Laser Machining

Several presentations were given at NASA’s 2019 Mirror Tech Days that highlighted the shortcomings of current mirror-fabrication technologies, particularly as they relate to demanding missions such as LUVOIR and HabEx. Many of the mirror deficiencies, such as areal density, surface figure error, stiffness, and surface figure changes over temperature, can be traced – either directly or indirectly – to mirror lightweighting. Current lightweighting processes result in pockets in the rear-side of the mirror that have abrupt stress-concentrating corners, poor front-rear symmetry, and poor material allocation in the webbing. The proposed laser machining process allows for the fabrication of cavities within a mirror that preserves front-rear symmetry, has no corners, and has a near ideal allocation of material within the webbing. The novel laser machining process utilizes a CO2 laser in an ablation regimen in which the focused beam strikes below the surface of the workpiece from the side (as opposed to the front or rear as is commonly done). Material between the focused beam and the surface is ejected by the shockwave produced by the laser’s pulse, greatly increasing the amount of material removed for each pulse. Further, the focused laser beam can be split in two and laterally separated; when pulsed the shockwave – and material removal – can bridge the gap between the focal spots and increase the removal rate further. We project that material removal rates exceeding 80 cubic millimeters per second are possible.

1. Lightweighting of astronomical mirrors and mirror segments. 2. Coarse grinding of optical prescriptions into the front surface of astronomical mirrors and mirror segments. 3. Coarse grinding of the rear side of astronomical mirrors and mirror segments.

1. Grinding prescriptions into the front and rear surface of optical components 2. Coarse grinding ceramic components to their near-net-shape.

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