Optically variable film, apparatus and method for making the same

A method of forming a microstructure for an optically variable film with an apparatus, the apparatus comprising a laser configured to emit a beam, a telescoping lens section having a first lens and a second lens spaced apart by a first distance and an interferometer configured to direct the beam toward a workpiece, the method comprising:

• operating the laser at a predetermined power level;
• selecting first and second lens focal lengths and determining the first distance;
• emitting the beam onto the workpiece;
• splitting the beam in the interferometer and directing the split beam toward the workpiece;
• ablating the workpiece with the split beam to form a pixel in the workpiece;
• and
• incrementally moving the workpiece relative to the laser and ablating the workpiece with the split beam to form further pixels in the workpiece, wherein the workpiece is further incrementally moved relative to the laser and pixels are further formed in the workpiece to form an array of pixels at a resolution of about 200-230 dpi,
• wherein the workpiece includes a layer of polyethylene terephthalate (PET) exposed to the beam in which the microstructure is formed, and
• wherein the PET layer melts in response to exposure to the split beam, and wherein the microstructure is randomized by melting the PET.