# Is there a way for a laser to work across a range of colors?

For lasers used for free space / mirror steered / diffuse beam communications or LIDAR scanning, would there be some way for a single laser to be able to selectively transmit across a range of colors, to a receiver that can similarly distinguish between colors?

This would be similar in operating principle to a radio transmitter that can adjust its transmitting frequency up or down across the radio spectrum, to a radio receiver that can distinguish what frequency it is receiving.

• As I recall, dye lasers are tunable within a range of frequencies. This might be a better question for physics.SE though, I think? – Hearth Aug 13 '19 at 18:03
• What do you mean by tunable? All lasers are tunable to some extent. Across a wide range of wavelengths? not really unless you get super expensive. – Voltage Spike Aug 13 '19 at 18:08
• I don't think you can tune photodiodes at all...the only method I have heard of is using multiple photodiodes or rotating different filters in front of them. – DKNguyen Aug 13 '19 at 18:20
• You can spectrally disperse the light with a prism or grating and use an array of spatially separated photodiodes - a spectrometer. – D Duck Aug 13 '19 at 19:29

Through the magic of nonlinear optics you can buy a super supercontinuum laser which outputs light in a very broad spectrum, typically 400 nm to 1,700 nm.

https://en.wikipedia.org/wiki/Supercontinuum

A small wavelength band may be selected with an acousto-optic modulator

See one in action tuning over the wavelength band: https://www.youtube.com/watch?v=I7_E_sOOl9U

• It appears to me that what you are describing is spectral broadening, with no easy way of tuning the wavelength. If so, then you have missed the point of the question. – Elliot Alderson Aug 13 '19 at 18:24
• I'd agree, though I can see how with a bit of mechanics, one could select a color – Marcus Müller Aug 13 '19 at 18:26
• The usual method is to use an acousto-optic modulator. – D Duck Aug 13 '19 at 18:39

There's very different kinds of lasers, and while there's tunable lasers, these really don't belong in the category of things you mount on a LIDAR scanner, at all.

So, no, no adjustable lasers themselves.

You can, however, frequencymix lasers with laser, and lasers with RF signals, and do all kinds of crazy photonic things. But: either that will be very discrete (mixing laser with laser: you can only get discrete lasers) or far below what you'd call "a range of colors": If you use a really high-frequency (e.g. 60 GHz) RF signal to modulate a red laser (say at 400.000 THz), then the resulting color will still be exactly as you can optically determine without mixing coherently with the original laser: red, the exact same red as before (now at 400.060 THz, congrats).

• I have a tunable argon laser. (And a nice HeNe.) It's not that big. But I haven't done anything with LIDAR, so I'm ignorant. I wish the OP wrote more about why there is a need for a "range of colors" and why "color" was chosen instead of "wavelength." Oh, well. I may learn something in this discussion. – jonk Aug 13 '19 at 18:14
• Nice :) What'd you use that laser for? – Marcus Müller Aug 13 '19 at 18:25
• @jonk It's the only way to get your weapons to bypass enemy shields. – DKNguyen Aug 13 '19 at 18:30
• @MarcusMüller Hehe. Mostly for show (and it does appear to work for sky writing, for example.) It's a $25\:\text{mW}$ laser that I got from Optical Data, Inc when they were selling old equipment. I got it really cheap. How could I turn it down? (They also were selling an HPLC, but the asking price, while cheap, was high enough that I could not justify it as a "toy" for my home. (Yes, I buy toys!!! Lots of toys!) Luckily, I have a large house and auxillary buildings and a large property (about 5 hectares.) – jonk Aug 13 '19 at 18:55
• @jonk you clearly did something right there. Nice! – Marcus Müller Aug 13 '19 at 18:57