Intense Terahertz Pulses from SLAC Linac Beams

The terahertz (THz) region of the electromagnetic spectrum spans frequencies roughly from 300 GHz to 20 THz, corresponding to wavelengths from 1 mm to 15 μm. Although this range overlaps the vibrational levels of many materials (for example, phonon modes of semiconductors), difficulties in developing adequate sources have slowed its exploitation, despite promising applications in imaging, chemistry, biology, and materials science. Recent progress in sources driven by both lasers and electron beams has started to fill this “terahertz gap.” Accelerator-based sources are now opening a new high-field regime with the potential to control materials with THz radiation by resonantly driving bonds, biasing a material with ultrashort electric or magnetic fields, or using the light as a catalyst. Some new sources can produce pulsed fields of sufficient intensity to drive nonlinear responses in matter.