Abstract-Cascaded Multicycle Terahertz-Driven Ultrafast Electron Acceleration and Manipulation

Dongfang Zhang, Moein Fakhari, Huseyin Cankaya, Anne-Laure Calendron, Nicholas H. Matlis, and Franz X. Kärtner

https://journals.aps.org/prx/abstract/10.1103/PhysRevX.10.011067

Terahertz (THz)-based electron acceleration and manipulation has recently been shown to be feasible and to hold tremendous promise as a technology for the development of next-generation, compact electron sources. Previous work has concentrated on structures powered transversely by short, single-cycle THz pulses, with millimeter-scale, segmented interaction regions that are ideal for acceleration of electrons in the sub- to few-MeV range, where electron velocities vary significantly. However, in order to extend this technology to the multi-MeV range, an investigation of approaches supporting longer interaction lengths is needed. Here, we demonstrate first steps in electron acceleration and manipulation using dielectrically lined waveguides powered by temporally long, narrow-band, multicycle THz pulses that copropagate with the electrons. This geometry offers centimeter-scale single-stage interaction lengths and offers the opportunity to further increase interaction lengths by cascading acceleration stages that recycle the THz energy and rephase the interaction. We prove the feasibility of THz-energy recycling for the first time by demonstrating acceleration, compression, and focusing in two sequential ${\mathrm{Al}}_2{O}_3$-based dielectric capillary stages powered by the same multicycle THz pulse. Since the multicycle THz energy achievable using laser-based sources is currently a limiting factor for the maximum electron acceleration, recycling the THz pulses provides a key factor for reaching relativistic energies with existing sources and paves the way for applications in future ultrafast electron diffraction and free-electron lasers.

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Abstract-On the effect of third-order dispersion on phase-matched terahertz generation via interfering chirped pulses

Spencer W. Jolly, Frederike Ahr, Koustuban Ravi, Nicholas H. Matlis, Franz X. Kärtner, and Andreas R. Maier

Chirp-and-delay experimental setup (a), identical to the previous work in Ahr et al. [18]. This HR-PR combination produces a train of pulses rather than two pulses of equal energy. A waveplate is used to match perfectly the polarization of the IR light to the PPLN crystal axis. The beam is matched to the aperture of the PPLN crystal using a telescope, the parameters of which depend on the PPLN aperture. A Teflon plate separates the drive laser from the generated THz at the output of the crystal, whose energy is detector using a pyroelectric detector (b). The frequency of the generated THz is verified using an interferometer (c).

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-27-24-34769

High-energy narrowband terahertz (THz) pulses, relevant for a plethora of applications, can be created from the interference of two chirped-pulse drive lasers. The presence of third order dispersion, an intrinsic feature of many high-energy drive lasers, however, can significantly reduce the optical-to-THz conversion efficiency and have other undesired effects. Here, we present a detailed description of the effect of third-order dispersion (TOD) in the pump pulse on the generation of THz radiation via phase-matching of broadband highly chirped pulse trains. Although the analysis is general, we focus specifically on parameters typical to a Ti:Sapphire chirped-pulse amplification laser system for quasi-phase-matching in periodically-poled lithium niobate (PPLN) in the range of THz frequencies around 0.5 THz. Our analysis provides the tools to optimize the THz generation process for applications requiring high energy and to control it to produce desired THz waveforms in a variety of scenarios.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Cascaded Multi-cycle terahertz driven ultrafast electron acceleration and manipulation

Dongfang Zhang, Moein Fakhari, Huseyin Cankaya, Anne-Laure Calendron, Nicholas H. Matlis, Franz X. Kärtner

https://arxiv.org/abs/1910.06639

Terahertz (THz)-based electron acceleration and manipulation has recently been shown to be feasible and to hold tremendous promise as a technology for the development of next-generation, compact electron sources. Previous work has concentrated on structures powered transversely by short, single-cycle THz pulses, with mm-scale, segmented interaction regions that are ideal for acceleration of electrons in the sub- to few-MeV range where electron velocities vary significantly. However, in order to extend this technology to the multi-MeV range, investigation of approaches supporting longer interaction lengths is needed. Here, we demonstrate first steps in electron acceleration and manipulation using dielectrically-lined waveguides powered by temporally long, narrowband, multi-cycle THz pulses that co-propagate with the electrons. This geometry offers centimeter-scale single-stage interaction lengths and offers the opportunity to further increase interaction lengths by cascading acceleration stages that recycle the THz energy and rephase the interaction. We prove the feasibility of THz-energy recycling for the first time by demonstrating acceleration, compression and focusing in two sequential Al2O3-based dielectric capillary stages powered by the same multi-cycle THz pulse. Since the multi-cycle energy achievable using laser-based sources is currently a limiting factor for the maximum electron acceleration, THz energy recycling provides a key enabling factor for reaching relativistic energies with existing sources.

Abstract-Full 3D+1 modelling of the tilted-pulse-front setups for single-cycle terahertz generation

Lu Wang, Tobias Kroh, Nicholas H. Matlis, Franz Kaertner

https://arxiv.org/abs/1908.09581

The tilted-pulse-front setup utilizing a diffraction grating is one of the most successful methods to generate single- to few-cycle terahertz pulses. However, the generated terahertz pulses have a large spatial inhomogeneity, due to the noncollinear phase matching condition and the asymmetry of the prism-shaped nonlinear crystal geometry, especially when pushing for high optical-to-terahertz conversion efficiency. A 3D+1 (x,y,z,t) numerical model is necessary in order to fully investigate the terahertz generation problem in the tilted-pulse-front scheme. We compare in detail the differences between 1D+1, 2D+1 and 3D+1 models. The simulations show that the size of the optical beam in the pulse-front-tilt plane sensitively affects the spatio-temporal properties of the terahertz electric field. The terahertz electric field is found to have a strong spatial dependence such that a few-cycle pulse is only generated near the apex of the prism. The part of the beam farther from the apex contains a large fraction of the energy but has a waveform that deviates from a few-cycle. This strong spatial dependence must be accounted for when using the terahertz pulses for strong-field physics and carrier-envelope-phase sensitive experiments such as terahertz acceleration, coherent control of antiferromagnetic spin waves and terahertz high-harmonic generation.

Abstract-Numerical investigation of imaging-free terahertz generation setup using segmented tilted-pulse-front excitation

György Tóth, László Pálfalvi, József A. Fülöp, Gergő Krizsán, Nicholas H. Matlis, Gábor Almási, and János Hebling

Fig. 1 The setup of the investigated hybrid NLES THz source. The dark blue lines represent the pump pulse front at different moments. After diffraction of the pump beam on the transmission grating (TG), it propagates horizontally. Consequently, the phase-fronts are vertical. All γ is measured from a vertical line.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-5-7762

Recently a hybrid-type terahertz (THz) pulse source was proposed for high energy terahertz pulse generation. It is the combination of the conventional tilted-pulse-front setup and a nonlinear crystal with a transmission stair-step echelon of period in the hundred-micrometer range etched into the front face. The tilt angle introduced by the conventional tilted-pulse-front setup (pre-tilt) was chosen to be equal to the tilt-angle needed inside the nonlinear crystal (62° for lithium niobate (LN)) in order to fulfill velocity-matching. In this case, plane-parallel nonlinear optical crystals can be used. The possibility of using a plane-parallel nonlinear optical crystal for producing good-quality, symmetric THz beams was considered the most important advantage of this setup. In the present paper, a thorough numerical investigation of a modified version of that setup is presented. In the new version, the tilted pulse-front is created by a transmission grating without any imaging optics, and a wedged nonlinear optical crystal with a small wedge angle is supposed. According to a 1D numerical code, significantly higher THz generation efficiency can be achieved with a transmission stair-step echelon-faced nonlinear crystal having a 5 – 15-degree wedge angle than with a plane-parallel one or with the conventional tilted-pulse-front setup. Because of the spatially-dependent group-delay dispersion introduced by the transmission grating, a small wedge in the nonlinear crystal improves the spatial homogeneity of the THz-generation process, resulting in higher efficiencies and better beam profiles. At 100 K temperature, and by using 800 nm pump pulses with 20 mJ pulse energy, 100 fs pulse length and 8 mm beam spot radius, approximately 4.5% conversion efficiency and close to 1 mJ terahertz pulse energy can be reached with the newly-proposed setup.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Towards Millijoule Narrowband Terahertz Pulses Using the Chirp-and-Delay Technique

Spencer W. Jolly, Frederike Ahr, Nicholas H. Matlis, Vincent Leroux, Timo Eichner, Koustuban Ravi, Hideki Ishizuki, Takunori Taira, Franz X. Kärtner, and Andreas R. Maier

https://www.osapublishing.org/abstract.cfm?uri=CLEO_QELS-2018-FF1E.3

We show generation of THz pulses of combined energy above 0.5 mJ at 0.361 THz using the chirp-and-delay technique.

© 2018 The Author(s)

Abstract-Segmented terahertz electron accelerator and manipulator (STEAM)

Dongfang Zhang, Arya Fallahi, Michael Hemmer, Xiaojun Wu, Moein Fakhari, Yi Hua, Huseyin Cankaya, Anne-Laure Calendron, Luis E. Zapata, Nicholas H. Matlis, Franz X. Kärtner

https://www.nature.com/articles/s41566-018-0138-z

Acceleration and manipulation of electron bunches underlie most electron and X-ray devices used for ultrafast imaging and spectroscopy. New terahertz-driven concepts offer orders-of-magnitude improvements in field strengths, field gradients, laser synchronization and compactness relative to conventional radiofrequency devices, enabling shorter electron bunches and higher resolution with less infrastructure while maintaining high charge capacities (pC), repetition rates (kHz) and stability. We present a segmented terahertz electron accelerator and manipulator (STEAM) capable of performing multiple high-field operations on the six-dimensional phase space of ultrashort electron bunches. With this single device, powered by few-microjoule, single-cycle, 0.3 THz pulses, we demonstrate record terahertz acceleration of >30 keV, streaking with <10 fs resolution, focusing with >2 kT m–1 strength, compression to ~100 fs as well as real-time switching between these modes of operation. The STEAM device demonstrates the feasibility of terahertz-based electron accelerators, manipulators and diagnostic tools, enabling science beyond current resolution frontiers with transformative impact.

Abstract-Millijoule-scale narrowband terahertz pulses via phase manipulation of pump laser pulses

Spencer W. Jolly, Nicholas H. Matlis, Frederike Ahr, Vincent Leroux, Timo Eichner, Anne-Laure Calendron, Hideki Ishizuki, Takunori Taira, Franz X. Kärtner, Andreas R. Maier

https://arxiv.org/abs/1802.02508

Electromagnetic radiation at terahertz (THz) frequencies is a useful tool in probing and controlling matter and light in new and interesting ways, especially at high peak-fields and pulse energies. Generating THz radiation often employs nonlinear optical processes, for which the overlapping of stretched, broadband near-infrared (NIR) pulse copies within nonlinear crystals is common. Here we show that for narrowband THz generation, the higher-order phase present on the NIR pulses offers control of the properties of the THz, for example creating temporally complex THz with multiplexed NIR pulses. We manipulate the phase of two NIR pump pulses independently to remove higher order effects and generate record mJ-level THz in two crystals simultaneously, with an average total energy of 604 microjoule at 361 GHz with 1% bandwidth. This high pulse energy combined with such a narrow bandwidth has broad implications for accelerator applications, resonant driven material studies, and nonlinear THz spectroscopy.

Abstract-Narrowband terahertz generation with chirped-and-delayed laser pulses in periodically poled lithium niobate

Frederike Ahr, Spencer W. Jolly, Nicholas H. Matlis, Sergio Carbajo, Tobias Kroh, Koustuban Ravi, Damian N. Schimpf, Jan Schulte, Hideki Ishizuki, Takunori Taira, Andreas R. Maier, and Franz X. Kärtner

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-42-11-2118&origin=search

We generate narrowband terahertz (THz) radiation in periodically poled lithium niobate (PPLN) crystals using two chirped-and-delayed driver pulses from a high-energy Ti:sapphire laser. The generated frequency is determined by the phase-matching condition in the PPLN and influences the temporal delay of the two pulses for efficient terahertz generation. We achieve internal conversion efficiencies up to 0.13% as well as a record multicycle THz energy of 40 μJ at 0.544 THz in a cryogenically cooled PPLN.

© 2017 Optical Society of America

Abstract-Narrowband terahertz generation with chirped-and-delayed laser pulses in periodically poled lithium niobate

Frederike Ahr, Spencer W. Jolly, Nicholas H. Matlis, Sergio Carbajo, Tobias Kroh, Koustuban Ravi, Damian N. Schimpf, Jan Schulte, Hideki Ishizuki, Takunori Taira, Andreas R. Maier, and Franz X. Kärtner

https://www.osapublishing.org/ol/abstract.cfm?uri=ol-42-11-2118

We generate narrowband terahertz (THz) radiation in periodically poled lithium niobate (PPLN) crystals using two chirped-and-delayed driver pulses from a high-energy Ti:sapphire laser. The generated frequency is determined by the phase-matching condition in the PPLN and influences the temporal delay of the two pulses for efficient terahertz generation. We achieve internal conversion efficiencies up to 0.13% as well as a record multicycle THz energy of 40 μJ at 0.544 THz in a cryogenically cooled PPLN.

© 2017 Optical Society of America