FOR2783 2022

12.09.2022, 12:15 → 14.09.2022, 13:15 Europe/Berlin

Lecture hall (LMU Munich - Garching)

Jörg Schreiber (LMU Munich)

Anual meeting research group "FOR2783 Probing the Quantum Vacuum
at the High-Intensity Frontier" in Garching n. Munich

Mo., 12. September

12:15 → 13:50 Arrival - lunch snacks

13:50 → 14:00 Welcome

14:00 → 15:30 Vacuum birefringence and X-ray polarimetry

14:00 Direct accessibility of the fundamental constants governing light-by-light scattering

Quantum field theory predicts the vacuum to exhibit a non-linear response to strong electromag- netic fields. This fundamental tenet has remained experimentally challenging and is yet to be tested in the laboratory. We present proof of concept and detailed theoretical analysis of an experimental setup for precision measurements of the quantum vacuum signal generated by the collision of a bril- liant x-ray probe with a high-intensity pump laser. The signal features components polarised parallel and perpendicularly to the incident x-ray probe. Our proof-of-concept measurements show that the background can be efficiently suppressed by many orders of magnitude which should not only facili- tate a detection of the perpendicularly polarised component of non-linear vacuum response, but even make the parallel polarised component experimentally accessible for the first time. Remarkably, the angular separation of the signal from the intense x-ray probe enables precision measurements even in presence of pump fluctuations and alignment jitter. This provides direct access to the low-energy constants governing light-by-light scattering.

Sprecher: Felix Karbstein

14:45 Avoiding Umweganregungen in X-ray polarizers

This was the topic of my Master thesis.
I will discuss the limitations of the polarization purity in X-ray channelcut polarizers due to Umweganregungen. To reach polarization purities in the range of 10^(-12) or better, these Umweganregungen has to be avoided. This can be done by align the azimuthal angle of the crystal very precicely. I developed a new and faster method, based on the anomalous transmission of X-rays close to Laue-reflections (Borrmann effect), to do this. This method was tested at an X-ray tube in the lab as well as at the European XFEL. In will discuss the results and show that this method provides the possibility to align not only the azimuthal angle but also the tilt angle of the crystals. In priciple any crystal can be aligned with this method in all 3 space dimensions.

Sprecher: Willi Hippler

15:30 → 16:00 Coffee break

16:00 → 17:30 Electron-positron pair creation

16:00 Strong-field Breit-Wheeler pair production with bremsstrahlung gamma-rays in the perturbative-to-nonperturbative transition regime

Motivated by corresponding experimental prospects (such as E3 or LUXE at DESY) we study strong-field Breit-Wheeler pair production by bremsstrahlung gamma-rays propagating through a high-intensity optical laser wave. The influence of the broad frequency spectrum of the bremsstrahlung on the properties of the process in the transition region between the perturbative and the non-perturbative interaction regimes is analysed by calculating the total yield of pair production and the energy and angular distributions of the produced particles for a range of laser intensities [1]. A continuous shift of the major contributing interval of the bremsstrahlung frequencies during the transition is shown and characteristic signatures of the laser-dressed particle mass are highlighted.

[1] A. Eckey, A. B. Voitkiv and C. Müller, Phys. Rev. A 105, 013105 (2022)

Sprecher: Alexandra Eckey (Heinrich-Heine-University Düsseldorf)

16:45 The role of laser focusing in nonlinear Breit-Wheeler pair production from collisions of bremsstrahlung $\gamma$ quanta and a tightly focused laser pulse

Current experimental efforts toward the detection of the nonperturbative nonlinear strong-field regime of Breit-Wheeler pair creation plan to combine incoherent sources of GeV $\gamma$ quanta and tightly focussed optical laser pulses. This endeavour calls for a theoretical understanding of how the pair yields depend on the applied laser field profile [1]. In the present discussion, we provide estimates for the number of pairs produced in a setup where the high-energy radiation is generated via bremsstrahlung. Particular attention is paid to the role of the transversal and longitudinal focussing of the laser field, along with the incorporation of a (super-)Gaussian pulse envelope. The results are compared with predictions from plane-wave models and determine the parameters of focused laser pulses which maximize the pair yield at fixed pulse energy.

[1] A. Golub, S. Villalba-Chavez and C. Mueller,
Nonlinear Breit-Wheeler pair production in collisions of bremsstrahlung $\gamma$ quanta and a tightly focused laser pulse,
Phys. Rev. D 105, 116016 (2022)

Sprecher: Alina Golub (Heinrich-Heine-Universität Düsseldorf)

17:30 → 19:00 PI meeting

Di., 13. September

08:45 → 09:15 Coffee

09:15 → 10:00 Electron-positron pair creation

09:15 The non-linear dynamical numerical solution of quantum electromagnetism for purely time-dependent electric scalar fields

In the paper Relativistic Quantum Transport Theory for
Electrodynamics by Zhuang, Heinz et al. a complete set of kinetic
equations for the covariant equal-time formulation of the quantum
kinetic theory is derived. We expand on this theory by computing
numerical solutions for time-dependent electric fields in the Schwinger
approximation. Early results suggest an important role of the feedback
generated by pair creation initiated via stimulation by an external
electric field.

Sprecher: Yukiko Song (Chair Ruhl, LMU)

10:00 → 11:30 Quantum vacuum nonlinearities in the all-optical regime

10:00 Applications of our Heisenberg-Euler Weak-Field Expansion Simulator in 1D and 2D

The calculation of colliding laser pulses in the weak-field limit of the
Heisenberg-Euler quantum vacuum up to three spatial dimensions is
carried out using our Heisenberg-Euler Weak-Field Expansion
Simulator (HEWES). With the aid of HEWES different scenarios
potentially relevant are investigated.

Sprecher: Baris Ölmez

10:45 Quantum Vacuum Signals in Two-Beam Collision from a Broader Perspective

I present results from a study of the collision of two optical laser pulses in a pump-probe setup using beams with circular and elliptic cross section and estimate the number of discernible signal photons induced by quantum vacuum nonlinearities. In this analysis we study strategies to optimize the quantum vacuum signal discernible from the background of the driving lasers. One of the main results is that the collision of two maximally focused lasers does not lead to the best discernible signal. Instead, widening the focus typically improves the signal to background separation in the far field.

Sprecher: Holger Gies (TPI, FSU Jena)

11:30 → 13:00 Lunch Break

13:00 → 15:15 Quantum vacuum nonlinearities in the all-optical regime

13:00 Photon merging in the collision of two laser pulses - revised

Quantum vacuum nonlinearity allows for the effect of laser photon merging in the collision of two (or more) laser beams. As the merged photons origin from a manifestly inelastic process, their energy differs significantly from the background photons of the driving lasers, making them accessible for experiments. However, the number of merged photons is typically considered to be very small.
In this talk, I will present results on the dependence of the $3\omega$-signal photon number on the laser parameters and the collision angle.

Sprecher: Chantal Sundqvist (FSU Jena)

photonmerging-revised.pdf

13:45 Precise intensity tagging for ultrashort high-power lasers

The LUXE (Laser Und XFEL Experiment) project at DESY Hamburg aims to measure processes in the strong-field quantum electrodynamics regime with high precision by colliding electrons or a high-energy photon beam with high-power, tightly focused laser beam at a repetition rate of 1Hz. Simulations [LUXE CDR, arXiv:2102.02032 [hep-ex]] predict that the probability of pair production responds highly non-linearly to the laser strength parameter. Consequently, small variations in the laser intensity lead to significant variations in the experimental observables. The required precision will be achieved by intensity tagging through precise measurements on the relative variation of intensity on a shot-by-shot basis, with an ultimate aim to monitor the shot-to-shot fluctuations with a precision below 1%. We present the results of a non-linear intensity tagging method, which provides a measure of the laser intensity by comparing the fundamental to a non-linear copy of the laser focal spot from a thin non-linear crystal. This method provides a reference to crosscheck the intensity fluctuations derived from independent measurements of energy, duration and fluence.

Sprecher: Xinhe Huang

14:30 Project E2 – photon photon scattering – progress and plans

The studies conducted during the first funding period led to a proposed set-up for a discovery experiment of photon-photon scattering in CALA (Munich) using two colliding laser pulses at fundamental frequency. In this talk we will give an update on our current understanding of the physics involved in the signal as well as background noise and report on the status of the final experiment design.

Sprecher: Herr Leonard Doyle (LMU)

15:15 → 16:00 Coffee Break

16:00 → 18:00 CALA tour: Laser and experiment caves

19:00 → 21:00 Workshop Dinner

Mi., 14. September

09:15 → 10:45 Electron-positron pair creation

09:15 First background measurements at CALA

Updates on the E3 experiment at CALA and the first background measurements with the single particle detectors.

Sprecher: Felipe Salgado (FSU Jena / Helmholtz-Institut Jena)

10:00 Update on the status of E3-experiments at CALA

We will present an update on project related preparatory studies at CALA.

Sprecher: Katinka von Grafenstein (Ludwig-Maximilians-Universität)

10:45 → 11:45 Visit Breit-Wheeler-Cave at CALA (E3)

11:45 → 13:15 Individual lunch & departure