A THz Lens Antenna fed by a Photoconductive Connected Dipole Array

Photoconductive antennas have been used extensively for THz radiation the last few years. In this thesis, we propose a photoconductive connected dipole array consisting of 36x36 elements that is used as a feed in a THz silicon lens and radiates in a band ranging from 100 GHz to 5 THz. Specifically, we compute theoretically the radiated field patterns of the array as well as the secondary field beyond the lens. Furthermore, we investigate the feasibility of the fabrication of such a photoconductive connected array, given the challenges in 3D printing of a um-sized microlens array that is used to focus the laser power to the excitation gaps of the dipoles. We conclude that microlenses of sufficient accuracy can be fabricated in the premises of TU Delft without compromising the efficiency expected in theory. Lastly, we build a Matlab GUI that computes the far field radiated by various types and sizes of lens antennas in transmission, provided that the field radiated by the feed is already known. This tool has been successfully validated and supported the work in the first part of the thesis at the calculation of the far field of our proposed THz silicon lens antenna

Ptychography-based characterization of wavelength-tunable vortex beams

We demonstrate monochromatic ptychographic reconstructions of vortex beams within a range of 0.2λ0. Modal decomposition of the vortices reveal that the pu-rity of the dominant LG01 mode exceeds 85% for the full investigated bandwidth

Ptychographic characterization of extreme ultraviolet vortex beams

We generate multi-wavelength extreme-ultraviolet vortex beams via high-harmonic generation. We characterize the wavefronts of these high orbital angular mo-mentum beams using ptychography

Multi-Wavelength Ptychography for Wavefront Sensing

Increasing the resolution of imaging systems has been a driving force for science, ranging from biomedicine to semiconductor applications. According to the diffraction limit, the achievable imaging resolution can be improved by using short wavelengths. Specifically, extreme ultraviolet (XUV) light enables nm-scale resolution. Coherent XUV light can be generated by means of high harmonic generation (HHG), where a driving laser with high pulse energy interacts with a non-linear medium. Since the use of lenses in this spectral range is highly challenging, lensless imaging methods such as ptychography [1] have proven to be effective [2]. In ptychography, complex-valued images of both the object and the wavefront of the light beam are numerically reconstructed from a series of diffraction patterns acquired by scanning an object laterally to the source. In this work we develop ptychography into a high-resolution, multi-wavelength XUV wavefront sensor, and use it to characterize our HHG source. The spectrally-resolved wavefront reconstructions provide insight into physical processes that happen during HHG, and can facilitate the use of the high harmonic beams for imaging purposes.</p

Observation of chromatic effects in high-order harmonic generation

High-harmonic generation sources can produce coherent, broadband radiation at extreme-ultraviolet and soft-x-ray wavelengths. The wavefronts of the generated high-order harmonics are influenced by the incident laser field, the generation conditions, and geometry. These influences depend on harmonic wavelength, which may result in wavelength-dependent focusing properties and spatiotemporal couplings that can affect attosecond physics experiments. We experimentally demonstrate and characterize these chromatic effects in high-harmonic generation by measuring the spectrally resolved high-harmonic wavefronts as a function of generation conditions. We find that the high-harmonic generation process can have significant intrinsic chromatic aberration, particularly for converging incident laser fields. Furthermore, we identify regimes where chromatic effects can be minimized, and show that analytical single-atom models allow accurate predictions of harmonic wavefronts produced by a specific driving field.</p

High-resolution wavefront sensing and aberration analysis of multi-spectral extreme ultraviolet beams

Coherent multi-spectral extreme ultraviolet beams have great potential for providing high spatial and temporal resolution for microscopy and spectroscopy applications. But due to the limitations of short-wavelength optics and the broad bandwidth, it remains a challenge to perform quantitative, high-resolution beam characterization. Here we present a wavefront sensing solution based on multiplexed ptychography, with which we show spectrally resolved, high-resolution beam reconstructions. Furthermore, using these high-fidelity quantitative wavefront measurements, we investigate aberration transfer mechanisms in the high-harmonic-generation process, where we present and explain harmonic-order-dependent astigmatism inheritance from the fundamental wavefront. This ptychographic wavefront sensing concept thus enables detailed studies of the high-harmonic-generation process, such as spatiotemporal effects in attosecond pulse formation

High-resolution wavefront sensing of multi-spectral high-harmonic generation sources using ptychography

We perform high-resolution multi-spectral wavefront sensing on extreme ultraviolet sources produced by high-harmonic generation processes. Using ptychography, we show spectrally resolved complex-valued beam reconstructions for eight harmonics simultaneously, with a spatial resolution of 1 µm

ptyLab: a cross-platform inverse modeling toolbox for conventional and Fourier ptychography

We present a cross-platform software, called ptyLab, enabling both conventional and Fourier ptychographic data analysis. The unified framework will accelerate cross-pollination between the two techniques. The code is available open-source in both MAT-LAB and Python

ptyLab: A cross-platform inverse modeling toolbox for conventional and Fourier ptychography

We present a cross-platform software, called ptyLab, enabling both conventional and Fourier ptychographic data analysis. The unified framework will accelerate cross-pollination between the two techniques. The code is available open-source in both MAT-LAB and Python