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Does there exist a laser that is tunable over the whole visible spectrum? If so does there exist one that is solid state? This is to settle a score with my dumb workmates.

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Specify what You mean: Tunable on the spot by turning a knob? Or do You content with a laser which needs some "work" (eg change parts) to tune over a big range. Last bust not least: CW or Impulse? –  Georg May 30 '11 at 4:02
    
Tunable on the spot. Either CW or Impulse is ok. I'm pretty sure it doesn't exist. –  Jeff Wong May 30 '11 at 4:19
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The only lasers which might do it is maybe something like "free electron" or similar. Such a laser should not have a cavity, because good mirrors covering entire visible are not available. –  Georg May 30 '11 at 4:47
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@Andrew, Great! I wonder how many layers this mirrors are made of? –  Georg May 31 '11 at 15:48

3 Answers 3

The Coherent Chameleon titanium-sapphire laser tunes over a pretty enormous range, mostly in the IR (680 to 1080 nm). With a frequency doubling crystal, it covers most of the visible (340 to 540 nm), and if you add an OPO, it can tune over the entire visible range with frequency doubling.

Supercontinuum sources cover the entire visible spectrum simultaneously, and are often operated with post-filtering if you want narrowband light.

Toptica's iChrome is a narrowband source that tunes over the entire visible by following supercontinuum generation with frequency doubling.

All these lasers are solid-state.

Now, regarding the spirit of your question. Does your bet with your dumb co-workers allow nonlinear optics like supercontinuum generation or frequency doubling? Does it allow mixtures of different gain media? Are you specifically curious about semiconductor lasers? Do you care about the coherence of the output, the bandwidth, or the brightness?

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The question is, are those sources lasers? (In the sense of the dumb participants of that bet) –  Georg May 31 '11 at 11:12
    
Yeah, it's possible the OP wants a single gain medium that amplifies from ~400-700 nm. I'm sure we could mix together enough laser dyes to cover this range, if efficiency is not a concern. –  Andrew May 31 '11 at 12:55

Georg is correct. The free electron laser is tunable:

Unlike gas, liquid, or solid-state lasers such as diode lasers, in which electrons are excited in bound atomic or molecular states, FELs use a relativistic electron beam as the lasing medium which moves freely through a magnetic structure, hence the term free electron.[ The free-electron laser has the widest frequency range of any laser type, and can be widely tunable, currently ranging in wavelength from microwaves, through terahertz radiation and infrared, to the visible spectrum, to ultraviolet, to X-rays.

But it is not a lasing that can be used in a pointer or a portable method. It needs accelerated electrons. So it depends what sort of argument you have with your friend.

Today, a free-electron laser requires the use of an electron accelerator with its associated shielding, as accelerated electrons are a radiation hazard. These accelerators are typically powered by klystrons, which require a high voltage supply. The electron beam must be maintained in a vacuum which requires the use of numerous vacuum pumps along the beam path. While this equipment is bulky and expensive, free-electron lasers can achieve very high peak powers, and the tunability of FELs makes them highly desirable in several disciplines, including medical diagnosis and non-destructive testing.

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Dye laser are tunalble too, but that is about some 50 nm maximal. If You want more You need to refill a different dye solution, maybe You have to chance the grating. –  Georg May 30 '11 at 8:50
    
The big one at JLAB takes a team of three operators to run. Admittedly that's a cutting edge, high power (10 kW, CW!), recirculating accelerator device. –  dmckee May 30 '11 at 18:57

For comparison, this company Radiantis sells OPOs that are tunable over almost the whole visible spectrum. OPOs are not lasers, but they are sources of coherent light which use a solid state gain medium.

Full disclosure: I do not work for and have never done business with Radiantis, but I have toured their lab once.

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What definition of solid state are you using? Semiconductor? –  Andrew May 31 '11 at 13:03
    
<facepalm> Yes... of course a PPLN or KTP crystal is also solid state. I will amend the answer. –  ptomato May 31 '11 at 14:20

protected by Qmechanic Oct 20 '13 at 10:23

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