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Nanopores with diameters from 20 to 50 nm in silicon nitride (SiN_x) windows are useful for single-molecule studies of globular macromolecules. While controlled breakdown (CBD) is gaining popularity as a method for fabricating nanopores with reproducible size control and broad accessibility, attempts to fabricate large nanopores with diameters exceeding ∼20 nm via breakdown often result in undesirable formation of multiple nanopores in SiN_x membranes. To reduce the probability of producing multiple pores, we combined two strategies: laser-assisted breakdown and controlled pore enlargement by limiting the applied voltage. Based on laser power-dependent increases in nanopore conductance upon illumination and on the absence of an effect of ionic strength on the ratio between the nanopore conductance before and after laser illumination, we suggest that the increased rate of controlled breakdown …