Bright prospects

the technological advances in lasers never cease to surprise. But the recent discovery of laser action in a light-trapping powder by scientists at the Northwestern University is astonishing. The importance of such powder lasers is that they could revolutionise flat panel displays which are an essential part of many consumer electronics nowadays.

Conventional lasers use mirrors to bounce light in a cavity which contains the material which generates laser action. The atoms in the material are pumped up into an excited state and when they de-excite, they emit light which is characteristic of lasers; the light is amplified and monochromatic, i.e. has a single wavelength. These properties are responsible for the many uses which lasers find in our everyday life.

Recently, H Cao and his collaborators at Northwestern University, Illinois, used powder films of semi-conductor material zinc oxide and gallium nitride to trap light. Ordinary powders would normally absorb all the light but because grain size is smaller here than the wavelength of light (about 500 nanometers) the light can propagate and even augment itself leading to typical laser action.

The scientists feel that the phenomenon can be used in flat panel displays where each pixel (the smallest unit of a display panel) emits an electron which excites the phosphor grains placed in front. If small enough phosphor grains are used, it might excite laser action in them, leading to brighter displays. This could lead to a phenomenal boost for the flat panel display technology where lack of sufficient brightness is a major drawback ( Physical Review Letters , Vol 82, No 11, p2278).

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