 000526031002145

• Self-referenced single-shot THz detection OPTICS EXPRESS Russell, B. K., Ofori-Okai, B. K., Chen, Z., Hoffmann, M. C., Tsui, Y. Y., Glenzer, S. H. 2017; 25 (14): 16140–50

  Abstract

  We demonstrate a self-referencing method to reduce noise in a single-shot terahertz detection scheme. By splitting a single terahertz pulse and using a reflective echelon, both the signal and reference terahertz time-domain waveforms were measured using one laser pulse. Simultaneous acquisition of these waveforms significantly reduces noise originating from shot-to-shot fluctuations. We show that correlation function based referencing, which is not limited to polarization dependent measurements, can achieve a noise floor that is comparable to state-of-the-art polarization-gated balanced detection. Lastly, we extract the DC conductivity of a 30 nm free-standing gold film using a single THz pulse. The measured value of σ0 = 1.3 ± 0.4 × 107 S m-1 is in good agreement with the value measured by four-point probe, indicating the viability of this method for measuring dynamical changes and small signals.

  View details for DOI 10.1364/OE.25.016140

  View details for Web of Science ID 000407815100049

  View details for PubMedID 28789123

• The 2017 terahertz science and technology roadmap JOURNAL OF PHYSICS D-APPLIED PHYSICS Dhillon, S. S., Vitiello, M. S., Linfield, E. H., Davies, A. G., Hoffmann, M. C., Booske, J., Paoloni, C., Gensch, M., Weightman, P., Williams, G. P., Castro-Camus, E., Cumming, D. S., Simoens, F., Escorcia-Carranza, I., Grant, J., Lucyszyn, S., Kuwata-Gonokami, M., Konishi, K., Koch, M., Schmuttenmaer, C. A., Cocker, T. L., Huber, R., Markelz, A. G., Taylor, Z. D., Wallace, V. P., Zeitler, J., Sibik, J., Korter, T. M., Ellison, B., Rea, S., Goldsmith, P., Cooper, K. B., Appleby, R., Pardo, D., Huggard, P. G., Krozer, V., Shams, H., Fice, M., Renaud, C., Seeds, A., Stoehr, A., Naftaly, M., Ridler, N., Clarke, R., Cunningham, J. E., Johnston, M. B. 2017; 50 (4)

  View details for DOI 10.1088/1361-6463/50/4/043001

  View details for Web of Science ID 000392153700001

• Single-shot terahertz time-domain spectroscopy in pulsed high magnetic fields OPTICS EXPRESS Noe, G., Katayama, I., Katsutani, F., Allred, J. J., Horowitz, J. A., Sullivan, D. M., Zhang, Q., Sekiguchi, F., Woods, G. L., Hoffmann, M. C., Nojiri, H., Takeda, J., Kono, J. 2016; 24 (26): 30328–37

  Abstract

  We have developed a single-shot terahertz time-domain spectrometer to perform optical-pump/terahertz-probe experiments in pulsed, high magnetic fields up to 30 T. The single-shot detection scheme for measuring a terahertz waveform incorporates a reflective echelon to create time-delayed beamlets across the intensity profile of the optical gate beam before it spatially and temporally overlaps with the terahertz radiation in a ZnTe detection crystal. After imaging the gate beam onto a camera, we can retrieve the terahertz time-domain waveform by analyzing the resulting image. To demonstrate the utility of our technique, we measured cyclotron resonance absorption of optically excited carriers in the terahertz frequency range in intrinsic silicon at high magnetic fields, with results that agree well with published values.

  View details for DOI 10.1364/OE.24.030328

  View details for Web of Science ID 000390809100103

  View details for PubMedID 28059309

• Femtosecond X-ray magnetic circular dichroism absorption spectroscopy at an X-ray free electron laser REVIEW OF SCIENTIFIC INSTRUMENTS Higley, D. J., Hirsch, K., Dakovski, G. L., Jal, E., Yuan, E., Liu, T., Lutman, A. A., MacArthur, J. P., Arenholz, E., Chen, Z., Coslovich, G., Denes, P., Granitzka, P. W., Hart, P., Hoffmann, M. C., Joseph, J., Le Guyader, L., Mitra, A., Moeller, S., Ohldag, H., Seaberg, M., Shafer, P., Stoehr, J., Tsukamoto, A., Nuhn, H., Reid, A. H., Duerr, H. A., Schlotter, W. F. 2016; 87 (3)

  Abstract

  X-ray magnetic circular dichroism spectroscopy using an X-ray free electron laser is demonstrated with spectra over the Fe L(3,2)-edges. The high brightness of the X-ray free electron laser combined with high accuracy detection of incident and transmitted X-rays enables ultrafast X-ray magnetic circular dichroism studies of unprecedented sensitivity. This new capability is applied to a study of all-optical magnetic switching dynamics of Fe and Gd magnetic sublattices in a GdFeCo thin film above its magnetization compensation temperature.

  View details for DOI 10.1063/1.4944410

  View details for Web of Science ID 000373713300011

  View details for PubMedID 27036761

• Time-domain electric field enhancement on micrometer scale in coupled split ring resonator upon terahertz radiation Lange, S. L., Iwaszczuk, K., Hoffmann, M., Broeng, J., Jepsen, P. U., IEEE IEEE. 2016

  View details for Web of Science ID 000391406200364

• Excitation of Coherent Oscillations in Underdoped Cuprate Superconductors by Intense THz Pulses Hoffmann, M. C., Lee, W., Dakovski, G. L., Turner, J. J., Gerber, S. M., Bonn, D., Hardy, W., Liang, R., Salluzzo, M., Rafailov, M. K., Mazur, E. SPIE-INT SOC OPTICAL ENGINEERING. 2016

  View details for DOI 10.1117/12.2224993

  View details for Web of Science ID 000381933900025

• Direct observation of lattice motion driven by strong THz pulses Kozina, M. E., Zhu, D., Glownia, J. M., van Driel, T., Bonetti, S., Staub, U., Hoffmann, M. C., IEEE IEEE. 2016

  View details for Web of Science ID 000391286401354

• Ultrafast Terahertz Gating of the Polarization and Giant Nonlinear Optical Response in BiFeO3 Thin Films ADVANCED MATERIALS Chen, F., Goodfellow, J., Liu, S., Grinberg, I., Hoffmann, M. C., Damodaran, A. R., Zhu, Y., Zalden, P., Zhang, X., Takeuchi, I., Rappe, A. M., Martin, L. W., Wen, H., Lindenberg, A. M. 2015; 27 (41): 6371-?

  Abstract

  Terahertz pulses are applied as an all-optical bias to ferroelectric thin-film BiFeO3 while monitoring the time-dependent ferroelectric polarization through its nonlinear optical response. Modulations in the intensity of the second harmonic light generated by the film correspond to on-off ratios of 220× gateable on femtosecond timescales. Polarization modulations comparable to the built-in static polarization are observed.

  View details for DOI 10.1002/adma.201502975

  View details for Web of Science ID 000364343700009

• Ultrafast Terahertz Gating of the Polarization and Giant Nonlinear Optical Response in BiFeO3 Thin Films. Advanced materials (Deerfield Beach, Fla.) Chen, F., Goodfellow, J., Liu, S., Grinberg, I., Hoffmann, M. C., Damodaran, A. R., Zhu, Y., Zalden, P., Zhang, X., Takeuchi, I., Rappe, A. M., Martin, L. W., Wen, H., Lindenberg, A. M. 2015; 27 (41): 6371-5

  Abstract

  Terahertz pulses are applied as an all-optical bias to ferroelectric thin-film BiFeO3 while monitoring the time-dependent ferroelectric polarization through its nonlinear optical response. Modulations in the intensity of the second harmonic light generated by the film correspond to on-off ratios of 220× gateable on femtosecond timescales. Polarization modulations comparable to the built-in static polarization are observed.

  View details for DOI 10.1002/adma.201502975

  View details for PubMedID 26389651

• Direct observation of ultrafast collective motions in CO myoglobin upon ligand dissociation SCIENCE Barends, T. M., Foucar, L., Ardevol, A., Nass, K., Aquila, A., Botha, S., Doak, R., Falahati, K., Hartmann, E., Hilpert, M., Heinz, M., Hoffmann, M. C., Koefinger, J., Koglin, J. E., Kovacsova, G., Liang, M., Milathianaki, D., Lemke, H. T., Reinstein, J., Roome, C. M., Shoeman, R. L., Williams, G. J., Burghardt, I., Hummer, G., Boutet, S., Schlichting, I. 2015; 350 (6259): 445–50

  Abstract

  The hemoprotein myoglobin is a model system for the study of protein dynamics. We used time-resolved serial femtosecond crystallography at an x-ray free-electron laser to resolve the ultrafast structural changes in the carbonmonoxy myoglobin complex upon photolysis of the Fe-CO bond. Structural changes appear throughout the protein within 500 femtoseconds, with the C, F, and H helices moving away from the heme cofactor and the E and A helices moving toward it. These collective movements are predicted by hybrid quantum mechanics/molecular mechanics simulations. Together with the observed oscillations of residues contacting the heme, our calculations support the prediction that an immediate collective response of the protein occurs upon ligand dissociation, as a result of heme vibrational modes coupling to global modes of the protein.

  View details for PubMedID 26359336

• Enhanced coherent oscillations in the superconducting state of underdoped YBa2Cu3O6+x induced via ultrafast terahertz excitation PHYSICAL REVIEW B Dakovski, G. L., Lee, W., Hawthorn, D. G., Garner, N., Bonn, D., Hardy, W., Liang, R., Hoffmann, M. C., Turner, J. J. 2015; 91 (22)

  View details for DOI 10.1103/PhysRevB.91.220506

  View details for Web of Science ID 000356791700002

• Combining THz laser excitation with resonant soft X-ray scattering at the Linac Coherent Light Source JOURNAL OF SYNCHROTRON RADIATION Turner, J. J., Dakovski, G. L., Hoffmann, M. C., Hwang, H. Y., Zarem, A., Schlotter, W. F., Moeller, S., Minitti, M. P., Staub, U., Johnson, S., Mitra, A., Swiggers, M., Noonan, P., Curiel, G. I., Holmes, M. 2015; 22: 621-625

  Abstract

  This paper describes the development of new instrumentation at the Linac Coherent Light Source for conducting THz excitation experiments in an ultra high vacuum environment probed by soft X-ray diffraction. This consists of a cantilevered, fully motorized mirror system which can provide 600 kV cm(-1) electric field strengths across the sample and an X-ray detector that can span the full Ewald sphere with in-vacuum motion. The scientific applications motivated by this development, the details of the instrument, and spectra demonstrating the field strengths achieved using this newly developed system are discussed.

  View details for DOI 10.1107/S1600577515005998

  View details for Web of Science ID 000353920300024

  View details for PubMedID 25931077

  View details for PubMedCentralID PMC4416678

• Optical laser systems at the Linac Coherent Light Source JOURNAL OF SYNCHROTRON RADIATION Minitti, M. P., Robinson, J. S., Coffee, R. N., Edstrom, S., Gilevich, S., Glownia, J. M., Granados, E., Hering, P., Hoffmann, M. C., Miahnahri, A., Milathianaki, D., Polzin, W., Ratner, D., Tavella, F., Vetter, S., Welch, M., White, W. E., Fry, A. R. 2015; 22: 526–31

  Abstract

  Ultrafast optical lasers play an essential role in exploiting the unique capabilities of recently commissioned X-ray free-electron laser facilities such as the Linac Coherent Light Source (LCLS). Pump-probe experimental techniques reveal ultrafast dynamics in atomic and molecular processes and reveal new insights in chemistry, biology, material science and high-energy-density physics. This manuscript describes the laser systems and experimental methods that enable cutting-edge optical laser/X-ray pump-probe experiments to be performed at LCLS.

  View details for PubMedID 25931064

  View details for PubMedCentralID PMC4416671

• Nonlinear THz Optics and Control in Complex Solids Hoffmann, M. C., IEEE IEEE. 2015

  View details for Web of Science ID 000370627101490

• Intense THz pulses for condensed matter physics Hoffmann, M. C., Vodopyanov, K. L. SPIE-INT SOC OPTICAL ENGINEERING. 2015

  View details for DOI 10.1117/12.2085105

  View details for Web of Science ID 000354360500012

• Ultrafast terahertz-induced response of GeSbTe phase-change materials APPLIED PHYSICS LETTERS Shu, M. J., Zalden, P., Chen, F., Weems, B., Chatzakis, I., Xiong, F., Jeyasingh, R., Hoffmann, M. C., Pop, E., Wong, H. P., Wuttig, M., Lindenberg, A. M. 2014; 104 (25)

  View details for DOI 10.1063/1.4884816

  View details for Web of Science ID 000338515900032

• THz Light Source at SLAC FACET User Facility Wu, Z., Fisher, A. S., Hoffmann, M. C., Bonetti, S., Higley, D., Durr, H., IEEE IEEE. 2014

  View details for Web of Science ID 000378889200288

• Selective THz excitation of collective modes in underdoped YBCO Dakovski, G. L., Lee, W., Turner, J. J., Hoffmann, M. C., IEEE IEEE. 2014

  View details for Web of Science ID 000369908600359

• Terahertz Nonlinear Optics in Semiconductors Turchinovich, D., Hvam, J. M., Hoffmann, M. C., IEEE IEEE. 2013

  View details for Web of Science ID 000345855300466

• Terahertz semiconductor nonlinear optics Turchinovich, D., Hvam, J. M., Hoffmann, M. C., Betz, M., Elezzabi, A. Y., Song, J. J., Tsen, K. T. SPIE-INT SOC OPTICAL ENGINEERING. 2013

  View details for DOI 10.1117/12.2000169

  View details for Web of Science ID 000322829300012

• Self-phase modulation of a single-cycle terahertz pulse by nonlinear free-carrier response in a semiconductor PHYSICAL REVIEW B Turchinovich, D., Hvam, J. M., Hoffmann, M. C. 2012; 85 (20)

  View details for DOI 10.1103/PhysRevB.85.201304

  View details for Web of Science ID 000304526800002

• THz quantum-confined Stark effect in semiconductor quantum dots Turchinovich, D., Monozon, B. S., Livshits, D. A., Rafailov, E. U., Hoffmann, M. C., Betz, M., Elezzabi, A. Y., Song, J. J., Tsen, K. T. SPIE-INT SOC OPTICAL ENGINEERING. 2012

  View details for DOI 10.1117/12.906448

  View details for Web of Science ID 000302550300002

• Nonlinear propagation of strong-field THz pulses in doped semiconductors Turchinovich, D., Hvam, J. M., Hoffmann, M. C., Betz, M., Elezzabi, A. Y., Song, J. J., Tsen, K. T. SPIE-INT SOC OPTICAL ENGINEERING. 2012

  View details for DOI 10.1117/12.906459

  View details for Web of Science ID 000302550300009

• Coherent single-cycle pulses with MV/cm field strengths from a relativistic transition radiation light source OPTICS LETTERS Hoffmann, M. C., Schulz, S., Wesch, S., Wunderlich, S., Cavalleri, A., Schmidt, B. 2011; 36 (23): 4473–75

  Abstract

  Terahertz (THz) pulses with energies up to 100 μJ and corresponding electric fields up to 1 MV/cm were generated by coherent transition radiation from 500 MeV electron bunches at the free-electron laser Freie-Elektronen-Laser in Hamburg (FLASH). The pulses were characterized in the time domain by electro-optical sampling by a synchronized femtosecond laser with jitter of less than 100 fs. High THz field strengths and quality of synchronization with an optical laser will enable observation of nonlinear THz phenomena.

  View details for PubMedID 22139213

• Intense ultrashort terahertz pulses: generation and applications JOURNAL OF PHYSICS D-APPLIED PHYSICS Hoffmann, M. C., Fueloep, J. 2011; 44 (8)

  View details for DOI 10.1088/0022-3727/44/8/083001

  View details for Web of Science ID 000287195000002

• MV/cm THz pulses from a coherent transition radiation source Hoffmann, M. C., Schulz, S., Wesch, S., Wunderlich, S., Schmidt, B., Koch, M. IEEE. 2011

  View details for Web of Science ID 000330296300156

• Ultrafast THz Saturable Absorption in Doped Semiconductors Turchinovich, D., Hoffmann, M. C., IEEE IEEE. 2011

  View details for Web of Science ID 000295612402337

• THz Electro-absorption Effect in Quantum Dots Turchinovich, D., Monozon, B. S., Livshits, D. A., Rafailov, E. U., Hoffmann, M. C., IEEE IEEE. 2011

  View details for Web of Science ID 000295612403302

• Semiconductor saturable absorbers for ultrafast terahertz signals APPLIED PHYSICS LETTERS Hoffmann, M. C., Turchinovich, D. 2010; 96 (15)

  View details for DOI 10.1063/1.3386542

  View details for Web of Science ID 000276794100010

• Observation of nonequilibrium carrier distribution in Ge, Si, and GaAs by terahertz pump-terahertz probe measurements PHYSICAL REVIEW B Hebling, J., Hoffmann, M. C., Hwang, H. Y., Yeh, K., Nelson, K. A. 2010; 81 (3)

  View details for DOI 10.1103/PhysRevB.81.035201

  View details for Web of Science ID 000274002300046

• Terahertz Kerr effect APPLIED PHYSICS LETTERS Hoffmann, M. C., Brandt, N. C., Hwang, H. Y., Yeh, K., Nelson, K. A. 2009; 95 (23)

  View details for DOI 10.1063/1.3271520

  View details for Web of Science ID 000272627700005

• Terahertz time-domain spectroscopy and imaging of artificial RNA OPTICS EXPRESS Fischer, B. M., Hoffmann, M., Helm, H., Wilk, R., Rutz, F., Kleine-Ostmann, T., Koch, M., Jepsen, P. U. 2005; 13 (14): 5205–15

  Abstract

  We use terahertz time-domain spectroscopy (THz-TDS) to measure the far-infrared dielectric function of two artificial RNA single strands, composed of polyadenylic acid (poly-A) and polycytidylic acid (poly-C). We find a significant difference in the absorption between the two types of RNA strands, and we show that we can use this difference to record images of spot arrays of the RNA strands. Under controlled conditions it is possible to use the THz image to distinguish between the two RNA strands. We discuss the requirements to sample preparation imposed by the lack of sharp spectral features in the absorption spectra.

  View details for DOI 10.1364/OPEX.13.005205

  View details for Web of Science ID 000230519100003

  View details for PubMedID 19498511