White laser?

White lasers have been around for quite awhile, in the form of frequency combs based on Ti:Sapphire lasers.

I didn't pay the $32, but it sounds like they've made three separate lasers by grading the composition of a quaternary alloy to avoid abrupt lattice mismatches. Sounds like a fun one, though how useful obviously remains to be seen.

Cheers

Phil Hobbs

Looks good. Technically it's actually three narrow-band laser sources on a common substrate - red, green and blue - but the human eye sees that as as white.

One can imagine situations where the difference would be perceptible - none of three laser wavelength would excite some narrow emission line sources - but they don't seem to come up often in real life.

Bees might be put off.

Someone needs to make a distinction between really white (spectrally flat) and visually white (two or three judiciously spaced colors).

Because visually white ain't the same as spectrally flat.

Things illuminated by laser light produce a speckling effect because of interference. I imagine much the same would happen if they were illuminated simultaneously by three different coloured lasers.

Sylvia.

It also works for sunlight e.g. on your thumbnail -- kind of subtle, but understandable when you realize what it is.

Sunlight is quite white, as we know, but it's got a certain coherency (namely, planarity) from travelling such a distance.

Tim

It doesn't take much spread in path lengths to make the laser light incoherent. Any real diffuser would do the job of providing multiple paths from the laser to the object illuminated.

Right - I suspected that at first too. However, the published articles clearly say three colors, but tunable to any color in between. I think the lasing is longitudinal in an alloy that has multiple band-gaps, so they can excite it continuously across the spectrum.

The keyword here being *tunable*.

With a thermal source, the (spatial) coherence area goes as 1/(angular subtense)**2. The Sun subtends about half a degree at the Earth, which is pretty large, so there are no visually significant coherence effects in sunlight.

Iridescence from thin films and gratings is not the same thing.

Cheers

Phil Hobbs

Does anything make spectrally flat white light other than things that require an intermediate conversion of energy to heat, like a light bulb does?

Spectrally white is black body radiation from something as hot as the surfa ce of the sun - about 6000K . You aren't interested in the near infra-red r adiation which carries a lot of the energy, so wrapping your 6000K source - typically a gas arc - in an IR reflector so that a lot of the energy is re flected back into the arc might save you some of the energy required to kee p it hot.

If you had enough narrow band sources you'd get something fairly close, and if you worked out a way of broadening the narrow band spectra - as in stic king them on a very-rapidly spinning disc so that you got loads of Doppler shift (up and down) - so that the narrow spectral bands got broadened enoug h to overlap - you'd be home and hosed.

Spectrally white is black body radiation from something as hot as the surfa ce of the sun - about 6000K . You aren't interested in the near infra-red r adiation which carries a lot of the energy, so wrapping your 6000K source - typically a gas arc - in an IR reflector so that a lot of the energy is re flected back into the arc might save you some of the energy required to kee p it hot.

If you had enough narrow band sources you'd get something fairly close, and if you worked out a way of broadening the narrow band spectra - as in stic king them on a very-rapidly spinning disc so that you got loads of Doppler shift (up and down) - so that the narrow spectral bands got broadened enoug h to overlap - you'd be home and hosed.

On Tue, 04 Aug 2015 08:54:49 +1000, Clifford Heath Gave us:

Broken link

Dang, I heard it was. I'll cease repeating it then!

Tim

What exactly do you mean by spectrally flat ?

Same power for every frequency band [W/THz], same power for every wavelength band [W/nm] or some black body radiation at 6000 K or some other temperature ?

I first noticed that when I was six or seven years old. All of the adults I asked about it thought I was making it up- NONE of them would just look at their damned thumbnails to see.

I soon stopped asking adults about stuff like that.

AKA spatial coherency as opposed to temporal coherency as seen in lasers.

Mark L. Fergerson

It still works for me. Did your newsreader/browser elide the < and >?

It is only white if you mix the independently fabricated and powered R,G,B lasers in the right proportions. It will have uses in display sign board projection systems if it can be made cheap enough.

"White" laser is misleading. It is strictly trichromatic at the three chosen laser frequencies. Used to illuminate a white target you can trick the eye into seeing any colour shade but illuminate a scene with it and you are at the mercy of its appearance at the chosen wavelengths.

BTW I misread the second paragraph as saying "White lasers were invented in 1960" and then realised it said "While".

Mainly projection TV and cinemas if they can avoid laser speckle.

It won't be replacing tunable dye lasers any time soon unless they develop a way to vary the wavelength emitted to order.

Strictly monochromatic radiation gives strange colour rendering.

rgb LEDs are "tunable" too.

...

That isn't what I read. They said red, green, blue or any color in between. Is that just prevaricating, and they don't really mean "tunable to any color in between?" Perhaps so - badly written if so.

Do you think they vary the atomic ratio to tune the three colors?

Indeed. You can easily show that under sodium vapour lighting.