Femtosecond Four-wave Mixing Spectroscopy Research Articles

Carrier diffusion in thin-film CH3NH3PbI3 perovskite measured using four-wave mixing

We report the application of femtosecond four-wave mixing (FWM) to the study of carrier transport in solution-processed CH3NH3PbI3. The diffusion coefficient was extracted through direct detection of the lateral diffusion of carriers utilizing the transient grating technique, coupled with the simultaneous measurement of decay kinetics exploiting the versatility of the boxcar excitation beam geometry. The observation of the exponential decay of the transient grating versus interpulse delay indicates diffusive transport with negligible trapping within the first nanosecond following excitation. The in-plane transport geometry in our experiments enabled the diffusion length to be compared directly with the grain size, indicating that carriers move across multiple grain boundaries prior to recombination. Our experiments illustrate the broad utility of FWM spectroscopy for rapid characterization of macroscopic film transport properties.

Effects of Interactions with Cyclic Solvent Molecules on Optical Dephasing of CdSe/ZnS Colloidal Quantum Dots Detected by Femtosecond Four-Wave Mixing Spectroscopy

We have studied the effects of interactions with cyclic solvent molecules on the optical dephasing of CdSe/ZnS colloidal quantum dots (QDs) by femtosecond four-wave mixing spectroscopy. We have found that the interactions with the cyclic solvents without π-bonds result in unexpectedly long dephasing times of QDs even at room temperature, while the interactions with the cyclic solvents including π-bonds make the optical dephasing of QDs extremely fast with a dephasing time of less than our time resolution.

Selective excitation of molecular modes in a mixture by optimal control of electronically nonresonant femtosecond four-wave mixing spectroscopy

Femtosecond time-resolved coherent anti-Stokes Raman scattering (fs-CARS) gives access to ultrafast molecular dynamics. Due to the spectrally broad laser pulses, usually poorly resolved spectra result from this spectroscopy. However, it can be demonstrated that by shaping the femtosecond pulses a selective excitation of specific vibrational modes is possible. We demonstrate that using a feedback-controlled optimization technique, molecule-specific CARS spectra can be obtained from a mixture of different substances. A careful analysis of the experimental results points to a nontrivial control of the vibrational mode dynamics in the electronic ground state of the molecules as underlying mechanism.

The investigation of excited-state processes in biologically relevant molecules by means of femtosecond time-resolved four-wave mixing spectroscopy

The investigation of excited-state processes in biologically relevant molecules by means of femtosecond time-resolved four-wave mixing spectroscopy

Femtosecond Four-Wave Mixing Spectroscopy of Molecular Aggregates

Two-photon resonance-enhanced four-wave mixing processes taking place in circular aggregates are considered theoretically with respect to their influences on pump−probe difference absorption measurements. Remarkable changes of the signal spectra around the zero time delay arising from the two-photon resonance transitions to the two-exciton states were discovered. Time- and frequency-resolved pump−probe measurements in the vicinity of zero delay times were shown to be sensitive to the manifestation of two-exciton states and, consequently, may be used for the analysis of the transition dipole orientation of the individual molecules as well as the extent of exciton localization in the circular aggregates.

Manifestation of the transition from the excited state by means of femtosecond four-wave mixing spectroscopy

The influence of the transition from the excited state on the coherent transients of pump-probe measurements in a three-level system is discussed. A theoretical study related to a selective scheme of differential absorption pump-probe spectroscopy is performed in the framework of a full semiclassical description of the interaction of light and matter. It is demonstrated how the coherent part of the modified signal may be used for detection of the up-transition from the excited state. Annihilation processes characteristic of molecular aggregates at high pump intensities are taken into account.