Comment by prewett | Hacker News Reader

Comment by prewett | Hacker News Reader

Interesting, although a bit light on details. From the article it would seem like the laser is essentially three lasers (red, green, blue) coupled together, and by changing the amount of R, G, and B you tune the color. I'm curious how coherent the R, G, and B are with each other. A true "white" laser would be coherent on all frequencies, but I'm guessing that's pretty hard to accomplish (so limited holography uses).

I question the claim that "lasers are brighter, [and] more energy efficient [than LEDs]," though. I'm assuming LEDs are much more efficient (more lumens of output per watt of input), but I'd believe that the laser might be more intense (more lumens/m^2). Typically lasers are pretty ineffient. [1] reports efficiencies of 7% - 8.9% with semiconductor lasers. Wikipedia [2] appears to be reporting LED efficiencies of 20% - 39%, and one research group [2] reports on getting over 100% efficency, with an LED emitting "more optical power than the electrical power it consumes," although at very low power levels.

[1] http://www.laserfocusworld.com/articles/print/volume-48/issu...

[2] https://en.wikipedia.org/wiki/Light-emitting_diode#Efficienc...

[3] http://phys.org/news/2012-03-efficiency.html

Whenever the word "white" is used in a scientific or quasi-scientific context, it should probably be specified whether the speaker means "perceived by the human eye to be white", or "emitting a continuous spectrum across all frequencies of visible light", or something in between.

A tricolor LED and a white (phosphor-based) LED can both emit light perceived by a human to be white when viewed directly. But the former is actually only trichromatic, and will have different color rendering properties when reflecting from nearby objects.

An R+G+B laser is not a white laser.

Not sure what you mean by "how coherent the R, G, and B are with each other". They are not coherent, since they have different frequencies.

FWiW you can have 3 or even more frequencies in a laser beam coherent with each other, i.e. where te phase of the waves is locked together. This allows you to interfere the waveforms of the different lasers in time, as their relative phases are locked. This is very hard to do with continuous wave lasers, but rather routine with short pulsed lasers (e.g. femtosecond).

From skimming an author's replies to the reddit thread linked above, they seem to be less excited about the demonstrated colors and more excited about the novel semiconductor growth technique that they used to generate the combination.

They mention that the various "components" could be tuned as necessary to generate different frequencies if needed, but the RGB was kind of their proof of concept.

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