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Multilayer-dielectric (MLD) diffraction gratings are used in high-power laser systems to compress laser-energy pulses. The peak power deliverable on target for these short-pulse petawatt class systems is limited by the laser-damage resistance of the optical components in the system, especially the MLD gratings. Recent experiments in our laboratory have shown that vapor treatment of MLD gratings at room temperature with organosilanes such as hexamethyldisilazane (HMDS) produces an increase in their damage threshold at 1054 nm (10-ps, 370-µm spot size) as compared to uncoated MLD grating control samples. The 1-on-1 laser-damage threshold of an HMDS-treated grating increased by 4.5% as compared to the uncoated control sample, while the N-on-1 damage threshold of an MLD grating treated with tetramethyldisilazane increased by 16.5%. For an MLD grating treated with bis-(trifluoropropyl)tetramethyldisilazane, the N-on-1 and 1-on-1 damage thresholds increased by 4.8% and 5.3%, respectively. Such increases in laser-damage threshold are unprecedented and counterintuitive because it is widely believed that the presence of organic materials or coatings on the surfaces of optical substrates will inevitably lead to reduced laser-damage resistance.