Episode #125 of the Stack Overflow podcast is here. We talk Tilde Club and mechanical keyboards. Listen now

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6

In a two-level system you can have stimulated emission, but you can't have gain. No gain, no laser amplification, no laser. Stimulated transitions work both ways with equal probability: up and down. As long as there is more population in the lower state there will be more "ups" than "downs", that is more absorption than gain. The best you can do is to ...


4

When light is reflected from objects with a well defined colour, we perceive the reflected light as this colour because it reflects this colour. But the truth is that other wavelengths are also reflected, but less of it. The absorption of light is typically $\alpha < 1$ but still $\alpha_{yellow} \gg \alpha_{green}$ for example. Our eyes perceive the ...


3

Your description of rotating by 90 degrees doesn't make any sense. You show an image from one plaque "5th place" then talk about rotating 90 degrees and show an image from another plaque "4th place". It's not clear if this is meant to show the "90 degrees rotated" behavior or just that you see similar behavior for different plaques. In any case what you are ...


3

"electrons' frequency" does sound ambiguous. It should be the plasma frequency. For example explained in here: Testing one of those promising mechanisms became possible by operating in the relativistically induced transparency (RIT) regime. RIT comes about in a laser-heated electron plasma when, because of the increased relativistic electron rest mass, ...


2

It is pretty easy for a focused, pulsed, laser beam to vaporize a metal surface MUCH faster than any reasonable cooling system could remove the heat. A graphite coated surface would absorb light more easily than a typical metal surface, so would vaporize even more easily. For a high power continuous (not pulsed) beam, a better defense might be to make the ...


1

The laser projects onto the plaque which causes a reflection onto the roof. On the vertical plane, the laser projects directly into a slit which causes diffraction of the light. This is why the second picture looks like a "stick" of light. But on the horizontal plane, think backwards. The projection onto the roof comes from the laser hitting it at an ...


1

When I was studying for the physics GRE I used the book Conquering the Physics GRE by Kahn and Anderson. There are laser questions, but usually there will probably just be one question. There is a section in this book that covers the basics of what you need to know for the various laser types. I don't think you need anything beyond what is covered in this ...


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