Abstract: Surface contamination and debris deposition associated with laser ablation or ion beam milling is reduced by combining a directed flow to a workpiece with suction at a suitable vacuum pressure. The vacuum pressure is typically selected so that any contaminants or debris have relatively short mean free paths to avoid build-up on distant surfaces in a vacuum chamber. A shutter can be used to shield portions of a charged-particle-beam optical column during processing. Processing at vacuum pressures associated with the relatively short MFPs can be combined with processing at vacuum pressures associated with relatively long MFPs to provide coarse and fine milling or ablation.