Jeffrey A. Myers

Two-color two-dimensional Fourier transform electronic spectroscopy with a pulse-shaper.

We report two-color two-dimensional Fourier transform electronic spectroscopy obtained using an acousto-optic pulse-shaper in a pump-probe geometry. The two-color setup will facilitate the study of energy transfer between electronic transitions that are widely separated in energy. We demonstrate the method at visible wavelengths on the laser dye LDS750 in acetonitrile. We discuss phase-cycling and polarization schemes to optimize the signal-to-noise ratio in the pump-probe geometry. We also demonstrate that phase-cycling can be used to separate rephasing and nonrephasing signal components.

Two-dimensional electronic spectroscopy with a continuum probe

We report 2D Fourier transform electronic spectroscopy obtained in the pump-probe geometry using a continuum probe. An acousto-optic pulse shaper placed in the pump arm of a standard pump-continuum probe experiment permits 2D spectroscopy that probes a broad spectral range. We demonstrate the method on a simple dye system exhibiting vibrational wavepacket dynamics that modulate the peak shapes of the 2D spectra. The broad spectral range of the continuum probe allows us to observe vibronic cross peaks in the 2D spectra.

Effects of chirp on two-dimensional Fourier transform electronic spectra

We examine the effect that pulse chirp has on the shape of two- dimensional electronic spectra through calculations and experiments. For the calculations we use a model two electronic level system with a solvent interaction represented by a simple Gaussian correlation function and compare the resulting spectra to experiments carried out on an organic dye molecule (Rhodamine 800). Both calculations and experiments show that distortions due to chirp are most significant when the pulses used in the experiment have different amounts of chirp, introducing peak shape asymmetry that could be interpreted as spectrally dependent relaxation. When all pulses have similar chirp the distortions are reduced but still affect the anti-diagonal symmetry of the peak shapes and introduce negative features that could be interpreted as excited state absorption.

Simulations of the Two-Dimensional Electronic Spectroscopy of the Photosystem II Reaction Center

We report simulations of the two-dimensional electronic spectroscopy of the Q(y) band of the D1-D2-Cyt b559 photosystem II reaction center at 77 K. We base the simulations on an existing Hamiltonian that was derived by simultaneous fitting to a wide range of linear spectroscopic measurements and described within modified Redfield theory. The model obtains reasonable agreement with most aspects of the two-dimensional spectra, including the overall peak shapes and excited state absorption features. It does not reproduce the rapid equilibration from high energy to low energy excitonic states evident by a strong cross-peak below the diagonal. We explore modifications to the model to incorporate new structural data and improve agreement with the two-dimensional spectra. We find that strengthening the system-bath coupling and lowering the degree of disorder significantly improves agreement with the cross-peak feature, while lessening agreement with the relative diagonal/antidiagonal width of the 2D spectra. We conclude that two-dimensional electronic spectroscopy provides a sensitive test of excitonic models of the photosystem II reaction center and discuss avenues for further refinement of such models.

Toward Broad Bandwidth 2-D Electronic Spectroscopy: Correction of Chirp From a Continuum Probe

Recent implementations of 2-D spectroscopy in the pump-probe geometry using a pulse-shaper demonstrate the ease with which frequency-resolved pump-probe experiments can be readily adapted to 2-D methods. Many frequency-resolved pump-probe experiments employ continuum probes to observe a broad range of electronic transitions. These continuum probes are often chirped, leading to distortions that can be post corrected by characterizing the chirp and appropriately adjusting the observed wavelength-dependent pump-probe time delay. We present an analogous chirp-correction scheme for 2-D spectroscopy, facilitating the use of continuum probing to expand the frequency information available in 2-D spectroscopy experiments. We demonstrate the method through experiments and simulations of a laser dye in solution.

Two-dimensional Fourier transform electronic spectroscopy with a pulse-shaper

We report two-color two-dimensional Fourier transform electronic spectroscopy obtained using an acousto-optic pulse-shaper in a pump-probe geometry. The two-color setup will facilitate the study of energy transfer between electronic transitions that are widely separated in energy. We demonstrate the method at visible wavelengths on the laser dye LDS750 in acetonitrile. We discuss phase-cycling and polarization schemes to optimize the signal-to-noise ratio in the pump-probe geometry. We also demonstrate that phase-cycling can be used to separate rephasing and nonrephasing signal components.

Two-color two-dimensional Fourier transform spectroscopy of energy transfer

We report two-color 2D electronic spectra obtained using a diffractive-optics based approach. We employ the two color method to study a simple system consisting of a donor/acceptor pair exhibiting fluorescence resonance energy transfer.

Two-dimensional electronic spectroscopy signatures of the glass transition

Two-dimensional electronic spectroscopy is a sensitive probe of solvation dynamics. Using a pump-probe geometry with a pulse shaper (Optics Express 15 (2007), 16681-16689; Optics Express 16 (2008), 17420-17428), we present temperature dependent 2D spectra of laser dyes dissolved in glass-forming solvents. At low waiting times, the system has not yet relaxed, resulting in a spectrum that is elongated along the diagonal. At longer times, the system loses its memory of the initial excitation frequency, and the 2D spectrum rounds out. As the temperature is lowered, the time scale of this relaxation grows, and the elongation persists for longer waiting times. This can be measured in the ratio of the diagonal width to the anti-diagonal width; the behavior of this ratio is representative of the frequency-frequency correlation function (Optics Letters 31 (2006), 3354-3356). Near the glass transition temperature, the relaxation behavior changes. Understanding this change is important for interpreting temperature-dependent dynamics of biological systems.

Two-Dimensional Electronic Spectroscopy of the Q y Band of Photosystem II Reaction Centers

We present two-dimensional electronic spectroscopy studies on the dynamics of D1-D2 cyt.b559 reaction center complexes from plant photosystem II at 77 K. Our two-dimensional spectra are compared with models based on current theory.

Strategies for Scatter Removal in Two-Dimensional Electronic Spectroscopy in the Pump-Probe Geometry

We present experimental strategies for removing scatter from multiple sources in two dimensional electronic spectroscopy in the pump-probe geometry. Uncorrected, pump-pump scatter and phase-matched pump-probe signals can distort 2-D peak shapes, complicating their interpretation.