Fabrication of x-ray spiral masks by laser ablation

The manipulation of x-rays by phase structures is becoming more common through devices such as compound refractive lenses, blazed zone-plates and other structures. A spiral phase modulation structure can be used to condition an x-ray beam to produce an x-ray vortex. An x-ray beam in this form can be used as the first step towards a self-collimating beam. Also it can be used as a controllable pathological feature in studies of x-ray phase retrieval. We describe the microfabrication of a spiral phase modulation structure by excimer laser ablation. A multi-step fabrication using 15 separate chrome-on-quartz mask patterns is used to create a 16 step spiral staircase structure approximating the desired spiral ramp. The results of simulations and initial experimental results are presented.

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