Revealing a full quantum ladder by nonlinear spectroscopy

Abstract

Coherent two-dimensional spectroscopy in the IR or the visible region is very effective for studying correlations, energy relaxation/transfer pathways in complex multi-chromophore or multi-mode systems. However, it is usually restricted up to two-quanta excitations and their properties. In this paper, an arbitrary level of excitation is suggested as the utility to scan nonlinear potential surfaces of quantum systems up to a desired excitation degree. This can be achieved by a simple three-pulse laser spectroscopy approach. Accurate evaluation of high-level anharmonicities as well as transition amplitudes can be directly obtained. Additionally, questions regarding the quantum nature of the probed system can be addressed by studying absolute peak positions.

Higher-Order Multidimensional and Pump–Probe Spectroscopies

“…Examples include, but are not limited to, multiexciton generation in quantum dots or Auger recombination . It was theoretically proposed to study a quantum system by systematically increasing the nonlinear order of excitation, i.e., by measuring increasing orders of the perturbative expansion . Our developed techniques of higher-order PP and 2D spectroscopy can be viewed as the experimental realization of this theoretical concept, allowing us to systematically excite higher and higher states of a quantum system.…”

Equation-of-Motion Methods for the Calculation of Femtosecond Time-Resolved 4-Wave-Mixing and N-Wave-Mixing Signals

“…A number of femtosecond 4WM experiments revealed that richer information on the photoinduced dynamics in atomic vapors, − polyatomic chromophores, − multichromophore aggregates, − and nanosystems − can be obtained by applying more intense laser pulses (see refs − for reviews). On the theoretical side, a variety of simulations of 4WM signals beyond the limit of weak system–field coupling have been reported. ,,,,− Single-molecule femtosecond spectroscopy of individual chromophores − and antenna complexes , also usually requires strong pulses. Nonlinear spectroscopy in nanocavities, in which material systems are strongly coupled to vacuum cavity electromagnetic modes, has become a booming research field recently. − …”

Interpretations of High-Order Transient Absorption Spectroscopies

“…HODQ has the advantage of being background-free, as there is only a signal if higher-lying excited states exist. 47 In contrast HOTA always has nonvanishing signals S (2n+1) for all n, even if the system only supports a single dipole-allowed transition. There are also other methods for measuring higher-order responses such as exciton−exciton interaction 2D spectroscopy (EEI2D), a fifthorder signal that gives excitation and emission/absorption lineshapes, as well as population dynamics, but is again more experimentally challenging than HOTA.…”

“…Many methods have been used or proposed to extract different high-order responses, frequently involving more than two pulses . References and discuss 3-pulse experiments that are high-order extensions of double-quantum (HODQ) spectroscopy . Both HOTA and HODQ extract the emission/absorption lineshapes for higher-lying excited states.…”

“…HOTA is experimentally simpler because it requires only a standard TA setup, whereas HODQ requires three pulses and phase-matching or phase-cycling routines. HODQ has the advantage of being background-free, as there is only a signal if higher-lying excited states exist . In contrast HOTA always has nonvanishing signals S (2 n +1) for all n , even if the system only supports a single dipole-allowed transition.…”