Accumulated Photon Echo Research Articles

The operation of combining sets for images in optical echo holography

The paper considers the implementation of logical operations with sets presented as images in the accumulated photon echo mode. It is shown that the photon echo mode may be used to perform the operation of combining sets.

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.

Correlated signals of the accumulated photon echo on CdSe – CdS quantum dots

The possibility of an observation of correlated signals of the accumulated photon echo under a three-photon excitation of a sample, which is an ensemble of semiconductor nanoparticles of “core – shell” type, by a femtosecond radiation of Ti:Sa laser is discussed. The phase matching conditions of such signals are obtained.

Laser frequency stabilization at 1.5 microns using ultranarrow inhomogeneous absorption profiles in Er 3+:LiYF 4

Single-frequency diode lasers have been frequency stabilized to 1.5 kHz Allan deviation over 0.05–50 s integration times, with laser frequency drift reduced to less than 1.4 kHz/min, using the frequency reference provided by an ultranarrow inhomogeneously broadened Er 3+: 4I 15/2→ 4I 13/2 optical absorption transition at a vacuum wavelength of 1530.40 nm in a low-strain LiYF 4 crystal. The 130 MHz full-width at half-maximum (FWHM) inhomogeneous line width of this reference transition is the narrowest reported for a solid at 1.5 μm. Strain-induced inhomogeneous broadening was reduced by using the single isotope 7Li and by the very similar radii of Er 3+ and the Y 3+ ions for which it substitutes. To show the practicability of cryogen-free cooling, this laser stability was obtained with the reference crystal at 5 K; moreover, this performance did not require vibrational isolation of either the laser or crystal frequency reference. Stabilization is feasible up to T=25 K where the Er 3+ absorption thermally broadens to ∼500 MHz. This stabilized laser system provides a tool for interferometry, high-resolution spectroscopy, real-time optical signal processing based on spatial spectral holography and accumulated photon echoes, secondary frequency standards, and other applications such as quantum information science requiring narrow-band light sources or coherent detection.

Low‐temperature dephasing mechanism of very small quantum dots: the role of confined phonons and surrounding matrices

Temperature dependence of the homogeneous linewidth of CuBr quantum dots in glass and NaBr matrices and CdSe quantum dots in glass matrix has been investigated using heterodyne-detected accumulated photon echo. We can reproduce the observed nonlinear temperature dependence considering two characteristic mechanisms: the small energy excitation in two-level system and the two-phonon Raman process of confined acoustic phonons. The interaction with the two-level system is dominant below 15 K and 10 K for CuBr and CdSe quantum dots, respectively. Above these temperatures the interaction with confined phonons is dominant. These results are similar to those of a previous study of CuCl quantum dots in glass, showing the universal influence of confined phonons and surrounding matrices on the low-temperature dephasing process of very small semiconductor quantum dots.

Coherent spectroscopy of semiconductor quantum dots

Coherent spectroscopy of semiconductor quantum dots, such as photon echo, accumulated photon echo, interferometric coherency measurement, quantum beat and coherent phonon measurement, are reviewed in relation to the historical progress in the coherent spectroscopy of semiconductors.

The Optical Dynamics of Excitons in Cylindrical J-Aggregates

The optical dynamics of excitons in cylindrical 5,5‘,6,6‘-tetrachloro-1,1‘-diethyl-3,3‘−di(4-sulfobutyl)-benzimidazolocarbocyanine (TDBC)/C8O3 aggregates have been investigated by ultrafast pump−probe spectroscopy and accumulated photon echo experiments. In the nonlinear optical interactions, both the one-exciton band and the two-exciton band are excited. The interpretation of the results involves the separation of the two-exciton states into two types: those that have predominantly “ring”-character, with energy separations determined by the circumference of the cylinder, and those that have predominantly “longitudinal”-character, with energy separations determined by the coherence length of the excitons along the length of the cylinder. At 1.5 K, the excitons were found to be delocalized over an area of, on average, 95 molecules. These excitons can move incoherently to other localized regions on the cylinder, leading to rapid relaxation within the one-exciton band.

Homogeneous Width of Confined Excitons in Quantum Dots at Very Low Temperatures

The temperature-dependent homogeneous width of confined excitons in CuCl, CuBr and CdSe quantum dots was investigated at very low temperatures down to 0.6 K by means of accumulated photon echo. The observed nonlinear temperature dependence of the homogeneous width at low temperatures is explained by the interaction with confined acoustic phonons for CdSe quantum dots or very small excitation in the two-level system for CuCl and CuBr quantum dots. At the lowest temperature, the homogeneous width of confined excitons in CuCl, CuBr and CdSe quantum dots becomes 1-2 μeV, 23-59 μeV and 0.16-0.25 meV, respectively. It depends on the surrounding matrix for CuCl quantum dots and the radius of dots for CuBr and CdSe quantum dots. These results suggest surroundings of quantum dots dominate the low temperature dephasing mechanism, i.e. homogeneous width of the optical spectra, of real quantum dots.

Exciton Dynamics in LH1 and LH2 of Rhodopseudomonas Acidophila and Rhodobium Marinum Probed with Accumulated Photon Echo and Pump−Probe Measurements

Exciton dynamics in the B850 and B875 bands of isolated complexes of Rhodopseudomonas acidophila (strain 10 050 and 7050) and in the B875 band of isolated complexes of Rhodobium marinum were investigated by means of accumulated photon echo and pump−probe techniques at different temperatures and wavelengths. For all three systems, the optical dephasing time T2 was found to be very similar: at 4.2 K, T2 is 116 and 106 ps for the B850 and B875 bands of Rhodopseudomonas acidophila, respectively, and 93 ps for the B875 band of Rhodobium marinum. The rapid dephasing, which displays glassy character, is a consequence of the strong pigment−protein interactions that arise through the rather short distances in these complexes. The observed dephasing time at the red edge of the B850 band of Rhodopseudomonas acidophila at 4.2 K reveals the existence of spectral diffusion in this system. From the wavelength dependence of the pump−probe signal in the B875 LH1 band of Rhodopseudomonas acidophila at 3 K it is concluded that energy transfer between energetically inequivalent LH1 rings occurs on a time scale of several tens picoseconds, while energy trapping takes place in about 250 ps.

Time domain investigation on vibrational dephasing and spectral diffusion in CO-doped solid N2

Infrared picosecond accumulated photon echo experiments have been performed for the first time, using the Orsay Free Electron Laser, on the v = 0-->v = 1 transition of CO in solid nitrogen. The vibrational dephasing time is found to be exceptionally long ( T2>/=120 ns) at low temperature. The analysis of the observed spectral diffusion leads one to assume different energy transfer mechanisms depending on the CO concentration.

Accumulated photon-echo spectroscopy for stained tissue samples

We performed phase relaxation-time measurements of the accumulated photon echo for normal and cancerous tissue samples of human liver, that were stained with several kinds of dye. Each dye interacted selectively with a specific kind of biomolecule in the tissues, for example, DNA, proteins, or lipids. The cancerous tissues showed a tendency to have shorter relaxation times than the normal tissues had. The difference of relaxation time observed between the normal and the cancerous tissues depended on the dyes that were used for staining, and the difference became most clear when the tissues were stained with a cyanine dye derivative, i.e., YO-PRO3 Iodide, which has a high selectivity for DNA. We performed the relaxation-time mapping of the accumulated photon echo (photon-echo imaging) for a liver tissue sample stained by YO-PRO3 Iodide. The photon-echo imaging was successful in showing a region of a highly differentiated hepatocellular carcinoma in the tissue sample, while fluorescence-intensity mapping could not identify the cancerous region in the same tissue sample. These results indicated a possibility that the reduction of accumulated photon-echo relaxation time observed in the cancerous tissues was caused by a change of microscopic dynamics of DNA.

Ultranarrow homogeneous broadening of confined excitons in quantum dots: Effect of the surrounding matrix

Ultranarrow homogeneous linewidth of a ${Z}_{3}$ exciton in CuCl quantum dots was studied by using accumulated photon echo. CuCl quantum dots embedded in two kinds of matrices, namely, an alminoborosilicate glass and a NaCl crystal, were studied. The narrowest homogeneous linewidth at low temperature was 1 $\ensuremath{\mu}\mathrm{eV}.$ The temperature dependence of the homogeneous linewidth was similar, above 5 K for both kinds of samples, but in the lower-temperature region, a remarkable difference was observed between them. It indicates that the matrix definitely affects the dephasing process of a confined exciton in quantum dots at low temperatures. The observed temperature dependence was explained by the contribution of the confined phonon in quantum dots and the two-level system in the matrix.

Observation of homogeneous broadening of confined excitons in CuCl quantum dots

Homogeneous broadening of CuCl quantum dots was studied by using accumulated photon echo in the temperature range from 0.7 to 30 K. Measurements were performed on two kinds of CuCl quantum dots embedded in different matrices: an alminoborosilicate glass and an NaCl crystal. Their temperature dependence was similar at temperatures above 5 K for both the samples, but was notably different at lower temperatures. It was reproduced by the sum of the contribution of the confined acoustic phonon and that of the two-level systems.

Observation of homogeneous optical spectrum in CdSe quantum dots using femtosecond accumulated photon echo

We performed heterodyne-detected accumulated photon echo experiments in CdSe quantum dots. The excitonic dephasing time T 2 was directly observed under very low excitation density of 10 −3 photons per dot. The echo signal consists of two exponential decays: the fast decay component is due to the confined acoustic phonon sideband, while the slow one to the zero–phonon line. The sharp zero–phonon line width increased linearly with the temperature rise, and its linear temperature coefficient was proportional to 1/ R 2. This feature agrees well with the theory based on the interaction between confined excitons and acoustic phonons through deformation potential. The 1/ R-dependent homogeneous broadening at the low temperature suggests the surface scattering.

Heterodyne-detected accumulated photon echo in CdSe quantum dots

The homogeneous optical spectra of CdSe quantum dots were investigated under very low excitation density of 10 −3 photons per dot by using the heterodyne-detected accumulated photon echo. The photon echo decay is composed of two exponential decays in femto- and picosecond time domains. The fast decay component comes from the confined acoustic phonon sideband, while the slow one comes from the zero-phonon line. The linewidth of the zero-phonon line at 0 K is inversely proportional to the radius of the dots and ranges from 0.1 to 0.2 meV, suggesting the dominant contribution of the surface scattering. It increases linearly with the temperature rise. The temperature broadening linear coefficient is inversely proportional to the square of the radius of the dots consistence with the theory based on the deformation potential coupling to the confined acoustic phonon modes.

Temperature dependence of the optical homogeneous width of mesoporphyrin and its aggregate in polyvinylalcohol at 1.8–50 K

The temperature dependence of the optical homogeneous width was investigated for mesoporphyrin and its aggregate doped in polyvinylalcohol from 1.8 to 50 K by means of persistent spectral hole burning and accumulated photon echo. Because the exponent of the temperature dependence changes around 10 K, there exist two dephasing mechanisms that are characteristic for amorphous polymers. At lower temperatures, phonon-assisted tunneling of two-level systems (TLS) is dominant. On the other hand, the Raman process of low-frequency phonons is dominant at higher temperatures.

Demonstration of partial erasing of picosecond temporal optical data by use of accumulated photon echoes

We demonstrated partial erasing of temporal optical data on a picosecond time scale by use of accumulated photon echoes. In a photon-echo memory the temporal data at time tau are stored as a frequency grating of period 1/tau in the absorption spectrum of a material. Partial erasing of the temporal data is achieved by irradiation of the material with a pulse pair at time separation tau , but the phase of one of the pulses is shifted 180 degrees . This process does not produce a frequency grating, and no echo is emitted. The experiment was performed with a dye-doped polymer film. The 180 degrees phase shift was obtained by use of a half-wave plate.

Strong coherent interaction of Nd 3+–Nd 3+ pair ions in CaF 2 crystal

Excited Kramers fine level splittings of Nd 3+ pair (M) and quartet (N) clusters in CaF 2 crystal have been found and investigated by using absorption spectroscopy and accumulated photon echo (APE) techniques. Absorption spectra on the 4I 9/2→ 4G 5/2 transition between Kramers states split into four lines with overall splitting ∼5 cm −1 ( T=9 K, NdF 3 concentration 0.1, 0.3 and 1 wt%). At the picosecond laser excitation of the M- and N-centers on the same transition the APE kinetics was observed to be strongly modulated with multiple coherent beatings on pico- and nano-second time scale. Fast Fourier Transform (FFT) of the APE kinetics decay shows that nearest-neighbour absorption lines splittings 0.9, 1.5 and 2.1 cm −1 (M-center) are clearly defined in FFT spectrum. Theoretical study revealed that in general case the electrostatic interionic coupling lifts completely the eightfold degeneracy of the excited level of a pair of similar ions. The selection rules for the forced electric-dipole, magnetic dipole and quadrupole intermultiplet transitions are stated. It is suggested that in the case of Nd 3+–Nd 3+ pair in CaF 2 (M-center), the strong quadrupole–quadrupole coupling is responsible for the fine splitting of the excited 4I 9/2× 4G 5/2 levels and leads to delocalization of the optical electrons within ion pair.

Persistent Spectral-Hole-Burning in Semiconductor Quantum Dots and its Application to Spectroscopy

Persistent spectral-hole-burning (PSHB) phenomena have been observed in many kinds of semiconductor quantum dots (QDs). Luminescence hole burning and charged excitons have been observed in CuCl QDs in NaCl crystals. The observed PSHB phenomena are explained by the ionization of QDs. The energy of photoionized QDs is changed from the original energy and their new energies depend on the spatial arrangement of trapped carriers. Quantum confinement of carriers and the resulting strong Coulomb interaction between confined carriers and trapped carriers cause the energy change. PSHB has been widely applied to site-selective spectroscopy of QDs. Size-dependent excited exciton quantum states in CuCl quantum cubes, size-dependent excited electron-hole quantum states in CdTe QDs and renormalization of longitudinal optical phonons confined in CuCl QDs have been revealed by studying sideband holes. This also allowed the measurement of accumulated photon echo, which clarified the very sharp homogeneous spectral linewidth of QDs under weak excitation conditions.

Accumulated photon echo in semiconductor microcrystalline quantum dots

The nonlinear coherent emission of excitons in CuBr quantum dots was investigated using a phase-stabilized photon-echo technique. The echo signal was observed to be quite strong, with the emission efficiency being three orders of magnitude larger than that of II-VI semiconductor quantum wells. Time resolving of the echo signal confirmed that the strong nonlinear emission originates from the accumulation effect of the population grating due to the presence of the bottleneck state. Formation and decay kinetics of the population grating was analyzed by taking into account the light-induced deexcitation effect.