Impulzushossz és hőmérséklet hatásai nagyenergiájú lítium-niobát alapú terahertzes forrásokra

Intense terahertz source development in the last decade allowed the growth of new areas of research. Tilted-pulse-front pumping of inorganic LiNbO3 (LN) shows good characteristics to achieve the highest possible pulse energies below 1 THz. Ultrafast carrier dynamics of semiconductors were measured by THz pump - THz probe measurements, molecule alignment with an intense field and electron wave streaking were also demonstrated. THz-assisted attosecond pulse generation, would also benefit from intense terahertz pulses. The above mentioned applications require peak electric fields on the order of 100 kV/cm. However, newly emerging areas as acceleration, longitudinal compression, and undulation of relativistic electron bunches, post-acceleration of laser-generated proton and ion beams with potential applications for hadron therapy, multispectral single-shot imaging, THz-enhanced attosecond-pulse generation with increased cut-off frequency would benefit from field strengths higher than currently provided. Multi-mJ and multi-10-MV/cm level sources are needed for these applications. Today extremely high field strengths up to 100 MV/cm are available only in the frequency range above 10 THz. Although the mentioned applications would highly benefit from low frequency THz sources, so that longer wavelength is preferably matching typical transversal sizes of particle beams, pulse energies and peak electric fields necessary for these applications is presently not available. Therefore, it is a priority to optimize THz pulses generated by optical rectification of fs laser pulses with tilted-pulse-front pumping in lithium niobate. Theoretical studies predict an increase in effciency with optimization of pump pulse duration and cryogenic cooling of LN source crystal

High energy Yb:CaF2 femtosecond laser for efficient terahertz generation in lithium niobate

We present a study on THz generation in lithium niobate pumped by a powerful and versatile Yb:CaF2 laser. The unique laser system delivers transform-limited pulses of variable duration (0.38-0.65 ps) with pulse energy of up to 15 mJ at a center wavelength of 1030 nm. From theoretical investigations it is expected that those laser parameters are ideally suited for efficient THz generation. Here we present experimental results on both the conversion efficiency and the THz spectral shape for variable pump pulse durations and for different crystal temperatures down to 25 K. We experimentally verify the optimum pump parameters for most efficient and broadband THz generation

Demonstration of a tilted-pulse-front pumped planparallel slab terahertz source

THz pulse generation in a nonlinear optical slab with an entrance surface having an echelon structure is demonstrated. The setup uses a transmission grating and a planeparallel lithium-niobate crystal slab, and ensures a good-quality, symmetric THz beam and enables scalability to high pulse energies

Demonstration of a tilted-pulse-front pumped plane-parallel slab terahertz source

A new type of tilted-pulse-front pumped terahertz (THz) source has been demonstrated, which is based on a lithium niobate plane-parallel slab with an echelon structure on its input surface. Single-cycle pulses of 1 microjoule energy and 0.30 THz central frequency have been generated with 0.05% efficiency from such a source. One order-of-magnitude increase in efficiency is expected by pumping a cryogenically cooled echelon of increased size and thickness with a Ti:sapphire laser. The use of a plane-parallel nonlinear optical crystal slab enables straightforward scaling to high THz pulse energies and to produce a symmetric THz beam with uniform pulse shape for good focusability and high field strength.Comment: 4 pages, 4 figure

Subcycle surface electron emission driven by strong-field terahertz waveforms

The advent of intense terahertz (THz) sources opened a new era when the demonstration of the acceleration and manipulation of free electrons by THz pulses became within reach. THz-field-driven electron emission was predicted to be confined to a single burst due to the single-cycle waveform. Here we demonstrate the confinement of single-cycle THz-waveform-driven electron emission to one of the two half cycles from a solid surface emitter. Either the leading or the trailing half cycle was active, controlled by reversing the field polarity. THz-driven single-burst surface electron emission sources, which do not rely on field-enhancement structures, will impact the development of THzpowered electron acceleration and manipulation devices, all-THz compact electron sources, THz waveguides and telecommunication, THz-field-based measurement techniques and solid-state devices

Towards Additive Manufacturing of Dielectric Accelerating Structures

Additive manufacturing techniques such as stereolithography have developed rapidly in the last decade and provide the ability to simplify prototyping and manufacturing of unique, complex structures. For the application to dielectric accelerating structures a precise knowledge of the dielectric permittivity of the material is essential to the design. Here we present the characterization of commercially available polymers used in stereolithographic manufacturing by means of refractive index and absorption in the frequency range from 220 GHz to 330 GHz, and around 60 GHz. Vacuum compatibility has been tested with respect to achievable pressure level and residual gas mass spectra. In the future the polymer properties will be applied to designs of accelerating structures as well as couplers for terahertz-driven dielectric accelerator components