Absolute Measurement of Femtosecond Pump–Probe Signal Strength

Cho, Byungmoon; Tiwari, Vivek; Hill, Robert J.; Peters, William K.; Courtney, Trevor L.; Spencer, Austin P.; Jonas, David M.

doi:10.1021/jp4019662

Cited by 14 publications

(39 citation statements)

References 52 publications

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“…Absorption strengths for each N are calculated from K N according to eq 4 and then recalculated to absorption cross sections (the absorption cross section of the ground state at the excitation wavelength was calculated from ⟨N⟩, and the absorption spectrum is known) and presented in Figure 4 and Figure S3 (Supporting Information), where the data points represent the relative absorption cross section for creating the (N + 1)th exciton. We present the data as ratios of the multiexciton to single-exciton cross sections in order to focus on the behavior characteristic to multiexcitons; absolute values can be calculated in the manner of Cho et al 46 At the higher exciton levels, we consider the highest-intensity case to provide the most reliable value (hollow circles in Figure 4a and stars in Figure S3, Supporting Information).…”

mentioning

confidence: 99%

Multiexciton Absorption Cross Sections of CdSe Quantum Dots Determined by Ultrafast Spectroscopy

Lenngren

Garting

Zheng

et al. 2013

J. Phys. Chem. Lett.

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Multiexciton absorption cross sections are important for analysis of a number of experiments, including multiple exciton generation and stimulated emisson. We present a rigorous method to determine these cross sections using transient absorption (TA) measurements. We apply the method to CdSe quantum dots (QDs) and core-shell (CdSe)ZnS QDs. The method involves measuring TA dynamics for various excitation intensities over a broad time range and analyzing the experiments in terms of a kinetic multiexciton model taking into account all contributions to the signal. In this way, we were able to quantify exciton and multiexciton absorption cross sections at different spectral positions. The absorption cross sections decrease with increasing number of excitations, qualitatively in agreement with the state-filling effective mass model but showing a slower decrease. The cross sections for single-exciton to biexciton absorption range between 57 and 99% of the ground to single-exciton cross section.

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mentioning

confidence: 99%

Multiexciton Absorption Cross Sections of CdSe Quantum Dots Determined by Ultrafast Spectroscopy

Lenngren

Garting

Zheng

et al. 2013

J. Phys. Chem. Lett.

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“…It successfully reproduces optical density effects on the integrated two-pulse photon echo signal decay rate and beam geometry distortions of relative cross-peak amplitudes in 2DFT infrared spectra . 2DFT spectra calculated using the 3DFT method at waiting times long compared to dipole dephasing dynamics connect to expressions for absolute pump–probe signal size , and to experimentally tested expressions for product 2D peak shapes …”

Section: Introductionmentioning

confidence: 78%

“…Inverting the numerical ratio of |Π 2D − |/|Π exit ideal |= 0.03828 using eq 37 with nẑ(ω eg ) = 0.9929 + 0.0003i and γ = 0.9929 yields OD max = 0.9997 ± 0.0003 (which agrees within error with OD max = 1). The attenuation factors appearing in eqs 36 and 37 have been experimentally tested to 10% accuracy in frequency-integrated pump−probe experiments for peak optical densities of up to 1 (see the absorption coefficient−dependent terms in eqs 24 and 26 of ref 15).…”

Section: ■ Computationmentioning

confidence: 99%

“…For sufficiently weak excitation fields, propagation distortions in nonlinear optics result from linear reshaping of the excitation pulses and emitted signal field as they propagate through an optically thick medium. ,,, For weak, resonant pulses shorter than the polarization decay time of a low optical density medium, each input field propagates almost without distortion, but is trailed by a reradiated field that is π out of phase with the input field and decays with the polarization decay time (the trailing linear free-induction decay or FID). , As the optical density increases, multiple absorption–reradiation cycles increasingly distort the input field and FID. In some work, this effect on the signal has been termed cascaded free-induction decay four-wave mixing because it arises from linear cascading of the input fields; such cascading is fully included in the treatment of propagation distortions here.…”

Section: Introductionmentioning

confidence: 99%

“…It successfully reproduces optical density effects on the integrated two-pulse photon echo signal decay rate 11 and beam geometry distortions of relative cross-peak amplitudes in 2DFT infrared spectra. 14 2DFT spectra calculated using the 3DFT method at waiting times long compared to dipole dephasing dynamics connect to expressions for absolute pump−probe signal size 15,16 and to experimentally tested expressions for product 2D peak shapes. 3 The 3DFT algorithm uses the nonlinear impulse response 36,37 (the time-dependent nonlinear polarization excited by three weak, delta-function pulses) as an essential input for the calculation of the signal field radiated by a macroscopic sample.…”

Section: ■ Introductionmentioning

confidence: 99%

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Pulse Propagation Effects in Optical 2D Fourier-Transform Spectroscopy: Theory

Spencer

Cundiff

et al. 2015

J. Phys. Chem. A

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A solution to Maxwell's equations in the three-dimensional frequency domain is used to calculate rephasing two-dimensional Fourier transform (2DFT) spectra of the D2 line of atomic rubidium vapor in argon buffer gas. Experimental distortions from the spatial propagation of pulses through the sample are simulated in 2DFT spectra calculated for the homogeneous Bloch line shape model. Spectral features that appear at optical densities of up to 3 are investigated. As optical density increases, absorptive and dispersive distortions start with peak shape broadening, progress to peak splitting, and ultimately result in a previously unexplored coherent transient twisting of the split peaks. In contrast to the low optical density limit, where the 2D peak shape for the Bloch model depends only on the total dephasing time, these distortions of the 2D peak shape at finite optical density vary with the waiting time and the excited state lifetime through coherent transient effects. Experiment-specific conditions are explored, demonstrating the effects of varying beam overlap within the sample and of pseudo-time domain filtering. For beam overlap starting at the sample entrance, decreasing the length of beam overlap reduces the line width along the ωτ axis but also reduces signal intensity. A pseudo-time domain filter, where signal prior to the center of the last excitation pulse is excluded from the FID-referenced 2D signal, reduces propagation distortions along the ωt axis. It is demonstrated that 2DFT rephasing spectra cannot take advantage of an excitation-detection transformation that can eliminate propagation distortions in 2DFT relaxation spectra. Finally, the high optical density experimental 2DFT spectrum of rubidium vapor in argon buffer gas [J. Phys. Chem. A 2013, 117, 6279-6287] is quantitatively compared, in line width, in depth of peak splitting, and in coherent transient peak twisting, to a simulation with optical density higher than that reported.

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