Generating mechanical frequencies

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    Frequencies Mechanical
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Discussion Overview

The discussion revolves around the concept of generating lower mechanical frequencies from higher frequencies in mechanical systems, particularly exploring the analogy between mechanical waves (like water waves) and lasers. Participants consider the potential for creating a mechanical "laser" that operates on principles similar to optical lasers but utilizes mechanical waves instead.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants propose that non-linear mechanical systems could mix frequencies, potentially generating both sum and difference frequencies from inputs.
  • Others argue that while non-linear systems may create harmonics, they are less likely to produce subharmonics from a single frequency input.
  • A participant suggests that mechanical oscillators with high Q factors could be analogous to lasers, emphasizing the importance of frequency locking rather than amplification.
  • Another participant challenges this view, stating that lasers are not merely high Q oscillators but also require amplification, raising questions about how a mechanical oscillator could incorporate amplification.
  • There is a discussion about the possibility of a mechanical system that absorbs waves at a specific frequency and transforms them into waves at another frequency, possibly accompanied by other forms of energy like heat.
  • Some participants express skepticism about the feasibility of a mechanically pumped "laser," while others explore the idea of coherent sound waves as a potential area of interest.
  • One participant mentions the analogy of optical amplifiers and discusses the differences between lasers and amplifiers in terms of signal amplification.
  • There is a request for resources on coherent sound waves and their mechanical amplification, indicating a desire for further exploration of the topic.

Areas of Agreement / Disagreement

Participants express differing views on the nature of lasers and their amplification mechanisms, with no consensus reached on the feasibility of a mechanical analog to an optically pumped laser. The discussion remains unresolved regarding the specifics of mechanical wave amplification and the potential for creating a mechanical laser.

Contextual Notes

Participants note the complexity of defining amplification in the context of lasers and mechanical systems, highlighting the need for clarity on terms and concepts. The discussion also reflects uncertainty about the practical implementation of mechanical systems that could achieve the proposed effects.

androz
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Hi there !

I have a question : does a mechanical system generating a lower frequency
when excited with a hig frequency exists ? In this case, would it be possible to start stimulated processes of emission of a lower frequency from a high frequency ? Then, we could imagine a kind of laser not made with photons but with mechanical waves like water waves...
 
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If you have a non-linear mechanical system, you should certainly be able to "mix" frequencies.

I.e. if you have frequency f1 and f2 as inputs, you should generate some components with frequency f1+f2 and some with frequency f1-f2.

However, if you only input a single frequency, I think a non-linear system will generate harmonics (f*2, f*3, etc) but not subharmonics (f/2, f/3 etc).

This is commonly done with non-linear electrical systems rather than non-linear mechanical systems, but the math is the same. A non-linear electrical system that adds frequencies is called a "mixer".
 
Any mechanical oscillater with a high Q factor is analogous to a laser. The defining charactersitic of a laser is not the amplification it can provide, but rather the narrow frequency range that the energy becomes locked in.

Claude.
 
I don't entirely agree with you Mr. Bile.
A laser is not only a high Q factor oscillator, it is also an amplifier placed in an oscillator. I can imagine a mechanical oscillator but I have more difficulties to imagine an amplifier.
My idea concerns water waves, they can be reflected by walls, diffracted ... we can do a lot a things with periodic arrays of obstacles like we do in optics. But the question I have is can we find a mechanical system, for water waves, that would absorbe the wave at a given frequency, and "transform" this wave in another wave at another frequency plus something else like heat or whatever ??
I have just read an interesting article this week in Physical Review Letters about refraction of water waves by periodic cylinder arrays. The results is quite similar as what we observe in optics. This is a very interesting article and subject. Imagine we could find an amplifing media for those waves, then we could easy reproduce the equivalent of a laser with water waves ! Water waves are easier to see and the time scale also is interesting. I was wondering how far we could investigate the analogy ??
 
Despite the acronym, lasers do not amplify anything. The correct acroynm for a laser is Light oscillation by stimulated emission of radiation, however this would result in the unfortunate acronym of 'Loser'. Lasers posses gain, but this is not necessarily synonymous with amplification.

You CAN have light amplification, but such devices do not have any feedback Erbium doped fibre amplifiers for example are true amplifiers.

Using an electrical analogue, a laser performs exactly the same function as an electrical oscillator, not an amplifier.

Claude.

P.S.

androz said:
But the question I have is can we find a mechanical system, for water waves, that would absorbe the wave at a given frequency, and "transform" this wave in another wave at another frequency plus something else like heat or whatever ??

Essentially you are asking whether it is possible to pump a mechanical 'laser' with another mechanical wave, analogous to an optically pumped laser. Many lasers are not optically pumped, they are pumped by other means, so you don't necessarily need to pump this 'laser' with a mechanical wave.
 
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Despite the acronym, lasers do not amplify anything. The correct acroynm for a laser is Light oscillation by stimulated emission of radiation, however this would result in the unfortunate acronym of 'Loser'.
Thank you for the exaplanation, but I am aware of the little history ... In fact I do not really agree with you when you say that a laser do not amplify anything. Yes it is an oscillator, but it is also a gain medium as an amplifier. From noise, you amplify the signal coherently at each pass in the oscillator (stimulated emission).
Using an electrical analogue, a laser performs exactly the same function as an electrical oscillator, not an amplifier.
Yes I know, but what you omit is that it is an oscillator PLUS a source term which represents the atoms in the media. You do not amplify the light going through the active media, but you amplify the light generated in the active media. Laser effect occurs however when resonance if achieved, or you generate only ASE. So you need an amplifier AND an oscillator.
Many lasers are not optically pumped, they are pumped by other means, so you don't necessarily need to pump this 'laser' with a mechanical wave.
Of course yes, but if such a "laser" is not pumped mechanically, my question wouldn't have any sense.
 
androz said:
Thank you for the exaplanation, but I am aware of the little history ... In fact I do not really agree with you when you say that a laser do not amplify anything. Yes it is an oscillator, but it is also a gain medium as an amplifier. From noise, you amplify the signal coherently at each pass in the oscillator (stimulated emission).

I see where you're coming from, I guess it depends on what you refer to when you say amplification. From a signals perspective, the laser, as a source, cannot amplify a signal, it simply emits coherently over a narrow range of frequencies. A true amplifier can amplify a signal, such optical amplifiers are simply lasers without mirrors (such as EDFAs).

I'm not trying to argue that your point of view is invalid, I am just explaining where I was coming from in my earlier comment.
 
Thank you Claude for all.
I don't want to argue on lasers which are my research area. All I wanted to know is if it exists an equivalent optically pumped laser in mechanics, a mechanically pumped "mechanical laser" ?

PS : an optical amplifier amplify the signal coherently too.
 
androz said:
Thank you Claude for all.
I don't want to argue on lasers which are my research area. All I wanted to know is if it exists an equivalent optically pumped laser in mechanics, a mechanically pumped "mechanical laser" ?
PS : an optical amplifier amplify the signal coherently too.

I am not an expert, although I am well versed in some aspects of physics.
Anyway, if I am understanding your question correctly, I doubt that what you propose is possible if you are referring to photons. If you are referring to creating a mechanical system that creates coherency with sound waves, yes, that is possible.
However, there IS a way to "mechanically" amplify a light source non-coherently, but the technique somewhat depends on "non-use" of the resultant amplification. For example, take a laser light and direct it at a mirror.
Now, from that reflection beam have another mirror that directs it to the same point as the reflection.
Minus reflection losses, one ends up with an almost doubled intensity impact on the first mirror.
 
  • #10
Hi Pallidin,

I'm referring to photons, but to mechanical waves.
Your example of the coherent sound waves interest me a lot. If you can direct me on a web link, an article, or whatever, that's would be appreciated.
I was in fact more interested with water waves, a way to amplify them mechanically an place them in a mechanical oscillator...
 

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