Today, most lasers are made on silicon wafers, but the researchers at the Centre for Molecular Materials for Photonics and Electronics and the Inkjet Research Centre - both in the Department of Engineering at the University of Cambridge - used chiral nematic liquid crystals (LCs), similar to the materials used in flat-panel LCD displays instead. If aligned properly, the helix-shaped structure of the LC molecules can act as an optically resonant cavity - an essential component of any laser. After adding a fluorescent dye, the cavity can then be optically excited to produce laser light.
Until now, high quality LC lasers have been produced by filling a thin layer of LC material between two accurately spaced glass plates a hundredth of a millimetre wide. The glass is covered with a specially-prepared polymer coating to align the LC molecules in a complex process that requires a cleanroom environment and involves multiple, intricate production steps. Furthermore, the range of substrates available is limited to glass or silicon.
Using a custom inkjet printing system, the researchers printed hundreds of small dots of LC materials on to a substrate covered with a wet polymer solution layer. As the polymer solution dries, the chemical interaction and mechanical stress cause the LC molecules to align and turn the printed dots into individual lasers.
The researchers believe that this simple process can form lasers on virtually any surface, rigid or flexible, and can potentially be applied using existing printing and publishing equipment (similar to the ones used to print papers or magazines).
The process has been developed initially to produce compact, tuneable laser sources and high-resolution laser displays. However, it can also be used to print fluorescence tag-based “lab-on-a-chip” arrays used extensively in biology and medicine. By being able to put lasers virtually anywhere, the potential applications are limited only by imagination.
A UK patent application to protect the invention has now been filed with the help