Time-dependent spectra of light emitted after two-photon excitation with nonresonant intermediate state are studied by the perturbation method. Two components are distinguished: a slow one ${I}_{s}$ connected with the excited-state population, and a fast one ${I}_{f}$ connected with the double-quantum optical coherence. For large detuning of the two-photon frequency from the excited-ground-state energy separation, the fluorescent light is found to be ${I}_{s}\ensuremath{-}|{I}_{f}|$, and the Raman-scattered light is ${I}_{f}$ . The influence of statistics of light, laser linewidth, spectral bandwidth of the detector, and transfer of coherence from the ground to the excited state are also taken into consideration.Time-dependent spectra of light emitted after two-photon excitation with nonresonant intermediate state are studied by the perturbation method. Two components are distinguished: a slow one ${I}_{s}$ connected with the excited-state population, and a fast one ${I}_{f}$ connected with the double-quantum optical coherence. For large detuning of the two-photon frequency from the excited-ground-state energy separation, the fluorescent light is found to be ${I}_{s}\ensuremath{-}|{I}_{f}|$, and the Raman-scattered light is ${I}_{f}$. The influence of statistics of light, laser linewidth, spectral bandwidth of the detector, and transfer of coherence from the ground to the excited state are also taken into consideration.

Physical Review AMar 1, 19802 citations

Radiative and Two-Photon Resonance Raman Processes Associated with Excitonic Molecules in CuCl

N. Nagasawa, Tsuneyoshi Mita, Masayasu Ueta

Giant two-photon absorption spectrum for the direct generation of excitonic molecules is measured with using a frequency tunable dye laser, and absorption peak is found at 3.1870 eV. Emission spectrum with excitation at the giant two-photon absorption band depends on the spectral width, $\varDelta\varOmega_{1}$ , of excitation light. In the case of $\varDelta\varOmega_{1}{=}0.25$ meV, the two-photon resonance Raman scattering is found to be predominant. The Raman process involves an excitonic molecule and a longitudinal exciton as the intermediate and final states, respectively. On the other hand, for the case of $\varDelta\varOmega_{1}{=}2.3$ meV, the emission spectrum shows a very sharp line at 3.1649 eV, which has been previously ascribed to be due to the Bose-Einstein condensation of excitonic molecules. Discussions are made on the dependence of emission spectrum upon the energy band-width of excitation light.Giant two-photon absorption spectrum for the direct generation of excitonic molecules is measured with using a frequency tunable dye laser, and absorption peak is found at 3.1870 eV. Emission spectrum with excitation at the giant two-photon absorption band depends on the spectral width, $\varDelta\varOmega_{1}$, of excitation light. In the case of $\varDelta\varOmega_{1}{=}0.25$ meV, the two-photon resonance Raman scattering is found to be predominant. The Raman process involves an excitonic molecule and a longitudinal exciton as the intermediate and final states, respectively. On the other hand, for the case of $\varDelta\varOmega_{1}{=}2.3$ meV, the emission spectrum shows a very sharp line at 3.1649 eV, which has been previously ascribed to be due to the Bose-Einstein condensation of excitonic molecules. Discussions are made on the dependence of emission spectrum upon the energy band-width of excitation light.

Journal of the Physical Society of JapanSep 15, 197696 citations

Time-dependent perturbation theory and two-photon absorption

N. Ionescu-Pallas, J. Maurer

Studii si Cercetari de FizicaJan 1, 19770 citations

Role of time-frequency correlations in two-photon-two-atom resonance energy transfer

Roberto de J. León‐Montiel, Arturo Pedroza-Rojas, Jorge-Alberto Peralta-Ángeles

Excitation energy transfer is a photophysical process upon which many chemical and biological phenomena are built. From natural small systems to synthetic multichromophoric macromolecules, energy transfer deals with the process of migration of electronic excitation energy from an excited donor to an acceptor. Although this phenomenon has been extensively studied in the past, the rapid evolution of quantum-enabled technologies has motivated the question on whether nonclassical sources of light, such as entangled photon pairs, may provide us with a better control (or enhancement) of energy transfer at the nanoscale. In this work, we provide a comprehensive study of the joint excitation of two non-interacting two-level atoms by time-frequency correlated photon pairs -- whose central frequencies are not resonant with the individual particles -- generated by means of spontaneous parametric down conversion (SPDC). We demonstrate that while strong frequency anti-correlation between photons guarantees a large two-photon excitation (TPE) probability, photons bearing a sine cardinal spectral shape exhibit a $\sim$3.8 times larger TPE signal than photons with a Gaussian spectrum. More importantly, we find that suppression of time-ordered excitation pathways does not substantially modify the TPE probability for two-photon states with a Gaussian spectral shape; whereas photons with a sine cardinal spectrum exhibit the strongest TPE signals when two-photon excitation pathways are not suppressed. Our results not only help elucidating the role of time-frequency correlations in resonance energy transfer with SPDC photons, but also provide valuable information regarding the optimal source to be used in its experimental implementation.Excitation energy transfer is a photophysical process upon which many chemical and biological phenomena are built. From natural small systems to synthetic multichromophoric macromolecules, energy transfer deals with the process of migration of electronic excitation energy from an excited donor to an acceptor. Although this phenomenon has been extensively studied in the past, the rapid evolution of quantum-enabled technologies has motivated the question on whether nonclassical sources of light, such as entangled photon pairs, may provide us with a better control (or enhancement) of energy transfer at the nanoscale. In this work, we provide a comprehensive study of the joint excitation of two non-interacting two-level atoms by time-frequency correlated photon pairs -- whose central frequencies are not resonant with the individual particles -- generated by means of spontaneous parametric down conversion (SPDC). We demonstrate that while strong frequency anti-correlation between photons guarantees a large two-photon excitation (TPE) probability, photons bearing a sine cardinal spectral shape exhibit a $\sim$3.8 times larger TPE signal than photons with a Gaussian spectrum. More importantly, we find that suppression of time-ordered excitation pathways does not substantially modify the TPE probability for two-photon states with a Gaussian spectral shape; whereas photons with a sine cardinal spectrum exhibit the strongest TPE signals when two-photon excitation pathways are not suppressed. Our results not only help elucidating the role of time-frequency correlations in resonance energy transfer with SPDC photons, but also provide valuable information regarding the optimal source to be used in its experimental implementation.

arXiv:2408.03903Aug 7, 20240 citations

Two-photon excitation in atoms and molecules

Richard E. Wallenstein

Optics CommunicationsJul 1, 197612 citations

Time-dependent spectra of light emitted after two-photon excitation with nonresonant intermediate state are studied by the perturbation method. Two components are distinguished: a slow one

{I}_{s}

connected with the excited-state population, and a fast one

{I}_{f}

connected with the double-quantum optical coherence. For large detuning of the two-photon frequency from the excited-ground-state energy separation, the fluorescent light is found to be ${I}_{s}\ensuremath{-}|{I}_{f}|$, and the Raman-scattered light is

{I}_{f}

. The influence of statistics of light, laser linewidth, spectral bandwidth of the detector, and transfer of coherence from the ground to the excited state are also taken into consideration.

\varDelta\varOmega_{1}

, of excitation light. In the case of

\varDelta\varOmega_{1}{=}0.25

meV, the two-photon resonance Raman scattering is found to be predominant. The Raman process involves an excitonic molecule and a longitudinal exciton as the intermediate and final states, respectively. On the other hand, for the case of

\varDelta\varOmega_{1}{=}2.3

meV, the emission spectrum shows a very sharp line at 3.1649 eV, which has been previously ascribed to be due to the Bose-Einstein condensation of excitonic molecules. Discussions are made on the dependence of emission spectrum upon the energy band-width of excitation light.