C. Flytzanis

Biphonon dynamics in crystals: Nitrous oxide

Abstract Coherent picosecond excitation and probe techniques are employed to measure the dephasing times of the very weak 2v2 two-phonon resonance in solid N2O as a function of temperature. T2 times are also obtained for the v1 one-phonon transition which is in feeble Fermi interaction with 2v2.

Impact of Dimensionality in the Optical Nonlinearities

New developments in nonlinear optics and implementation [1] of several nonlinear effects in devices is conditionned by a substantial improvements of several characteristics of the nonlinear optical materials. These are of very diverse nature but the ones most relevant for the nonlinear process are: a) the susceptibility χ(n) (magnitude, phase or sign) b) its recovery time τ c) the real index of refraction n d) the absorption coefficient α e) the relevant frequency domain Δω.

Biphonon dynamics in ordered ammonium chloride

Abstract The relaxation dynamics of the longitudinal lower-energy component of the ((ν 2 + ν 4 ), ν 3 ) polar two-phonon Fermi quadruplet in the ordered ammonium chloride crystal are investigated by coherent picosecond techniques. The results indicate that both frequency-modulation and occupation-number change play an important role in the coherent decay of this state.

High Sensitivity Time-Resolved Study of the Coherence and Parametric Instabilities of Two-Phonon States

Coherent picosecond excitation and probe techniques have recently been extended [1–4] to the selective investigation of the dynamics of vibrational overtones and multiphonon states in condensed media. These states,which involve the creation and annihilation of several phonons,are essential for the understanding and the description of large amplitude vibrational motion in condensed matter and the anharmonic forces that come into play there. Through the study of their time evolution, much insight can also be gained about phonon breakdown and large wave vector phonon dynamics.

Fano interference effects in the vibronic coupling of one-dimensional conjugated semiconductors

Abstract In a one-dimensional conjugated semiconductor a discrete vibronic state of energy above the main absorption peak can interact with the continuum of electronic states in the conduction band and give rise to Fano-type interference effects in the absorption spectrum. The effect is quantitatively evaluated and illustrated in the case of polydiacetylene crystals.

Quantum Size Effects and Photocarrier Dynamics in the Optical Nonlinearities of Semiconductor Microcrystallites

In semiconductor crystals, the electrons are delocalized over several unit cells. As a consequence many details of the interactions they are subject to are averaged out and their behavior is correctly described1 within the effective mass approximation. The averaging takes place over spherical regions of radii ae = ħ2e/mee2 and ah = ħ2e/mhe2 for electrons and holes respectively where me and mh are the corresponding effective masses and e is the permittivity of the medium. If the extension of the crystal is reduced in one or more directions close to these lengths the averaging procedure breaks down and the electron is faced with the bare interactions within the confined space and its walls. On these grounds one expects size dependent effects on their properties in general and on the optical ones in particular. Such effects, also termed quantum confinement effects, constitue an area of intensive theoretical and experimental activity. The goal is certainly the design2,3 of promising nonlinear optical materials for technological applications but these effects are of fundamental interest as well since they throw new light on some physical aspects which are suppressed in the infinitely large systems.

Photo-induced polarization rotation in semimagnetic semiconductor quantum wells

Giant photo-induced Faraday rotations were observed in CdTe-CdMnTe multiple quantum wells when the laser frequency is close to the excitonic resonance, which is enhanced through the quantum confinement. Moreover, we recently demonstrated that large photo-induced polarization rotations (-7 degrees) could be obtained even in the absence of an external magnetic field when using circularly polarized pump pulses. In this paper we present a spectrally and temporally resolved analysis of this phenomenon and show that it results from the combined effect of photo-induced magnetization, many body interactions, and spectral hole burning. The sample contained ten 47 /spl Aring/ thick CdTe wells with 950 /spl Aring/ thick CdMnTe barriers on a CdZrTe substrate.

Time-Resolved Nonlinear Faraday Rotation in Semimagnetic Quantum Wells

We investigate the dynamics of the Faraday rotation angle by means of time-resolved pump/probe experiments in CdTe/Cd1—xMnxTe multiple quantum wells under high excitation conditions. During the first step of the optical excitation, stimulated emission and amplification of the Faraday rotation is observed. Spectrally resolved measurements reveal that large photoinduced rotation changes can be achieved when the frequency is tuned close to the excitonic resonance and saturation sets in.

Phonon-polariton transmission through a vacuum layer

the transmission of a short phonon-polariton pulse through a vacuum layer separating two identical noncentrosymmetric crystals (NH4Cl) is investigated in real time and space by use of the nonlocal time-resolved CARS technique. The results yield selective information on the impact of an interface on the polariton wave-packet coherence.

Evolution in Real Time and Space of Short Polariton Pulses in Crystals

We demonstrate that short polariton pulses in real time and space can be directly studied by a nonlocal time resolved nonlinear technique. One can directly determine the propagation characteristics and decay of coherence of both bare and dressed polariton pulses in crystals. The technique in particular allows one to differentiate the impact of phonon anharmonicity from that of the dielectric disorder on the polariton coherence.