Spatial control of extreme ultraviolet light with opto-optical phase modulation

Extreme-ultraviolet (XUV) light is notoriously difficult to control due to its strong interaction cross-section with media. We demonstrate a method to overcome this problem by using Opto-Optical Modulation guided by a geometrical model to shape XUV light. A bell-shaped infrared light pulse is shown to imprint a trace of its intensity profile onto the XUV light in the far-field, such that a change in the intensity profile of the infrared pulse leads to a change in the shape of the far-field XUV light. The geometrical model assists the user in predicting the effect of a specific intensity profile of the infrared pulse, thus enabling a deterministic process

Attosecond pulse shaping using a seeded free-electron laser

Attosecond pulses are central to the investigation of valence- and core-electron dynamics on their natural timescales1–3. The reproducible generation and characterization of attosecond waveforms has been demonstrated so far only through the process of high-order harmonic generation4–7. Several methods for shaping attosecond waveforms have been proposed, including the use of metallic filters8,9, multilayer mirrors10 and manipulation of the driving field11. However, none of these approaches allows the flexible manipulation of the temporal characteristics of the attosecond waveforms, and they suffer from the low conversion efficiency of the high-order harmonic generation process. Free-electron lasers, by contrast, deliver femtosecond, extreme-ultraviolet and X-ray pulses with energies ranging from tens of microjoules to a few millijoules12,13. Recent experiments have shown that they can generate subfemtosecond spikes, but with temporal characteristics that change shot-to-shot14–16. Here we report reproducible generation of high-energy (microjoule level) attosecond waveforms using a seeded free-electron laser17. We demonstrate amplitude and phase manipulation of the harmonic components of an attosecond pulse train in combination with an approach for its temporal reconstruction. The results presented here open the way to performing attosecond time-resolved experiments with free-electron lasers

Complex attosecond waveform synthesis at fel fermi

Free-electron lasers (FELs) can produce radiation in the short wavelength range extending from the extreme ultraviolet (XUV) to the X-rays with a few to a few tens of femtoseconds pulse duration. These facilities have enabled significant breakthroughs in the field of atomic, molecular, and optical physics, implementing different schemes based on two-color photoionization mechanisms. In this article, we present the generation of attosecond pulse trains (APTs) at the seeded FEL FERMI using the beating of multiple phase-locked harmonics. We demonstrate the complex attosecond waveform shaping of the generated APTs, exploiting the ability to manipulate independently the amplitudes and the phases of the harmonics. The described generalized attosecond waveform synthesis technique with an arbitrary number of phase-locked harmonics will allow the generation of sub-100 as pulses with programmable electric fields

Control of Coherent Extreme Ultraviolet Light and Light Sources

Coherent extreme ultraviolet (XUV) light sources are necessary for the investigation of physical processes in the natural length and time scales of atoms. These experiments require a high degree of control of the coherent XUV light. The optical components and techniques, which are available for visible and infrared light, unfortunately cannot be used for controlling XUV light. In this thesis, novel techniques to control ultraviolet to XUV light are presented. The sources of XUV light discussed in this thesis include: high-order harmonic generation, free electron lasers and nitrogen air lasing. These sources are complementary and are suited for different applications.High-order harmonic generation produces XUV light with a very large spectral bandwidth, which can be compressed to produce the shortest light pulses to date. The yield of XUV light that can be produced through high-order harmonic generation is limited since the conversion efficiency of this process is low. Our experiments therefore aim to develop low-loss techniques for controlling the XUV light. We demonstrate techniques to measure and control the spatial phase of the harmonics using quantum path interference, and to control the XUV light after it is generated using opto-optical modulation.In contrast to high-order harmonic generation, free electron lasers can produce XUV pulses with very high intensities and at tunable wavelengths. Furthermore, there are free electron lasers where the amplitude and phase control of the XUV light, when compared to other sources, is unparalleled. The pulses that are produced with FELs, however, are not sufficiently short to perform attosecond ($1\cdot10^{-18}$s) experiments. In this thesis, we describe a free electron laser experiment, where sub-femtosecond waveform structures are generated in a controlled and reproducible way. The results from this experiment present the possibility to perform attosecond physics using free electron lasers, a field which was previously confined to the high-order harmonic generation community.Finally, experiments with nitrogen air lasing are also presented in this thesis. Unlike the other techniques, nitrogen air lasing does not produce XUV light. Instead, this technique produces coherent ultraviolet light, which is promising for atmospheric remote sensing. Since the mechanism generating the light with this technique is currently not understood, a recollision model, similar to the model describing high-order harmonics generation, is tested.None of the aforementioned sources have the same intensity, coherence or possibility to be controlled as conventional lasers. Instead, these sources excel within their own parameter space. Our experiments aim to push these techniques to cover the gaps where none of these sources currently can be used

Achromatic dual-waveplate for inline two color high-order harmonic generation

Abstract: We propose a design of an achromatic dual-waveplate intended to align the polarization of orthogonal two-color pulses in an inline configuration. The waveplate acts as a half-waveplate for pulses with a carrier wavelength of 1300 nm over a bandwidth of 300 nm. For the second harmonic of the pulses the waveplate acts as a full-waveplate, centered at 650 nm with a bandwidth of 100 nm. By experimentally measuring the transmission of this optic when placed between two parallel linear polarizers we show that the polarization directions are aligned as expected. This experiment is then verified by calculating the transmission through the optic using Jones calculus. This waveplate could be useful in two-color experiments with few-cycle pulses, or pulses with a tunable wavelength, that need to be aligned with their second harmonics. Graphical abstract: [Figure not available: see fulltext.]

Spatial control of extreme ultraviolet light with opto-optical phase modulation

Extreme ultraviolet (XUV) light is notoriously difficult to control due to its strong interaction cross section with media. We demonstrate a method to overcome this problem by using opto-optical modulation guided by a geometrical model to shape XUV light. A bell-shaped infrared light pulse is shown to imprint a trace of its intensity profile onto the XUV light in the far-field, such that a change in the intensity profile of the infrared pulse leads to a change in the shape of the far-field XUV light. The geometrical model assists the user in predicting the effect of a specific intensity profile of the infrared pulse, thus enabling a deterministic process

Unexpected Sensitivity of Nitrogen Ions Superradiant Emission on Pump Laser Wavelength and Duration

Nitrogen molecules in ambient air exposed to an intense near-infrared femtosecond laser pulse give rise to cavity-free superradiant emission at 391.4 and 427.8 nm. An unexpected pulse duration-dependent cyclic variation of the superradiance intensity is observed when the central wavelength of the femtosecond pump laser pulse is finely tuned between 780 and 820 nm, and no signal occurs at the resonant wavelength of 782.8 nm (2ω 782.8 nm = ω 391.4 nm). On the basis of a semiclassical recollision model, we show that an interference of dipolar moments of excited ions created by electron recollisions explains this behavior

A novel attosecond timing tool for free-electron laser experiment

We demonstrate a novel timing tool for Free-Electron Lasers to determine the delay between an attosecond pulse train and infrared pulse with sub-optical-cycle resolution