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Microcavity exciton polaritons, the fundamental optical excitations of semiconductor microcavities with quantum wells inside, have been proposed as promising candidates for observing stimulated scattering, condensation and other phenomena related to the bosonic nature of excitons. Having a light mass, quantum degeneracy of polaritons can be reached at low densities and high temperatures. But the radiative time of polaritons is very short (in the picosecond range) and usually prevents an efficient thermaliza

Modifying the photonic environment of a semiconductor quantum well by embedding it in a high-reflectivity microcavity gives rise to new fundamental optical excitations, half-quantum well excitons, half-photons. These particles, called polaritons, have a light mass, as cavity photons, meaning that they have a large De Broglie wavelength. On the other hand, polaritons, like excitons, are subject to Coulomb interaction, a feature generating strong optical nonlinearities. Such properties favour quantum degenera

Cavity polaritons, the elementary optical excitations of semiconductor microcavities, may be understood as a superposition of excitons and cavity photons(1). Owing to their composite nature, these bosonic particles have a distinct optical response, at the same time very fast and highly nonlinear. Very efficient light amplification due to polariton-polariton parametric scattering has recently been reported in semiconductor microcavities at liquid-helium temperatures(2-11). Here we demonstrate polariton param

An investigation of the parametric amplification and its coherent control in a semiconductor micro-cavity is presented. The time and angle resolved pump and probe experiments show that several ps after pumping parametric scattering is still phase coherent. The experimental data are in qualitative agreement with the numerical data obtained from a relatively simple theoretical model based on three polarisation components, pump, probe, and idler. This model also predicts that under particular circumstances, th

In a pump-probe experiment, we have been able to control, with phase-locked probe pulses, the ultrafast nonlinear optical emission of a semiconductor microcavity, arising from polariton parametric amplification. This evidences the coherence of the polariton population near k = 0, even for delays much longer than the pulse width. The control of a large population at k = 0 is possible although the probe pulses are much weaker than the large polarization they control. With rising pump power the dynamics of the

We study the subpicosecond gain dynamics in a high-finesse semiconductor microcavity containing quantum wells by means of degenerate pump-probe spectroscopy. Tuning the optical excitation in resonance with both the exciton and the cavity modes, at high pump fields the probe pulses are strongly amplified near the energy of the empty-cavity mode. At zero probe delay, integration of the probe spectrum yields a net gain of several percents. The coherent nature of the gain is demonstrated by its oscillatory beha

In this work we present the coherent control of polariton parametric scattering with weak phase locked probe pulses. It is demonstrated that the signal emission arising from the parametric scattering is completely coherent for moderate excitation power, whereas at high pump density the dynamics appears less coherent due to the depletion of the pump polariton reservoir. It is furthermore demonstrated that the phase of the probe pulses controls the emission from signal, pump, and idler at the same time.

We have studied the femtosecond dynamics of excitonic resonances in quantum well microcavities under strong excitation. Very strong non-linearities are observed, which bear clear resemblance to the non-linearities of an atomic two-level system. The fact that the excitonic system undergoes Rabi flopping and AC Stark splitting is clearly evidenced in a number of cases. Excitation induced dephasing shows an effect much stronger than the light dressing and prevents the observation of the Rabi flopping only when

We investigate the mechanisms leading to the optical non-linearities observed on a strongly excited semiconductor microcavity containing quantum wells. This study of a coupled exciton-cavity system is possible owing to the availability of a sample of exceptionally high quality, permitting to exclude effects of disorder and inhomogeneous broadening. Sub-picosecond pump and probe experiments are performed, in the regime of an incoherent exciton gas of high density. For such a gas the dephasing due to collisio

We present femtosecond gain measurements in microcavity-embedded quantum wells. When the excitonic transition is saturated by an intense pump field, the spectrum measured with a weak probe pulse is strongly modulated by pump-probe wave mixing processes. A giant probe amplification occurs within the bandwidth of the empty-cavity mode. The optical feedback provided by the microcavity is responsible for a net gain of the broadband probe pulse. [S0163-1829(99)50424-4].

The coherent optical response of high quality microcavities containing quantum wells is investigated. The dynamics of the ac Stark effect is investigated by degenerate pump-probe experiments, by exciting the quantum well excitons at various intensities and detunings. The evolution from a simple dynamical excitonic Stark shift to a splitting is dearly observed, even when the excitation is degenerate with the continuum states. The experimental results agree well with the predictions of a theoretical model bas

We report novel oscillator strength transfer phenomena induced by the exciton-exciton correlation. A high quality semiconductor microcavity is resonantly excited by intense circularly polarised sigma(+) pump pulses (100 fs long) and probed at different delays by weak counter-polarised sigma(-) test pulses. We show that the presence of sigma(+) excitons can completely inhibit the creation of sigma(-) excitons. With increasing sigma(+) exciton density the oscillator strength of the a- transition is transferre

We study the coherent optical response of a very high-finesse microcavity with a single quantum well by means of degenerate subpicosecond pump-probe spectroscopy. The dynamics of the ac Stark effect versus Pump intensity is investigated upon tuning the empty-cavity;mode-below and above the exciton transition energy, at the exciton continuum onset. The evolution from a simple dynamical excitonic shift to a dynamical splitting is clearly observed in both eases. The qualitative, agreement with numerical calcul

We investigate a semiconductor microcavity containing a quantum well, a sample of exceptional quality. We observe a four-wave mixing response which resembles that of an inhomogeneously broadened exciton system, while the linear transmission measurements are affected by the homogeneous part of the broadening and have a completely different decay time. We show that the four-wave mixing response cannot be calculated using the excitonic parameters (linewidth and relaxation time) extracted from the linear transm

Ultrafast pump-probe measurements evidence the dynamical Stark splitting in the exciton absorption spectrum of a single semiconductor quantum well. The intensity of the Stark sidebands in the spectrum is comparable to the linear absorption and their separation scales as the pump field amplitude. In the time domain the Rabi oscillations are observed. The semiconductor Bloch equations solved in the Hartree-Fock approximation demonstrate that the coherent exciton-light coupling dominates over the many-body dep

We engineer a semiconductor microcavity through an appropriate choice of geometry and materials in order to maximise the exciton-photon coupling. The polaritonic nonlinearities in such devices survive at high temperatures and high excitation densities. We measure parametric polariton amplification up to 220 K in CdTe microcavities and up to 120 K in GaAs ones. The amplification is also outstanding, reaching as much as 5000 at low temperature. The experimental observations suggest that the operating temperat

Pump-probe measurements in a microcavity containing a quantum well show that a population of circularly polarized (sigma(+)) excitons can completely inhibit the transition to sigma(-) one-exciton states by transferring the oscillator strength to the biexcitonic resonance. With increasing pump intensity the linear exciton-polariton doublet evolves into a triplet polariton structure and finally into a shifted biexciton-polariton doublet. A theoretical model of interacting excitons demonstrates that the crosso

Michele Saba

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Towards a room-temperature polariton amplifier

Polariton amplification in semiconductor microcavities

Polariton parametric amplification in semiconductor microcavities

High-temperature ultrafast polariton parametric amplification in semiconductor microcavities

Quantum kinetics of parametric polariton scattering in microcavities

Coherent control of polariton parametric scattering in semiconductor microcavities

Net coherent optical gain in strongly pumped semiconductor microcavities

Coherence properties of polaritons in semiconductor microcavities

Femtosecond dynamics and non-linearities of exciton-photon coupling in semiconductor microstructures

Intrinsic non-linearities in exciton-cavity-coupled systems

Strong coherent gain from semiconductor microcavities in the regime of excitonic saturation

The microcavity AC Stark triplet: Excitation in the exciton continuum

Crossover from exciton to biexciton cavity polaritons

Direct observation of an ac Stark splitting in semiconductor microcavities excited above the continuum onset

The importance of disorder in very high quality semiconductor microcavities

Direct observation of the excitonic ac Stark splitting in a quantum well

Towards a room temperature polariton amplifier

Crossover from exciton to biexciton polaritons in semiconductor microcavities

Optical coherence and stimulated scattering in semiconductor microcavities

The excitonic AC Stark effect in high energy excited semiconductor microcavities