Femtosecond magnito-optics based on photon echoes

A textured three-layer ZnO/Si(P)/Si(B) film in an uniform longitudinal magnetic field with a stregth of 0.4 T exhibits the effect of the polarization plane’s rotation from a stimulated photon echo signal formed at room temperature on the exciton states. At time interval τ₁₂ set to zero and time interval τ₂₃ = 720 and 900 fs, the angles of rotation are 27° and 19°, respectively.     

Femtosecond coherent spectroscopy of four-wave mixing and photon echoes in a GaAs/AlGaAs heterostructure at room temperature

The results from experiments employing coherent femtosecond spectroscopy in a layer of two-dimensional electron gas at the boundary of the GaAs/AlGaAs heterojunction at room temperature are presented. The decay curves of primary femtosecond photon echo are obtained. The decoherence time in two-dimensional electron gas depends strongly on the power of the exciting pulse and varies from 36 to 54 fs. The dephasing time is studied for the first time as a function of the power of exciting pulses at room temperature. It is established that this dependence obeys the law T ₂ ∼ N ^−0.22, which differs from the typical law T ₂ ∼ N ⁻¹ for unscreened electron-electron interaction in semiconductor crystals. Analysis shows that electron-phonon interaction plays an important part along with electron-electron interaction. The induced spin gratings in the GaAs/AlGaAs heterostructure are studied with an eye to their possible application in spintronics.     

Regeneration of photon echoes with amplified photon echoes

Photon-echo-based devices have been proposed for many applications in data storage, image processing, and optical communications. Many of these applications would benefit if the output from the photon-echo process could be used as input in a second photon-echo process. We demonstrate the generation of such secondary echoes, using the amplified output from an initial photon-echo process. The amplification is performed with a Pr:ZBLAN fiber amplifier, which gives a gain of more than 300 at 606 nm when pumped with 320 mW of power at 476 nm.     

Femtosecond primary and stimulated photon echoes in a dye-doped polymer film at room temperature

The signals of both primary and stimulated femtosecond photon echoes are observed and investigated in a dye-doped polymer film at room temperature using a modernized femtosecond echo-spectrometer. It should be noted that stimulated photon echo in the solid-state sample is observed for the first time at such a high temperature. Experimentally obtained decay curves of these signals have a nonexponential character. The spectra of these echo signals are also measured. It is found that the spectrum of the primary photon echo is short-wave shifted with respect to the spectrum of excitation. This can be used for the coherent laser cooling of a sample. The spectrum of the stimulated photon echo is also shifted to the short-wave range relative to the spectrum of excitation, but its shift is much less than that of the primary photon echo. The experiment shows that the femtosecond echo signals at room temperature are excited via the phonon-side band of the absorption line.     

Light-induced gaps in semiconductor band-to-band transitions

We observe a triplet around the third harmonic of the semiconductor band gap when exciting 50-100 nm thin GaAs films with 5 fs pulses at 3 x 10(12) W/cm(2). The comparison with solutions of the semiconductor Bloch equations allows us to interpret the observed peak structure as being due to a two-band Mollow triplet. This triplet in the optical spectrum is a result of light-induced gaps in the band structure, which arise from coherent band mixing. The theory is formulated for full tight-binding bands and uses no rotating-wave approximation.     

Superfluorescence-stimulated photon echoes

Two closely spaced 778 nm, 4-ps pulses, two-photon resonant with the 5S-5D transition in Rb vapor generate a ground state grating, which later is excited by a similar third pulse, producing conical yoked superfluorescence echo on the 5S-6P, 420-nm transition. The intensity of this emission as a function of the relative delay between the leading excitation pulses is governed by the dynamics of Doppler dephasing and rephasing. This is the first observation of an echo effect induced by a spontaneous relaxation process.     

Nutational stimulated photon echoes

Stimulated photon echoes (SPEs) with time duration comparable to the coherent lifetime and Rabi period have been investigated theoretically and experimentally with an angled beam configuration. The Rabi oscillation effects on both the transmitted field (optical nutation) and the SPE fields are explained by analytic solutions of Maxwell-Bloch equations. The theory also predicts that an echo can exist in the noncausal direction, and this was confirmed by experiments with Tm:YAG crystal.     

Reradiation effects,lifetimes and probabilities of band-to-band transitions in direct A3B5 compounds of GaAs type

A determination has been made of the efficiency and decay time of edge emission for some direct band-gap A₃B₅ semiconductor compounds (the active region of matched heterostructures) with the reradiation effect being taken into account. It has been established that the lifetime of minority carriers is due to band-to-band radiative transitions, the rate of which correspond to the simple quantum-mechanical theory.     

Total dephasing-rephasing balancing in Stark-pulse-modulated photon echoes

Using Stark-pulse-modulated photon echoes, we observe a novel type of rephasing phenomenon in a Eu(3+) - and Pr(3+) -codoped Y(2)SiO(5) crystal. By adjusting the Stark pulse during the rephasing and dephasing periods one can observe a full recovery of the photon echo, corresponding to perfect dephasing-rephasing balancing of the perturbations. We propose to use this effect as a spectroscopic technique to distinguish between reversible and irreversible Stark interactions.     

Theory of photon echoes in dressed atoms

A theory is presented which describes the formation of photon echoes in an atomic vapor when a cw laser field (the “dressing” field) drives an atomic transition while a sequence of pulses is applied to a coupled transition. It is found that, with a two-pulse excitation scheme, as many as nine echoes may be produced. The relationship of these “dressed-atom” echoes to conventional photon echoes is discussed.     

Photon echoes upon Raman transitions

An analytical review of the development of the Raman echo technique is presented. We show that the use here of femtosecond extremely short pulses broadens the possibilities of Raman media.     

Surface photon echoes in the infrared range

We discuss the possibility of observing photon echoes in the infrared range from a surface monolayer. Three different detection schemes are considered: direct infrared detection, external up-conversion, and in-situ up-conversion. The external up-conversion scheme appears most promising, while the in-situ up-conversion scheme has the advantage of being highly surface specific. Dephasing relaxations of surface vibrational excitations should be measurable.     

Time-domain Fresnel-to-Fraunhofer diffraction with photon echoes

A photon echo experiment in Tm(3+):YAG is reported that shows, for the first time to the authors' knowledge, the time-domain equivalent of the transition from near- to far-field diffraction, including Talbot self-imaging effects. The experiment demonstrates the huge dispersion capability of photon echoes and opens the way to further exploration of space-time duality.     

Demonstration of highly efficient photon echoes

Highly efficient two-pulse and stimulated photon echoes are experimentally demonstrated in an absorbing medium. Recall efficiencies of 235% and 150% with excellent signal contrast are measured for two-pulse and stimulated photon echoes, respectively, in a Tm:YAG crystal with an absorption length of 3.8. The reported efficiencies do not include any correction for decay or beam profile. We believe that this is the first demonstration of an uncorrected echo efficiency greater than 100% with good signal fidelity in an optically thick medium.     

Time-to-frequency Fourier transformation with photon echoes

We propose to use photon echoes in rare-earth-doped crystals to implement the Fourier-transform chirp algorithm. The process is considered for application to spectral analysis of fast radio-frequency signals. Compared with surface acoustic wave devices, the proposed scheme gives access to the larger bandwidths of rare-earth-doped crystals and greater flexibility. An experimental demonstration of the proposed process is reported.     

Femtosecond luminescence measurements in GaAs

We report luminescence measurements in GaAs with femtosecond time resolution. This represents more than an order-of-magnitude improvement over previous luminescence measurements and allows us to study initial relaxation processes of photoexcited carriers. We show that the relaxation of photoexcited carriers to the band extrema is delayed by 750 fsec when the excitation density is reduced from 3 × 10¹⁸ cm^-3 to 1 × 10¹⁷ cm^-3. We have measured luminescence rise and decay curves at various photon energies ranging from 1.45 eV to 1.70 eV. These results are discussed in terms of carrier-carrier and carrier-phonon interactions.