# Changing wavelength of light. PS: Hello

check
First off, I'm new to the board so hello! I hope to be a regular.
Now that that's out of the way:

Is there any way to change the wavelength of monochromatic light (other than the doppler effect)?

Thanks!

Gold Member
Welcome to these fine boards!

Yes, one other way is to pass it through another medium(like glass or something). The frequency of the light will NOT change, but the wavelength will change along with its speed(well, better put, the time it takes for the light to travel a certain distance increases)

You can find the speed of light in any medium by the equation

v=c/n where c is the speed of light (about 3*10^8 m/s), n is the index of refraction of the medium, and v is your new speed

Then, by the equation v=f*[lamb] you can substitute the new velocity in, and the frequency of the light to get:

[lamb]=c/(n*f) Where [lamb] is your new wavelength, c is the speed of light, n is the index of refraction of the material and f is the frequency of the light (which stays constant)

You can also change both wavelength and frequency by letting light pass via media in which polarization changes with magnitude of electric field (non-linear crystals, for example). Then you'll get second, third, etc. harmonics.

At high intensity of field (say, focused laser beam) almost any media is non-linear.

check
Originally posted by dav2008

Then, by the equation v=f*[lamb] you can substitute the new velocity in, and the frequency of the light to get:

[lamb]=c/(n*f) Where [lamb] is your new wavelength, c is the speed of light, n is the index of refraction of the material and f is the frequency of the light (which stays constant)

Thanks. Yeah, I figured a medium with a differnet index of refraction would change the wavelength, but then once it passes through the medium, it would return to it's original wavelength.

I was thinking more along the lines of changing the colour of monochromatic light, such as a laser, by passing it through a 'filter' (using the term lightly here becuase it doesn't really 'filter' out anything) where the exiting beam is of a different colour.
Possible? Practical? Thanks!

Staff Emeritus
Gold Member
Originally posted by check
I was thinking more along the lines of changing the colour of monochromatic light, such as a laser, by passing it through a 'filter' (using the term lightly here becuase it doesn't really 'filter' out anything) where the exiting beam is of a different colour.
No.

- Warren

meteor
Yes, one other way is to pass it through another medium(like glass or something). The frequency of the light will NOT change, but the wavelength will change along with its speed(well, better put, the time it takes for the light to travel a certain distance increases)
No, what do changes is the frequency, remaining the wavelenght equal
Any idea why it happens?

Gold Member
Originally posted by meteor
No, what do changes is the frequency, remaining the wavelenght equal
Any idea why it happens?
I asked my physics teacher when we were doing this unit..he said that the frequency stays the same, but the wavelength changes

Yes, I think velocity and wavelength change, but frequency f and energy hf stays same in media.

maximus
check this link out. brand spanking new discovery.

Whoa, that would be awesome of that is the case!

Gold Member
Dearly Missed
Originally posted by check
First off, I'm new to the board so hello! I hope to be a regular.
Now that that's out of the way:

Is there any way to change the wavelength of monochromatic light (other than the doppler effect)?

Thanks!

Among the methods mentioned in the article is this:

"Right now, the only way to shift the frequency of a light beam involves sending an extremely intense light pulse _ with a power of many megawatts or even gigawatts _ along next to it.

This interacts with the first beam and alters its frequency, but the technique is expensive, requires high-power equipment, and is generally pretty inefficient."

Would anyone like to describe this method in more detail and
explain it? It looks as if the two beams couple in a medium and the booster beam gives energy to the weaker one and shifts it to a higher frequency. this is apparently (judging from what it says) not just producing harmonics but actually producing a small shift in frequency. Also this is not the NEW method with photonic device but an already known method. Any explanations? Links?

Staff Emeritus
Gold Member

Gold Member
Dearly Missed
Originally posted by Integral

I remember that thread, and maximus referred to it and brought the link over from that thread----it was one you started.

I was asking about the more established method that they mentioned in passing----which they say works but is inefficient---it does not use a photonic crystal but just uses an intense parallel beam of light which goes along side the beam you want to upshift and gives it a little energy. I'm curious because it is unintuitive to me that this would happen, except possibly in a special kind of medium.

It is a different, and older, method to raise the frequency of light and it would be nice to have a link giving an idea how the coupling works. If anyone has one.

Basicly bouncing a photon using moving mirrors is same as bouncing tennis ball between moving walls - ball gets higher and higher energy if walls move toward each other and loses its energy if walls move away from each other. Photon bouncing between moving and non-moving mirror gets blue shifted if distance between mirrors is decreasing and red shifted in distance is increasing.

Bouncing visible light photons from relativistic (= moving with high speed) mirror may shift their energy well into x-ray and even gamma-ray range as observed in experiments with irradiating relativistic electron beam by a laser. This effect is proposed as a possible mechanism of generating short x-ray and gamma-ray bursts seen in distant supernova explosions.

wimms
Originally posted by marcus
I was asking about the more established method that they mentioned in passing----which they say works but is inefficient---it does not use a photonic crystal but just uses an intense parallel beam of light which goes along side the beam you want to upshift and gives it a little energy. I'm curious because it is unintuitive to me that this would happen, except possibly in a special kind of medium.
Yes, anyone know? Does the energy density of pulse cause space distortions that interference with other light would make seem similar to 'moving walls'? Afterall, weren't photons supposed to not interact with each other?

FZ+
There are chemical methods of absorbing radiation of one frequency and reemitting it at another frequency/wavelength. For example, in florescent tube lights, uv radiation is converted into visible white/blue light. It may well be possible to have chemicals that convert other frequencies.