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You assume that a laser beam is a single, fine line—as if it would project one tiny, millimeter-wide red dot. But all practical lasers produce divergent beams. You can arbitrarily narrow the beam by shining it out through a telescope, but I'm pretty sure that the narrowest beam we can practically generate still will illuminate many square miles of the lunar ...

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The papers described in the report you've linked to demonstrate examples of sound amplification by spontaneous emission. This is independent of the characteristics of the waves that those source produce. As it happens, for sound (as opposed to light) it is relatively easy to create waves that have high spatial coherence and well-defined wave vectors $\vec k$...

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It is an insightful question, and the answer is "Yes". What you describe is often called "frequency mixing", and can be used to generate practically any wavelength we want. Note, however, that to modulate a laser at 100 THz, you need a source to produce a 100THz signal. And, by the way, you seem to be mixing up wavelengths and frequencies. 630 nm (...

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You will need at least three states for lasing to occur (with reasonable probability) but that does not mean that other states cannot be present. If the pump frequencies are not tuned to reach these other states then they will not be occupied with any appreciable probability and hence will not influence the lasing process.

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The extinction in the atmosphere is a function of atmospheric conditions, dust and aerosol concentrations, the angle to the vertical the laser is fired at, and of course the wavelength. A typical value at 589 mm (sodium laser) in a clean atmosphere and a vertical beam would be about a 15% attenuation. It could easily be a factor of a few worse in more ...

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Well, sorry for the short answer, but "laser flux power density" is just $I_0$, which is the power per unit surface area (which is why it is called flux power density) and the Raman intensity is proportional to $I_R$, so by this equation you can see that when $I_0$ increases, so does $I_R$

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In this link stimulated emission is explained in the third page: Note that the energy of the incoming photon doing the stimulation is $E_2-E_1$ the two energy levels . This means the first photon passes and a second one comes out, which when conditions are appropriate can lead to the lazing phenomenon. This is with pictures and words, but coherence is a ...

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I can rule out momentum transfer from the laser. Even though radiation pressure is a thing, it is far too low to be noticeable. Let's do the math: Radiation pressure p=I/c (c speed of light) is determined by the intensity I of the laser beam. Since pressure in general is p=F/A (F Force and A Area), you get F=I*A/c for the force that results from the ...

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1- 50/50. At the point of inversion both probabilities are the same. 2-I think you are missing some key points here. You always need to include the energy structure. For example in a 4-level system: $E_0$ ground level, $E_1$ upper pump level, $E_2$ upper laser level, $E_3$ lower laser level. The inversion between ground state $E_0$ and upper-pump level $E_1$...

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Given the terms you're using, I'll assume you're asking about a current-pumped diode laser. The key additional information you need is the carrier lifetime due to nonradiative recombination and spontaneous emission events, call it $\tau_R$. Then the current required to maintain a carrier density of $N$ is $$I=\frac{qNV}{\tau_R}$$ where $q$ is the ...

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