S. R. Bolton

Period doubling and quasi-periodicity in additive-pulse mode-locked lasers

We have observed period doubling and quasi-periodicity in an additive-pulse mode-locked F-center laser. Experiments show that period doubling is often present even though standard diagnostics such as pulse autocorrelations and spectra give no indication of it. Numerical simulations show that the period doubling is associated with strong pulse reshaping.

CARRIER RELAXATION IN INGAAS HETEROSTRUCTURES

We present time‐resolved measurements of carrier dynamics in bulk and quantum wells InGaAs, using differential absorption spectroscopy. We find that the carrier thermalization time is 200–300 fs regardless of layer width for sample thickness ranging from 100 to 6000 A. The efficiency of screening relative to phase space filling is larger in the bulk than in the quantum wells.

Generation of high-power femtosecond pulses near 1.5 mu m using a color-center laser system

The authors have developed a high-power F-center laser system capable of generating femtosecond pulses with energies exceeding 50 pJ at wavelengths near 1.5 mu m. Short pulses (140 fs) from an additive-pulse mode-locked NaCl laser are amplified in a multipass NaCl amplifier at kilohertz repetition rates. The system can generate peak powers approaching 500 MW, with wavelengths tunable from 1.52 to 1.64 mu m. The amplified pulses are used to generate a continuum in various solid media without optical damage. The continuum generated in BaF/sub 2/ is extremely broad, extending from below 400 nm to 3.5 mu m. Construction and operating details are discussed as well as the systems utility for femtosecond measurements in the infrared and high-power experiments. >

Effects of Electronic Fourth‐Order Correlations on the Pump–Probe Response of Semiconductors

The pump-and-probe response of a ZnSe quantum well is investigated. In this particular sample the binding energy far exceeds both the exciton damping and the inhomogeneous broadening. A comparison between experimental data and model calculations shows that with co-circularly polarized beams the nonlinear mean-field contributions dominate those induced by four-particle correlations. In contrast, only the four-particle correlations contribute to the signal in counter-circular configuration. For this configuration, the exciton–biexciton interaction dominates the response for resonant excitation of the exciton. The occurrence of exciton–biexciton transitions leads to a renormalization of the period of coherent oscillations at negative pulse delay.

Sixth-order Coulomb correlations identified in a semiconductor single quantum well

Summary form only given. The nonlinear optical response in semiconductors has traditionally been treated in a mean field approximation at the 2-particle level. Recent work, in particular comparisons of four-wave mixing (FWM) with microscopic theory, have demonstrated the importance of 4-particle correlations. Such experiments, however, are not optimally sensitive to correlations at the 6-particle level. In order to probe such six-particle correlations, we compare the results of six-wave mixing (SWM) measurements with a detailed microscopic theory based on the dynamics controlled truncation scheme (DCT). Experiments were performed on a single 5 nm ZnSe quantum well.

Polariton–biexciton transitions in a ZnSe-based microcavity

Abstract The optical third-order nonlinearity of a ZnSe-based microcavity is investigated by the pump-and-probe method. In the specially designed non-monolithic sample the biexciton binding energy exceeds all damping constants and the normal-mode splitting between exciton and cavity photon. For counter-circular polarized beams the nonlinear response exhibits strong oscillatory structures in the spectral vicinity of the polariton–biexciton transition. Comparison to model calculations shows that in this case the coherent nonlinearity is completely dominated by biexciton–exciton interactions beyond the Hartree–Fock approximation.

Spatio-temporal nonlinear dynamics in a mode-locked Ti:sapphire laser

We present results of a study of nonlinear dynamics in a cw-pumped, Kerr-lens mode-locked (KLM) laser with gain aperturing. Previous to this work, the only measurements of nonlinear dynamics in ultrafast laser systems have been performed in additive pulse modelocked (APM) systems. These revealed a variety of interesting dynamics, however the APMs reliance on interferometric stability severely limited comparison between theory and experiment. In contrast, KLM mode-locking in Ti:sapphire is extremely robust. This has allowed us to perform the first, to our knowledge, detailed measurements of nonlinear dynamics in any femtosecond laser system. We have observed period two, period three, and higher quasi-periodic dynamics in the laser pulse trains, and studied these dynamics as functions of cavity configuration, nonlinearity, and dispersion.