i i “tesi_phd_21_3” — 2019/5/29 — 19:02 — page i — #1 i i Novel control knobs for multidimensional stimulated Raman spectroscopy Sapienza, Università di Roma Dottorato di ricerca in Modelli matematici per l’Ingegneria, Elettromagnetismo e Nanoscienze XXXI Ciclo Candidate: Giuseppe Fumero ID number 1347711 Thesis advisor: Prof. Tullio Scopigno A thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Mathematical models for Engineering, Electromagnetics and Nanosciences November 2018 i i i i i i “tesi_phd_21_3” — 2019/5/29 — 19:02 — page ii — #2 i i Thesis defended on 4 February 2019 in front of a Dissertation Committee composed by: Prof. Giulio Cerullo Prof. Antonio Morini Prof. Massimo Santarsiero Novel control knobs for multidimensional stimulated Raman Spectroscopy Ph.D. thesis. Sapienza – Università di Roma © 2018 Giuseppe Fumero. All rights reserved This thesis has been typeset by LATEX. Frontispiece inspired by the Sapthesis class. Version: January 27, 2019 Contact: [email protected] i i i i i i “tesi_phd_21_3” — 2019/5/29 — 19:02 — page iii — #3 i i Alla mia famiglia: Amedeo, Vittoria, Carlo Alberto & Marco i i i i i i “tesi_phd_21_3” — 2019/5/29 — 19:02 — page iv — #4 i i i i i i i i “tesi_phd_21_3” — 2019/5/29 — 19:02 — page v — #5 i i Contents Preface vii Introduction ix 1 Stimulated Raman spectroscopy in the time and frequency domains 1 1.1 Spectroscopic tools . .1 1.2 Spontaneous vs stimulated Raman Scattering . .4 1.3 Different protocols to measure stimulated Raman signals . .8 1.3.1 Stimulated Raman in the frequency domain . .8 1.3.2 Stimulated Raman in the time domain . .9 1.4 The multidimensional approach . 11 1.4.1 Excursus in the frequency domain: using resonances in broadband Stim- ulated Raman Scattering . 13 2 Perturbative description and diagrammatic tools 17 2.1 Dynamics in the Liouville space . 17 2.1.1 Density matrix formalism . 17 2.1.2 Liouville equation . 19 2.1.3 Interaction picture . 21 2.2 Semiclassical and full quantum treatment of nonlinear optics . 23 2.2.1 Maxwell equations and wave mixing . 23 2.2.2 Quantum electrodynamics . 26 2.3 Double sided Feynman Diagrams . 29 2.3.1 Rules in time and frequency domain . 32 3 Experimental Realization 35 3.1 Overview of the optical setup . 35 3.2 Pulses generation and detection . 37 3.2.1 Laser Source . 37 3.2.2 White light probe generation and detection . 39 3.2.3 Impulsive Actinic and Raman pulse . 40 3.2.4 Narrowband Raman pulse . 41 3.3 Collecting the experimental data . 42 3.3.1 Delay line calibration . 42 3.3.2 TA . 43 3.3.3 ISRS . 43 3.3.4 SRS . 45 3.4 Data Analysis . 45 3.4.1 Pump-probe dynamics and baseline subtraction . 45 3.4.2 Zero padding and windowing . 46 3.4.3 Measurement of time zero and chirp . 46 v i i i i i i “tesi_phd_21_3” — 2019/5/29 — 19:02 — page vi — #6 i i vi Contents 4 Broadband Impulsive stimulated Raman Spectroscopy with shaped pulses 49 4.1 Different approaches to broadband ISRS . 50 4.1.1 Linear detection of a non equilibrium state by a phase shaped probe . 50 4.1.2 Two beam geometry . 52 4.2 Using the probe chirp as a control knob . 54 4.2.1 Chirp in a Gaussian pulse . 54 4.2.2 Vibrational mode tuning in the off resonant two beam geometry . 55 4.2.3 Excited state selectivity of vibrational features . 59 4.3 Conclusions . 61 5 Probing electron-phonon coupling on femtosecond time scale in Lead Halide Perovskites 63 5.1 Photoinduced charge carriers in hybrid organic-inorganic perovskites . 63 5.1.1 Structure and optoelectronic properties . 63 5.1.2 Charge relaxation and recombination processes . 65 5.1.3 Free carriers vs excitons . 67 5.1.4 Polarons . 68 5.2 Impulsive stimulated Raman spectroscopy on lead bromide perovskites . 69 5.2.1 Preparation and characterization of MAPbBr3 ............... 70 5.2.2 ISRS experimental results . 72 5.2.3 Discussion . 74 5.3 Conclusions . 78 6 Vibronic couplings during ultrafast chemical reactions probed by 2D Impul- sive Stimulated Raman Spectroscopy 79 6.1 Multidimensional spectroscopies of vibronic interactions . 79 6.2 Concepts of resonant 2D Impulsive Stimulated Raman Spectroscopy . 80 6.2.1 Derivation of the signal . 82 6.2.2 The harmonic model of the molecular Hamiltonian . 85 6.3 Assigning the origin of the 2D ISRS peaks in the harmonic model . 89 6.3.1 Linearly Displaced Harmonic model . 89 6.3.2 Mode Mixing . 91 6.4 Excited-State Two-Dimensional Raman Spectroscopy on Green Fluorescent Protein 92 6.4.1 Experimental results . 93 6.4.2 Discussion . 95 6.5 Conclusions . 97 7 Conclusions and perspectives 99 Appendix 103 Calculation of transition integrals in the linearly displaced harmonic model 103 List of publications and conferences 105 References 107 i i i i i i “tesi_phd_21_3” — 2019/5/29 — 19:02 — page vii — #7 i i Preface This thesis collects the main results I have obtained during the three years spent work- ing at Sapienza University as a PhD student and University of California, Irvine as a visiting scholar. During this time, I participated in theoretical and experimental research activities mainly devoted to ultrafast spectroscopy and, in particular, to time and frequency domain co- herent Raman spectroscopies. As a member of the Femtoscopy group in Rome, I participated in the development of the pump-probe and stimulated Raman research lines. In particular, my experimental activity consisted in the optimization of the impulsive Raman setup and data acquisition software and in gathering the data reported in chapter 4 and 5. Moreover, I had a major role in data analysis and interpretation of the measurements presented in chapter 5 and collaborated in the elaboration of the models and simulations for resonant stimulated Raman and impulsive Raman presented in chapters 1 and 4. I developed the theoretical framework for resonant two dimensional Raman spectroscopy and performed the interpretation and fit of the data collected by the Kukura’s group in Oxford, presented in chapter 6. I also participated in writing research articles based on these works, which are enumerated at the end of the thesis. I would like to thank prof. Tullio Scopigno, prof. Shaul Mukamel, prof. Annamaria Petrozza and prof. Philipp Kukura together with the members of their groups for these ultrafast three years of exciting hikes in science. G.F. vii i i i i i i “tesi_phd_21_3” — 2019/5/29 — 19:02 — page viii — #8 i i viii Preface i i i i i i “tesi_phd_21_3” — 2019/5/29 — 19:02 — page ix — #9 i i Introduction Understanding the behavior of complex systems is greatly simplified when the proper energy and time scales over which their evolution occurs are investigated. Consequently, deciphering the dynamics of atoms and molecules requires to access the domain of femtoseconds, and even shorter timescales are involved in the case of electrons. Probing such extreme phenomena is the challenging task at which ultrafast spectroscopy aims. In the last forty years, the development of pulsed laser sources and nonlinear optical tech- niques has allowed the study of phenomena invisible to electronic devices, through the ma- nipulation of matter macroscopic phases on picosecond and sub-picosecond timescales. This technological leap provided sophisticated and customized ultrashort spectroscopic protocols in a wide energy range, from terahertz to x rays, fully realizing the pioneering view of the ultrafast stroboscope, dreamed by the father of femtochemistry Ahmed Zewail. Indeed, using the proper technique, short flashes of light are currently able to record stop-motion images of a dynamic processes as fast as a chemical reaction. The study of the nonlinear response due to external impulsive optical perturbations has been applied to a wide range of scientific cases, fueling a parallel boost in electronic and vibrational spectroscopies. The frontier in ultrafast sciences is now gradually shifting to tackle the interplay between these two degrees of freedom. Vibronic coupling is considered at the grounds of fascinating processes which connect conceptual topics from the foundation of quantum mechanics, as the breakdown of the Born-Oppenheimer approximation, to technological application, as the co- herent energy transfer in biomimic photosynthetic devices or the bewildering effects of strong electron-phonon coupling in novel materials as graphene and third generation semiconductors. Probing electronic and vibrational interactions at the same time is complicated by the time and energy scale separation between the two. Thus, one dimensional spectroscopies are weakened by resolution limits which may partially hamper their use in this direction. Multidimensional tech- niques can cope this limit spreading the information on separate spectroscopic axes, consequently disentangling the relative resolutions. Couplings between different agents in the microscopic de- scription of the sample dynamics are directly revealed through the presence of cross peaks in the multidimensional maps. In this context, the research presented in this thesis has been devoted to the design, realiza- tion and interpretation of novel approaches to multidimensional Impulsive Stimulated Raman Spectroscopy (ISRS). Coherent Raman techniques are indeed able to measure vibrational spec- tra using visible light, which provides at the same time information about the electronic degrees of freedom when tuned resonant with the absorption edges of the sample. A concerted combina- tion between theory and experiments is the key to successfully probe the quantum properties of the matter on which the vibronic interactions rely. For this reason, the experimental efforts have been flanked by a powerful theoretical toolbox given by the nonlinear response formalism. This framework represents a natural link between theory and experiments and supplies a common language to describe very different techniques, gathering their features to design new experimen- tal protocols.