Scale used: the information bar at the bottom of input.tif (OCR plus pixel inspection) reads X5,000 (magnification), WD 10.0 mm, with a scale bar labelled 1 um. The white scale bar measures 53 px (columns 1202-1254), so 1 um / 53 px = 18.9 nm per pixel (image 1280 x 1024 px, about 24 um wide). The magnification reading is from my own glyph read and the label is from OCR; I could not view the image directly.

Method: I cropped off the info bar (rows 0-939) and removed the background with a Gaussian high-pass filter. I then ran Hann-windowed, zero-padded 2D FFTs on the whole image, on central and corner crops, and on 256 x 256 px tiles. The strongest, most consistent spectral peaks (tiles with a peak-to-background ratio above 8) lie at a spatial period of 44-48 px. The median is about 46 px, which gives about 870 nm. Whole-image peaks gave 43-50 px (about 810-945 nm).

Orientation: the wave vector lies close to the image x-axis (about 175 deg, within roughly +/-10 deg). The ripples/stripes therefore run roughly vertically in the image, with a slight tilt of up to about 10 deg that varies across the field. They are quasi-periodic laser-induced periodic surface structures (LIPSS-like) with a spacing of about 0.87 um. Weaker components at 100-150 px (about 2-3 um) come from larger-scale undulations and are not the dominant period.

RESULT: period = 870 nm
