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558 KiB

Open AccessArticle

Self Referencing Heterodyne Transient Grating Spectroscopy with Short Wavelength

by Jakob Grilj, Emily Sistrunk, Jaewoo Jeong, Mahesh G. Samant, Alexander X. Gray, Hermann A. Dürr, Stuart S. P. Parkin and Markus Gühr

Photonics 2015, 2(2), 392-401; https://doi.org/10.3390/photonics2020392 - 15 Apr 2015

Cited by 5 | Viewed by 6361

Abstract

Heterodyning by a phase stable reference electric field is a well known technique to amplify weak nonlinear signals. For short wavelength, the generation of a reference field in front of the sample is challenging because of a lack of suitable beamsplitters. Here, we [...] Read more.

Heterodyning by a phase stable reference electric field is a well known technique to amplify weak nonlinear signals. For short wavelength, the generation of a reference field in front of the sample is challenging because of a lack of suitable beamsplitters. Here, we use a permanent grating which matches the line spacing of the transient grating for the creation of a phase stable reference field. The relative phase among the two can be changed by a relative translation of the permanent and transient gratings in direction orthogonal to the grating lines. We demonstrate the technique for a transient grating on a VO₂ thin film and observe constructive as well as destructive interference signals. Full article

(This article belongs to the Special Issue Extreme UV Lasers: Technologies and Applications)

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283 KiB

Open AccessArticle

Towards Realistic Simulations of Macromolecules Irradiated under the Conditions of Coherent Diffraction Imaging with an X-ray Free-Electron Laser

by Beata Ziaja, Zoltan Jurek, Nikita Medvedev, Vikrant Saxena, Sang-Kil Son and Robin Santra

Photonics 2015, 2(1), 256-269; https://doi.org/10.3390/photonics2010256 - 4 Mar 2015

Cited by 24 | Viewed by 6015

Abstract

Biological samples are highly radiation sensitive. The rapid progress of their radiation damage prevents accurate structure determination of single macromolecular assemblies in standard diffraction experiments. However, computer simulations of the damage formation have shown that the radiation tolerance might be extended at very [...] Read more.

Biological samples are highly radiation sensitive. The rapid progress of their radiation damage prevents accurate structure determination of single macromolecular assemblies in standard diffraction experiments. However, computer simulations of the damage formation have shown that the radiation tolerance might be extended at very high intensities with ultrafast imaging such as is possible with the presently developed and operating x-ray free-electron lasers. Recent experiments with free-electron lasers on nanocrystals have demonstrated proof of the imaging principle at resolutions down to 1:6 Angstroms. However, there are still many physical and technical problems to be clarified on the way to imaging of single biomolecules at atomic resolution. In particular, theoretical simulations try to address an important question: How does the radiation damage progressing within an imaged single object limit the structural information about this object recorded in its diffraction image during a 3D imaging experiment? This information is crucial for adjusting pulse parameters during imaging so that high-resolution diffraction patterns can be obtained. Further, dynamics simulations should be used to verify the accuracy of the structure reconstruction performed from the experimental data. This is an important issue as the experimentally recorded diffraction signal is recorded from radiation-damaged samples. It also contains various kinds of background. In contrast, the currently used reconstruction algorithms assume perfectly coherent scattering patterns with shot noise only. In this review paper, we discuss the most important processes and effects relevant for imaging-related simulations that are not yet fully understood, or omitted in the irradiation description. We give estimates for their contribution to the overall radiation damage. In this way we can identify unsolved issues and challenges for simulations of x-ray irradiated single molecules relevant for imaging studies. They should be addressed during further development of these simulation tools. Full article

(This article belongs to the Special Issue Extreme UV Lasers: Technologies and Applications)

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2292 KiB

Open AccessArticle

Extreme Ultraviolet Stokesmeter for Pulsed Magneto-Optics

by Mabel Ruiz-Lopez, Francesco Barbato, Yasin Ekinci and Davide Bleiner

Photonics 2015, 2(1), 241-255; https://doi.org/10.3390/photonics2010241 - 16 Feb 2015

Cited by 1 | Viewed by 5406

Abstract

Several applications in material science and magnetic holography using extreme ultraviolet (EUV) radiation require the measurement of the degree and state of polarization. In this work, an instrument to measure simultaneously both parameters from EUV pulses is presented. The instrument determines the Stokes [...] Read more.

Several applications in material science and magnetic holography using extreme ultraviolet (EUV) radiation require the measurement of the degree and state of polarization. In this work, an instrument to measure simultaneously both parameters from EUV pulses is presented. The instrument determines the Stokes parameters after a reflection on an array of multilayer mirrors at the Brewster angle. The Stokesmeter was tested at Swiss Light Source at different EUV wavelengths. The experimental Stokes patterns of the source were compared with the simulated pattern. Full article

(This article belongs to the Special Issue Extreme UV Lasers: Technologies and Applications)

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6834 KiB

Open AccessArticle

Transverse Electromagnetic Mode Conversion for High-Harmonic Self-Probing Spectroscopy

by Antoine Camper, Amélie Ferré, Nan Lin, Emmanouil Skantzakis, David Staedter, Elizabeth English, Bastian Manschwetus, Frédéric Burgy, Stéphane Petit, Dominique Descamps, Thierry Auguste, Olivier Gobert, Bertrand Carré, Pascal Salières, Yann Mairesse and Thierry Ruchon

Photonics 2015, 2(1), 184-199; https://doi.org/10.3390/photonics2010184 - 10 Feb 2015

Cited by 12 | Viewed by 7955

Abstract

We report on high-order harmonic (HHG) two-source interferometry (TSI) in molecular gases. We used a 0-\(\pi\) phase plate to create two bright spots at the focus of a lens by converting a Gaussian laser beam into a TEM please define \(_{01}\) Transverse Electromagnetic [...] Read more.

We report on high-order harmonic (HHG) two-source interferometry (TSI) in molecular gases. We used a 0-\(\pi\) phase plate to create two bright spots at the focus of a lens by converting a Gaussian laser beam into a TEM please define \(_{01}\) Transverse Electromagnetic Mode. The two bright foci produce two synchronized HHG sources. One of them is used to probe on-going dynamics in the generating medium, while the other serves to heterodyne the signal. The interference of the emissions in the far–field gives access to the phase difference between the two sources. In self–probing HHG phase spectroscopy, one of the two sources is used as a reference while the other one probes some on goin dynamics in the generating medium. We first compute overlap integrals to investigate the mode conversion efficiency. We then establish a clear relation between the laser phase-front curvature and the far-field overlap of the two HHG beams. Both Fresnel diffraction calculations and an experimental lens position scan are used to reveal variations of the phase front inclination in each source. We show that this arrangement offers \(\frac{\lambda_{XUV}}{100}\) precision, enabling extremely sensitive phase measurements. Finally, we use this compact setup for TSI and measure phase variations across the molecular alignment revival of nitrogen and in vibrating sulfur hexafluoride. In both gases, the phase variations change sign around the ionization threshold of the investigated molecule. Full article

(This article belongs to the Special Issue Extreme UV Lasers: Technologies and Applications)

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542 KiB

Open AccessArticle

Optimum Pump Pulse Duration for X-Ray Ar-Plasma Lasing

by Leili Masoudnia and Davide Bleiner

Photonics 2015, 2(1), 164-183; https://doi.org/10.3390/photonics2010164 - 10 Feb 2015

Cited by 7 | Viewed by 4931

Abstract

In plasma-driven X-ray lasers, it is critical to optimize the duration and time delay between pump pulses. In this study, we have done parametric simulations in order to systematically investigate the optimum time configuration of pump pulses. Here, we are mainly interested in [...] Read more.

In plasma-driven X-ray lasers, it is critical to optimize the duration and time delay between pump pulses. In this study, we have done parametric simulations in order to systematically investigate the optimum time configuration of pump pulses. Here, we are mainly interested in soft X-ray lasers created using a Ar target irradiated with laser pulses, which operate at a wavelength \(\lambda=46.9\) nm in the \(2p^5 3p^1(J=0)\rightarrow 2p^5 3s^1(J=1)\) laser transition. It is shown that the optimum time scale required to achieve Ne-like ions, as well as the time required to generate a population inversion depend on the combined effect of the electron temperature and electron density. The electron density and temperature are respectively a factor of \(\approx\)\(2.1\)- and \(\approx\)\(5\)-times higher in the case of a short pulse of \(0.1\) ps in comparison to a long pulse of 1,000 ps (at a constant fluence). The most effective lasing happens with short pulses with a pulse duration comparable to the total relaxation time from the upper level, namely \(\Delta\tau_p\leq35\) ps. Power laws to predict the optimum laser intensity to achieve Ne-like \(Ar^{+8}\) are obtained. Full article

(This article belongs to the Special Issue Extreme UV Lasers: Technologies and Applications)

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976 KiB

Open AccessArticle

Quantum Path Interference and Multiple Electron Scattering in Soft X-Ray High-Order Harmonic Generation

by Jozsef Seres, Enikoe Seres, Bjoern Landgraf, Bastian Aurand, Thomas Kuehl and Christian Spielmann

Photonics 2015, 2(1), 104-123; https://doi.org/10.3390/photonics2010104 - 23 Jan 2015

Cited by 5 | Viewed by 7444

Abstract

High-order harmonic generation is an important mechanism to generate coherent radiation in the few–100-eV spectral range with ultrashort laser pulses. Moreover, a closer inspection of the measured spectra provides unique information about the underlying physics and allows deriving guidelines for improvements. The long-range [...] Read more.

High-order harmonic generation is an important mechanism to generate coherent radiation in the few–100-eV spectral range with ultrashort laser pulses. Moreover, a closer inspection of the measured spectra provides unique information about the underlying physics and allows deriving guidelines for improvements. The long-range modulation of the spectral envelope is linked to phase matching, and we will show how to improve it with a double-pulse excitation scheme. Additionally, the spectrum contains only every fourth harmonic, which can be well explained by the quantum interference of multiple scattered electrons, and two dominant electron trajectories were selected by X-ray parametric interaction. Full article

(This article belongs to the Special Issue Extreme UV Lasers: Technologies and Applications)

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826 KiB

Open AccessArticle

Photo-Ionization of Noble Gases: A Demonstration of Hybrid Coupled Channels Approach

by Vinay Pramod Majety and Armin Scrinzi

Photonics 2015, 2(1), 93-103; https://doi.org/10.3390/photonics2010093 - 16 Jan 2015

Cited by 13 | Viewed by 5581

Abstract

We present here an application of the recently developed hybrid coupled channels approach to study photo-ionization of noble gas atoms: Neon and Argon. We first compute multi-photon ionization rates and cross-sections for these inert gas atoms with our approach and compare them with [...] Read more.

We present here an application of the recently developed hybrid coupled channels approach to study photo-ionization of noble gas atoms: Neon and Argon. We first compute multi-photon ionization rates and cross-sections for these inert gas atoms with our approach and compare them with reliable data available from R-matrix Floquet theory. The good agreement between coupled channels and R-matrix Floquet theory show that our method treats multi-electron systems on par with the well established R-matrix theory. We then apply the time dependent surface flux (tSURFF) method with our approach to compute total and angle resolved photo-electron spectra from Argon with linearly and circularly polarized 12 nm wavelength laser fields, a typical wavelength available from Free Electron Lasers (FELs). Full article

(This article belongs to the Special Issue Extreme UV Lasers: Technologies and Applications)

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642 KiB

Open AccessArticle

Toward the Extreme Ultra Violet Four Wave Mixing Experiments: From Table Top Lasers to Fourth Generation Light Sources

by Riccardo Cucini, Andrea Battistoni, Filippo Bencivenga, Alessandro Gessini, Riccardo Mincigrucci, Erika Giangrisostomi, Emiliano Principi, Flavio Capotondi, Emanuele Pedersoli, Michele Manfredda, Maya Kiskinova and Claudio Masciovecchio

Photonics 2015, 2(1), 57-70; https://doi.org/10.3390/photonics2010057 - 12 Jan 2015

Cited by 1 | Viewed by 5254

Abstract

Three different Transient Grating setups are presented, with pulsed and continuous wave probe at different wavelengths, ranging from infrared to the extreme ultra violet region. Both heterodyne and homodyne detections are considered. Each scheme introduces variations with respect to the previous one, allowing [...] Read more.

Three different Transient Grating setups are presented, with pulsed and continuous wave probe at different wavelengths, ranging from infrared to the extreme ultra violet region. Both heterodyne and homodyne detections are considered. Each scheme introduces variations with respect to the previous one, allowing moving from classical table top laser experiments towards a new four wave mixing scheme based on free electron laser radiation. A comparison between the various setups and the first results from extreme ultra violet transient grating experiments is also discussed. Full article

(This article belongs to the Special Issue Extreme UV Lasers: Technologies and Applications)

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424 KiB

Open AccessArticle

Liquid Carbon Reflectivity at 19 nm

by Riccardo Mincigrucci, Erika Giangrisostomi, Emiliano Principi, Andrea Battistoni, Filippo Bencivenga, Riccardo Cucini, Alessandro Gessini, Maria Grazia Izzo and Claudio Masciovecchio

Photonics 2015, 2(1), 50-56; https://doi.org/10.3390/photonics2010050 - 9 Jan 2015

Cited by 2 | Viewed by 4715

Abstract

We hereby report on a pump-probe reflectivity experiment conducted on amorphous carbon, using a 780 nm laser as a pump and a 19 nm FEL emission as probe. Measurements were performed at 50 degrees with respect to the surface normal to have an [...] Read more.

We hereby report on a pump-probe reflectivity experiment conducted on amorphous carbon, using a 780 nm laser as a pump and a 19 nm FEL emission as probe. Measurements were performed at 50 degrees with respect to the surface normal to have an un-pumped reflectivity higher than 0.5%. A sub-10 fs time synchronization error could be obtained exploiting the nearly jitter-free capabilities of FERMI. EUV FEL-based experiments open the way to study the behaviour of a liquid carbon phase being unaffected by plasma screening. Full article

(This article belongs to the Special Issue Extreme UV Lasers: Technologies and Applications)

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359 KiB

Open AccessArticle

Grating Configurations for the Spectral Selection of Coherent Ultrashort Pulses in the Extreme-Ultraviolet

by Fabio Frassetto, Paolo Miotti and Luca Poletto

Photonics 2014, 1(4), 442-454; https://doi.org/10.3390/photonics1040442 - 26 Nov 2014

Cited by 7 | Viewed by 5782

Abstract

The design and realization of grating instruments to handle and condition coherent ultrafast pulses in the extreme ultraviolet spectral region are discussed. The main application of such instruments is the spectral selection of high-order laser harmonics and free-electron-laser pulses in the femtosecond time [...] Read more.

The design and realization of grating instruments to handle and condition coherent ultrafast pulses in the extreme ultraviolet spectral region are discussed. The main application of such instruments is the spectral selection of high-order laser harmonics and free-electron-laser pulses in the femtosecond time scale. Broad-band monochromators require the use of diffraction gratings at grazing incidence. Here, we discuss two configurations useful for the realization of grating monochromator with ultrafast response: the single-grating design, applied to high-order laser harmonics, and the time-delay-compensated configuration with two gratings, applied to free-electron lasers. Full article

(This article belongs to the Special Issue Extreme UV Lasers: Technologies and Applications)

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Review

Jump to: Research

1414 KiB

Open AccessReview

On the Importance of Electron Beam Brightness in High Gain Free Electron Lasers

by Simone Di Mitri

Photonics 2015, 2(2), 317-341; https://doi.org/10.3390/photonics2020317 - 27 Mar 2015

Cited by 27 | Viewed by 6550

Abstract

Linear accelerators delivering high brightness electron beams are essential for driving short wavelength, high gain free-electron lasers (FELs). The FEL radiation output efficiency is often parametrized through the power gain length that relates FEL performance to electron beam quality at the undulator. In [...] Read more.

Linear accelerators delivering high brightness electron beams are essential for driving short wavelength, high gain free-electron lasers (FELs). The FEL radiation output efficiency is often parametrized through the power gain length that relates FEL performance to electron beam quality at the undulator. In this review article we illustrate some approaches to the preliminary design of FEL linac-drivers, and analyze the relationship between the output FEL wavelength, exponential gain length and electron beam brightness. We extend the discussion to include FEL three-dimensional effects and electron beam projected emittances. Although mostly concentrating on FELs based upon self-amplified spontaneous emission (SASE), our findings are in some cases highly relevant to externally seeded FELs. Full article

(This article belongs to the Special Issue Extreme UV Lasers: Technologies and Applications)

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1527 KiB

Open AccessReview

Electron Interference in Molecular Circular Polarization Attosecond XUV Photoionization

by Kai-Jun Yuan and André D. Bandrauk

Photonics 2015, 2(1), 71-92; https://doi.org/10.3390/photonics2010071 - 12 Jan 2015

Cited by 3 | Viewed by 6139

Abstract

Two-center electron interference in molecular attosecond photoionization processes is investigated from numerical solutions of time-dependent Schrödinger equations. Both symmetric H\(_2^+\) and nonsymmetric HHe\(^{2+}\) one electron diatomic systems are ionized by intense attosecond circularly polarized XUV laser pulses. Photoionization of these molecular ions shows [...] Read more.

Two-center electron interference in molecular attosecond photoionization processes is investigated from numerical solutions of time-dependent Schrödinger equations. Both symmetric H\(_2^+\) and nonsymmetric HHe\(^{2+}\) one electron diatomic systems are ionized by intense attosecond circularly polarized XUV laser pulses. Photoionization of these molecular ions shows signature of interference with double peaks (minima) in molecular attosecond photoelectron energy spectra (MAPES) at critical angles \(\vartheta_c\) between the molecular \(\textbf{R}\) axis and the photoelectron momentum \(\textbf{p}\). The interferences are shown to be a function of the symmetry of electronic states and the interference patterns are sensitive to the molecular orientation and pulse polarization. Such sensitivity offers possibility for imaging of molecular structure and orbitals. Full article

(This article belongs to the Special Issue Extreme UV Lasers: Technologies and Applications)

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552 KiB

Open AccessReview

Recent Developments in UV Optics for Ultra-Short, Ultra-Intense Coherent Light Sources

by Daniele Cocco

Photonics 2015, 2(1), 40-49; https://doi.org/10.3390/photonics2010040 - 8 Jan 2015

Cited by 26 | Viewed by 6802

Abstract

With the advent of Free Electron Lasers and general UV ultra-short, ultra-intense sources, optics needed to transport such radiation have evolved significantly to standard UV optics. Problems like surface damage, wavefront preservation, beam splitting, beam shaping, beam elongation (temporal stretching) pose new challenges [...] Read more.

With the advent of Free Electron Lasers and general UV ultra-short, ultra-intense sources, optics needed to transport such radiation have evolved significantly to standard UV optics. Problems like surface damage, wavefront preservation, beam splitting, beam shaping, beam elongation (temporal stretching) pose new challenges for the design of beam transport systems. These problems lead to a new way to specify optics, a new way to use diffraction gratings, a search for new optical coatings, to tighter and tighter polishing requirements for mirrors, and to an increased use of adaptive optics. All these topics will be described in this review article, to show how optics could really be the limiting factor for future development of these new light sources. Full article

(This article belongs to the Special Issue Extreme UV Lasers: Technologies and Applications)

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