Ultrashort laser micro-texture printing

A system of modifying a medium so that a grayscale image is obtainable from the medium, the system comprising:

• a laser source capable of outputting a laser beam comprising a plurality of optical pulses having a pulse width less than about 100 picoseconds;
• a support for holding a medium having a surface;
• a scanning system configured to relatively scan the laser beam with respect to the surface of the medium;
• and
• a controller configured to vary optical energy delivered by the laser beam to different regions of the surface of the medium based on a desired grayscale, thereby altering at least one of reflectivity, absorptivity, and diffractivity of the regions to provide the grayscale image obtainable from the medium.

A method of modifying a medium having a surface so that a grayscale image is obtainable from the medium, the method comprising multiple scans relative to the surface to improve visibility of the grayscale image, the method comprising:

• scanning a first laser beam relative to the surface at a first scan speed, the first laser beam comprising a plurality of optical pulses having a first pulse width less than about 100 picoseconds, the first laser beam delivering first optical energy to an area of the surface of the medium;
• varying the first optical energy delivered to different regions of the area by the first laser beam, thereby altering at least one of the reflectivity, absorptivity, and diffractive properties of the regions in the area to provide a first grayscale image obtainable from the medium, the first grayscale image having a first visibility;
• scanning a second laser beam relative to the surface at a second scan speed, the second scan speed greater than the first scan speed, the second laser beam comprising a plurality of optical pulses having a second pulse width less than about 100 picoseconds, the second laser beam delivering second optical energy to at least a portion of the area scanned by the first laser beam;
• and
• varying the second optical energy delivered to different regions in the area, thereby providing a second grayscale image obtainable from the medium, the second grayscale image having a second visibility, the second visibility greater than the first visibility.