Universal Behavior of Highly Confined Heat Flow in Semiconductor Nanosystems: From Nanomeshes to Metalattices.

Nanostructuring on length scales corresponding to phonon mean free paths provides control over heat flow in semiconductors and makes it possible to engineer their thermal properties. However, the influence of boundaries limits the validity of bulk models, while first-principles calculations are too computationally expensive to model real devices. Here we use extreme ultraviolet beams to study phonon transport dynamics in a 3D nanostructured silicon with deep nanoscale feature size and observe dramatically reduced thermal conductivity relative to bulk.

Luminous, relativistic, directional electron bunches from an intense laser driven grating plasma.

Bright, energetic, and directional electron bunches are generated through efficient energy transfer of relativistic intense (~ 10 W/cm), 30 femtosecond, 800 nm high contrast laser pulses to grating targets (500 lines/mm and 1000 lines/mm), under surface plasmon resonance (SPR) conditions. Bi-directional relativistic electron bunches (at 40° and 150°) are observed exiting from the 500 lines/mm grating target at the SPR conditions. The surface plasmon excited grating target enhances the electron flux and temperature by factor of 6.

Structural and Elastic Properties of Empty-Pore Metalattices Extracted Nondestructive Coherent Extreme UV Scatterometry and Electron Tomography.

Semiconductor metalattices consisting of a linked network of three-dimensional nanostructures with periodicities on a length scale <100 nm can enable tailored functional properties due to their complex nanostructuring. For example, by controlling both the porosity and pore size, thermal transport in these phononic metalattices can be tuned, making them promising candidates for efficient thermoelectrics or thermal rectifiers. Thus, the ability to characterize the porosity, and other physical properties, of metalattices is critical but challenging, due to their nanoscale structure and thickness.

Measurement and control of optical nonlinearities in dispersive dielectric multilayers.

Dispersive dielectric multilayer mirrors, high-dispersion chirped mirrors in particular, are widely used in modern ultrafast optics to manipulate spectral chirps of ultrashort laser pulses. Dispersive mirrors are routinely designed for dispersion compensation in ultrafast lasers and are assumed to be linear optical components. In this work, we report the experimental characterization of an unexpectedly strong nonlinear response in these chirped mirrors.

Magnetic turbulence in a table-top laser-plasma relevant to astrophysical scenarios.

Turbulent magnetic fields abound in nature, pervading astrophysical, solar, terrestrial and laboratory plasmas. Understanding the ubiquity of magnetic turbulence and its role in the universe is an outstanding scientific challenge. Here, we report on the transition of magnetic turbulence from an initially electron-driven regime to one dominated by ion-magnetization in a laboratory plasma produced by an intense, table-top laser.

Intense femtosecond laser driven collimated fast electron transport in a dielectric medium-role of intensity contrast.

Ultra-high intensity (> 10 W/cm), femtosecond (~30 fs) laser induced fast electron transport in a transparent dielectric has been studied for two laser systems having three orders of magnitude different peak to pedestal intensity contrast, using ultrafast time-resolved shadowgraphy. Use of a 400 nm femtosecond pulse as a probe enables the exclusive visualization of the dynamics of highest density electrons (> 7 × 10 cm) observed so far. High picosecond contrast (~10) results in greater coupling of peak laser energy to the plasma electrons, enabling long (~1 mm), collimated (divergence angle ~2°) transport of fast electrons inside the dielectric medium at relativistic speeds (~0.

Contrasting levels of absorption of intense femtosecond laser pulses by solids.

The absorption of ultraintense, femtosecond laser pulses by a solid unleashes relativistic electrons, thereby creating a regime of relativistic optics. This has enabled exciting applications of relativistic particle beams and coherent X-ray radiation, and fundamental leaps in high energy density science and laboratory astrophysics. Obviously, central to these possibilities lies the basic problem of understanding and if possible, manipulating laser absorption.

Terahertz acoustics in hot dense laser plasmas.

We present a hitherto unobserved facet of hydrodynamics, namely the generation of an ultrahigh frequency acoustic disturbance in the terahertz frequency range, whose origins are purely hydrodynamic in nature. The disturbance is caused by differential flow velocities down a density gradient in a plasma created by a 30 fs, 800 nm high-intensity laser (∼5×10(16)  W/cm(2)). The picosecond scale observations enable us to capture these high frequency oscillations (1.

Ultrafast optics of solid density plasma using multicolor probes.

We present time-resolved reflectivity and transmissivity of hot, overdense plasma by employing a multicolor probe beam, consisting of harmonics at wavelengths of 800 nm, 400 nm and 266 nm. The hot-dense plasma, formed by exciting a fused silica target with a 30 fs, 2 × 10(17) W cm(-2) intensity pulse, shows a sub-picosecond transition in reflectivity (transmissivity), and a wavelength-dependent fall (rise) in the reflected (transmitted) signal. A simple model of probe absorption in the plasma via inverse bremsstrahlung is used to determine electron-ion collision frequency at different plasma densities.

High-resolution measurements of the spatial and temporal evolution of megagauss magnetic fields created in intense short-pulse laser-plasma interactions.

A pump-probe polarimetric technique is demonstrated, which provides a complete, temporally and spatially resolved mapping of the megagauss magnetic fields generated in intense short-pulse laser-plasma interactions. A normally incident time-delayed probe pulse reflected from its critical surface undergoes a change in its ellipticity according to the magneto-optic Cotton-Mouton effect due to the azimuthal nature of the ambient self-generated megagauss magnetic fields. The temporal resolution of the magnetic field mapping is typically of the order of the pulsewidth, limited by the laser intensity contrast, whereas a spatial resolution of a few μm is achieved by this optical technique.