The waterjet-guided laser technology, first presented in 1995, has found a broad range of applications in the precision micro machining field. The waterjet-guided laser (also called Laser MicroJet or LMJ) is used today in a wide range of industrial fields, such as semiconductor, solar, electronics, medical, tooling, high-brightness LED, watch and automotive industries.
The LMJ principle is to couple a high power, pulsed laser beam into a hair-thin, low-pressure waterjet. A schematic view of the principle is shown in Figure 1. The beam of a high power laser is transmitted by a fibre optic cable to an optical head. In the optical head the laser beam is focused through a transparent window into a nozzle placed at the bottom of a thin water-filled chamber. Pure deionised, degassed and filtered water is introduced into the water-filled chamber. Pure deionised, degassed and filtered water is introduced into the water-filled chamber. The water pressure ranges from 50 to 500 bar, depending on the nozzle diameter. Larger nozzle diameters require a smaller water pressure. Typical nozzle diameters range from 30 μm to 80 μm but may also be larger, up to a few 100 μm. The laminar waterjet exiting the nozzle guides the laser beam by means of total internal reflection at the water/air interface, similarly to conventional glass fibres. When it reaches the workpiece, the laser ablates the material by melting and vaporisation.