Lasers ♦ news digest
amplification required much less power than previous attempts at the technology. The team’s prototypes are claimed to be the first lasers of their kind.
Red, green, and blue lasers have become small and cheap enough to find their way into products ranging from BluRay DVD players to fancy pens. But each colour is made with different semiconductor materials and by elaborate crystal growth processes.
Now a new innovative technology demonstrates all three of those colours coming from one material. That could open the door to making products, such as high-performance digital displays, that employ a variety of laser colours all at once.
glue.
Chemists at QD Vision synthesised the nanocrystals using a wet chemistry process that allows them to precisely vary the nanocrystal size by varying the production time. Size is all that needs to change to produce different laser light colours: 4.2 nm cores produce red light, 3.2 nm ones emit green light and 2.5 nm ones shine blue. Different sizes would produce other colours along the spectrum.
The cladding and the nanocrystal structure are critical advances beyond previous attempts to make lasers with colloidal quantum dots, said lead author Cuong Dang, a senior research associate and nanophotonics laboratory manager in Nurmikko’s group at Brown. Because of their improved quantum mechanical and electrical performance, he said, the coated pyramids require 10 times less pulsed energy or 1,000 times less power to produce laser light than previous attempts at the technology.
Quantum nail polish
VCSEL colloidal quantum dots, also known as nanocrystals, can produce lasers of many colours. Cuong Dang manipulates a green beam that pumps the nanocrystals with energy, in this case producing red laser light. (Credit: Mike Cohea/ Brown University)
“Today in order to create a laser display with arbitrary colours, from white to shades of pink or teal, you’d need these three separate material systems to come together in the form of three distinct lasers that in no way shape or form would have anything in common,” notes Arto Nurmikko, professor of engineering at Brown University and senior author of a paper describing the innovation. “Now enter a class of materials called semiconductor quantum dots.”
The materials in prototype lasers described in the paper are nanometre-sized semiconductor particles called colloidal quantum dots (CQDs) or nanocrystals with an inner core of cadmium and selenium alloy and a coating of zinc, cadmium, and sulphur alloy and a proprietary organic molecular
When chemists at QDVision brew a batch of colloidal quantum dots for Brown-designed specifications, Dang and Nurmikko get a vial of a viscous liquid that Nurmikko said somewhat resembles nail polish.
To make a laser, Dang coats a square of glass, or a variety of other shapes, with the liquid. When the liquid evaporates, what’s left on the glass are several densely packed solid, highly ordered layers of the nanocrystals. By sandwiching that glass between two specially prepared mirrors, Dang creates one of a VCSEL. The Brown-led team says it was the first to make a working VCSEL with colloidal quantum dots.
The nanocrystals’ outer coating alloy of zinc, cadmium, sulphur and that molecular glue is important because it reduces an excited electronic state requirement for lasing and protects the nanocrystals from a kind of crosstalk that makes it hard to produce laser light, Nurmikko says. Every batch of colloidal quantum dots has a few defective ones, but normally just a few are enough to interfere with light amplification.
June 2012
www.compoundsemiconductor.net 75
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105