Photon Echo Signal Research Articles

Photon echo on excitons for the development of nanoelectronic devices based on a quantum-size structures in a thin zinc oxide films

The relaxation decays of photon echo signals in thin zinc oxide films produced by magnetron sputtering have been studied. Echo signals are excited at a wavelength of 800 nm at transitions between quantum levels that arise when excitonic states are localized in quantum-sized structures in the two-photon absorption mode of laser pulses with a wavelength of 800 nm.

Ultrafast four-wave-mixing spectroscopy with two vacuum fields and coincidence-double-heterodyne detection

In classical macroscopic ultrafast optical four-wave mixing signals, phase matching selects three classes of light–matter interaction pathways: double quantum coherence; non-rephasing; and photon-echo. Multiple pathways contribute to each of these signals. We show that a coincidence-double-heterodyne detection scheme that employs two classical and two vacuum fields can isolate a single pathway contribution to each of these signals. We further demonstrate the advantage of the proposed technique by comparing it with the classical photon-echo signal for a model Frenkel-exciton dimer.

Spontaneous (two-pulse) photon echo in the nanoscale structure of self-organized quantum dots

We consider the coherent response of a medium with quasi-zero-dimensional structural units in the form of a photon echo upon resonant selective pulsed excitation of interband optical transitions, the inhomogeneous broadening of which is largely determined by the polydisperse composition of the nanocomposite. The process of formation of a photon echo is analyzed, when optical excitation leads to the formation of exciton complexes by resident electrons, which are localized in nanosized microcrystals in the limiting cases of strong and weak size quantization. By studying the coherent dynamics of the components of the pseudospin electric dipole vector, an expression is derived for the macroscopic specific polarization at the moment of emission of the photon echo signal. The consideration is carried out for a model nanocomposite medium on the example of a dielectric matrix with a system of semiconducting spherical inclusions (spherical quantum dots), the distribution over the radii of which is described by the Lifshitz-Slyozov formula.

Signal distortion awakened from optical memory estimated using a calculation method with spatiotemporal separation.

The fidelity of photonic storage and retrieval is an essential criterion in long-distance all-optical network nodes. However, the recovered signals from optical memories based on the photon echo (PE) protocol are accompanied by undesired waveform variation and temporal drift. In this study, we use a numerical calculation method with spatiotemporal separation to investigate the essence of signal distortion. The results show that the asynchronous evolution of the macroscopic population difference and the macroscopic dipole moment with time is responsible for echo signal real distortion caused by phase shifts at the in-phase point of the recorded information. The constructive interference of the dipoles at the moment of reaching the in-phase point induces the photon emission, and this point with a nonspecific phase will be naturally accompanied by waveform changes, a small amount of time advance and delay of the PE signal, which is actually a false signal distortion. Such radiation mechanism of the inhomogeneous broadening media provides a perspective to accurately and correctly recognize the temporal drift and waveform variation of the recovered optical signal.

Fluorescence-Detected Two-Quantum Photon Echoes via Cogwheel Phase Cycling.

Two-dimensional (2D) electronic spectroscopy can separate homogeneous and inhomogeneous broadening. While established methods usually probe a photon-echo signal, i.e., a third-order response, to access the homogeneous line width of singly excited states, the homogeneous line width of doubly excited states remained spectroscopically inaccessible. Here we demonstrate the acquisition of two-quantum (2Q) photon echoes using fluorescence-detected 2D spectroscopy. In these eighth-order signals, 2Q coherences are rephased with themselves, leading to line-narrowed 2Q-2Q 2D spectra. By using cogwheel phase cycling, adapted from nuclear magnetic resonance spectroscopy, we isolate the 2Q-2Q 2D spectra of a squaraine dimer and a squaraine polymer and verify the same selectivity of cogwheel phase cycling compared to traditional "nested" phase cycling. The observed difference, between the two systems, in the homogeneous line width of the biexciton can be rationalized as a signature of the interplay of exciton-exciton annihilation, exciton diffusion, and exciton delocalization.

Photon echo from free excitons in a CH3NH3PbI3 halide perovskite single crystal

Halide perovskites show great potential for a variety of optoelectronic applications. The presence of robust exciton resonance in these materials makes them promising for use in information photonics. In this paper, we demonstrate the possibility of writing and delayed reading of the optical coherence in halide perovskite by the spontaneous (two-pulse) photon echo in ${\mathrm{MAPbI}}_{3}$ (${\mathrm{MA}}^{+}$ = ${\mathrm{CH}}_{3}{\mathrm{NH}}_{3}^{+}$) lead-halide perovskite single crystal on picosecond time scales. The spectral and polarimetric measurements of the photon echo signal confirm the free excitonic origin of the excitation under study. Observed relatively long dephasing time, high exciton oscillator strength, and weakly pronounced excitation-induced dephasing make halide perovskites a promising media for applications.

Extending the time of coherent optical response in ensemble of singly-charged InGaAs quantum dots

The ability to extend the time scale of the coherent optical response from large ensembles of quantum emitters is highly appealing for applications in quantum information devices. In semiconductor nanostructures, spin degrees of freedom can be used as auxiliary, powerful tools to modify the coherent optical dynamics. Here, we apply this approach to negatively charged (In,Ga)As/GaAs self-assembled quantum dots which are considered as excellent quantum emitters with robust optical coherence and high bandwidth. We study three-pulse spin-dependent photon echoes subject to moderate transverse magnetic fields up to 1 T. We demonstrate that the timescale of coherent optical response can be extended by at least an order of magnitude by the field. Without magnetic field, the photon echo decays with T2 = 0.45 ns which is determined by the radiative lifetime of trions T1 = 0.26 ns. In the presence of the transverse magnetic field, the decay of the photon echo signal is given by spin dephasing time of the ensemble of resident electrons T2,e ∼ 4 ns. We demonstrate that the non-zero transverse g-factor of the heavy holes in the trion state plays a crucial role in the temporal evolution and magnetic field dependence of the long-lived photon echo signal.

Vibrational dynamics of iron pentacarbonyl in cryogenic matrices.

Iron pentacarbonyl is a textbook example of fluxionality. We trap the molecule in cryogenic matrices to study the vibrational dynamics of CO stretching modes involved in the fluxional rearrangement. The infrared spectrum in Ar and N2 is composed of about ten narrow bands in the spectral range of interest, indicating the population of various lattice sites and a lowering of the molecular symmetry in the trapping sites. The vibrational dynamics is explored by means of infrared stimulated photon echoes at the femtosecond scale. Vibrational dephasing and population relaxation times are obtained. The non-linear signals exhibit strong oscillations useful to disentangle the site composition of the absorption spectrum. The population relaxation involves at least two characteristic times. An evolution of the photon echo signals with the waiting time is observed. The behavior of all the signals can be reproduced within a simple model that describes the population relaxation occurring in two steps: relaxation of v = 1 (population time T1 < 100ps) and return to v = 0 (recovery time > 1ns). These two steps explain the evolution of the oscillations with the waiting time in the photon echo signals. These results discard fluxional rearrangement on the time scale of hundreds of ps in our samples. Dephasing times are of the same order of magnitude as T1: dephasing processes due to the matrix environment are rather inefficient. The photon echo experiments also reveal that intermolecular resonant vibrational energy transfers between guest molecules occur at the hundreds of ps time scale in concentrated samples (guest/host > 104).

Ab Initio Quasiclassical Simulation of Femtosecond Time-Resolved Two-Dimensional Electronic Spectra of Pyrazine.

Two-dimensional (2D) electronic spectroscopy is a powerful nonlinear technique which provides spectroscopic information on two frequency axes as well as dynamical information as a function of the so-called waiting time. Herein, an ab initio theoretical framework for the simulation of electronic 2D spectra has been developed. The method is based on the classical approximation to the doorway-window representation of three-pulse photon-echo signals and the description of nuclear motion by classical trajectories. Nonadiabatic effects are taken into account by a trajectory surface-hopping algorithm. 2D electronic spectra were simulated with ab initio on-the-fly trajectory calculations using the ADC(2) electronic-structure method for the pyrazine molecule, which is a benchmark system for ultrafast radiationless decay through conical intersections. It is demonstrated that 2D spectroscopy with subfemtosecond UV pulses can provide unprecedented detailed information on the ultrafast photodynamics of polyatomic molecules.

Long-lived dark coherence brought to light by magnetic-field controlled photon echo

Larmor precession of the quasiparticle spin about a transverse magnetic field leads to the oscillations in the spontaneous photon echo signal due to the shuffling of the optical coherence between optically accessible (bright) and inaccessible (dark) states. Here we report on a new non-oscillating photon echo regime observed in the presence of non-equal dephasing rates of bright and dark states. This regime enables the observation of the long-living dark optical coherence. As a simple mechanical analogy, we suggest a charged particle moving in the magnetic field through the medium with anisotropic viscous friction. We demonstrate the dark coherence retrieval in the spontaneous photon echo from excitons in the InGaAs/GaAs quantum well.

Subcycle Nonlinear Response of Doped 4H Silicon Carbide Revealed by Two-Dimensional Terahertz Spectroscopy

We investigate single-cycle terahertz (THz) field-induced nonlinear absorption in doped silicon carbide. We find that the nonlinear response is ultrafast, and we observe up to 20% reduction of transmission of single THz pulses at peak field strengths of 280 kV/cm. We model the field and temperature dependence of the nonlinear response by finite-difference time-domain simulation that incorporates the temporally nonlocal nonlinear conductivity of the silicon carbide. Nonlinear two-dimensional THz spectroscopy reveals that the nonlinear absorption has an ultrafast sub-picosecond recovery time, with contributions from both sum-frequency generation and four-wave mixing, in the form of a photon-echo signal. The ultrafast nonlinearity with its equally fast recovery time makes silicon carbide an interesting candidate material for extremely fast nonlinear THz modulators.

Kinetics of a Collision-Induced Photon Echo

The nonmonotonic kinetics of a collision-induced photon echo has been investigated for a number of buffer atoms. The collision-induced photon echo was generated at the 174Yb (6s2) 1S0 ↔ (6s6p) 3P1 (0 ↔ 1) transition by a pair of linearly and mutually orthogonally polarized resonant radiation pulses in ytterbium vapor and its mixtures with He, Ne, Ar, Kr, and Xe. The kinetics of the conventional photon echo generated by pulses with identical linear polarizations was recorded in the same mixtures. The derived decay rate constants for both types of echo are equal to within the measurement errors. For the collisions of 174Yb atoms between themselves and with other ytterbium isotopes in a natural mixture of isotopes, an upper limit for the anisotropy parameter has been estimated, 0.22 ± 0.07 of the photon echo signal decay rate.

Photon echo using imperfect x-ray pulse with phase fluctuation

We study the impact of inter-pulse phase fluctuation in an x-ray free-electron laser on the signal in photon echo spectroscopy, which is one of the simplest nonlinear spectroscopic methods. A two-pulse echo model is considered with two-level atoms as the sample. The effect of both fluctuation amplitude and correlation strength of the random phase is studied both numerically and analytically. We find that the random phase leads to the changed amplitude and the unchanged rephasing time of the photon echo signal, and show that the relaxation time can be obtained with a previous photon echo setup by an additional average across the signals in different repeated measurements for the pulses with random phase.

Analysis and characterization of accumulated photon echo signals by noncolinear laser pulses based on rare earth ion-doped crystal

Photon echo technique based on rare earth ion-doped crystal has potential applications in optical signal processing. However, the coexistence of different types of photon echo lead to a great reduction of signal-to-noise ratio (SNR). Noncolinear scheme can be adopted to improve SNR by separating such echo signals in the space domain. In this paper, by using the noncolinear beam configuration, we present a detailed analysis and characterization of the accumulated photon echo signals based on rare earth ion-doped crystal. Accumulated photon echo signals occurred at different moment can be analytically predicted using Cayley–Klein parameters method, which is confirmed with the numerical results by solving the Maxwell–Bloch equations. The performance of the spatial-spectral grating has been evaluated, including the grating period, grating amplitude and grating shape. Finally, in the case of noncolinear configuration, the influence parameters related to echo signal intensity has also been discussed compared with the collinear geometry. The results presented here may be helpful to gain new insights on the typical parameters for optical signal processing by using photon echo technology.

A deeper look into Herzberg-Teller vibronic coupling effect and spectroscopic signature of non-Condon systems

A physical explanation with rigorous basis for the newly emerging vibrational progressions due Herzberg-Teller vibronic coupling that show up in absorption spectra and quantum beats in photon echo signals, respectively, in linearly coupled non-Condon systems besides those arising under the Condon regime, thereby leading to further broadening of the make-up of the phonon-side-band, is provided. The spectroscopic signature of non-Condon systems, whose electronic transition dipole moment depends on nuclear coordinates exponentially, with linear electron-phonon coupling seems to increase the Condon intensity or both increase the Condon intensity and give rise to new bands with different intensity of linear and nonlinear absorption spectra. Model system calculations of a single-site (homogeneous) linear absorption spectra and pump-probe signals are provided.

Dual frequency comb photon echo spectroscopy

Dual frequency comb (DFC) nonlinear spectroscopy is an emerging technique that can be used to study a variety of molecular nonlinear responses by exploiting the automatic pulse-to-pulse time delay scanning and fast data acquisition characteristics of the DFC techniques. Here, we propose a DFC-based photon echo spectroscopy (DFC-PES), where two optical frequency comb lasers have slightly different repetition rates and are also allowed to have different carrier frequencies. We first demonstrate our theoretical approach for DFC linear spectroscopy. Then, the signals expected from the proposed DFC-PES are theoretically calculated. The slight offset in the pulse repetition rates enables asynchronous optical sampling and automatic scanning of the time intervals between different field–matter interaction events, making frequency tuning unnecessary. Analytic expression of the third-order photon echo signal is demonstrated in two frequency dimensions for a simple two-level model system. The signal has a well-defined and simple connection to the underlying third-order response function and exhibits the expected down-conversion features from the optical frequency into the radio frequency region with a down-conversion factor that is experimentally controllable.

Linear and nonlinear Herzberg-Teller vibronic coupling effects. I: Electronic photon echo spectroscopy

The dependence of the transition dipole moment on nuclear coordinates gives rise to non-Condon interaction, signaling that the adiabatic Herzberg-Teller vibronic coupling should be considered. This coupling manifests itself in linear spectroscopy through the breakdown of the mirror image symmetry between the absorption and emission spectra. The stronger the non-Condon interaction, the more pronounced is the absorption-emission asymmetry. A nuclear exponential function is used as a simple model to represent the electronic transition dipole moment, the purpose of which is to avoid the use of eigenstate-approach, convergence issues, and finally be able to extend its applicability to nonlinear spectroscopy inexpensively while accounting for linear and nonlinear non-Condon effects (Herzberg-Teller vibronic coupling). The non-Condon effects on linear and nonlinear spectroscopic signals (e.g. 2-pulse photon echo) are examined. Closed-form expressions of the non-Condon electronic transition dipole moment time correlation functions, accounting for Herzberg-Teller vibronic coupling effects, are derived. It is shown that nonlinear optical signals in time domain such as 2-pulse photon echo signal, conspicuously reflects the degree of the non-Condon interaction (mostly constructive interference in this work) despite the inhomogeneous broadening disguising the homogeneous structural aspects of the molecular system of interest. As such, this study should be useful in relation to extracting structural and dynamical information of condensed molecular systems. Model calculations of absorption and emission spectra and 2-pulse photon echo signals of Herzberg-Teller vibronically coupled systems are presented. The method presented here seems to more efficient computationally, fast and stable compared to the methods which involve perturbation theory and eigenstate expansion.

Stark shift in Y2SiO5:Er3+ by the photon echo beating method

The coefficient of a linear Stark shift of the 4F9/2–4I15/2 transition of Er3+ ion in Y2SiO5 is measured (14.3 kHz V−1 cm) by splitting the upper and lower levels of the transition by a pulsed electric field and measuring the splitting frequency from the period of beatings of the temporal form of a photon echo signal (stark photon echo beating method). The linear Stark coefficients of Er3+ transitions in Y2SiO5 have not been measured before, and this is a valuable result for a number of applications such as gradient echo memory, group velocity control via spectral hole burning, etc.

Long Exciton Dephasing Time and Coherent Phonon Coupling in CsPbBr2Cl Perovskite Nanocrystals

Fully inorganic cesium lead halide perovskite nanocrystals (NCs) have shown to exhibit outstanding optical properties such as wide spectral tunability, high quantum yield, high oscillator strength as well as blinking-free single photon emission, and low spectral diffusion. Here, we report measurements of the coherent and incoherent exciton dynamics on the 100 fs to 10 ns time scale, determining dephasing and density decay rates in these NCs. The experiments are performed on CsPbBr2Cl NCs using transient resonant three-pulse four-wave mixing (FWM) in heterodyne detection at temperatures ranging from 5 to 50 K. We found a low-temperature exciton dephasing time of 24.5 ± 1.0 ps, inferred from the decay of the photon-echo amplitude at 5 K, corresponding to a homogeneous line width (fwhm) of 54 ± 5 μeV. Furthermore, oscillations in the photon-echo signal on a picosecond time scale are observed and attributed to coherent coupling of the exciton to a quantized phonon mode with 3.45 meV energy.

Spectrally resolved photon-echo spectroscopy of CdSe quantum dots at far from resonance excitation condition $$^{\S }$$ §

Spectrally resolved photon echo spectroscopy in the off-resonance condition is reported for the first time to study the coherence and population dynamics of CdSe quantum dots. In this case, the information related to the system dynamics can be inferred indirectly. This is especially useful when such dynamical information might be hidden under the absorption maxima of the sample. We observe that a substantial intensity of the photon echo signal was obtained in two different CdSe quantum dot samples (CdSe 610 and CdSe 640), which have absorption maxima at 620 nm and 590 nm, respectively. Due to the difference in sizes of these two quantum dots, a small change is observed in the molecular dynamics of these two quantum-dot samples. Specifically, the spectral diffusion of CdSe 640 occurs within the first 50 fs, whereas that for CdSe 610 occurs at about 100 fs timescale. The integrated plots of the photon echo signal, as a function of population time, result in two decay constants. The faster among the two decay components is pulse width limited and is in between 30 and 40 fs at different fixed coherence times for both samples. The slower decay component for the CdSe 610 sample is found to be in the range of 75–85 fs, while that for CdSe 640, it is between 82 and 92 fs at different fixed coherence times. SYNOPSIS Excitonic dynamics of CdSe quantum-dots is presented using time-dependent spectrally-resolved photon-echo spectroscopy at 810 nm, which is ~160 nm red-shifted from their absorption maxima. Information related to system dynamics is inferred indirectly from such ‘far-from-resonance’ photon-echo experiments, which would be especially useful when the information is hidden within the sample’s absorption maxima.