Recent content by androz

Hi all ! I've looked at a strange video on the net of an obscure compagnie that pretend to create electricity (5 times more energy than it consume). This video was very entertaining, I laughed a lot. But, there was something special that intrigate me... The pseudo-scientist take a permanent...

Hi, You're welcome. I doubt that Bessel beams are simpler to deal with mathematically... In fact, gaussian beams are really useful. All you need is the beam waist and the radius of curvature to entirely define a gaussian beam in the paraxial approximation. And what is VERY useful, is that...

I've found some interesting links for your question pervect. So the first man who have proposed the discussed term "nondiffracting beam" is named J. Durnin, and the first time was in 1986-1987. Another man has published a lot in this area : Z. Bouchal Here are some links to the subject. The...

Well... I've only read articles in scientific publications like the ones of the Optical Society of America or whatever. But I don't know anything that is free. If you are not so far from a university, perhaps I could search for some references and give them to you. I'm not sure I am allowed to...

I would like to add something to this discussion. There are beam that are not affected by diffraction too much. Those beam shapes are called non-diffracted beams. A good example is Bessel like beams. Bessel beams can be generated with axicon (conical lens). With this special lens, you can...

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...

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.

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...

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...

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...

Hi all ! Ok, I'll try to give you some new informations (I don't have read all the replies so forgive me if I say something already said). Well, it is possible that an electron in an excited state absorbs another (pump) photon to be in a much higher energy level. Such a mechanism is known...

Hi all ! There is a question I can't find an appropriate answer. Conceptually, I can see what is ASE (amplified spontaneous emission) in lasers such as fiber lasers, but... what information does a measurement of the ASE spectrum give to us ? I know that reducing the ASE is of great...

Light velocity... Hi, There is a question that I can't figure out. What's the difference between signal and group velocity for a light pulse ? What I understood so far is that the signal velocity is the velocity of the first detectable photon and the groupe velocity is the velocity of...

Thank you very much Zz. The phonons ever wake up my interest but I didn't ever have a good idea of how it can interact whith EM wave. I think I understant better now. How could I go farther in this area, just for my culture ? Are there articles or books I could read on the subject ?

Thank you Zz do you mean that in a glass for example (phonon that are not well defined) the band structure of the phonons is extended and that there are more energy band permitted ?