Question about frequency versus wavelength

  • Thread starter noospace
  • Start date
  • #1
75
0
This is something I really should know but found I was unable to explain it to myself. When a ray of light passes from one medium to another its frequency remains invariant, but it slows down, forcing the wavelength to decrease according to [itex]c = \nu\lambda[/itex].

The frequency of the wave will correspond to the frequency of the elementary charged oscillators responsible for its production.
What is it about the frequency of the wave that leaves it unaffected, as opposed to the wavelength which is free to change? This leads me to a related question: is it practically possible to change the frequency of a ray of light, how would one do that anyway?
 

Answers and Replies

  • #2
dst
377
0
Because the energy of a photon is dictated by its frequency, and not its wavelength, it must remain unchanged. As far as I know, anyway.
 
  • #3
75
0
Conservation of energy eh? I like that explanation.

What assurance do we have that the photon does not exchange energy with its surroundings in passing from one medium to another?

Is it it possible to `bump up' the energy of a photon that is part of a self-propagating electromagnetic wave, thereby changing its frequency?
 
  • #4
DaveC426913
Gold Member
20,085
3,394
Is it it possible to `bump up' the energy of a photon that is part of a self-propagating electromagnetic wave, thereby changing its frequency?

I speak out of turn here but -

Seems to me, the photon would have to be absorbed and then another emitted at a different freq.

Which is fluorescence. Or is it phosphorescence?
 
  • #5
pam
458
1
It is really a simple classical effect. In going from one medium to another the wave boundary conditions at the interface must hold at all times. This requires the time dependence of the transmitted wave to be the same as that of the incident wave.
 
  • #6
jtbell
Mentor
15,829
4,219
The wave has to be continuous across the boundary at all times. This can be true only if the wave oscillates at the same frequency on both sides.
 

Attachments

  • waves.gif
    waves.gif
    13.8 KB · Views: 463
  • #7
Claude Bile
Science Advisor
1,471
19
Nonlinear optical materials are used to convert laser light from one frequency to another. This is done by exploiting that fact that in a nonlinear material, the frequencies you get out do not necessarily equal the frequencies you put in.

Essentially, by shaking atoms hard enough, you can get them to wobble with additional frequency components, such as the second and third harmonics.

One widespread use of this phenomenon is in the use of Nd:YAG lasers (which have a wavelength of 1064 nm) to generate 532 nm (green) light via the generation of a second harmonic within a crystal such as Lithium Niobate.

Claude.
 
  • #8
Normally you change medium at a fixed place and continuously in time. If you could change the index of refraction of an extended area, but at the same time, then the wavelength would stay fixed and the frequency would change. A cute thought problem, but I'm not certain if it has ever been done experimentally.
 

Related Threads on Question about frequency versus wavelength

  • Last Post
Replies
7
Views
5K
Replies
16
Views
33K
Replies
21
Views
5K
  • Last Post
Replies
2
Views
8K
  • Last Post
Replies
18
Views
4K
  • Last Post
Replies
6
Views
3K
  • Last Post
Replies
16
Views
3K
Replies
1
Views
1K
  • Last Post
Replies
10
Views
23K
Replies
8
Views
6K
Top