Ultrafast Spectral Interferometry Research Articles

Shock compression of magnesium alloy by ultrashort loads driven by sub-picosecond laser pulses

The shock compression of magnesium (Mg-4Al-2Zn) alloy polycrystalline films on glass under ultrashort loads driven by sub-picosecond laser pulses was investigated. The continuous diagnostics of motion and reflectivity changes of the free rear surface of the samples was carried out in the picosecond range (≤200 ps) in a single pulse mode using ultrafast spectral interferometry. We present the data on elastoplastic shock wave evolution at a propagation distance of several hundreds of nanometers, elastic precursor decay, shear, and tensile strengths at the extreme strain rate of ∼109 s−1.

Merging transformation optics with electron-driven photon sources

Relativistic electron beams create optical radiation when interacting with tailored nanostructures. This phenomenon has been so far used to design grating-based and holographic electron-driven photon sources. It has been proposed recently that such sources can be used for hybrid electron- and light-based spectroscopy techniques. However, this demands the design of a thin-film source suitable for electron-microscopy applications. Here, we present a mesoscopic structure composed of an array of nanoscale holes in a gold film which is designed using transformation optics and delivers ultrashort chirped electromagnetic wave packets upon 30–200 keV electron irradiation. The femtosecond photon bunches result from coherent scattering of surface plasmon polaritons with hyperbolic dispersion. They decay by radiation in a broad spectral band which is focused into a 1.5 micrometer beam waist. The focusing ability and broadband nature of this photon source will initiate applications in ultrafast spectral interferometry techniques.

Real-time observation of transient electron density in water irradiated with tailored femtosecond laser pulses

Ionization mechanisms in water irradiated with bandwidth-limited and temporally asymmetric femtosecond laser pulses are investigated via ultrafast spectral interferometry. By using a novel common-path interferometer with an enlarged temporal measurement window, we directly observe the dynamics of free-electron plasma generated by shaped pulses. We found that a temporally asymmetric pulse and its time-reversed counterpart address multiphoton and avalanche ionization mechanisms in a different fashion. Positive third-order dispersion shaped pulses produce a much higher free-electron density than negative ones at the same fluence, instantaneous frequency and focusing conditions. From the experimental data obtained after irradiation with bandwidth-limited and shaped pulses the multiphoton and avalanche coefficients were determined using a generic rate equation. We conclude that temporal tailored femtosecond pulses are suitable for manipulation of the initial steps in laser processing of high band gap materials.

Experimental Investigation of Quantum Effects in Time-Resolved Resonant Rayleigh Scattering from Quantum Well Excitons

Resonant Rayleigh scattering from quantum well excitons is investigated using ultrafast spectral interferometry. We isolate the coherent Rayleigh scattering from incoherent luminescence in a single speckle. Averaging the resonant Rayleigh intensity over several speckles allows us to identify features in support of quantum corrections to the classical description of the underlying scattering process.

Femtosecond Spectral Interferometry of Resonant Secondary Emission from Quantum Wells: Resonance Rayleigh Scattering in the Nonergodic Regime

We report the first investigation of resonant secondary emission from quantum well excitons using ultrafast spectral interferometry. Observation of high-contrast spectral fringes demonstrates a significant phase correlation of the spectral components of the Rayleigh scattered light and allows us to determine the temporal dynamics of the coherent emission. The results contradict the present theories for resonant Rayleigh scattering based on ensemble averaging, and show the nonergodic nature of resonance Rayleigh scattering from semiconductor quantum wells.