The possibility of using a minimal-volume photoacoustic cell to perform spectroscopy of samples is discussed. It is shown that this alternative signal-to-noise-enhanced photoacoustic configuration allows one to obtain both absorption and transmission spectra with minimal experimental arrangement and cell machining requirements. The theoretical model is presented, the use of which is exemplified by a complete optical and thermal characterization of leaves.

We present investigations of fs time resolved coherent wave mixing under high magnetic field. Our experiments reveal a new regime at high magnetic field and low excitation density dominated by the Coulomb interaction. This regime is inconsistent with the semiconductor Bloch equations. A model which includes exciton-exciton correlation successfully describes many features of this regime.[S0031-9007(97)

We have calculated the electronic structure of spherical PbS, PbSe, and PbTe quantum dots using a fourband envelope-function formalism that accounts for band anisotropy. By comparing our results with an analytical calculation that assumes a spherical approximation of the k ជ •p ជ Hamiltonian, we show that the effects of band anisotropy are more pronounced for the excited states and increase with the confinement. We also show how the same technique can be applied to ellipsoidal quantum dots.

Mean-field, Hartree-Fock theory has been successful in explaining many nonlinear optical experiments in semiconductors. But recently experiments have shown important cases where the mean-field theory ͑the semiconductor Bloch equations͒ fails. One such case is bulk GaAs in a strong magnetic field. Here the excitonexciton interaction can be tuned by varying the magnetic field, providing an excellent method for studying the transition from a regime where mean-field theory is valid to a regime where exciton-exciton correlations must be taken into account. We perform ultrafast time-resolved four-wave mixing on bulk GaAs in a magnetic field, and compare our experimental results with theoretical calculations which go beyond Hartree-Fock theory. We find excellent qualitative agreement. Furthermore, because of the strong correlations that are present, GaAs in a magnetic field presents an excellent opportunity to study the exciton-exciton correlations themselves. We investigate the coherence of the exciton-exciton correlations as the temperature and free-carrier density are varied, and find a surprising sensitivity of the exciton-exciton correlation coherence to these parameters.

We study the transition from a dense continuum to a sparse quasicontinuum in the Fano problem. Transmission measurements on epitaxial layers of GaAs in a high magnetic field and calculations of the optical absorption show how the Fano interference disappears as quantum confinement discretizes the continuum states. The transition between quasi-one-dimensional and quasi-zero-dimensional systems occurs at length scales which are unusually large for optical experiments. [S0031-9007(97)02443-5] PACS numbers: 78.66.Fd, 32.80.Dz, 73.20.Dx Quantum size effects have been thoroughly investigated since advances in material synthesis made possible the growth of semiconductor heterostructures with atomic monolayer accuracy. They become apparent in a physical phenomenon when at least one dimension of the sample becomes comparable to or smaller than the length scale that governs the quantum mechanics of that phenomenon. In the optical domain the exciton Bohr radius a o is usually the relevant length scale, and quantum confinement dominates the optical properties of semiconductor structures of size L # a o [1,2]. In the case of transport the carrier de Broglie wavelength l B determines the length scale at which quantum transport effects are observed [3]. In this Letter we present a new example of quantum size effects, apparent in the line shape of an optical resonance involving the quantum mechanical coupling between a localized, discrete state and a quasicontinuum. As shown below, the size effect is a direct consequence of the energy quantization due to the finite sample thickness. Remarkably, it appears for length scales L . 15a o that are unusually large for the optical domain.Quantum mechanical interference between a discrete state and a quasicontinuum is a fundamental problem in physics. It is one of a few exactly solvable models in many-body theory [4], and as such it gives insight into other many-particle phenomena. This problem was simultaneously formulated by Anderson and Fano. Anderson applied it to the mixing of localized impurity orbitals and extended conduction band states in solid state physics [5]. Fano used it to describe the interference of electronic transitions in atomic spectra [6]. The coupling of the discrete state to the quasicontinuum in the Fano-Anderson model is, furthermore, a prototype of irreversible decay [7,8]. It can represent various fundamental relaxation mechanisms, such as spontaneous emission, nuclear decay, the autoionization of excited atoms originally discussed by Fano [6], intramolecular relaxation, and coupling to a phonon bath [9]. The quantum interference manifests itself as a resonance in the optical absorption spectrum with a characteristic asymmetric line shape. Very close to its peak, a pronounced minimum occurs at an energy where the transition amplitudes of the discrete state and the continuum interfere destructively. It has been observed in a variety of atomic, molecular, and semiconductor systems [10], and recently in the optical absorption of bulk semiconductors in high mag...

We present a study of carrier dynamics in GaAs during and just after creation by ultrashort laser pulses. We observe a quasi-instantaneous spread of the carrier population in momentum-energy space. Attempts to fit the scattering rates in the relaxation time approximation result in parameters outside the range of validity of the theory. We interpret this as a failure of the Boltzmann kinetic approach in the quantum kinetic regime. [S0031-9007(96)01340-3]

Autonomous Vehicles (AV) are expected to bring considerable benefits to society, such as traffic optimization and accidents reduction. They rely heavily on advances in many Artificial Intelligence (AI) approaches and techniques. However, while some researchers in this field believe AI is the core element to enhance safety, others believe AI imposes new challenges to assure the safety of these new AI-based systems and applications. In this non-convergent context, this paper presents a systematic literature review to paint a clear picture of the state of the art of the literature in AI on AV safety. Based on an initial sample of 4870 retrieved papers, 59 studies were selected as the result of the selection criteria detailed in the paper. The shortlisted studies were then mapped into six categories to answer the proposed research questions. An AV system model was proposed and applied to orient the discussions about the SLR findings. As a main result, we have reinforced our preliminary observation about the necessity of considering a serious safety agenda for the future studies on AIbased AV systems.

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