Lasers turn pure aluminum … ‘gold’

The ultimate goal of the Old World alchemist was to turn inexpensive metals
into gold. Modern-day physicists at the University of Rochester’s Institute of
Optics (Rochester, NY), have turned aluminum and other metals gold—in color
if not chemistry. A femtosecond laser processing technique created by professor
Chunlei Guo and his assistant Anatoliy Vorobeyv alters the surface properties
of aluminum, platinum, titanium, tungsten, silver, and gold to create tints
of gold, blue, gray, black, and even multicolored irridescence. The technique
involved a Ti:sapphire laser system emitting 800 nm, 65 fs pulses at about
1.1 mJ/pulse. The horizontally polarized laser beam can modify single spots as
small as 10 μm in size, or large areas using a scanned laser beam. The laser
induces periodic nanostructures that change the refl ectance and absorption properties of incoming light. As the simple
technique is refi ned, says Guo, possible applications could include using a single laser to create colored metal bike
frames, etching full-color pictures of your family onto your refrigerator door, or creating an engagement ring the color of
your fi ancé’s eyes