We report on compact and efficient laser-based THz generation in the terahertz frequency gap (1-10 THz). The radiation is generated by optical rectification of a midinfrared laser in a large-size, partitioned nonlinear organic crystal assembly. This enables up-scaling of presently field-limited tabletop THz sources to GV=m electric and several tesla magnetic field at millijoule pulse energy. In agreement with simulations, the THz beam properties at focus are shown to be not deteriorated by the discontinuity of the emitter surface. The high laser-to-THz energy conversion efficiency exceeds the Manley-Rowe limit and is explained by a cascaded χ ð2Þ process in the organic crystals accompanied by a significant redshift of the pump spectrum. The scheme provides a compact, tabletop THz source for single-cycle transients at field strength equivalent or even higher to linear accelerator and FEL-based THz sources. This opens an avenue toward novel nonlinear THz applications.

In Terahertz (THz) science, one of the long-standing challenges has been the formation of spectrally dense, single-cycle pulses with tunable duration and spectrum across the frequency range of 0.1–15 THz (THz gap). This frequency band, lying between the electronically and optically accessible spectra hosts important molecular fingerprints and collective modes which cannot be fully controlled by present strong-field THz sources. We present a method that provides powerful single-cycle THz pulses in the THz gap with a stable absolute phase whose duration can be continuously selected between 68 fs and 1100 fs. The loss-free and chirp-free technique is based on optical rectification of a wavelength-tunable pump pulse in the organic emitter HMQ-TMS that allows for tuning of the spectral bandwidth from 1 to more than 7 octaves over the entire THz gap. The presented source tunability of the temporal carrier frequency and spectrum expands the scope of spectrally dense THz sources to time-resolved nonlinear THz spectroscopy in the entire THz gap. This opens new opportunities towards ultrafast coherent control over matter and light.

No abstract

Intense pulses at low terahertz (THz) frequencies of 0.1-2 THz are an enabling tool for constructing compact particle accelerators and for strong-field control of matter. Optical rectification in lithium niobate provided sub-mJ THz pulse energies, but it is challenging to increase it further. Semiconductor sources suffered from low efficiency. Here, a semiconductor (ZnTe) THz source is demonstrated, collinearly pumped at an infrared wavelength beyond the three-photon absorption edge and utilizing a contact grating for tilting the pump-pulse front. Suppression of free-carrier absorption at THz frequencies in this way resulted in 0.3% THz generation efficiency, two orders of magnitude higher than reported previously from ZnTe. Scaling the THz energy to the mJ level is possible simply by increasing the pumped area. This unique THz source with excellent focusability, pumped by novel, efficient infrared sources, opens up new perspectives for THz high-field applications. Terahertz (THz) pulses with high energy and field strength are enabling novel applications [1-4], including resonant control over ionic motion, bound and free electrons, as well as nonresonant and strong-field interactions [3]. Intense THz pulses hold promise for the development of a new generation of compact particle and x-ray sources [1,2]. Laser-and THz-driven particle accelerators with unprecedented flexibility can be important for free-electron lasers [2,5] and materials science and could revolutionize medical therapy with x-ray, electron, or proton beams [1,2].Single-cycle or nearly single-cycle THz pulses with high energy can be generated by optical rectification of femtosecond laser pulses. The highest so far THz pulse energy reported from such a source, utilizing the novel organic nonlinear material DSTMS, was 0.9 mJ [6]. The spectrum obtained from organic materials is typically centered in the 2 to 10 THz range, well suited for nonlinear spectroscopic studies. THz sources with lower frequencies are optimally fitted to the requirements of particle acceleration [1,2,7]. The frequency range below 2 THz can be better accessed with another nonlinear material, lithium niobate, utilizing pump pulses with a tilted intensity front for non-collinear phase matching [8]. THz pulses with more than 0.4 mJ energy were generated with 0.77% efficiency using this technique [7]. However, increasing the THz energy further turned out to be very challenging because of the large pulse-front tilt angle (63°) and the associated large angular dispersion of the pump [9,10]. The effect of a strong THz field on the pump pulse, owing to their nonlinear interaction, leads to additional difficulties involving the reduction of the THz generation efficiency [11] and the distortion of the THz beam [12].Semiconductor nonlinear materials have been extensively used to access the low-frequency part of the THz spectrum. The most popular material is ZnTe, where collinear phase matching is possible at the commonly used 0.8 μm pump wavelength of Ti:sapphire lasers. The highest THz pu...

Abstract:The accurate measurement of the arrival time of a hard X-ray free electron laser (FEL) pulse with respect to a laser is of utmost importance for pump-probe experiments proposed or carried out at FEL facilities around the world. This manuscript presents the latest device to meet this challenge, a THz streak camera using Xe gas clusters, capable of pulse arrival time measurements with an estimated accuracy of several femtoseconds. An experiment performed at SACLA demonstrates the performance of the device at photon energies between 5 and 10 keV with variable photon beam parameters. © 2014 Optical Society of AmericaOCIS codes: (120.0120) Instrumentation, measurement, and metrology; (020.0020) Atomic and molecular physics; (140.2600) Free-electron lasers (FELs). Kumagai, "A compact X-ray free-electron laser emitting in the sub-angstrom region," Nat. Photonics 6(8), 540-544 (2012). 4. E. Allaria, C. Callegari, D. Cocco, W. M. Fawley, M. Kiskinova, C. Masciovecchio, and F. Parmigiani, "The FERMI@Elettra free-electron-laser source for coherent x-ray physics: photon properties, beam transport system and applications," New J. Phys. 12(7), 075002 (2010). 5. P. Oberta, U. Flechsig, and R. Abela, "The SwissFEL facility and its preliminary optics beamline layout," Proc. Krausz, "X-ray pulses approaching the attosecond frontier," Science 291(5510), 1923-1927 (2001). 18. M. Uiberacker, E. Goulielmakis, R. Kienberger, A. Baltuska, T. Westerwalbesloh, U. Keineberg, U. Heinzmann, M. Drescher, and F. Krausz, "Attosecond metrology with controlled light waveforms," Laser Phys. 15, 195-204 (2005). 19. B. L. Henke, E. M. Gullikson, and J. C. Davis, "X-ray interactions-photoabsorption, scattering, transmission, and reflection at E=50-30,000 eV, z=1-92," At. Data Nucl. Data Tables 54(2), 181-342 (1993). 20. D. Irimia, D. Dobrikov, R. Kortekaas, H. Voet, D. A. van den Ende, W. A. Groen, and M. H. M. Janssen, "A short pulse (7 micros FWHM) and high repetition rate (dc-5 kHz) cantilever piezovalve for pulsed atomic and molecular beams," Rev. Sci. Instrum. 80(11), 113303 (2009). 21. O. F. Hagena and W. Obert, "Cluster formation in expanding supersonic jets-effect of pressure, temperature, nozzle size, and test gas," J. References and links: