Effect of locking of photon echo signals in multichannel data recording

The effect of locking of a long-lived photon echo is investigated in the case where nonresonant laser radiation (a standing or traveling wave with an artificially created spatial inhomogeneity) serves as an inhomogeneous external perturbation, which results in random shifts or splitting of the initial monochromatic components of the inhomogeneously broadened line. The use of the mutual spatial orientation of the gradients of electric fields as an associative key of access to recorded information allows one to produce a large number of independent channels of data recording. It is demonstrated that the proposed scheme for recording and associative sampling of information has the advantage that, in each channel, information is recorded simultaneously at all optical centers (the whole inhomogeneously broadened resonance line), which does not decrease the intensity of the response from each channel. Moreover, the echo holographic information coded in the wavefronts of the exciting pulses can also be recorded in each channel, which does not affect the independence of individual channels of data recording.     

Amplification of photon echo signals by use of a fiber amplifier

The efficiency of photon-echo processes typically lies in the 0.1-1% range. For many photon-echo-based applications suggested in optical storage and all-optical communication the photon-echo output pulses would need to be used as input data to a new photon-echo process. In such cases amplification of the photon-echo output signals would be necessary for an acceptable signal-to-noise ratio to be obtained. We show that a Pr-doped ZBLAN fiber is able to produce significant amplification of photon-echo signals generated in Pr-doped Y(2)SiO(5) at 606 nm.     

Peculiarities of femtosecond photon echo signals in dye-doped polymer films at high temperatures

Some results of femtosecond echo experiments on polyvinylbutyral polymer films doped with phtalocyanine molecules at high (up to room) temperatures are reported. Special attention is paid to the stimulated femtosecond photon echo (SFPE), which was observed in a solid-state medium at room temperature for the first time. A decay curve of the SFPE signal has been obtained and theoretically analyzed. The results of the analysis indicate that the random interaction between impurity molecules and quasi-localized low-frequency vibration modes in an amorphous matrix plays the dominant role in the character of optical dephasing at high temperatures.     

Two-frequency correlation of photon echo signals in a medium excited by a few-cycle pulses

Two-frequency correlation between the profiles of signals of the primary and long-lived (stimulated) photon echos in a three-level medium excited by combined sequences of resonance quasimonochromatic (encoding) signals and femtosecond pulses consisting of a few optical oscillations (down to one) is predicted. It is shown that the profiles of echo responses of both frequencies correlate with each other and with the profiles of encoding pulses, copy them, and induce mirror rotations, as well as scaling transformations in time in dependence on the methods of forming exciting sequences.     

Spatial regularities in the effect of locking of photon echo signals and associative optical memory

The efficiency of suppression of the generation of a photon echo response depending on the mutual spatial orientation of gradients of external nonumform electric fields acting on a resonant medium is studied. The possibility of creating an associative memory where the mutual orientation of the gradients of external electric fields is an associative key is discussed.     

Structure of photon echo signals under excitation of a medium by few-cycle optical pulses

The results of original theoretical investigations of the primary and long-lived photon echo, generated by sequences of broadband and quasi-monochromatic pulses, are reported. Both echo responses and the effect of correlation of their profiles with the profiles of excitation pulses have a two-frequency character.     

TE mode photon echo in slab waveguides

A theory of TE mode photon echo in slab waveguides is developed. It is found that the conditions for generation of a photon echo in waveguides can substantially differ from those in bulk material. For the photon echo in waveguides there is an optimum value of the Rabi frequency, and the echo energy does not depend periodically on the Rabi frequency as in the case of bulk material photon echo. Moreover, it is shown that the capability for echo generation is different for different modes. In particular there are several modes in the waveguide which cannot, in principle, generate an echo.     

Non-Faraday rotation of the photon echo polarization vector under variation in the interval between exciting pulses and its application to range finding

Formation modes are investigated and detection accuracy is evaluated for the non-Faraday rotation of the polarization vector of the photon echo in a gas. Possible applications of this effect for construction of optical measuring systems are discussed.     

Using two-dimensional photon echo spectroscopy to probe the fine structure of the ground state biexciton of CdSe nanocrystals

The origin of the fine structure of the ground state single- and biexciton of CdSe nanocrystals is reviewed, along with the theoretical framework used to describe these states. Calculations were performed to determine the transition dipole moments of optically allowed transitions from the single- to biexciton fine structure states. Two-dimensional photon echo spectroscopy measurements for a sample of CdSe nanocrystals are reported. The two-dimensional electronic spectrum at a population time of 0 fs is analyzed using a simulation based on k.p theory predictions of the exciton and biexciton manifolds of states. The analysis suggests that a particular excited state absorption transition from the single- to biexciton fine structure dominates the 2D spectra. These excited state absorptions are clearly resolved in 2D spectra and the method therefore has promise for gaining clearer insights into quantum dot spectroscopy.     

Conventional and collision photon echo in ytterbium vapor

The polarization properties of the photon echo generated by two linearly polarized pulses of resonant radiation at the (6s6p)³ P ₁ ? (6s ²)¹ S ₀ transition of ¹⁷⁴Yb are investigated. A complicated polarization behavior of the photon echo versus an angle between the polarization vectors of the excitation pulses is revealed in a mixture of ytterbium vapor with inert gas. For the angles ranging from 0° to 75°, a conventional echo with its linear polarization coinciding with the second excitation pulse dominates and the echo amplitude decreases with an increasing angle. For the angles ranging from 75° to 89°, the photon echo is elliptically polarized. Finally, for an angle of 90°, the conventional echo disappears and the collision echo becomes linearly polarized along the first excitation pulse.     

Single-pulse nuclear echo signals in magnetically ordered media

An analytical expression for the amplitude of a single-pulse nuclear echo signal generated in magnetically ordered materials is obtained taking into account the inhomogeneous broadening of the spectroscopic transition and the inhomogeneous distribution of the gain with an average value of greater than unity. It is shown that, in this signal, summation of the oscillations of nuclear magnetic moments with equal amplitudes and phases occurs at each instant of time. The cause of the effective suppression of the nuclear magnetic moment oscillations in the initial portion of the free precession signal is revealed analytically. The dependence of the amplitude of the one-pulse echo signal on the strength of an external alternating magnetic field, the pulse duration, and the width of the gain distribution is determined. The results obtained are compared with the experimental data for a Co₂MnSi ferromagnetic polycrystalline sample.     

Long-lived stimulated photon echo in optically thick van vleck paramagnets

Long-lived stimulated photon echo (LSPE) excitation by the sequence ofN pulse pairs in optically thick LaF₃:Pr³⁺ crystals is investigated numerically. Hyperfine structure of the ground and excited states of medium atoms is taken into account. Stable LSPE amplification along the total sample length is realized in the case when the total initial area of the pulse sequence is larger than the threshold value π. Cumulative effect depends on the threshold conditions and the crystal length. At measuring medium spectroscopic parameters the large evaluation errors can be introduced due to neglect of light propagation effects.     

Femtosecond photon echo in dye-doped polymer films at room temperature

The signals of primary and stimulated femtosecond photon echo in polymer films doped with dye (phthalocyanine) molecules have been experimentally investigated at room temperature. A femtosecond echo spectrometer for these echo experiments is described. The decay curves of echo signals with increasing time intervals between excitation femtosecond pulses are obtained and blue shifts of the spectra of femtosecond echo signals with respect to the spectrum of excitation pulses are revealed. The possibilities of using the studied doped polymer films as recording media for high-temperature echo processors and coolants in optical refrigerators are analyzed.