43 W, 1.55 μm and 12.5 W, 3.1 μm dual-beam, sub-10 cycle, 100 kHz optical parametric chirped pulse amplifier

We present a 100 kHz optical parametric chirped pulse amplifier (OPCPA) developed for strong-field attosecond physics and soft-x-ray transient absorption experiments. The system relies on noncollinear potassium titanyl arsenate booster OPCPAs and is pumped by a 244 W, 1.1 ps Yb:YAG Innoslab chirped pulse laser amplifier. Two optically synchronized infrared output beams are simultaneously available: a 430 μJ, 51 fs, carrier-envelope phase stable beam at 1.55 μm and an angular-dispersion-compensated, 125 μJ, 73 fs beam at 3.1 μm

Two-Dimensional Electronic Spectroscopy Unravels sub-100 fs Electron and Hole Relaxation Dynamics in Cd-Chalcogenide Nanostructures

We use two-dimensional electronic spectroscopy (2DES) to disentangle the separate electron and hole relaxation pathways and dynamics of CdTe nanorods on a sub-100 fs time scale. By simultaneously exciting and probing the first three excitonic transitions (S1, S2, and S3) and exploiting the unique combination of high temporal and spectral resolution of 2DES, we derive a complete picture for the state-selective carrier relaxation. We find that hot holes relax from the 1Ï3/2to the 1Ï1/2state (S2 â S1) with 30 ± 10 fs time constant, and the hot electrons relax from the Ïâ² to the Ï state (S3 â S1) with 50 ± 10 fs time constant. This observation would not have been possible with conventional transient absorption spectroscopy due to the spectral congestion of the transitions and the very fast relaxation time scales

Two-Dimensional Electronic Spectroscopy Unravels sub-100 fs Electron and Hole Relaxation Dynamics in Cd-Chalcogenide Nanostructures

We use two-dimensional electronic spectroscopy (2DES) to disentangle the separate electron and hole relaxation pathways and dynamics of CdTe nanorods on a sub-100 fs time scale. By simultaneously exciting and probing the first three excitonic transitions (S1, S2, and S3) and exploiting the unique combination of high temporal and spectral resolution of 2DES, we derive a complete picture for the state-selective carrier relaxation. We find that hot holes relax from the 1Ï3/2to the 1Ï1/2state (S2 â S1) with 30 ± 10 fs time constant, and the hot electrons relax from the Ïâ² to the Ï state (S3 â S1) with 50 ± 10 fs time constant. This observation would not have been possible with conventional transient absorption spectroscopy due to the spectral congestion of the transitions and the very fast relaxation time scales

Unraveling electron and hole relaxation dynamics in colloidal CdTe nanorods: A two-dimensional electronic spectroscopy study

In this work we study the ultrafast exciton dynamics in CdTe nanorods by using two-dimensional electronic spectroscopy (2DES). By simultaneously exciting the lowest three excitonic transitions (i.e. S1, S2 and S3) we extract the electron and hole relaxation pathways, owing to the combined temporal and spectral resolution of 2DES. In particular, we directly observe hot hole relaxation from the second to the first exciton state in about 30 fs by excitation of the S2 transition. Additionally, we extract a direct charge relaxation to S1 by disentangling the overlapping bleach and excited state induced energy level shifts after excitation of S3

Carotenoid-to-bacteriochlorophyll energy transfer through vibronic coupling in LH2 from Phaeosprillum molischianum

The peripheral light-harvesting antenna complex (LH2) of purple photosynthetic bacteria is an ideal testing ground for models of structure–function relationships due to its well-determined molecular structure and ultrafast energy deactivation. It has been the target for numerous studies in both theory and ultrafast spectroscopy; nevertheless, certain aspects of the convoluted relaxation network of LH2 lack a satisfactory explanation by conventional theories. For example, the initial carotenoid-to-bacteriochlorophyll energy transfer step necessary on visible light excitation was long considered to follow the Förster mechanism, even though transfer times as short as 40 femtoseconds (fs) have been observed. Such transfer times are hard to accommodate by Förster theory, as the moderate coupling strengths found in LH2 suggest much slower transfer within this framework. In this study, we investigate LH2 from Phaeospirillum (Ph.) molischianum in two types of transient absorption experiments—with narrowband pump and white-light probe resulting in 100 fs time resolution, and with degenerate broadband 10 fs pump and probe pulses. With regard to the split Qx band in this system, we show that vibronically mediated transfer explains both the ultrafast carotenoid-to-B850 transfer, and the almost complete lack of transfer to B800. These results are beyond Förster theory, which predicts an almost equal partition between the two channels.European Research Council Advanced Grant STRATUSLaserlab-EuropeGrant Agency of the Czech Republic GACRCzech Grant AgencyOeAD WTZ-projectCzech-Austrian Mobility MSMT Gran

Ultrafast relaxation dynamics in a polymer: fullerene blend for organic photovoltaics probed by two-dimensional electronic spectroscopy

Ultrafast charge transfer from a photoexcited donor to an acceptor moiety is at the heart of the energy conversion in organic photovoltaics (OPVs). Efficient charge transfer on ultrafast, sub-100-fs timescales has been reported in many OPV materials. Yet at present, the elementary mechanisms underlying this process in OPV materials, in particular the role of coupled electronic and nuclear motion for the transfer dynamics and yield, are still unclear. Here, we use ultrafast two-dimensional electronic spectroscopy (2DES) to investigate vibronic couplings in the initial, light-induced charge separation dynamics in a blend of poly-3-hexyl-thiophene (P3HT) and [6,6]-phenyl-C61 butyric acid methyl ester (PCBM), a prototypical OPV system. At early times, we observe a distinct breakup of the unstructured linear spectrum into a series of well-resolved vibronic resonances. A comparison to 2DES spectra of pure P3HT suggests that these resonances arise from the vibronic coupling between donor states of the polymer and charge-separated states involving the PCBM acceptors. We identify new, short-lived diagonal peaks, decaying substantially within only about 20–30 fs and lacking a well-resolved cross-peak structure. We argue that these unexpected dynamics likely arise from strong anharmonic couplings to several vibrational modes. One possibility to explain the rapid decay of the blend peaks would be passing of the photoexcited wavepacket through a conical intersection. Our results suggest that nonadiabatic dynamics on multidimensional potential energy surfaces (PESs) might be highly relevant for the initial steps of light-induced charge separation in organic materials. Since theoretical investigations of vibronically-assisted dynamics in such complex organic systems are just emerging, we hope that our results will stimulate further experimental and theoretical work on the role of such dynamics in artificial energy conversion materials. To this end, coherent multidimensional spectroscopy might be a key experimental tool