Science Questions

Can a laser be any spectrum of light?

Sun, 13th Jun 2010

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Klv8r, via Twitter asked:

Can a laser be any spectrum of light?


We put this question to Dr Graeme Hirst, from the STFC's Central Laser Facility...

Graeme -   These days they can, yes.  The very first laser that was produced worked in the near infrared.  It was really, really bright, so you could probably see it, but only just about.  Gradually, as time went on, more and more lasers were developed with a wider range of available colours – a wider range of available wavelengths.  And these days, the range is spectacular.  Just last year, a group of scientists in America demonstrated a really high power laser that’s actually working in the x-ray region.


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I thought the first laser was a ruby laser emitting 694.3nm which is visible red light. Bored chemist, Tue, 15th Jun 2010

I still think the first laser was a ruby laser emitting 694.3nm which is visible red light. Bored chemist, Wed, 16th Jun 2010

You are correct and you validated the Dr. statement  694.3nm is near (780-3,000 nm)infrared portion of the spectrum.
I looked it up on the net.
So what is your point? tommya300, Wed, 16th Jun 2010


"the near infrared" is the portion of the infrared that is near the visible NOT the portion of the visible that is near the infrared.  BC has a valid point

- near infrared (infrared A) is 750-1400 nm and is not visible.
- the light from a artificial ruby laser is (per BC) 694 nm and in the red portion of the visible spectrum.

Matthew imatfaal, Wed, 16th Jun 2010

Matthew I am a bit confused here... but not any more... I am looking at everything in layman's terms and I am learning

Because near infrared was not capitalize, I looked at it as a position close to,
Not as a noun Near Infrared labling the entity.
With this in mind, looking below, you can clearly see my thought process.

Am I reading the chart incorrectly?
Rounding out 694 ---> 700nm is in the red which is near or closer
to the upper portion to the scale into the infrared that is described as being less than 1000nm

Hear is different chart listing

IR-A: 700 nm–1400 nm (0,7 µm – 1.4 µm) ----> I think I see 694nm is close enough to say it is near 700nm
IR-B: 1400 nm–3000 nm (1.4 µm – 3 µm)
IR-C: 3000 nm–1 mm (3 µm – 1000 µm)

Really, am scratching my head, it was mentioned the laser light was border line visible...
They, the wavelength, are both numerically neighboring the border of each others scale

(degrees Kelvin)  WHAT WE SEE 
Near-Infrared  (0.7-1) to 5  740 to (3,000-5,200)  Cooler red stars
Red giants
Dust is transparent
Mid-Infrared  5 to (25-40)  (92.5-140) to 740  Planets, comets and asteroids
Dust warmed by starlight
Protoplanetary disks
Far-Infrared  (25-40) to (200-350)  (10.6-18.5) to (92.5-140)  Emission from cold dust
Central regions of galaxies
Very cold molecular clouds 

tommya300, Wed, 16th Jun 2010

Hmm...  using the quote button for the Doc doesn't seem to work, but anyway...

The x-ray lasers planned for the now defunct SDI were going to be rather powerful, what with being powered by a nuclear bomb.  I gather that the only test that was carried out was inconclusive though.

Did Dr. Hirst mention anything about gamma ray lasers?  I believe there's some speculation that these may be possible. LeeE, Wed, 16th Jun 2010

There's a big difference between "in the near infrared" and "near the infrared".

In neither case is the word "near" a noun and most nouns are not given capital letters in English anyway.

The point is that, if I'm right about the first laser being a ruby laser then it's plain visible red light.
This "It was really, really bright, so you could probably see it, but only just about. "makes no sense if the first laser was a ruby laser.

If the first laser wasn't a ruby laser then I'd really like to know what it was.
There were masers before lasers, so there might have been some weird "not strictly L or M" ASER that worked in the IR.
I guess it would be an ISER.
Bored chemist, Wed, 16th Jun 2010

got it!
ok tommya300, Wed, 16th Jun 2010

BC and Tommy

Here is a video of the Ted Maiman's first laser being redemonstrated - personally I cannot see the red dot amongst the white that they comment on in the video.  But, from the context it is quite clear that those in the audience and the presenter can see the red dot - therefore it is visible light.

Matthew imatfaal, Thu, 17th Jun 2010

The eye can sense 695nm, but it is very insensitive to it - something like only 1% of the sensitivity that you would get at 620nm which is a bright slightly orangey red.

So to a fair extent it is true to say that you'd see it but that it needs to be quite bright.

See also my webpage at:

There isn't a distinct cutoff between deep red and infra-red, although there may be wavelengths defined by convention.
At 760nm the eye is about 1/100th as sensitive as at 700nm, so it is reasonable to define anything much beyond that as invisible IR. techmind, Fri, 18th Jun 2010

I checked before I posted and I can assure you that I can see light at 694nM.
I used an ordinary desk lamp and a monochromator. It's not all that bright but it is still perfectly visible. Bored chemist, Sat, 19th Jun 2010

I had a colleague who worked with ruby lasers, and the beam, while not bright to the eyes, really had high power, enough to burn though photo paper with every pulse.

Laser theory does not disallow any colour, just requiring electrons that are excited and can drop to a lower energy by emitting light, in a medium that will allow lasing to occur. This means you can now get a laser that provides output in almost any colour from microwaves to x rays, though you need a good many units to cover the band, and many are low power devices or only work once as they are destroyed by the emission ( X ray lasers) or can only operate in pulsed mode.

SeanB, Sat, 19th Jun 2010

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