Ultrafast Dynamics of Carrier Multiplication in Quantum Dots

A quantum-kinetic approach to the ultrafast dynamics of carrier multiplication in semiconductor quantum dots is presented. We investigate the underlying dynamics in the electronic subband occupations and the time-resolved optical emission spectrum, focusing on the interplay between the light-matter and the Coulomb interaction. We find a transition between qualitatively differing behaviors of carrier multiplication, which is controlled by the ratio of the interaction induced time scale and the pulse duration of the exciting light pulse. On short time scales, i.e., before intra-band relaxation, this opens the possibility of detecting carrier multiplication without refering to measurements of (multi-)exciton lifetimes.Comment: 12 pages, 7 figures, submitte

Measurements of the neutron electric to magnetic form factor ratio G_(En)/G_(Mn) via the ^2H(e, e'n)^1H reaction to Q^2 = 1.45 (GeV/c)^2

We report values for the neutron electric tomagnetic form factor ratio,G_(En)/G_(Mn), deduced frommeasurements of the neutron’s recoil polarization in the quasielastic ^2H(e, e'n)^1H reaction, at three Q^2 values of 0.45, 1.13, and 1.45 (GeV/c)^2. The data at Q^2 = 1.13 and 1.45 (GeV/c)^2 are the first direct experimental measurements of G_(En) employing polarization degrees of freedom in the Q^2 > 1 (GeV/c)^2 region and stand as the most precise determinations of G_(En) for all values of Q^2

Polarization-dependent nonlinear optical microscopy methods for the analysis of crystals and biological tissues

The ability to solve a high-resolution protein structure is largely dependent on the successful generation and identification of protein crystals prior to X-ray diffraction (XRD). For novel protein targets, high-throughput crystallography often involves generation of multiple targets and thousands of crystallization trials per target to generate diffraction-quality crystals. Second harmonic generation (SHG) imaging has been developed as a fast, non-destructive and sensitive method for the selective identification of protein crystals, even in highly scattering environments. Polarization-dependent SHG microscopy methods were developed to assess the presence of multidomain crystals to provide a handle on crystal quality. In addition, polarization-dependent two-photon excited fluorescence (TPEF) microscopy was developed as a complementary method to SHG, providing selectivity based on the presence of protein and crystalline order, thereby reducing the potential for false negatives and positives that can arise with SHG and conventional TPEF imaging. Novel instrumentation, data acquisition methods, and data analysis techniques were developed for quantitative polarization-modulated SHG microscopy at imaging speeds up to video rate, offering significantly greater signal to noise ratios compared to polarization modulation through the manual rotation of wave plates. Quantitative polarization-dependent SHG imaging was extended to the analysis of collagen structures in biological tissues, where local-frame second order susceptibility tensors were solved for every pixel within an image of collagenous tissue and combined with ab initio modeling to assess internal ordering of collagen fibers in different tissue types

Laser diagnostics and minor species detection in combustion using resonant four-wave mixing

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