Laser Seeding of the Storage-Ring Microbunching Instability for High-Power Coherent Terahertz Radiation

J. M. Byrd, Z. Hao, M. C. Martin, D. S. Robin, F. Sannibale, R. W. Schoenlein, A. A. Zholents, and M. S. Zolotorev

Ernest Orlando Lawrence Berkeley National Laboratory, One Cyclotron Road, Berkeley, California 94720, USA

(Received 24 May 2006; published 18 August 2006)

We report the first observation of laser seeding of the storage-ring microbunching instability. Above a threshold bunch current, the interaction of the beam and its radiation results in a coherent instability, observed as a series of stochastic bursts of coherent synchrotron radiation (CSR) at terahertz frequencies initiated by fluctuations in the beam density. We have observed that this effect can be seeded by imprinting an initial density modulation on the beam by means of laser "slicing." In such a situation, most of the bursts of CSR become synchronous with the pulses of the modulating laser and their average intensity scales exponentially with the current per bunch. We present detailed experimental observations of the seeding effect and a model of the phenomenon. This seeding mechanism also creates potential applications as a high-power source of CSR at terahertz frequencies.

©2006 The American Physical Society

URL: http://link.aps.org/abstract/PRL/v97/e074802

doi:10.1103/PhysRevLett.97.074802

PACS: 41.60.Ap, 07.05.Tp, 07.57.Hm, 29.27.Bd

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Tracking the motion of charges in a terahertz light field by femtosecond X-ray diffraction

A. Cavalleri^1,2, S. Wall¹, C. Simpson¹, E. Statz³, D. W. Ward³, K. A. Nelson³, M. Rini⁴ and R. W. Schoenlein⁴

Nature 442, 664-666(10 August 2006) | doi:10.1038/nature05041; Received 1 May 2006; Accepted 30 June 2006

In condensed matter, light propagation near resonances is described in terms of polaritons, electro-mechanical excitations in which the time-dependent electric field is coupled to the oscillation of charged masses^1,2. This description underpins our understanding of the macroscopic optical properties of solids, liquids and plasmas, as well as of their dispersion with frequency. In ferroelectric materials, terahertz radiation propagates by driving infrared-active lattice vibrations, resulting in phonon-polariton waves. Electro-optic sampling with femtosecond optical pulses^3,4,5 can measure the time-dependent electrical polarization, providing a phase-sensitive analogue to optical Raman scattering^6,7. Here we use femtosecond time-resolved X-ray diffraction^8,9,10, a phase-sensitive analogue to inelastic X-ray scattering^11,12,13, to measure the corresponding displacements of ions in ferroelectric lithium tantalate, LiTaO₃. Amplitude and phase of all degrees of freedom in a light field are thus directly measured in the time domain. Notably, extension of other X-ray techniques to the femtosecond timescale (for example, magnetic or anomalous scattering) would allow for studies in complex systems, where electric fields couple to multiple degrees of freedom¹⁴.

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1. Department of Physics, Clarendon Laboratory, University of Oxford, Oxford OX1 3PU, UK
2. Central Laser Facility & Diamond Light Source, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, UK
3. Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
4. Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA

Correspondence to: A. Cavalleri^1,2 Correspondence and requests for materials should be addressed to A.C. (Email: a.cavalleri1@physics.ox.ac.uk).

Received 1 May 2006 |Accepted 30 June 2006

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Universal Features of Terahertz Absorption in Disordered Materials

S. N. Taraskin,^1,2 S. I. Simdyankin,² S. R. Elliott,² J. R. Neilson,^2,3 and T. Lo⁴

¹St. Catharine's College, Trumpington Street, Cambridge CB2 1RL, United Kingdom

²Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom

³Department of Materials Science and Engineering, Lehigh University, Bethlehem, Pennsylvania 18015, USA

⁴Teraview Ltd., Platinum Building, St. John's Innovation Park, Cambridge CB4 OW5, United Kingdom

(Received 10 March 2006; published 2 August 2006)

Using an analytical theory, experimental terahertz time-domain spectroscopy data, and numerical evidence, we demonstrate that the frequency dependence of the absorption coupling coefficient between far-infrared photons and atomic vibrations in disordered materials has the universal functional form, C()=A+B², where the material-specific constants A and B are related to the distributions of fluctuating charges obeying global and local charge neutrality, respectively.

©2006 The American Physical Society

URL: http://link.aps.org/abstract/PRL/v97/e055504

doi:10.1103/PhysRevLett.97.055504

PACS: 63.50.+x, 61.43.Fs, 78.30.Ly

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The IRMMW-THz 2006 Conference

Joint 31st International Conference on Infrared and Millimeter Waves and 14th International Conference on Terahertz Electronics

September 18-22, 2006, Shanghai ,China

The IRMMW-THz 2006, currently in its 31st year, is the oldest continuous forum specifically devoted to the field of ultra high frequency electronics and applications. The scope of the conference extends from millimeter wave devices, components and systems to infrared detectors and instruments, and encompasses micro-scale structures to large-scale Tokamaks and Gyrotrons. In recent years the organizing committee has expanded the conference scope and the participating research communities with a special focus on terahertz techniques and applications, including both the traditional radio frequency domain and the new fast pulse time domain approaches to generating, detecting and using high frequency energy. The conference offers attendees a chance to hear and participate in a wide range of topic areas that span all aspects of Infrared, Terahertz and Millimeter-Wave technology and applications from quantum physics, chemistry and biology to radio astronomy and plasma physics.
	The following is a representative list of topics to be covered at the conference:
IR, THz, and MMW Sources, Detectors and Receivers Terahertz Devices, Components, Subsystems and Instruments; both Frequency and Time Domain. Novel Devices and Instruments for IR, THz and MMW IR, THz and MMW Spectroscopy, Instrumentation and Material Properties MMW and Submillimeter-Wave Radar and Communications Ultra High Speed MMW Digital Devices IR, THz and MMW Imaging MMW Systems, Transmission Lines and Antennas Gyro-Oscillators and Amplifiers, Plasma Diagnostics Free Electron Lasers and Synchrotron Radiation IR, THz and MMW Astronomy, Atmospheric and Environmental Science Applications Ultra-fast Components and Measurements in Chemistry and Physics IR, THz, and MMW Applications in Security and Industry. New IR, THz and MMW Applications in Biology and Medicine IR, THz and MMW Future Applications, Markets and Directions

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