A thin layer of ice crystals turns into a maze of microscopic water channels when heated by near-infrared light.
Water molecules can form a variety of intricate patterns. The molecules self-organize into snowflakes, for example, and laser beams can bore microscopic channels into ice cubes. Now, Ido Braslavsky at the Hebrew University of Jerusalem in Rehovot, Israel, and his colleagues have demonstrated that simply shining light on a partially frozen water sample can create complex structures.
The team's experiments involved 13-micrometre-thick ice crystals bathed in sugar water. The researchers illuminated the entire sample with near-infrared light while keeping the apparatus at a constant temperature.
As a result, the water stayed cool while the light melted small holes into the ice, which absorbs the chosen frequency of light three times more effectively than water does. Adjacent holes occasionally merged to form channels, and over an hour, these channels grew into labyrinthine patterns in the ice crystals.
The researchers suggest that this technique of prefentially heating ice rather than water could be used to carefully thaw biological samples that have been preserved by freezing.