first ever white laser developed

Not enough red but great they have this, I am sure they will perfect it but it is not really a white laser, just sensed that way by our eyes when RGB are emitted together.

Alaskan said:

it is not really a white laser, just sensed that way by our eyes when RGB are emitted together.

Click to expand...

So you're saying white light doesn't exist?

first ever white laser developed

Click to expand...

This is categorically wrong. Google mixed gas lasers and supercontinuum lasers. I think Pr:BYF lasers can also do white under the right circumstances.

lasers could produce more than 400 lumens per watt

Click to expand...

Bullshit. A 100% efficient emitter of green light at 555nm would be 683 lumens per watt. A 100% efficient RGB light source with any decent color rendering can do maybe 350lm/w depending on the spectrum. But good luck finding a visible laser diode that does much over 30% efficiency, much less 100%.

Cyparagon said:

So you're saying white light doesn't exist?.

Click to expand...

A broad (visible) spectrum white, or one of these which is a partial spectrum output as RGB which appears white to our eyes? As the laser forum God of laser knowledge, you would be better providing answers than asking questions of someone who is a novice

internet in space just got a whole lot better lol jk jk This is pretty cool

Cyparagon said:

This is categorically wrong. Google mixed gas lasers and supercontinuum lasers. I think Pr:BYF lasers can also do white under the right circumstances.

Click to expand...

Don't know how many people I had to point that out to on Reddit. We've had whitelight lasers for decades now. The breakthrough here is that this produces all three colours from one solid state structure.

Cyparagon said:

So you're saying white light doesn't exist?



This is categorically wrong. Google mixed gas lasers and supercontinuum lasers. I think Pr:BYF lasers can also do white under the right circumstances.



Bullshit. A 100% efficient emitter of green light at 555nm would be 683 lumens per watt. A 100% efficient RGB light source with any decent color rendering can do maybe 350lm/w depending on the spectrum. But good luck finding a visible laser diode that does much over 30% efficiency, much less 100%.

Click to expand...

This is based on combining blue and yellow emissions, as quoted below. This is from https://www.google.com/url?sa=t&source=web&rct=j&url=http://www.ecse.rpi.edu/~schubert/Reprints/1999-Guo-et-al-(IEDM)-Photon-recycling-semiconductor-light-emitting-diode.pdf&ved=0CDkQFjAHahUKEwikg4e6lYPHAhXB84AKHS_SATw&usg=AFQjCNFNiGe3aqIOsF3nKoD5GNccZGNg-A&sig2=bXXVMSWAKsLCvpi0a_tluw. There are plenty more articles on the subject if you simply Google "400 lumens per watt".


"Currently, white-light LEDs are based on photo-
excitation of phosphors by a GaInN/GaN LED emitting
in the blue or ultraviolet (UV) range of the spectrum.
The quantum efficiencies of both, optically excited high-
quality semiconductors and photoluminescent
phosphors, can be close to 100 % 1,2,3."

"One can show that the most efficient white light source consists of two monochromatic sources emitting at complementary wavelengths. For two 100 % efficient monochromatic sources emitting at 448 nm and 569 nm3,5, the maximum theoretical luminous efficacy to produce white light is 400 lumens per Watt of optical power 1,5."

diachi said:

Don't know how many people I had to point that out to on Reddit. We've had whitelight lasers for decades now. The breakthrough here is that this produces all three colours from one solid state structure.

Click to expand...

Exactly.

It is an every color combination that can be made by additive mixing with 3 variable output Red, Green, and Blue lasers, laser.
I think the "white" part is just clever marketing of the guys work to attract additional funding for the substancial amount of additional work that needs to be done for it to have any real practical value beyond novelty value.

I think most didn't bother to read the article or misread if they scanned it for whatever reasons.

The explainatory supplemental information is here: http://www.nature.com/nnano/journal/vaop/ncurrent/extref/nnano.2015.149-s1.pdf

What the nanophotonics team managed to do was to add a blue layer to what others had already accomplished.

"In typical LED-based lighting, a blue LED is coated with phosphor materials to convert a portion of the blue light to green, yellow and red light. This mixture of colored light will be perceived by humans as white light and can therefore be used for general illumination."
"Sandia National Labs in 2011 produced high-quality white light from four separate large lasers. The researchers showed that the human eye is as comfortable with white light generated by diode lasers as with that produced by LEDs, inspiring others to advance the technology."
"Six years ago, under U.S. Army Research Office funding, they demonstrated that one could indeed grow nanowire materials in a wide range of energy bandgaps so that color tunable lasing from red to green can be achieved on a single substrate of about one centimeter long. Later on they realized simultaneous laser operation in green and red from a single semiconductor nanosheet or nanowires. These achievements triggered Ning's thought to push the envelope further to see if a single white laser is ever possible" From: ASU engineers demonstrate the world?s first white lasers

So in this case what the guys did was make a nano device that is a "white" laser in the same sense that a RGB laser light show projector is a "white" laser. What is interesting is the R, G, and B areas of the monolithic block can be independently controlled enough to produce any color output desired, not just white as a RGB laser light show projector can do and anyone with three hand held R,G, and B can do to show white by additive mixing of primary colors.

"The researchers have created a novel nanosheet -- a thin layer of semiconductor that measures roughly one-fifth of the thickness of human hair in size with a thickness that is roughly one-thousandth of the thickness of human hair--with three parallel segments, each supporting laser action in one of three elementary colors. The device is capable of lasing in any visible color, completely tunable from red, green to blue, or any color in between. When the total field is collected, a white color emerges." from asu.edu article above

Is a pretty amazing accomplishment in and of itself, what Dr. Ning and team accomplished/ did. Now if the team can get it to work powered by electricity instead of having to be light pumped by UV laser (Newport, Explorer OEM 349nm).---they will be on to very valuable something economically viaable if efficiency and high output can be achieved additionally.

I invited the guy, Dr. Cun-Zheng Ning, who headed the team that did the work, via email, to take a look at the two threads on LPF about his work and come on as a guest/visitor to explain and answer any questions members might have.. Thought it would be enjoyable and interesting for members to have him come here and perhaps go online and answer a few questions.

Is a very good and capable bright guy--Dr Cun-Zheng Ning, Professor of Electrical Engineerging.
See: ASU Ning's Nanophotonics Group http://nanophotonics.asu.edu/

Will call and see if he can/will do, next week.

This was the email I sent to him:

""Dear Dr. Ning:
I tried to reach you on telephone today but was probably too late at 6:30PM EST. Will try again tomorrow or earlier in the day next week.

I wanted/want to contact for 3 reason.
1. To remark how brilliant the marketing of your nanophotonics project nano RGB wire as World’s First White Laser is—love what you are doing---hope/wish the promotion brings excellent funding and 大获成功 (great success).

2. To let you know about a forum group http://laserpointerforums.com .
I participate in the forum and there are 2 posts about your work there you might like to see. The forum has many highly technologically knowledgeable members along with many no so much so ---they all have one thing in common that they enjoy lasers and laser technology as a hobby.
Here is a link to the most busy post about your work first ever white laser developed http://laserpointerforums.com/f54/first-ever-white-laser-developed-94549.html and here is the link to the other one White semiconductor lasers? Please explain. http://laserpointerforums.com/f44/white-semiconductor-lasers-please-explain-94544.html

3. To invite you to post a comment on either of the threads or whatever you think would be appropriate in either of the 2 threads about your work---am certain the laser enthusiasts of LPF would be thrilled if you were to do so---is not often that people of your level doing R,D,T and E engineering of new laser technology post comments but is always a day to celebrate when they do so.

Best regards,"

TaterMay said:

"One can show that the most efficient white light source consists of two monochromatic sources emitting at complementary wavelengths. For two 100 % efficient monochromatic sources emitting at 448 nm and 569 nm3,5, the maximum theoretical luminous efficacy to produce white light is 400 lumens per Watt of optical power 1,5."

Click to expand...

The color rendering index of a light source with two wavelengths is near zero, which makes it horrible for use as a light source.

Alaskan said:

A broad (visible) spectrum white, or one of these which is a partial spectrum output as RGB which appears white to our eyes?

Click to expand...

I'd say anything that appears white IS white.

I'd be happy to consider another definition, but your suggestion of "broad" is pretty vague. How many wavelengths are required for the spectrum to be "broad"? If the spectrum needs to be continuous and have a curve matching the blackbody radiation profile, that would mean fluorescent lights, LEDs, HID lamps, and basically any light source besides tungsten isn't white.

Cyparagon said:

The color rendering index of a light source with two wavelengths is near zero, which makes it horrible for use as a light source.

I'd say anything that appears white IS white.

I'd be happy to consider another definition, but your suggestion of "broad" is pretty vague. How many wavelengths are required for the spectrum to be "broad"? If the spectrum needs to be continuous and have a curve matching the blackbody radiation profile, that would mean fluorescent lights, LEDs, HID lamps, and basically any light source besides tungsten isn't white.

Click to expand...

Excellent points, Cyparagon -- I agree.
With regard to what is white---yes anything that's called white is white.--same goes for any other "colors"--whatever it is called, which depends upon many factors--is what it is.

I also, however, understand what Alaskan is saying---we were all taught --those of us old enough anyway, as kids, that white is simply the entire visable spectrum combined. This view is a left over one from long ago before anyone knew about waveslengths and frequencies of the visable specturm for that matter before there was any knowledge of the " electromagnetic spectrum" or of how eyesight and color vision worked.

Is the fault of 1600's super hero --Isaac Newton -- In 1666, Isaac Newton demonstrated that white light could be broken up into its composite colors(now called the visable spectrum, approx.400nm to 700nm) by passing it through a prism, then using a second prism to reassemble them to create white again. Newton hypothesized light to be made up of "corpuscles" (particles) of different colors.
Before Newton, most scientists believed that white was the fundamental color of light.

So there you go, Alaskan's "broad" (visible spectrum) white -- Isaac Newton's white--still alive in 2015 for many reasons!

Little did they know in the 1600s of the actual nature of light or of RGB sensitive cells , rods and cones of the eye and how the brain puts all that input together such that a healthy 20 yr. old human can distinguish something on the order of 7 to 10 million colors. That human vision system "language" of color is a number greater than the number of words in the English language (the largest language on earth).

When we see the entire visible spectral range our eyes read all of it as various combinations of RG&B sensitive rods cells and cone cells of the retina can react electromagnetic frequency-wise. Is not a simple process is very complicated but the point is that "color" is a function of the human visual system, and is not an intrinsic property of objects. Objects don't "have" color, they give off/emit and/or reflect light that "appears" to a human observer to be a "color". It is understood in modern times that frequency determines color, but wavelength is easier to measure for light thus nm/wavelength terminology is most commonly in use. Wavelength varies with the speed of light, which varies with the medium. The speed of light is about 0.03% slower in air than in vacuum. If you're trying to understand color, however, wavelength is just as good as frequency

The International Commission on Illumination defines white (adapted) as "a color stimulus that an observer who is adapted to the viewing environment would judge to be perfectly achromatic and to have a luminance factor of unity. The color stimulus that is considered to be the adapted white may be different at different locations within a scene. "Adapted" mentioned in the CIE definition is the chromatic adaptation by which the same colored object in a scene experienced under very different illuminations will be perceived as having nearly the same color.

A very interesting/excellent article on color for anyone wanting a detailed but not too detailed overview of "color" appears in The Physics Hypertextbook, here:Color - The Physics Hypertextbook from which I took the following quotes:
"Color is a function of the human visual system, and is not an intrinsic property. Objects don't "have" color, they give off light that "appears" to be a color. Spectral power distributions exist in the physical world, but color exists only in the mind of the beholder."
"There is no physical significance in color names. It's all a matter of culture and culture depends on where you live, what language you speak, and what century it is. A given wave of light has the same frequency no matter who is viewing it, but the person perceiving the color will call it a word appropriate to their culture"


:can:

Alaskan said:

Not enough red but great they have this, I am sure they will perfect it but it is not really a white laser, just sensed that way by our eyes when RGB are emitted together.

Click to expand...

Obviously. The novelty is that you get red, green and blue lines emitted from the same cavity with the same beam characteristics. This is different compared to the systems we typically use to achieve white light with several discrete lasers plus beam combiners and such.

If 'white' means a continous spectrum or just one that integrates to looking white in our visual system is another matter. There is better terminology do describe the detials of that.

Surely you could combine only two monochromatic lasers to create a beam that appears to be white (e.g. blue and orange). This light would appear white at first glance and have a color temperature depending on the mix ratio too, but it would have a horrible color rendering index (CRI).

CRI is important for practical applications. Things like tungsten/halogen filament bulbs have a CRI near 100%, but for other light sources it varies wildly. A very good fluorescent has over 90%, but a low pressure sodium streetlight has about 0% (or even negative if you follow the strict calculations).

Benm said:

Obviously. The novelty is that you get red, green and blue lines emitted from the same cavity with the same beam characteristics. This is different compared to the systems we typically use to achieve white light with several discrete lasers plus beam combiners and such.

If 'white' means a continous spectrum or just one that integrates to looking white in our visual system is another matter. There is better terminology do describe the detials of that.

Surely you could combine only two monochromatic lasers to create a beam that appears to be white (e.g. blue and orange). This light would appear white at first glance and have a color temperature depending on the mix ratio too, but it would have a horrible color rendering index (CRI).

CRI is important for practical applications. Things like tungsten/halogen filament bulbs have a CRI near 100%, but for other light sources it varies wildly. A very good fluorescent has over 90%, but a low pressure sodium streetlight has about 0% (or even negative if you follow the strict calculations).

Click to expand...

It seems to me that "white" is "white", is "white", is "white", no matter how you get there from light that produces a chromatic human visual system response. Light that produces an achromatic(hueless) human visual system response is just that, and commonly called "white"

"Daylight spectra and colour temperature"
" Daylight is light from the sun and the sky. The source of all daylight is the sun. Scattering of sunlight in the atmosphere by air, water vapour, dust, and so on gives the sky the appearance of a self-luminous source of light. Light emitted by the sun closely approximates a black body radiator with a temperature of 5,800K, i.e. very similar to an incandescent source with the same temperature. Light of all colours is scattered by the atmosphere, but because blue light is scattered slightly more than red light, the clear sky appears blue. When we view the sun directly, this scattering of light (i.e. its removal from the direct beam) is referred to as absorption. So the sun appears red when at the horizon because the preferential scattering (or ‘removal’) of blue light from white light leaves red light. A blue sky and a red sunset are therefore produced by the same physical process: the preferential scattering of blue light perceived from different points of view. These effects combine with meteorological conditions to produce a wide variety of daylight ‘phases’ based on the time of day, the degree of clearness of the sky, the type of clouds,etc..
"The absorption of the direct beam of sunlight by the atmosphere changes the colour (i.e. temperature) of the light, reducing the apparent temperature of the light dependingon how much air the light beam has passed through. The colour temperature of direct midsummer sunlight is almost the same as that of the extraterrestrial sunlight, i.e. ≥5,800K. For average summer sun – when the sun is a little lower in the sky –the colour temperature of the sunlight is about 5,400K. When the sun is at the horizon the sunlight passes through about twenty-five times more air than when the sun is at an altitude of around 40 degrees.. Thus the magnitude of the scattering is much greater, and so the apparent colour temperature of horizon sunlight reduces to that of glowing embers, i.e. less than 1,000K."
"Under normal viewing conditions the perceived colour of an object depends both on the colour of the object and the spectrum of the light under which it is viewed.Because of a process called chromatic adaptation whereby the the human visual system ‘corrects’ for shifts in colour appearance caused by illumination or light sources that are not ‘neutral’, i.e. not typical, white daylight. Although the human visual system has this ability to ‘correct’ for colour appearance to some degree, tasks involving the critical discrimination of colour will be impaired under illumination that deviates markedly from the reference illuminant which is ‘white’ daylight with a CCT of 6,500K." from: http://sageglass.com/wp-content/uploads/2011/08/How_to_maintain_neutral_daylight_illumination_wtih_SageGlass_EC_Glazing.pdf

Re: CRI --CRI is an antique however "important for practical applications" in some part of the world it may still be for lack of a replacement better index---The color rendering index (CRI) is intended to be a quantitative measure of the ability of a light source to reproduce the colors of various objects faithfully in comparison with an ideal or natural light source. CRI was formulated at a time when the two most common artificial light sources were incandescent and florescent, and it was the incandescent that was taken as the ‘reference’ source with a possible maximum CRI rating of 100 – even though colors illuminated by incandescent sources will appear ‘yellowish’ compared to standard daylight. Obviously this standard is a dinosaur as most places on earth no longer even use incandescent lighting.

In USA reference "white" has been defined as natural sunlight at 12 o'clock noon on the 4th of July in Washington, DC ----that is as white as "white" light gets.



:can:

I don't agree CRI is obsolete. It is old fashioned, basically based on the color rendition of a test card under illumination of the source in question rather than on real spectrofotometric analysis.

The concept of it is still valid however: colors render differently under light sources with different spectra, even if their color temperature is the same.

And it is very applicable today for LED systems which can have pretty funky spectra with a color temperature that appears fine but having a limited CRI. How much this matters to the average person is debatable, though most people will notice the difference between a crusty old "60+ CRI" tube light and a proper triphosphor one with a 80 or 90+ CRI.

Also, a high CRI does not mean 'white' per se. A pretty common fluorescent specification is 827 or 927, meaning a 2700k color temperature with a CRI of >80 or >90 respectively. Compared to the light from an overcast sky these definitely look yellow, but will render all colors well.

The same goes for the 'reference' incandescent source though: even a halogen bulb isn't likely to have a color temperature of over 3000K, far short of 'daylight white'.

It's been my experience anything over CRI of 40 is good enough for general purpose lighting (however subjective that is)

It's very subjective indeed, "general purpose" is such a vague term. A CRI is good enough to find your way around, but things will defitely look 'off' where color is concerned.

The trade-off is usually between cost and performance. For this reason lamps with a CRI of 0 (low pressure sodium) are often used along highways. Low initial cost, high efficiency and resonable lamp life make them ideal.

For home use these lamps are useless (apart from the cri, they have long startup times etc).

I think for domestic application there is little reason to go for a low CRI solution. Fluorescent lights with proper CRI (>80) are not that much more expensive than the old ones, and just as efficient if not better.

With LED lights it's a bit more difficult, efficiency suffers a bit for warm white and/or high CRI. Unfortunately there is so much on the market that you could find warm white lamps with high cri that are more efficient than cool white lamps with some ghastly color tone. The latter is obviously caused by using really crappy leds, and makes ordering these things online a pain.