Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

The Journal of Chemical Physics

Pulse overlap artifacts and double quantum coherence spectroscopy

Albin Hedse, Alex Arash Sand Kalaee, A. Wacker, Tõnu Pullerits

Published Mar 24, 2023• 10 citations
Publisher

Abstract

The double quantum coherence (DQC) signal in nonlinear spectroscopy gives information about the many-body correlation effects not easily available by other methods. The signal is short-lived, consequently, a significant part of it is generated during the pulse overlap. Since the signal is at two times the laser frequency, one may intuitively expect that the pulse overlap-related artifacts are filtered out by the Fourier transform. Here, we show that this is not the case. We perform explicit calculations of phase-modulated two-pulse experiments of a two-level system where the DQC is impossible. Still, we obtain a significant signal at the modulation frequency, which corresponds to the DQC, while the Fourier transform over the pulse delay shows a double frequency. We repeat the calculations with a three-level system where the true DQC signal occurs. We conclude that with realistic dephasing times, the pulse-overlap artifact can be significantly stronger than the DQC signal. Our results call for great care when analyzing such experiments. As a rule of thumb, we recommend that only delays larger than 1.5 times the pulse length should be used.

DOI
10.1063/5.0146148

Related papers

Pulse overlap ambiguities in multiple quantum coherence spectroscopy

Ulrich Bangert, Lukas Bruder, Frank Stienkemeier

Coherent two-dimensional electronic spectroscopy probes ultrafast dynamics using femtosecond pulses. In the case where the time scale of the studied dynamics become comparable to the pulse duration, pulse overlap effects may compromise the experimental data. Here, we perform one-dimensional coherence scans and study pulse overlap effects in clean two-level systems. We find parasitic multiple-quantum coherences as a consequence of the arbitrary time ordering during the temporal pulse overlap. Surprisingly, the coherence lifetimes exceed the pulse coherence time by a factor of 1.85. These findings have important implications for the interpretation of higher-order coherent two-dimensional and related spectroscopy experiments.

arXiv:2206.06740•Optics Letters•Dec 21, 2022•7 citations

Phase control of photon-echo dynamics with overlapping pulse pairs

Sharad Joshi, C. R. Pidgeon, Benedict N Murdin +1 more

We report on the dynamics of two-pulse photon echoes in a two-level system. We consider two different types of excitation pulse pairs: pulses with the same carrier envelope phases (CEP pulse pairs) and pulse pairs cut from the same carrier wave train (labeled as normal pulse pairs). We show that for CEP pulse pairs when the pulses overlap somewhat the photon-echo emission time is strongly sensitive to the relative phase (i.e., delay time) between the two pulses. We also show how the photon-echo emission time for such CEP pulse pairs depends on the dephasing time of the polarization (${T}_{2}$) and the pulse width of the applied pulses. This phase sensitivity can be utilized to control the emission time of the photon echo which may prove useful in storing and retrieving light signals from an atomic ensemble. Our results also inform the interpretation of photon-echo signals at short delay time when used to measure fast coherence decay rates.

Physical Review A•Jan 30, 2017•0 citations

Nonlinear Spectroscopy and Quantum Interferometry : Towards Nonlinear Entangled-Photon Spectroscopy

Albin Hedse

Nonlinear spectroscopy is a powerful method for measuring complex systems with significant inter-state correlations. Even methods such as these are, however, still vulnerable to spectral congestion. One of the proposed methods to enhance the resolution of this already powerful technique is to harness the strong correlations of photon-frequency entanglement. This is easier said than done of course, but this doctoral thesis presents work in nonlinear spectroscopy and towards practical implementations of entangled-photon spectroscopy.Initially, we present some theoretical analysis of problems which may arise in nonlinear spectroscopy when pulse overlap is an issue. This is carried out in Paper I, which also numerically quantifies a fundamental theoretical limitation that pulse overlap presents, especially for short-lived signals.We then go on to experimental data analysis of the origins of coherent beatings and the size-dependence of primarily biexciton binding energies in CdSe quantum dots. These are covered in Papers II and III respectively.Finally, we perform an investigation of the possible upper bounds of an entangled-two photon absorption cross-section. Claims of strong quantum advantages in low-flux regimes have warranted further observation, and in examining them we are taking the first steps towards nonlinear entangled spectroscopy. This is done through use of a Franson interferometer, used here in a novel way by performing delay-dependent coincidence measurements for the purpose of obtaining an upper bound on entangled two-photon absorption cross-sections. This work is covered in Paper IV. We then discuss possible future directions for entangled-photon spectroscopy and the forms it can take.

•Jan 1, 2026•0 citations

Non-Markovian correlation effects in time-delayed femtosecond absorption spectroscopy

W. Vogel, D.‐G. Welsch, B. Wilhelmi

The dependence of the electronic absorption spectrum of a dye molecule on the time of delay between the excitation of the molecule by a pump-laser pulse and the probing of the absorption by a test-laser pulse is studied. The effect of dephasing of the molecular transition arising from the interaction with dissipative systems is described by a stochastic modulation of the electronic transition frequency. It is shown that in the case when the two laser pulses are short compared with the correlation time of the frequency modulation and when the spectral linewidth of the pump-laser light is smaller than the bandwidth of the equilibrium absorption spectrum, hole burning appears although the molecules have equal mean transition frequencies. This effect arises from non-Markovian correlations between the dephasings of the molecule during the actions of the pump- and the test-laser pulse. With increasing delay time the holes are smoothed out and disappear when the delay time exceeds the correlation time. Such effects were found in recent femtosecond absorption experiments by Shank et al. [in Ultrafast Phenomena V, dited by G. R. Fleming and A. E. Siegman (Springer, Berlin, 1986), p. 179].

Physical Review A•May 1, 1988•47 citations

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

Austin P. Spencer, Hebin Li, Steven T. Cundiff +1 more

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.

The Journal of Physical Chemistry A•Apr 16, 2015•42 citations

Effects of phase accumulation in frequency-comb-based multidimensional coherent spectroscopy

Bachana Lomsadze, Skyler C. Weight, Peter K. D. Hovland

In recent years, frequency-comb-based multidimensional coherent spectroscopy has emerged as a very powerful optical method for studying samples with long dephasing times. It enables the measurement of comb resolution multidimensional coherent spectra in seconds as opposed to hours or even days required by traditional mechanical stage-based spectrometers. However, for some samples (e.g., cold atoms and molecules) the dephasing times could be longer than the repetition periods of the excitation lasers which means that the generated signal will not fully decay between the pulses. Depending on the relative phase or time between the pulses, the signals generated by the subsequent laser pulses can constructively or destructively interfere with each other. In this paper we study this behavior by solving the optical Bloch equations and provide a theoretical description of frequency-comb-based multidimensional coherent spectroscopy.

Physical Review A•Sep 12, 2022•3 citations
The double quantum coherence (DQC) signal in nonlinear spectroscopy gives information about the many-body correlation effects not easily available by other methods. The signal is short-lived, consequently, a significant part of it is generated during the pulse overlap. Since the signal is at two times the laser frequency, one may intuitively expect that the pulse overlap-related artifacts are filtered out by the Fourier transform. Here, we show that this is not the case. We perform explicit calculations of phase-modulated two-pulse experiments of a two-level system where the DQC is impossible. Still, we obtain a significant signal at the modulation frequency, which corresponds to the DQC, while the Fourier transform over the pulse delay shows a double frequency. We repeat the calculations with a three-level system where the true DQC signal occurs. We conclude that with realistic dephasing times, the pulse-overlap artifact can be significantly stronger than the DQC signal. Our results call for great care when analyzing such experiments. As a rule of thumb, we recommend that only delays larger than 1.5 times the pulse length should be used.
Coherent two-dimensional electronic spectroscopy probes ultrafast dynamics using femtosecond pulses. In the case where the time scale of the studied dynamics become comparable to the pulse duration, pulse overlap effects may compromise the experimental data. Here, we perform one-dimensional coherence scans and study pulse overlap effects in clean two-level systems. We find parasitic multiple-quantum coherences as a consequence of the arbitrary time ordering during the temporal pulse overlap. Surprisingly, the coherence lifetimes exceed the pulse coherence time by a factor of 1.85. These findings have important implications for the interpretation of higher-order coherent two-dimensional and related spectroscopy experiments.
We report on the dynamics of two-pulse photon echoes in a two-level system. We consider two different types of excitation pulse pairs: pulses with the same carrier envelope phases (CEP pulse pairs) and pulse pairs cut from the same carrier wave train (labeled as normal pulse pairs). We show that for CEP pulse pairs when the pulses overlap somewhat the photon-echo emission time is strongly sensitive to the relative phase (i.e., delay time) between the two pulses. We also show how the photon-echo emission time for such CEP pulse pairs depends on the dephasing time of the polarization (T2{T}_{2}T2​) and the pulse width of the applied pulses. This phase sensitivity can be utilized to control the emission time of the photon echo which may prove useful in storing and retrieving light signals from an atomic ensemble. Our results also inform the interpretation of photon-echo signals at short delay time when used to measure fast coherence decay rates.
Nonlinear spectroscopy is a powerful method for measuring complex systems with significant inter-state correlations. Even methods such as these are, however, still vulnerable to spectral congestion. One of the proposed methods to enhance the resolution of this already powerful technique is to harness the strong correlations of photon-frequency entanglement. This is easier said than done of course, but this doctoral thesis presents work in nonlinear spectroscopy and towards practical implementations of entangled-photon spectroscopy.Initially, we present some theoretical analysis of problems which may arise in nonlinear spectroscopy when pulse overlap is an issue. This is carried out in Paper I, which also numerically quantifies a fundamental theoretical limitation that pulse overlap presents, especially for short-lived signals.We then go on to experimental data analysis of the origins of coherent beatings and the size-dependence of primarily biexciton binding energies in CdSe quantum dots. These are covered in Papers II and III respectively.Finally, we perform an investigation of the possible upper bounds of an entangled-two photon absorption cross-section. Claims of strong quantum advantages in low-flux regimes have warranted further observation, and in examining them we are taking the first steps towards nonlinear entangled spectroscopy. This is done through use of a Franson interferometer, used here in a novel way by performing delay-dependent coincidence measurements for the purpose of obtaining an upper bound on entangled two-photon absorption cross-sections. This work is covered in Paper IV. We then discuss possible future directions for entangled-photon spectroscopy and the forms it can take.
The dependence of the electronic absorption spectrum of a dye molecule on the time of delay between the excitation of the molecule by a pump-laser pulse and the probing of the absorption by a test-laser pulse is studied. The effect of dephasing of the molecular transition arising from the interaction with dissipative systems is described by a stochastic modulation of the electronic transition frequency. It is shown that in the case when the two laser pulses are short compared with the correlation time of the frequency modulation and when the spectral linewidth of the pump-laser light is smaller than the bandwidth of the equilibrium absorption spectrum, hole burning appears although the molecules have equal mean transition frequencies. This effect arises from non-Markovian correlations between the dephasings of the molecule during the actions of the pump- and the test-laser pulse. With increasing delay time the holes are smoothed out and disappear when the delay time exceeds the correlation time. Such effects were found in recent femtosecond absorption experiments by Shank et al. [in Ultrafast Phenomena V, dited by G. R. Fleming and A. E. Siegman (Springer, Berlin, 1986), p. 179].
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.
In recent years, frequency-comb-based multidimensional coherent spectroscopy has emerged as a very powerful optical method for studying samples with long dephasing times. It enables the measurement of comb resolution multidimensional coherent spectra in seconds as opposed to hours or even days required by traditional mechanical stage-based spectrometers. However, for some samples (e.g., cold atoms and molecules) the dephasing times could be longer than the repetition periods of the excitation lasers which means that the generated signal will not fully decay between the pulses. Depending on the relative phase or time between the pulses, the signals generated by the subsequent laser pulses can constructively or destructively interfere with each other. In this paper we study this behavior by solving the optical Bloch equations and provide a theoretical description of frequency-comb-based multidimensional coherent spectroscopy.