DVN's new laser technology report focuses mainly on laser-pumped remote phosphor architecture for automotive road-illumination applications: in short, laser-based headlamps. In a phosphor-converted white LED, the pump source is a blue LED emitter. Yellow phosphor is applied; the blue light plus the light from the excited phosphor yields a white output. Similarly, a laser-pumped remote-phosphor light source has two primary components: the 450-nm laser diode and the remote phosphor module, as in this schematic drawing:
The first component of the system is the laser. A laser's beam is usually highly directional and coherent (does not diverge or spread significantly even over long distances) coherence. It is also often polarised. For that reason, a laser beam can be easily focused to a very small spot, or collimated. This characteristic can be exploited for easy and fast beam shaping and light bending. In comparison, the light output from an LED is incoherent and usually has a wide divergence. Therefore, beam coupling into an optical fibre or light guide is generally much more efficient with a laser than with an LED, and LED light coupling demands thicker fibres than the ones required for laser beam coupling.
There are several kinds of inorganic phosphors offering a wide range of broadband wavelengths. Many manufacturers of phosphors for the LED lighting market supply powdered phosphors to the OEMs who mix and coat the blue LED chips according the requirements for output efficacy, correlated colour temperature (CCT) and colour fidelity (per CRI). Until recently, the phosphor has been in close proximity to whatever was generating the blue light to excite the phosphor: it was placed right overtop of the blue LED, or coating the inside of the fluorescent lamp with the electric arc passing directly under it.
Now a new type of arrangement has emerged, the "remote phosphor" architecture. As the name implies, the phosphor is physically separated from the blue excitation light source. Instead of coating the blue LED chips with phosphor, transparent glass or polycarbonate substrates can be coated with phosphor. Because remote-phosphor architecture is rather new, the phosphor world is still working to catch up. Today's ommercially available remote phosphors are generally designed to be used with blue LEDs. The extremely high intensity from a focused laser beam can exceed the design limits of the phosphor and eventually damage it; this must be considered at the design phase. Advances in phosphor technology and technique will probably reduce and eventually eliminate this issue eventually. Until then, it is assumed that OEMs interested in laser pumped phosphor systems will continue to work on application-specific remote phosphor modules designed for a particular project.