Photon Doppler velocimetry (PDV) is a ubiquitous diagnostic method in dynamic compression experiments. It typically requires the roughening of the test surface to ensure scattering of the probe light back into the PDV probe at non-normal angles of incidence. Although surface scattering plays an essential role in the quality of PDV data, surface scattering properties for common materials and preparations have not previously been studied with specific relevance to PDV. Here, we present detailed measurements of the bidirectional reflectance distribution function for four different surface preparations (Scotch-Brite hand and drill roughened, ball-rolled, and grit blasted) and four different materials (copper, aluminum, stainless steel, and tantalum). These measurements employ a conventional PDV probe and obtain a diffraction limited angular resolution with 10 pW accuracy and 2.6% repeatability. In addition to scattering data, we employ scattering theory and simulations to accurately emulate the measured data. We also present a straightforward method to derive the average scattering distribution from surface profilometry and observe several qualitative aspects of the scattering data that may help to optimize PDV signals.
Single crystal fibers are an intermediate between laser crystals and doped glass fibers. They have the advantages of both guiding laser light and matching the efficiencies found in bulk crystals, which is making them ideal candidates for high-power laser and fiber laser applications. This work focuses on the growth of a flexible fiber with a core of dopant (Er, Nd, Yb, etc…) that will exhibit good wave guiding properties. Direct growth or a combination of growth and cladding experiments are described. Scattering loss measurements at visible wavelengths along with dopant profile characterization are also presented. Laser characterization for these fibers is in progress.
Single crystal fibers are an intermediate between laser crystals and doped glass fibers. They can combine the
advantages of both by guiding laser light and matching the efficiencies found in bulk crystals, making them ideal
candidates for high-power laser and fiber laser applications. In particular, a very interesting feature of single crystal fiber
is that they can generate high power in the eye-safe range (Er:YAG) with a high efficiency, opening new possibilities for
portable directed energy weapons. This work focuses on the growth of a flexible fiber with a core of dopant (Er, Nd, Yb,
etc…) that will exhibit good waveguiding properties. Direct growth or a combination of growth and cladding
experiments are described. We have, to date, demonstrated the growth of a flexible foot long 45 microns doped YAG
fiber. Scattering loss measurements at visible wavelengths along with dopant profile characterization are also presented.
Laser characterization for these fibers is in progress.
A fluorescent solar collector (FSC) is a waveguide device that can concentrate both diffuse and direct sunlight on to a solar cell. The electrical output of the device depends strongly on the photon fluxes that are absorbed, emitted, and trapped inside the FSC plate. For this reason, it is important to study the photon transport losses inside the collector. One of the losses in FSC to be investigated is scattering, which increases the probability of the escape cone losses. We determine the scattering contributions in FSC by using angle dependence of light internally reflected in the FSC. The cause of scattering in spin-coated polymethylmethacrylate on top of the glass collector is identified as roughness from the top surface, rather than bulk losses. This loss can be suppressed to less than 2% using an index-matching planarization layer.
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