<title>Evaluation of a diffractive microlens-array beam shaper for use in acceleration of laser-driven flyers</title>

Abstract

A promising new tool in shock wave physics is the generation of shock waves in test materials through the impact of small, laser-accelerated discs ("flyers"). In order to achieve the necessary one-dimensional condition of uniaxial strain in the shockloaded material, it is vital that flyers maintain a nearly planar geometry during the acceleration and impact processes. The geometry of the flyer is significantly influenced by the spatial intensity profile of the driving laser beam. With the goal of achieving a nearly uniform drive intensity for this application, we have evaluated a diffractive, microlens-array beam shaper for use with a high-energy, Nd:Glass laser driver. Based on the near-field spatial profile of this multimode laser, a 30-mmdiameter array containing multiple hexagonal diffractive lenslets was designed and fabricated. In combination with a primary integrator lens of 76.2-mm focal length, this optical element was intended to produce a uniform intensity distribution over a 2-mm-diameter spot at the focal plane of the primary lens. Beam profiling studies were performed to determine the performance of this optical assembly. At the focal plane of the primary lens, the beam shaping optics generated a reasonably uniform profile over a large portion of the focused beam area. However, a small amount of undiffracted light resulted in a high-intensity, on-axis spike. A beam profile approaching the desired "top hat" geometry could be obtained by moving the flyer launch plane a few mm inside or outside of the focal plane. The planarity of flyers generated using this optical assembly was evaluated using a line-imaging, optically recording velocity interferometer system (ORVIS). Results of these measurements demonstrate the deleterious effect of the on-axis spike on flyer planarity. Acceptable conditions for useful flyer impact experiments can be obtained by operating at a position that provides a near-top-hat profile.

Laser propulsion of microelectronic components: releasing mechanism investigation

“…Fast development of ultra-short pulse lasers makes ablative laser propulsion a very promising technique [3,4]. On a more modest scale there are developments of micro Laser Plasma Thruster [5,6] and laser -driven flyer plates [7,8,9]. In terms of specific impulse, energy conversion efficiency and mass-power ratios, ablative laser propulsion is superior to other laser propulsion schemes.…”

Characteristics of Step-Shaped Laser-Driven Flyers on Fiber End Face Based on a Ti/Al Ablation Layer

“…Since then, monolithic Al film of different thicknesses and Al/Al 2 O 3 /Al composite films have been fabricated by coating end faces of fibers with a 400 μm core diameter. It was found that the composite films containing the Al 2 O 3 insulation layer demonstrated better performance than the monolayer Al films. , Researchers at the Sandia National Laboratory utilized a multimode fiber with a 400 μm core diameter to transmit laser pulse with an energy of 30 mJ and pulse width of 25 ns. Laser pulse ablated the Al film with a thickness of about 10 μm on the fiber end face to achieve a peak flyer velocity of 3 km/s .…”

Diamond turning and soft lithography processes for liquid tunable lenses

“…This drives the active research on microlenses, which increasingly requires design of free form surface relief to optimize the optical performance of the lens systems targeted for a specific application. Applications that have benefited from the use of free form optical surfaces include beam shaping [6][7][8], imaging systems [9,10], optical data storage systems [11,12] and aberration reduction [5,[13][14][15]. In many instances, free form optical elements can also reduce lens count, thereby enabling the miniaturizing of optical systems.…”