World's first white laser
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asunews.asu.edu
[1] https://www.reddit.com/r/science/comments/3f0oyo/the_first_w...
> Actually, there are a few key points we wanted to make with this paper. First, yes this is semiconductor-based, which offers a few advantages over optical fiber technology. The second is that this was accomplished in a single growth run, unlike several other devices we cite which essentially just run multiple lasers in parallel. Third, the growth mechanism for these nanosheets is novel. Also, as far as we could tell, we provided the first direct evidence for the nanobelt-nanosheet conversion mechanism. It had been previously proposed before in a single paper, but did not have any experimental evidence to back up the claim.
> Also, the linked article is somewhat sloppy. We are by no means reporting the first ever white laser, and in fact we cite several examples of previous setups used to produce white lasing. In this paper we report the first monolithic, semiconductor-based laser.
That's why I love Hacker News and some subreddits. Whenever there's an interesting story in the news, it's usually full of misinterpretations and sometimes outright lies. But on their HN/Reddit discussion threads you can often meet people who are either directly involved in the project or know someone who is first-hand, who can cut through the bullshit and say how things actually are.
http://www.leica-microsystems.com/science-lab/white-light-la...
http://www.nktphotonics.com/product_cat/supercontinuum-laser...
Apparently this discovery is actually the first semiconductor white light laser, which is pretty neat - but not what the headline claims.
A picture of the output of a fully coherent white light laser spanning from the uv to ir: http://www.laserfocusworld.com/articles/2011/09/sub-femtosec...
For more cool physics related to this read about frequency combs, which are (most of the time) frequency stabilized supercontinuum lasers.
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...
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.
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.
Given that it makes it an excellent candidate for intra-satellite communications. Imagine satellite clusters which can effectively be very large aperture sensors if they know their exact relationship to each other and can communicate with picosecond accuracy. Very cool.
My imagination is getting ahead of me, but you could potentially have lightbulbs+LIDAR in your roof, to track occupants and things.
Then there's the problem of means-of-detection; Phillips had a cool setup that relied on the rolling shutter of phone cameras; but as soon as someone comes up with a global shutter for phones, such systems are toast.
Forgive my weak physics background, but aren't lasers generally known for having narrow frequency ranges? So if this is just creating white additively using RGB lasers, won't it be more like 3 frequencies, not a full spectral band?
It sounds like it's only 'white' from a human standpoint, not a physical one...
Firstly it's not at all equivalent to an AM radio. It is an AM modulated carrier but that's about it. The detection scheme direct detection and not coherent like in an AM radio.
Also your power spectral density would be fairly low as your AM modulation would be distributed over a huge wavelength range. So taking a narrow slice with a tunable optical filter (which aren't that narrow really) would mean the detector would see a very small signal indeed.
Given that it's so broadband, my guess is that it's probably not low intensity noise at all (modern communications lasers are ~-140dB/Hz) and thus wouldn't make a great direct detection OOK source. So this would limit ultimately the sensitivity of such an AM modulated system. Being so broadband means that it's not at all suitable for phase modulated signal because by definition it would have high phase noise. Overall the spectral efficiency of such a source as a communications device is abysmal.
Additionally the silicon detectors that are needed to convert the light signal back into an electrical signal have low responsivity and speed. So the poor detector speed places an upper bound on the supportable BW and poor Si responsivity places a limit on the overall sensitivity of the system.
It's much, much more efficient to use IR sources all the way around. Materials in the IR are really efficient for both light generation and detection. There are lots of other reasons why IR is better for free-space communications as well (less scattering and higher material transparencies generally).
No a white laser is good for other reasons. There are lots of places where we still use things like Xenon lamps for measurement of things.
Brighter is not necessarily a good thing. I've noticed a trend of monitors increasing in brightness over the years, and my current pair of monitors which is already a few years old is more than bright enough at the lowest (0) brightness setting - I've turned it down from the eye-watering maximum it was set to when I got them, and left it there ever since. I don't think we need more brightness in ordinary monitors; maybe niche applications like outdoor-readable displays would benefit. At the very extreme, it causes the eye damage well known of high-power lasers.
A few years ago I saw Andrew Tridgell talk about his current plaything: autopiloted model aircraft (using a linux project whose name I can't recall). Anyway, as the aircraft were used outdoors, he needed a laptop bright enough to use in sunlight.
After much faffing about, he settled on simply taking the plastic back and lighting panel off a normal laptop, and simply letting the ambient sunlight shine through the LED panel. We saw it in use later out on the field, and it worked pretty well. Of course, it's not going to work for night use...
The project Tridge is working on is ardupilot - https://github.com/diydrones/ardupilot
Brightness: energy/area
Which has several uses for a laser, especially as it goes more bright than anything you should be looking directly at
With laser projectors can be made much smaller, and they can run cooler.
It seems like this could also be used for cheaper tri-color (or quad-color) holography. Such features are used as security elements in passports and banknotes.