Here, we use R/1 methodology to test the onset of catastrophic damage and isolated growth under simulated use conditions of representative MLD coatings used in large-aperture petawatt-class lasers. In Fig. 2(a), we illustrate a typical fluence ramp exposure at a single-site location, i.e., 10 shots per fluence step. The half-wave plate is advanced every 10 shots to increase the fraction of the beam energy directed toward the test sample. In situ inspection of the sample surface being irradiated is performed after each sequence of 10 shots. When damage is detected (defined as a visible change at the sample surface), the test is terminated and the highest fluence shot recorded during the last ramp step is used to construct the R/1 damage probability curve versus fluence, as shown in Fig. 2(b). The R/1 test measures the so-called laser-induced damage threshold (LIDT) and may include, by design, a laser conditioning effect due to the gradual increase in fluence at each test site; the statistics of LIDT are built by repeating the test at 20 or more different locations on the sample. It should be noted that due to shot-to-shot laser fluctuations and uncertainty in the exact shot (out of 10) that initiated laser damage, the damage site morphology varies somewhat and in most cases includes damage growth. If the starting locations chosen for R/1 tests are pristine, the results inform on the onset of catastrophic damage and provide an upper limit for the coating damage resistance. The same procedure is also useful in examining isolated locations on the sample where pre-existing (PE) flaws are observed, as is the case for -size defects found on MLD coatings, which are introduced during the manufacturing process. For this purpose, we use the in situ microscope to align a defect with the incident beam location and perform an R/1 test to assess whether or not those isolated defects are more prone to initiate damage and lead to damage growth upon multiple shot exposures compared to the pristine locations. We can detect the onset of damage growth and even quantify growth rate versus fluence by using more frequent in situ damage inspections in combination with modified fluence exposure sequences, e.g., fewer shots at each step, ramp-up fluence until damage initiation occurs followed by lower fluence and/or reduced fluence step afterward.