# Tag Info

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Regarding to your logic, the total amount of electrons at states with E2 and E3 altogether could be bigger than at ground state (with E1). It is inversion, isn't so? Thus the thermal invertion could be realized in three-level scheme but it is impossible at two-level system.

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I'll take a stab at this, although I am not an expert in the laser fields. Negative temperatures likely do not work: One concept that may seem closely related to the possible "thermal excitation of a laser" is that of "negative temperature". In a state of negative temperature higher energy levels have higher occupation probabilities than lower ...

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About 30 GHz, according to this. Check "Bandwidth-limited Pulses". Because of Fourier transform, the product of the temporal duration and spectral width is ≈ 0.44 for Gaussian-shaped pulses. See also this.

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The simple answer is no, but that's because two separate laser beams cannot directly "com(ing) from same direction". Any two beams from separate sources which shine on a target with the centers aligned will have slightly different angles, and the distances from the emitter (and therefor the relative phase) will vary with location on the target. It's true ...

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For two perfect laser sources without noise (infinite narrow linewidth) and of same amplitude, you could achieve this when both sources have the same frequency and same polarization. You need to control the length of one pathway to control the relative phase to $\phi_0=\pi$: $E=E_1+E_2=E_0 (sin(\omega t)+sin(\omega t+\phi_0))$ The problem in general will ...

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It depends, if the frequency is identical and the waves are in the same phase, they do not cancel out. Only when the phase is exactly 1/2 out of phase, they will completely cancel out.(if you point them from the exact same location) !http://cns-alumni.bu.edu/~slehar/PhaseConjugate/PhaseConjugate_files/image009.jpg You can take a look here. This aren't two ...

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CO2 lasers tend to be very high power. Often they will have 100 W in the beam. They can be much higher. Some will burn through safety goggles about as fast as you can blink. Optical elements used with such lasers need to be designed for such power. When light strikes a coating, it is transmitted, reflected, or absorbed. Absorption must be kept down to a few ...

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Your laser cavity is a Fabry-Pérot interferometer. The free spectral range tells you how close two neighboring laser modes can get: $\Delta \nu=\frac{c}{2nl}$ (for a linear resonator, length l, refractive index n). The resolution of your spectrometer needs to be smaller than this free spectral range. You can increase the free spectral range by either ...

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Each laser is made up of three main part: pump, amplifying medium and cavity. White laser is semiconductor laser; which means the amplifying medium is a semiconductor. In semiconductor lasers, pumping is electrical; which means the amplifying medium requires electrical power to be stimulated. The semiconductor of the white laser is an alloy made of zinc, ...

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The semiconductor lasers that are used to produce white light are powered by electricity, so that solves your problem. As lasers emit monochromatic light (1 single frequency or colour), they cannot be white. To get white laser light, you start with a blue laser. This blue light is directed at some phosphorescent material (a "phosphor") which, when activated ...

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For practical purposes we can say that laser light only moves in one direction and that its intensity at any point that is in line with the laser light is independent of distance. That is not the case, depending on what exactly you mean by "for practical purposes". If you are using a laser beam to illuminate a target that is larger than the divergence ...

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There are two different answers which might be "reasonable" to this question. Taking your question very literally, laser light, by definition, is light amplified by stimulated emission from a pumped gain medium with population inversion. In practice, one of the easiest ways of exploiting amplification by spontaneous emission is through multiple passes of ...

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Dynamical point of view: below threshold, the only stable solution for a laser is $I=0$. At and above threshold, $I=0$ is still a solution for the system, but it looses its stability, and another solution with $I>0$ becomes stable. Above threshold, the system can fall out of the unstable solution $I=0$ (and land on the new stable one $I>0$) only if ...

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For gamma-ray wavelengths a much better alternative are Free Electron Lasers, since their gain medium is the Bestrahlung and synchrotron electron radiation inside the undulators. They also have the benefit of not being constrained to a nuclear energy state, and they can operate on a range of wavelengths

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Positive dispersion means that the lower frequencies are ahead of the higher frequencies in time, and this is caused by the fact that the crystal's group index (derivative of refractive index) is smaller for lower frequencies, giving them faster group velocity going through the crystal. To compensate, the pair of prisms gets the higher frequencies to catch ...

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Very Short and Quick Answer Yes, it is possible so long as one has a large enough set of mirrors and the focal points are determined accurately enough (ignoring heat dissipation, which might be an issue in space). There is a solar furnace in France that does just this, though it is based on ground and has on the order of 10,000 mirrors, each of which ...

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Also, if the mirror you use is not surface silvered (or aluminised), there will be internal reflections between the front surface of the mirror, and the silvered rear surface. This show up any imperfections in the mirror - ie its surfaces not being flat, and any irregularities in its composition. These will all result in light being scatterred, rather than ...

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There are 2 things: you might see a spot on the mirror itself, especially if dirty or poor quality surface. you already see a laser beam going toward your eye even when you are a bit out of its axe (and you should better put your eye out of its axe !). It's because a bit of light is scattered in light, and at at grazing view angle (either direct or through ...

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