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We demonstrate the existence of the excited state of an exciton-polariton in a semiconductor microcavity. The strong coupling of the quantum well heavy-hole exciton in an excited 2s state to the cavity photon is observed in non-zero magnetic field due to surprisingly fast increase of Rabi energy of the 2s exciton-polariton in magnetic field. This effect is explained by a strong modification of the wave-function of the relative electron-hole motion for the 2s exciton state., 5 pages, 5 figures

We demonstrate the existence of a novel quasiparticle: an exciton in a semiconductor doubly dressed with two photons of different wavelengths: near infrared cavity photon and terahertz (THz) photon, with the THz coupling strength approaching the ultra-strong coupling regime. This quasiparticle is composed of three different bosons, being a mixture of a matter-light quasiparticle. Our observations are confirmed by a detailed theoretical analysis, treating quantum mechanically all three bosonic fields. The doubly dressed quasiparticles retain the bosonic nature of their constituents, but their internal quantum structure strongly depends on the intensity of the applied terahertz field., Comment: 12 pages, 9 figures

We demonstrate the occurrence of spatial multistability using laterally confined microcavity exciton-polaritons. By coherently exciting with a blue detuned laser a series of confined polariton modes, we investigate the effects of multistability on the transmitted laser beam as a function of the excitation power. At each threshold of the hysteresis loop, a switching of the mode profile of the laser beam is associated with a significant energy jump of each of the confined polariton modes in the mesa. A simulation of this behavior is achieved with a multimode generalization of the Gross-Pitaevskii equations in the exciton photon basis. The mechanism behind the spatial multistability is identified as a repulsive cross interaction between polaritons in different modes.

We present the optical tomography of the probability density of microcavity polaritons, confined in three dimensions by cylindrical traps of various sizes. Collecting the photoluminescence emitted by the quasimodes under continuous nonresonant laser excitation, we reconstruct a three dimensional mapping of the photoluminescence, from which we can extract the spatial distribution of the confined states at any energy. We discuss the impact of the confinement shape and size on the probability density patterns.

We performed studies on microcavity polaritons trapped along the three dimensions of space, under resonant excitation on a confined lower polariton state. We observed various nonlinear behaviors as a function of the pump power, without any apparent loss of the strong-coupling. That may be understood as effects of Coulomb interaction. Indications of bistable behaviors in the system are observed and discussed.

We develop an analytical approximate method for determining the Bohr radii of Wannier-Mott excitons in thin quantum wells under the influence of magnetic field perpendicular to the quantum well plane. Our hybrid variational-perturbative method allows us to obtain simple closed formulas for exciton binding energies and optical transition rates. We confirm the reliability of our method through exciton-polariton experiments realized in a GaAs/AlAs microcavity with an 8 nm In-x Ga1-xAs quantum well and magnetic field strengths as high as 14 T.

We detail the influence of a magnetic field on exciton-polaritons inside a semiconductor microcavity. Magnetic field can be used as a tuning parameter for exciton and photon resonances. We discuss the change of the exciton energy, the oscillator strength, and redistribution of the polariton density along the dispersion curves due to the magnetically induced detuning. We have observed that field-induced shrinkage of the exciton wave function has a direct influence not only on the exciton oscillator strength, which is observed to increase with the magnetic field, but also on the polariton linewidth. We discuss the effect of the Zeeman splitting on polaritons the magnitude of which changes with the exciton Hopfield coefficient and can be modeled by independent coupling of the two spin components of excitons with cavity photons.

We detail an innovative laser device based on a new relaxation mechanism for confined exciton-polaritons which preserves nonlinearity. We demonstrate the selective activation of polariton lasers at different wavelengths allowing to perform all-optical logic operations with fully coherent output [1]. (C) 2014 Optical Society of America

International audience; We report on noise-induced spin ordering in a collective quasiparticle system: spinor stochastic resonance. Synergetic interplay of a polarization-modulated signal and a polarization noise allows us to switch coherently between the two metastable states of a microcavity-polariton spin bistable system. Spinor stochastic resonance is demonstrated in a zero-dimensional GaAs based microcavity. The resonance behaviors of both the spin amplification and the signal-to-noise ratio are experimentally evidenced as a function of the noise strength for different amplitude modulations. They are theoretically reproduced using a spinor Gross-Pitaevskii equation driven by a randomly polarized laser field.

We report on the origin of the excitonic luminescence in quantum wells. This study is carried out by time-resolved photoluminescence experiments performed on a very high-quality InGaAs quantum well sample in which the photoluminescence contributions at the energy of the exciton and at the band edge can be clearly separated and traced over a broad range of times and densities. This allows us to compare the two conflicting theoretical approaches to the question of the origin of the excitonic luminescence in quantum wells: the model of the exciton population and the model of the Coulomb correlated plasma. We measure the exciton formation time and we show the fast exciton formation and its dependence with carrier density. We are also able to give the boundaries of the Mott transition in our system, and to show the absence of observable renormalization of the gap below the onset of this transition. We detail the characteristics of the trion formation and evidence the possible formation of both positive and negative trions in the absence of any resident free carrier populations.

We present the results of a detailed time resolved luminescence study carried on a very high quality InGaAs quantum well sample. We clearly separate the contributions to the total intensity at the energy of the exciton and at the band by performing experiments with the proper spectral resolution and sensitivity, allowing to keep the observation of these two separate contributions over a broad range of times and densities. This enables us to access to the exciton formation rate over a broad range of pair densities. We also evidence the dominant contribution of excitons to the luminescence signal even when their population is small, and the absence of thermal equilibrium between excitons and free carriers at low enough densities. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We present results of cw and time resolved luminescence of a very high quality InGaAs quantum well sample where the contributions at the energy of the exciton and at the band edge can be clearly separated. We perform time resolved luminescence experiments with a spectral resolution and a sensitivity of the set-up allowing to keep the observation of separate structures. This allows to evidence an exciton formation time of several hundreds of ps. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Ecole Polytechnique Fdrale de Lausanne, EPFL, CH-1015 Lausanne, SwitzerlandReceived 15 September 2003, accepted 18 September 2003Published online 2 February 2004PACS 73.21.Fg, 78.47.+p, 78.55.Cr, 78.67.DeWe present an experimental study of the properties of a dense electron–hole plasma in GaAs/AlGaAsquantum wells. A high spatial resolution Photoluminescence setup including spectral and temporal ana-lysis has been developed to test the possibility of collective emission from an electron-hole plasma.

The influence of magnetic field on confined exciton-polariton modes inside a semiconductor microcavity is discussed. The three-dimensional confinement for exciton-polaritons is achieved by the mesa structures confining the photonic part of polaritons. We observe a strong increase of the polariton emission intensity and we argue that this effect is due to the change of the oscillator strength of the excitonic component of polaritons and the change of the excitonic content in polariton state as the magnetic field increases.

We have developed optically pumped passively mode-locked vertical-external-cavity surface-emitting lasers. We achieved as much as 950 mW of mode-locked average power in chirped 15-ps pulses, or 530 mW in 3.9-ps pulses with moderate chirp. Both lasers operate at a repetition rate of 6 GHz and have a diffraction-limited output beam near 950 nm. In continuous-wave operation, we demonstrate an average output power as high as 2.2 W. Device designs with a low thermal impedance and a smooth gain spectrum are the key to such performance. We discuss design and fabrication of the gain structures and, particularly, their thermal properties

Polaritons have often been proposed as promising candidates for the realization of all-optical devices due to the easy manipulation and control of their density and spin. In this paper we present a relaxation mechanism for confined polaritons and its application in a device based on polariton lasing in which the incoming monochromatic beam can be channeled into several polariton lasers at different wavelengths. Polaritons are injected in a 3 mu m diameter trap by an incoming beam slightly detuned with respect to a confined state, and the resulting optical bistability is then imprinted on the lower confined states through an efficient relaxation mechanism which combines phonon interaction and bosonic stimulation. Above threshold, all the confined states behave like lasers and the onset of coherence is demonstrated by spectral narrowing. Moreover, the initial polarization of the laser is conserved during the relaxation process allowing for spin logic operations. In this paper we demonstrate that, due to the nonlinear behavior, it is possible to switch ON and OFF the lasing from the confined states of the trap by tailoring the input beam. All the experimental findings are validated and very well reproduced in the framework of the generalized Gross-Pitaevskii equation.

We investigate the nonlinear optical properties of low-temperature-grown (LT) GaAs. It is shown that the strength of the absorptive nonlinearity is weak in as-grown undoped LT-GaAs with a fast recovery time of the nonlinear absorption. The reason for this behavior is revealed by a quantitative study of the nonlinear optical properties of the most important defect transition from the neutral As antisite to the conduction band. Based on this analysis, we demonstrate two methods for the improvement of the ultrafast nonlinearity of LT-grown semiconductors: post-growth annealing or Be doping of LT-GaAs yields a material with a strong ultrafast nonlinear optical response.

We report what we believe to be the first demonstration of a SESAM (semiconductor saturable absorber mirror)-based femtosecond Cr3+:LiSrAlF6 laser pumped by narrow-stripe AlGaInP laser diodes that have diffraction-limited output beams. A highly asymmetric, four-mirror laser cavity design is described for which 57 fs duration pulses at an average output power of 6.5 mW are obtained for only 72 mW of incident pump power. Pump powers of this order were maintained for over 14 h using just six 1.5 V AA batteries as the electrical power source. We have shown that mode-locking can be sustained for incident pump powers as low as 21.5 mW.

We demonstrate self-starting 6.5-fs pulses from a Kerr-lens-mode-locked Ti:sapphire laser with an average output power of 200 mW at a pulse repetition rate of 86 MHz. We have achieved a mode-locking buildup time of only 60 /spl mu/s, using a broad-band semiconductor saturable absorber mirror to initiate the pulse formation. The dispersion has been compensated with a prism pair in combination with improved double-chirped mirrors. The prism pair allows for the flexible adjustment of both the duration and the center wavelength of the pulse. The double-chirped mirrors show a high reflectivity better than 99.8% over the full bandwidth of 300 nm and a controlled group delay over more than 250 nm. The choice of a proper output coupler turns out to be critical for ultrashort pulse generation directly from the laser.

We generated self-starting sub-10-fs pulses from a Ti:sapphire laser using a combination of a broadband semi- conductor saturable absorber mirror (SESAM), novel double- chirped mirrors, and Kerr-lens modelocking. We present a de- tailed overview of broadband SESAMs used in Ti:sapphire lasers and discuss their design issues. Using such a SESAM to assist the KLM process, we have generated pulses with a duration of only 6: 5f s, the shortest to date directly from the laser. Pulses as short as 13 fs were generated by soliton modelocking alone. Higher-order dispersion compensation was achieved with novel double-chirped mirrors in combina- tion with intracavity prisms.

We study an asymmetric double InGaAs quantum well using optical two-dimensional coherent spectroscopy. The collection of zero-quantum, one-quantum, and two-quantum two-dimensional spectra provides a unique and comprehensive picture of the double well coherent optical response. Coherent and incoherent contributions to the coupling between the two quantum well excitons are clearly separated. An excellent agreement with density matrix calculations reveals that coherent interwell coupling originates from many-body interactions.

We study asymmetric double InGaAs quantum well samples, featuring three different barrier widths, using optical two-dimensional Fourier transform spectroscopy. Depending on the barrier width, we observe different coupling mechanisms between the two wells.

Coherent excitonic interactions in an InGaAs asymmetric double quantum well are studied using two-dimensional coherent spectroscopy. Density matrix calculations reveal that an excitation-induced shift is the dominant many-body interaction responsible for the coupling.

We report the first observation of stochastic resonance in confined exciton-polaritons. We evidence this phenomena by tracking the polaritons behavior through two stochastic resonance quantifiers namely the spectral magnification factor and the signal-to-noise ratio. The evolution of the stochastic resonance in function of the modulation amplitude of the periodic excitation signal is studied. Our experimental observations are well reproduced by numerical simulations performed in the framework of the Gross-Pitaevskii equation under stochastic perturbation., Comment: Accepted for publication in Phys. Rev. Lett

Capacitance‐voltage (C‐V) analysis of high quality MBE grown quantum well samples shows that carrier distributions are averaged over the scale of the Debye length. This averaging process results in strongly temperature dependent C‐V‐deduced doping distributions that can be very different from the actual ones. The doping distribution of the structure is obtained by fitting numerically simulated curves to the measured C‐V curves and doping profiles, respectively. Although the calculations do not take quantum size effects into account they show good agreement with the measured data.

The characterization of sub-micron gratings is usually performed on scanning electron microscopes, although the dimensions of the features often make the observations difficult. We report here on a new method applicable to III - V and II - VI semiconductors: we use transmission electron microscopy on wedge-shaped samples oriented along a [111] zone axis. Grating parameters can be obtained with a precision of 1 nm, along with information on the shape and the regularity of the ridge profile, the surface quality as well as the local chemical composition.

Photoluminescence (PL) and electroluminescence (EL) measurement of GaAs/AlGaAs quantum wires (QWR) located in the active region of a p-i-n junction are reported. The samples are fabricated by molecular-beam epitaxial growth on V-grooved substrates. Good control of the interface, defect density and doping profile have been achieved. Homogeneous current injection into the quantum wires is achieved with efficiencies comparable to current injection into a quantum well control sample. PL with and without an applied voltage across the junction was measured at 86 K and 300 K for different excitation densities. Peaks appearing with an applied voltage correspond to the active-region QWR transitions and are also observed on the EL spectra measured at 120 K and at 300 K. Clear evidence of 1D confinement is observed in both PL and EL spectra. They show a one-dimensional splitting of about 24 meV and a saturation of the ground state at high excitation density. The polarisation of the PL and EL is in good agreement with the expected anisotropy of the 1D matrix elements.

International audience; Polariton fluids have revealed huge potentialities in order to investigate the properties of bosonic fluids at the quantum scale. Among those properties, the opportunity to create dark as well as bright solitons has been demonstrated recently. In the present experiments, we image the formation dynamics of oblique dark solitons. They nucleate in the wake of an engineered attractive potential that perturbs the polariton quantum fluid. Thanks to time and phase measurements, we assess quantitatively the formation process. The formation velocity is observed to increase with increasing distance between the flow injection point and the obstacle which modulates the density distribution of the polariton fluid. We propose an explanation in terms of the increased resistance to the flow and of the conditions for the convective instability of dark solitons. By using an iterative solution of the generalized Gross-Pitaevskii equation, we are able to reproduce qualitatively our experimental results.

Exciton polaritons have been shown to be an optimal system in order to investigate the properties of bosonic quantum fluids. We report here on the observation of dark solitons in the wake of engineered circular obstacles and their decay into streets of quantized vortices. Our experiments provide a time-resolved access to the polariton phase and density, which allows for a quantitative study of instabilities of freely evolving polaritons. The decay of solitons is quantified and identified as an effect of disorder-induced transverse perturbations in the dissipative polariton gas.

In this paper we introduce a new paradigm for nanowire growth that explains the unwanted appearance of parasitic nonvertical nanowires. With a crystal structure polarization analysis of the initial stages of GaAs nanowire growth on Si substrates, we demonstrate that secondary seeds form due to a three-dimensional twinning phenomenon. We derive the geometrical rules that underlie the multiple growth directions observed experimentally. These rules help optimizing nanowire array devices such as solar or water splitting cells or of more complex hierarchical branched nanowire devices.

We experimentally demonstrate a technique for the generation of optical beams carrying orbital angular momentum using a planar semiconductor microcavity. Despite being isotropic systems with no structural gyrotropy, semiconductor microcavities, because of the transverse-electric–transverse-magnetic polarization splitting that they feature, allow for the conversion of the circular polarization of an incoming laser beam into the orbital angular momentum of the transmitted light field. The process implies the formation of topological entities, a pair of optical vortices, in the intracavity field. Published version

The photoluminescence (PL) peak positions of the ground state heavy and light‐hole excitons on high‐quality Molecular Beam Epitaxy grown GaAs/AlxGa1−xAs (x=0.3 and 1) multiquantum‐well structures have been experimentally determined in the temperature range 4.2≤T≤340 K. Using these values and the well‐known low‐temperature energy of the GaAs Γ8V‐Γ6C gap [EgΓ(GaAs,T=0 K)=1.5192 eV], we propose the temperature dependence to be EgΓ(GaAs,T)= 1.5192+5.16×10−5×T−1.99×10−6×T2 +2.60×10−9×T3 (EgΓ in eV). The nearly linear variation of EgΓ(GaAs,T) versus the temperature in the range 170 K≤T≤340 K can be approximated by a coefficient (dEgΓ/dT)=−4.4×10−4 eV/K, in excellent agreement with theoretical predictions.

We resonantly excite exciton-polariton states confined in cylindrical traps. Using a homodyne detection setup, we are able to image the phase and amplitude of the confined polariton states. We evidence the excitation of vortex states, carrying an integer angular orbital momentum m, analogous to the transverse TEM01∗ “donut” mode of cylindrically symmetric optical resonators. Tuning the excitation conditions allows us to select the charge of the vortex. In this way, the injection of singly charged (m=1 and m=−1) and doubly charged (m=2) polariton vortices is shown. This work demonstrates the potential of in-plane confinement coupled with selective excitation for the topological tailoring of polariton wave functions.

We study the wave functions of exciton polaritons trapped in the elliptical traps of a patterned microcavity. A homodyne detection setup with numerical off-axis filtering allows us to retrieve the amplitude and the phase of the wave functions. Doublet states are observed as the result of the ellipticity of the confinement potential and are successfully compared to even and odd solutions of Mathieu equations. We also show how superpositions of odd and even states can be used to produce "donut" and "eight-shape" states which can be interpreted as polariton vortices.

We report on the dynamics of confined zero-dimensional polaritons. We excite resonantly discrete polariton states optically with a tailored picosecond laser pulse and observe their emission time resolved in the two-dimensional k space or real space. We are able to distinguish between three regimes. When the laser excites only one state no dynamics are observed. When a small number of well separated states are excited, the dynamics are described in terms of interference. When a quasicontinuum of states is excited, the dynamics are described in terms of ballistically propagating two-dimensional (2D) polaritons which scatter elastically at the potential barriers. The measured propagation velocities are reproduced with the theory of 2D polaritons, which sustains our interpretation.

Coherent manipulation of spin ensembles is a key issue in the development of spintronics. In particular, multivalued spin switching may lead to new schemes of logic gating and memories. This phenomenon has been studied with atom vapours 30 years ago, but is still awaited in the solid state. Here, we demonstrate spin multistability with microcavity polaritons in a trap. Owing to the spinor nature of these light-matter quasiparticles and to the anisotropy of their interactions, we can optically control the spin state of a single confined level by tuning the excitation power, frequency and polarization. First, we realize high-efficiency power-dependent polarization switching. Then, at constant excitation power, we evidence polarization hysteresis and determine the conditions for realizing multivalued spin switching. Finally, we demonstrate an unexpected regime, where our system behaves as a high-contrast spin trigger. These results open new pathways to the development of advanced spintronics devices and to the realization of multivalued logic circuits.

GaAs/AlxGa1-xAs multiple-quantum-well structures with identical well thicknesses (almost-equal-to 119 angstrom) but with different Al contents x in the barrier (x almost-equal-to 0. 1, 0.2, 0.45, and 1) were grown by molecular-beam epitaxy. We report the characterization of the structures by a combination of different techniques. The x-ray-diffraction technique allows us to estimate the Al content x and to measure the period of the structure with good accuracy. Using the photographs given by high-resolution transmission electron microscopy on cleaved wedges, we investigate directly the key parameters of the structures, such as the regularity, the layer thickness, and the Al content x. The photoluminescence measurements carried out in detail from 4 K to room temperature show the excitonic character of the radiative recombination in these structures up to room temperature. The influence of x on the photoluminescence is investigated systematically. The data confirm the theoretical results calculated using finite barrier heights. The increase of transition energies with increasing x is due to the increase of confinement energies and exciton binding energies. A good agreement of the structure parameter values obtained by the above techniques is given.

We present an experimental technique that allows for the detection of pump-induced transmission and phase changes with high sensitivity and ultrafast temporal resolution over an arbitrarily wide time window. This is achieved combining spectral interferometry with high-frequency-chopping differential transmission measurements. With this setup, exciton and continuum nonlinearities in a semiconductor are studied for broadband excitation. We find that the pump-induced phase changes at the exciton and in the continuum decay on distinctly different time scales, indicating different microscopic origins.

Control of the wave function of confined microcavity polaritons is demonstrated experimentally and theoretically by means of tailored resonant optical excitation. Three dimensional confinement is achieved by etching mesas on top of the microcavity spacer layer. Resonant excitation with a continuous-wave laser locks the phase of the discrete polariton states to the phase of the laser. By tuning the energy and momentum of the laser, we achieve precise control of the momentum pattern of the polariton wave function. This is an efficient and direct way for quantum control of electronic excitations in a solid.

We show a double path mechanism for the formation of charged excitons (trions); they are formed through bi- and trimolecular processes. This directly implies that both negatively and positively charged excitons coexist in a quantum well, even in the absence of excess carriers. The model is substantiated by time-resolved photoluminescence experiments performed on a very high quality InxGa1-xAs quantum well sample, in which the photoluminescence contributions at the energy of the trion and exciton and at the band edge can be clearly separated and traced over a broad range of times and densities. The unresolved discrepancy between the theoretical and experimental radiative decay time of the exciton in a doped semiconductor quantum well is explained by the same model.

We experimentally investigate the relaxation of spatially confined microcavity polaritons. We measure the time- and energy-resolved photoluminescence under resonant excitation and in the low-density regime. In this way, we have access to the time evolution of the energy distribution of the polariton population. We show that, when one confined level is resonantly excited, after an initial transient, the population of the confined levels is thermally distributed. The reported efficiency of the relaxation process strongly depends on the confinement size. These experimental findings are well reproduced by a theoretical model accounting for the coupling between the confined states and a bath of acoustic phonons. Our results thus suggest that the phonon-mediated relaxation mechanisms are enhanced in the presence of spatial confinement.

We have developed a femtosecond-resolved near-field scanning optical microscope, using a diffraction-limited pump and near-field probe configuration, which allows us to measure carrier dynamics with a spatial resolution of ∼150 nm and a time resolution of ∼250 fs. This instrument is used for near-field degenerate pump–probe studies of carrier dynamics in GaAs/AlGaAs single quantum well samples locally patterned by focused-ion-beam (FIB) implantation. We find that lateral carrier diffusion across the nanometer-scale FIB pattern plays a significant role in the decay of the excited carriers.

Diode-pumped Yb:phosphate and Yb:silicate glass lasers have been passively mode locked for the first time to the authors’ knowledge. Reliable self-starting mode locking without critical cavity alignment has been achieved with intracavity semiconductor saturable-absorber mirrors and soliton mode locking. We generated pulses as short as 58??fs with the Yb:phosphate laser and 61??fs with the Yb:silicate laser at average output powers of 65 and 53??mW, respectively. The pulse repetition rate was 112??MHz. Additionally, we demonstrated tunability of femtosecond pulses from 1025 to 1065??nm for the Yb:phosphate and from 1030 to 1082??nm for the Yb:silicate glasses. The highest mode-locked output power was 405??mW, with 183-fs pulses from the phosphate glass. The diode pump power was 1.68??W, corresponding to 24% optical-to-optical efficiency. The highest cw output power was 510??mW at the same incident pump power.

We have demonstrated 175-fs pulses with 1 W and 300-fs pulses with 1.2 W of average output power at a pulse repetition rate of 117 MHz from a Nd:phosphate (Schott LG 760) glass laser pumped by a 1-cm-wide, 20-W diode laser bar. Stable soliton mode locking was achieved by use of an intracavity semiconductor saturable absorber mirror. We obtained more than 2 W of average power without mode locking. Using cylindrical cavity mirrors, we adapted the laser mode inside the Nd:glass to the highly elliptical pump beam in both dimensions (tangential and sagittal axes) while maintaining a nearly ideal circular TEM(00) output beam with M(2) approximately 1.2 . Overpumping the laser mode in the tangential plane and efficient unidirectional heat removal in the sagittal plane using a 0.8-mm thin Nd:glass also contributed to the good output-beam quality.

We demonstrate what is to our knowledge the first mode-locked Yb:KGd(WO(4))(2) laser. Using a semiconductor saturable-absorber mirror for passive mode locking, we obtain pulses of 176-fs duration with an average power of 1.1 W and a peak power of 64 kW at a center wavelength of 1037 nm. We achieve pulses as short as 112 fs at a lower output power. The laser is based on a standard delta cavity and pumped by two high-brightness laser diodes, making the whole system very simple and compact. Tuning the laser by means of a knife-edge results in mode-locked pulses within a wavelength range from 1032 to 1054 nm. In cw operation, we achieve output powers as high as 1.3 W.

We demonstrate a passively mode-locked thin-disk Yb:YAG laser that generates solitonlike pulses with durations that are continuously tunable in a very wide range from 3.3 to 89 ps or from 0.83 to 1.57 ps. The average powers are typically ~12 W . Previously [Opt. Lett. 25, 859 (2000)], only pulse durations in a narrow range near 0.7 ps could be obtained from such lasers because of the effect of spatial hole burning. We achieved this much wider range by constructing a laser cavity with two different angles of incidence on the thin disk, which greatly reduces the effect of spatial hole burning.

We experimentally demonstrate that the differential transmission (DT) response of bulk semiconductors excited well above the band edge can be manipulated by chirping of the broadband excitation and readout pulses. In particular, the maximum transmission change in spectrally integrated DT experiments can be modified on the 20 fs time scale. Spectrally resolved DT studies explain this chirp dependence. Depending on the sign of the chirp, positive or negative DT contributions at low or high photon energies are probed with varying efficiency around zero time delay. These results demonstrate that chirp can become an additional degree of freedom for the optimization of device performance in ultrafast all-optical switching.

4.6 ps pulses at 910 MHz produced by a passively mode-locked VECSEL were amplified by ytterbium doped fiber amplifiers to average powers greater than 200 W and subsequently compressed to 430 fs duration.