World's first white laser

https://asunews.asu.edu/20150728-worlds-first-white-laser

by ChuckMcM • 11 years ago

116 37 11 years ago

asunews.asu.edu

ChuckMcM• 11 years ago

The actual paper is behind the Nature paywall but this development is pretty important. Modulating a white laser would make it much easier to pick up a reliable signal, imagine an AM radio transmitter that transmitted on every frequency of the AM band, even the crappiest tuner would give you a clear signal.

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.

Schwolop5• 11 years ago

I like the idea of LiFi communications. Might be hard for devices to upload data, but beaming stuff from your light bulbs down to your devices might be a very high bandwidth possibility.

My imagination is getting ahead of me, but you could potentially have lightbulbs+LIDAR in your roof, to track occupants and things.

CHY872• 11 years ago

The current issue is because light is line-of-sight. Such systems traditionally need a lanyard of some kind to provide unobstructed access, and this is super inconvenient for the user.

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.

XaspR8d• 11 years ago

imagine an AM radio transmitter that transmitted on every frequency of the AM band

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...

btoptical• 11 years ago

Really none of that is correct.

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.

zik• 11 years ago

Unfortunately this isn't the world's first white laser. They've been around for a few years and they're sold by a few companies.

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.

Schwolop5• 11 years ago

Unless I'm misunderstanding (which I could well be - this isn't my field!) those use several narrow-band coloured lasers and combine the output. This article is a single wide-band semiconductor.

steve19• 11 years ago

According to the article they generate three lasers from the same silicon. I think the benefits are size and/or simplicity, cost etc.

fsilva2• 11 years ago

Actually supercontinuum lasers are not a recombination of different (incoherent) lasers but rather a 'processed' output from a single laser. You start with a high peak power laser pulse (e.g. a femtosecond mode locked oscillator) and excite a highly nonlinear process that generates new frequencies (e.g. using a special kind of optical fiber), and at the output you have a continuous broad spectrum. What happens in the fiber is actually similar to sea waves arriving on the beach - a very long and well beahaved wave steepens in the leading edge (which means new frequencies were generated) and eventually breaks/collapses into many small waves of much shorter period. The laser in this article is probably 100x or even more cheaper than a setup like this, but also does not have the full coherence supercontinuum sources have, so it will be used for different things.

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.

brodo• 11 years ago

When I read the headline I expected a interesting anecdote from way back when it was invented. White lasers are pretty common at big raves and have been for at least 10 years.

Florin_Andrei• 11 years ago

And "white" here really means tri-color, not continuous spectrum - although with lasers that's probably to be expected.

flyinghamster• 11 years ago

Exactly. This will be great for displays and perhaps decorative lighting, but not for general illumination. I've always noticed how even a brightly lit monitor or TV screen doesn't illuminate things well, since it's just emitting three bright wavelengths and not a continuous spectrum.

userbinator• 11 years ago

Lasers are brighter, more energy efficient, and can potentially provide more accurate and vivid colors for displays like computer screens and televisions

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.

vacri• 11 years ago

applications like outdoor-readable displays

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...

gambiting• 11 years ago

I had to use a laptop to control some equipment outside while working for a refinery, after one day of not being able to see anything I just brought a cardboard cutout that I would place over the display - problem solved.

dharma12• 11 years ago

That's a great idea :)

The project Tridge is working on is ardupilot - https://github.com/diydrones/ardupilot

Schwolop5• 11 years ago

I tried to do inertially stabilised projection with a laser projector for an augmented reality concept. Unfortunately, laser projectors were only around 15 lumens at the time - I needed bright ambient light for the SLAM stabilisation to work, but simultaneously low light for the laser to be visible. I'm still waiting for high-lumen hand-held laser projection to be viable.

nitrogen• 11 years ago

Can you just do SLAM in infrared?

Retra• 11 years ago

Dimming a bright monitor is much easier than brightening a dim one.

raverbashing• 11 years ago

This has nothing to do with your monitor in reality

Brightness: energy/area

Which has several uses for a laser, especially as it goes more bright than anything you should be looking directly at

dharma12• 11 years ago

not sure I would want to stare at a laser monitor, but they are great for projectors, where brightness IS a big issue.

With laser projectors can be made much smaller, and they can run cooler.

cwp• 11 years ago

In the article, they talk about brightness in terms of lumens per watt. That boils down to energy efficiency: you can get a brighter display with the same battery life, OR keep the same brightness and get better life.

fffrad• 11 years ago

... And we are not going to show you any pictures except a 232x309 small consolidated jpeg.

Reefersleep• 11 years ago

So many scientific articles cause this response in me. "Invention X causes fantastic visual product Y". Alright alright, talk at length about X all you want, but for the love of internet kittens, show me Y!

toufka• 11 years ago

Reddit discussion with the author is pretty good [1]. The author tries to dispel some of the superlatives in the public statements about the work, and provides good detail about what they've done: a novel way to produce a single material ("nanosheet") that when pumped, emits at multiple (three gets you white light, and what they did here) wavelengths.

[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.

TeMPOraL• 11 years ago

Thank you for linking that.

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.

prewett• 11 years ago

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

sigterm• 11 years ago

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.

fsilva2• 11 years ago

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).

logfromblammo2• 11 years ago

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.

ethbro• 11 years ago

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.

Polarity• 11 years ago

thats racist

fiveoak• 11 years ago

Here's a link to the actual journal article in Nature: http://nature.com/articles/doi:10.1038/nnano.2015.149 (unfortunately probably pay-walled)

logfromblammo2• 11 years ago

One application I can think of would be bouncing RGB colors off of three digitally modulated mirrors (like the Texas Instruments DLP chip), then combining the reflected beams into one. You could project a movie onto a screen from a mile away.

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.

World's first white laser

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