Image: Caspar Benson
In Brief
- Solid-state lasers can produce light in the red and blue parts of the spectrum but not the green.
- Recent research suggests that this "green gap" could be plugged as early as this year.
- The advance will allow for laser-based video displays that are small enough to fit in a cell phone.
On a rainy Saturday morning in January 2007, Henry Yang, chancellor of the University of California, Santa Barbara, took an urgent phone call. He excused himself abruptly from a meeting, grabbed his coat and umbrella, and rushed across the windswept U.C.S.B. campus to the Solid State Lighting and Display Center. The research group there included one of us (Nakamura), who had just received the Millennium Technology Prize for creating the first light-emitting diodes (LEDs) that emit bright blue light. Since that breakthrough over a decade earlier, Nakamura had continued his pioneering research on solid-state (semiconductor) lighting, developing green LEDs and the blue laser diodes that are now at the core of modern Blu-ray disc players.
As Yang reached the center about 10 minutes later, people were milling about a small test lab. "Shuji had just arrived and was standing there in his leather jacket asking questions," he recalled. Nakamura's colleagues Steven DenBaars and James C. Speck were speaking with a few graduate students and postdoctoral researchers as they took turns looking into a microscope. They parted for Yang, who peered into the eyepiece to witness a brilliant blue-violet flash emanating from a glassy chip of gallium nitride (GaN).
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12 Comments
Add CommentThe article reads that "...They should help speed the introduction of laser projectors for televisions and movie theaters- which will display much richer colors than other systems..."
Reply | Report Abuse | Link to thisWhat does "richer" mean? What is the quality of "rich" measure in a color?
Dan
Good news for MVIS products
Reply | Report Abuse | Link to thisColor gamut, I'd imagine.
Reply | Report Abuse | Link to thisIndeed ;)
Reply | Report Abuse | Link to thisExcellent article!
Reply | Report Abuse | Link to thisHowever, as someone familiar with green lasers, I did happen to notice technical inaccuracies in your sidebar titled "What About Green Laser Pointers?" that appeared in the print edition of your fine magazine.
Such devices actually employ a three-step process, not two-step as described. The statement that semiconductor lasers inside these devices emit radiation ~1060nm is also incorrect. For a variety of reasons, it is not practical to utilize a ~1060nm laser diode to directly drive a frequency-doubling crystal in such devices.
Rather, these devices employ a 808nm IR laser diode "pump". The output of this laser is then used to "pump", or excite, a second, solid-state laser, typically a Neodymium-doped Nd:YVO4 or Nd:YAG crystal (similar to how a flash lamp is used to pump another well-known solid-state laser - the ruby laser!) This second laser produces a beam at ~1064nm.
This arrangement is called a Diode-Pumped Solid-State (DPSS) Laser.
For a green pointer, a third step is required. The ~1064nm output of the second (solid-state) laser is fed into a precisely-aligned non-linear Second Harmonic Generator (SHG) frequency-doubling crystal (such as KTP), which doubles the frequency (and thus halves the wavelength) of the solid-state laser's 1064nm output (IR) to 532nm (green).
I believe the statements that a change in temp of the second (SHG) crystal alters the wavelength, and that a laser diode would solve that, may also be in error, given that the second crystal is simply acting as a doubler to the Nd:YAG 1064nm line being fed into it by the first crystal. Conversely, laser diodes ARE known to vary wavelength based on temperature.
However, current (DPSS-type) green lasers DO suffer from a variety of problems, including low efficiency, unstable output power levels, sensitivity to cold (reduced output or stops functioning), and require maintaining very precise crystal alignments in order to operate properly. A true "green" laser diode (in addition to being smaller), could eliminate all of these problems, and would be welcome news indeed!
Other than the aforementioned technical issues on the sidebar, however, I found this a most interesting & informative article on an important area of scientific research! Keep up the good work!
Other than the technical inaccuracies the format of SciAm web pages is difficult to read.
Reply | Report Abuse | Link to thisHow about a "single page" view that is not the full-width print screen?
nice but very weird <><
Reply | Report Abuse | Link to thisInteresting story. Hard to read with all the commas missing, though...
Reply | Report Abuse | Link to thisits great to know it aall
Reply | Report Abuse | Link to thisyou always winge on SciAm pages, lighten up!
Reply | Report Abuse | Link to thissolid green emitters:
Reply | Report Abuse | Link to thiswert+ (emerald), 500 nm, coumarin 307
wert, 501 nm, coumarin 50
wert, 504 nm, coumarin 314
wert, 505 nm, InGaN
wert-, 510 nm, coumarin 51
green+, 515 nm, coumarin 3
green, 521 nm, coumarin 334
green, 522 nm, coumarin 522
green, 522 nm, porf�ropsin
green, 525 nm, InGaN
lime+, 532 nm, porf�ropsin
lime+, 534 nm, athallofotopsin-retinal iodopsin
lime+, 535 nm, coumarin 7
lime+, 536 nm, sulfaflavine
lime+, 537 nm, coumarin 6
lime, 540 nm, coumarin 153
lime, 540 nm, ZnS:Cu,Al,Au P22G
leek+, 552 nm, uranin
leek+, 553 nm, fluorescein 27
Many are too broadband/white, and -ish would go on their hues.
-Aut
It's cool,because I have already bought a green laser pointer from http://www.freaklasers.com
Reply | Report Abuse | Link to this