Seminario: Ultrafast optics con Ursula Keller

Prof. Ursula Keller

Lunes 10 de marzo, 10 a 13 h. Aula 1401, Edificio Cero + Infinito.

Introduction to Mode Locking and Frequency Combs 
These lectures will provide foundational knowledge based on Keller's textbook, *Ultrafast Lasers* (Springer Verlag)

• Basic principles and motivation: Modelocked lasers and their impact for many new discoveries
• Linear pulse propagation in time and frequency domain
• Active modelocking: Siegman-Haus theory
• Passive modelocking with and without dynamic gain saturation
• Passive modelocking: Fast saturable absorber
• Problems with self-starting, Q-switching, long open net-gain window, too much SPM
• Passive modelocking: Soliton modelocking
• Frequency comb and CEO phase stabilization CEO: carrier envelope offset phase
• New concepts: Dual-comb modelocking

Miércoles 12 de marzo, 10 a 13 h. Aula 1401, Edificio Cero + Infinito.

Attosecond Measurements and the Unresolved Question of Tunneling Time 
A graduate-level introduction to ultrafast measurement techniques (e.g., pump-probe, streaking, etc.) followed by a detailed discussion on tunneling time measurements and their unresolved aspects.

• Time in Quantum Mechanics is challenging (more later with tunneling time)

• Motivation for THz to PHz Spectroscopy

• High Harmonic Generation (HHG) and attosecond pulses

• Attosecond Streak Camera

• RABBITT

• Conclusion and Outlook

Inscripciones hasta el 3 de marzo, aquí.

Coloquio: Cuantificando la complejidad de secuencias evolucionadas

Ignacio Sanchez
UBA - Conicet

Coloquio: Auto-organización y fenómenos críticos en atmósferas planetarias

Pablo Mininni 

Departamento de Física & INFINA - UBA-CONICET

¿Cómo se organizan los movimientos aleatorios en atmósferas planetarias para formar estructuras de gran escala? Este proceso requiere de la existencia de procesos de auto-organización de la energía que han sido propuestos teóricamente desde hace 70 años, pero bajo condiciones que no son las de la atmósfera de la Tierra o de otros planetas. En esta charla revisaré un conjunto de resultados recientes que permiten aplicar herramientas de la mecánica estadística y la dinámica de fluidos en sistemas de complejidad creciente, culminando en un estudio con simulaciones numéricas con muy alta resolución espacial que muestra que flujos rotantes y estratificados pueden soportar procesos de auto-organización en condiciones aplicables a las de la Tierra. Los resultados explican cómo puede surgir orden espontáneamente en una atmósfera como la de la Tierra, y modifican nuestro entendimiento del balance de energía en atmósferas planetarias.

Coloquio: Control of attosecond entanglement and coherence

Marc Vrakking - Max-Born Institute

Attosecond science is a branch of ultrafast laser physics that aims to investigate and possibly control electronic motion on its natural timescale by means of pump-probe experiments. Attosecond pulses are formed by the process of high-harmonic generation. Their generation and characterization were recently recognized by the 2023 Physics Nobel Prize, which was given to Anne L’Huillier, Pierre Agostini and Ferenc Krausz. Attosecond pulses have wavelengths in the extreme ultra-violet (XUV) to soft X-ray spectral range. Accordingly, attosecond pulses are ionizing radiation for any medium (solid, liquid or gaseous) that is placed in its path. Photoionization splits a quantum system under investigation into an ion and a photoelectron. The ion and photoelectron will commonly display quantummechanical entanglement, which influences the coherence that attosecond pump-probe experiments rely on. In my talk I will discuss experimental and numerical work demonstrating the role of ion-photoelectron entanglement in attosecond pump-probe experiments, by taking as an example the vibrational and electronic wavepacket dynamics that is induced in H2 + cations upon ionization of H2 by an attosecond laser pulse [1-4] I will show how tailoring the properties of the attosecond pulses (i.e. forming a pair of these pulses, or chirping these pulses) can be used to control the degree of ion-photoelectron entanglement that occurs, as indicated by the degree of vibrational, respectively electronic coherence that can be observed in the ion. In the calculations, the conclusions are furthermore supported by evaluation of the purity and a Schmidt decomposition of the ion + photoelectron wavefunction that results from the ionization process.

References

[1] M.J.J. Vrakking, Control of Attosecond Entanglement and Coherence. Physical Review Letters, 2021. 126(11): p. 113203.

[2] L.-M. Koll, et al., Experimental Control of Quantum-Mechanical Entanglement in an Attosecond Pump-Probe Experiment. Physical Review Letters, 2022. 128(4): p. 043201.

[3] M.J.J. Vrakking, Ion-photoelectron entanglement in photoionization with chirped laser pulses. Journal of Physics B-Atomic Molecular and Optical Physics, 2022. 55(13).

[4] L.-M. Koll, et al., The role of ion-photoelectron entanglement in electron localization following attosecond ionization of H2 (working title). (in preparation), 2024.