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The past decade has witnessed a sharp rise of interest in coherent terahertz (THz) light sources for applications in condensed-matter physics. These sources are a powerful tool for studying collective excitations in solid-state systems: THz light can directly couple to low-energy excitations on the meV-scale such as the collective excitations of spins and phonons. Furthermore, coherent excitation of the material spin or phonon subsystem by a THz light pulse allows for tailoring the material’s macroscopic properties. This enables the creation of materials with new dynamic functionalities. To fully exploit the potential of the control of materials’ properties, a new generation of versatile sources of intense short-pulse THz light is needed. This thesis addresses the principles of generation of intense single-cycle THz pulses in an accelerator-based light source. The overarching principle is the phase-locked coherent emission of frequency-chirped waveforms from a specially prepared train of electron bunches inside a tapered undulator. The first part of the thesis (Ch. 1-2) motivates the THz light source development. It surveys the available light sources and scientific applications in the field of low-energy electrodynamics. Looking at a wide selection of THz-induced phenomena, the desired parameters of the proposed undulator-based THz source are determined. The second part (Ch. 3-4) focuses on the technicalities of the accelerator-based THz light source. It addresses the questions of electron beam requirements, photocathode gun performance, dynamics of electrons in an RF gun and in a superconducting linear accelerator. The beam dynamics simulations are carried out and the required characteristics of the electron bunch train are demonstrated. In what follows, the process of waveform-controlled single-cycle emission from an undulator is described: starting from the case of a single electron bunch and then proceeding to the single-cycle emission by the electron bunch tra

As we read this text, our eyes dynamically adjust the focal length to keep the image in focus on the retina. Similarly, in many optics applications the focal length must be dynamically tunable. In the quest for compactness and tunability, flat lenses based on metasurfaces were introduced. However, their dynamic tunability is still limited because their functionality mostly relies upon fixed geometry. In contrast, we put forward an original concept of a tunable Optical Magnetic Lens (OML) that focuses photon beams using a subwavelength-thin layer of a magneto-optical material in a non-uniform magnetic field. We applied the OML concept to a wide range of materials and found out that the effect of OML is present in a broad frequency range from microwaves to visible light. For terahertz light, OML can allow 50% relative tunability of the focal length on the picosecond time scale, which is of practical interest for ultrafast shaping of electron beams in microscopy. The OML based on magneto-optical natural bulk and 2D materials may find broad use in technologies such as 3D optical microscopy and acceleration of charged particle beams by THz beams.

Research at modern light sources continues to improve our knowledge of the natural world, from the subtle workings of life to matter under extreme conditions. Free-electron lasers, for instance, have enabled the characterization of biomolecular structures with sub-angstrom spatial resolution, and paved the way to controlling the molecular functions. On the other hand, attosecond temporal resolution is necessary to broaden our scope of the ultrafast world. Here we discuss attosecond pulse generation beyond present capabilities. Furthermore, we review three recently proposed methods of generating attosecond x-ray pulses. These novel methods exploit the coherent radiation of microbunched electrons in undulators and the tailoring of the emitted wavefronts. The computed pulse energy outperforms pre-existing technologies by three orders of magnitude. Specifically, our simulations of the proposed Soft X-ray Laser at MAX IV (Lund, Sweden) show that a pulse duration of 50-100 as and a pulse energy up to 5 mu J is feasible with the novel methods. In addition, the methods feature pulse shape control, enable the incorporation of orbital angular momentum, and can be used in combination with modern compact free-electron laser setups.

Inspired by light source upgrades, such as ESRF-EBS (Extremely Brilliant Source) and APS-U, I present some modern lattices for a medium-sized 4th-generation synchrotron radiation source. They incorporate new elements, such as anti-bend magnets. The composed lattices are optimized using a simple double-objective algorithm. Its goal is to minimize the natural emittance and absolute chromaticities simultaneously. Then, the lattices are analyzed and compared to a version of the ESRF-EBS lattice scaled down in size. The design is performed to meet the needs of the user community of the Siberian Synchrotron and Terahertz Radiation Centre under the umbrella of the Budker Institute of Nuclear Physics.

The production of intense attosecond light pulses is an active area in accelerator research, motivated by the stringent demands of attosecond science: (i) short pulse duration for resolving the fast dynamics of electrons in atoms and molecules; (ii) high photon flux for probing and controlling such dynamics with high precision. While the free-electron laser (FEL) can deliver the highest brilliance amongst laboratory x-ray sources today, the pulse duration is typically 10-100 femtoseconds. A major obstacle to attaining attosecond duration is that the number of optical cycles increases with every undulator period. Hence, an FEL pulse typically contains tens or hundreds of cycles. In recent years, several novel concepts have been proposed to shift this paradigm, providing the basis for single-cycle pulses and paving the way towards high-brilliance attosecond light sources. This article gives an overview of these concepts.

The space-charge field at the cathode limits the current density extracted from particle sources such as photoinjectors. For a long time, the maximum current has been estimated by using the classical Child-Langmuir law, which is derived with an assumption inconsistent with the conditions of modern laser-driven electron guns. Here, we introduce a theoretical model that accurately accounts for space-charge effects in transversely confined particle beams emerging from photocathodes. The model enables us to (i) determine the maximum current density extractable from the photocathode for an arbitrary cathode radius, (ii) reveal its dependence on the transverse profile of the particle beam, and (iii) predict its upper limit for structured beams such as the ones produced by surface-plasmon resonance-enhanced photocathodes.

This Letter builds upon a recent concept [Phys. Rev. Lett. 113, 104801 (2014)] for producing ultrashort optical pulses through the coherent radiation of electrons in an undulator. Each pulse contains only a single oscillation cycle, and has a controlled waveform (and hence a stable carrier-envelope phase). While the concept had been demonstrated numerically, this Letter provides an analytical model for the radiation mechanism, thereby revealing three key observations: (i) the correlation between the waveforms of the optical and undulator fields; (ii) the free-space dispersion of transversely confined light; and (iii) the dependence of the optical pulse shape on the undulator field strength.

The operation of Ultrafast Electron Diffractometers (UEDs) and Free-Electron Lasers (FELs) relies on high-brightness electron beams produced by radio-frequency (RF) photocathode guns. The next generation of high-repetition rate UEDs and FELs requires electron beams with a high average brightness. To this end, we introduce a continuous wave RF photocathode gun at 325 MHz with an APEX-like geometry. The gun allows for the production of electron beams with very high both peak and average 5D brightness while having moderate RF power consumption. The gun is operated in blowout regime with an energy gain of 0.4 MeV and a peak cathode field of 35 MV/m. Via massive numerical simulations, we exemplify three regimes of the gun operation: (i) 160 fC electron beams with a 5-nm-scale emittance for UEDs, (ii) 1.6 pC beams with a 20-nm-scale emittance for table-top FELs and dielectric-based accelerators, and (iii) 16 pC beams with a 50-nm-scale emittance for inverse Compton sources and other accelerator-based photon sources. We introduce a simple analytical model for the formation of the virtual cathode - the onset of the suppression of photoemission current due to space-charge forces. The model accounts for the laser pulse duration. Furthermore, our extensive numerical simulations indicate a well-pronounced maximum in the 5D beam brightness for the laser spot radius approximately 150% of that corresponding to the onset of the virtual cathode. The finding does not support the common approach in the literature that in the blowout regime the laser spot radius must be much larger than the critical radius corresponding to the virtual cathode onset.

The operation of Ultrafast Electron Diffractometers (UEDs) and Free-Electron Lasers (FELs) relies on high-brightness electron beams produced by radio-frequency (RF) photocathode guns. The next generation of high-repetition rate UEDs and FELs requires electron beams with a high average brightness. To this end, we introduce a continuous wave RF photocathode gun at 325 MHz with an APEX-like geometry. The gun allows for the production of electron beams with very high both peak and average 5D brightness while having moderate RF power consumption. The gun is operated in blowout regime with an energy gain of 0.4 MeV and a peak cathode field of 35 MV/m. Via massive numerical simulations, we exemplify three regimes of the gun operation: (i) 160 fC electron beams with a 5-nm-scale emittance for UEDs, (ii) 1.6 pC beams with a 20-nm-scale emittance for table-top FELs and dielectric-based accelerators, and (iii) 16 pC beams with a 50-nm-scale emittance for inverse Compton sources and other accelerator-based photon sources. We introduce a simple analytical model for the formation of the virtual cathode - the onset of the suppression of photoemission current due to space-charge forces. The model accounts for the laser pulse duration. Furthermore, our extensive numerical simulations indicate a well-pronounced maximum in the 5D beam brightness for the laser spot radius approximately 150% of that corresponding to the onset of the virtual cathode. The finding does not support the common approach in the literature that in the blowout regime the laser spot radius must be much larger than the critical radius corresponding to the virtual cathode onset.

The operation of Ultrafast Electron Diffractometers (UEDs) and Free-Electron Lasers (FELs) relies on high-brightness electron beams produced by radio-frequency (RF) photocathode guns. The next generation of high-repetition rate UEDs and FELs requires electron beams with a high average brightness. To this end, we introduce a continuous wave RF photocathode gun at 325 MHz with an APEX-like geometry. The gun allows for the production of electron beams with very high both peak and average 5D brightness while having moderate RF power consumption. The gun is operated in blowout regime with an energy gain of 0.4 MeV and a peak cathode field of 35 MV/m. Via massive numerical simulations, we exemplify three regimes of the gun operation: (i) 160 fC electron beams with a 5-nm-scale emittance for UEDs, (ii) 1.6 pC beams with a 20-nm-scale emittance for table-top FELs and dielectric-based accelerators, and (iii) 16 pC beams with a 50-nm-scale emittance for inverse Compton sources and other accelerator-based photon sources. We introduce a simple analytical model for the formation of the virtual cathode - the onset of the suppression of photoemission current due to space-charge forces. The model accounts for the laser pulse duration. Furthermore, our extensive numerical simulations indicate a well-pronounced maximum in the 5D beam brightness for the laser spot radius approximately 150% of that corresponding to the onset of the virtual cathode. The finding does not support the common approach in the literature that in the blowout regime the laser spot radius must be much larger than the critical radius corresponding to the virtual cathode onset.

The operation of Ultrafast Electron Diffractometers (UEDs) and Free-Electron Lasers (FELs) relies on high-brightness electron beams produced by radio-frequency (RF) photocathode guns. The next generation of high-repetition rate UEDs and FELs requires electron beams with a high average brightness. To this end, we introduce a continuous wave RF photocathode gun at 325 MHz with an APEX-like geometry. The gun allows for the production of electron beams with very high both peak and average 5D brightness while having moderate RF power consumption. The gun is operated in blowout regime with an energy gain of 0.4 MeV and a peak cathode field of 35 MV/m. Via massive numerical simulations, we exemplify three regimes of the gun operation: (i) 160 fC electron beams with a 5-nm-scale emittance for UEDs, (ii) 1.6 pC beams with a 20-nm-scale emittance for table-top FELs and dielectric-based accelerators, and (iii) 16 pC beams with a 50-nm-scale emittance for inverse Compton sources and other accelerator-based photon sources. We introduce a simple analytical model for the formation of the virtual cathode - the onset of the suppression of photoemission current due to space-charge forces. The model accounts for the laser pulse duration. Furthermore, our extensive numerical simulations indicate a well-pronounced maximum in the 5D beam brightness for the laser spot radius approximately 150% of that corresponding to the onset of the virtual cathode. The finding does not support the common approach in the literature that in the blowout regime the laser spot radius must be much larger than the critical radius corresponding to the virtual cathode onset.

The operation of Ultrafast Electron Diffractometers (UEDs) and Free-Electron Lasers (FELs) relies on high-brightness electron beams produced by radio-frequency (RF) photocathode guns. The next generation of high-repetition rate UEDs and FELs requires electron beams with a high average brightness. To this end, we introduce a continuous wave RF photocathode gun at 325 MHz with an APEX-like geometry. The gun allows for the production of electron beams with very high both peak and average 5D brightness while having moderate RF power consumption. The gun is operated in blowout regime with an energy gain of 0.4 MeV and a peak cathode field of 35 MV/m. Via massive numerical simulations, we exemplify three regimes of the gun operation: (i) 160 fC electron beams with a 5-nm-scale emittance for UEDs, (ii) 1.6 pC beams with a 20-nm-scale emittance for table-top FELs and dielectric-based accelerators, and (iii) 16 pC beams with a 50-nm-scale emittance for inverse Compton sources and other accelerator-based photon sources. We introduce a simple analytical model for the formation of the virtual cathode - the onset of the suppression of photoemission current due to space-charge forces. The model accounts for the laser pulse duration. Furthermore, our extensive numerical simulations indicate a well-pronounced maximum in the 5D beam brightness for the laser spot radius approximately 150% of that corresponding to the onset of the virtual cathode. The finding does not support the common approach in the literature that in the blowout regime the laser spot radius must be much larger than the critical radius corresponding to the virtual cathode onset.