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| Wave interference - If I shine 2 lasers on a spot,will there be actual blinking? |
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| CatalinaWOW:
It all boils down to the details. Not only would the two lasers have to be 2 Hz away, but the line widths would have to be much less than 2 Hz. Lasers aren't actually monochromatic, just very narrow band. I haven't run the numbers, but you would have to operate said lasers very cold to get thermal noise that low, and thermal is just one of the sources. Think of things like doppler on the end mirrors from vibration and piezo effects. That one part in ten to the 14th is tough. It may be possible theoretically (not even sure of that), but in practice it just can't be done. |
| awallin:
--- Quote from: CatalinaWOW on January 21, 2016, 05:24:54 pm ---It all boils down to the details. Not only would the two lasers have to be 2 Hz away, but the line widths would have to be much less than 2 Hz. Lasers aren't actually monochromatic, just very narrow band. I haven't run the numbers, but you would have to operate said lasers very cold to get thermal noise that low, and thermal is just one of the sources. Think of things like doppler on the end mirrors from vibration and piezo effects. That one part in ten to the 14th is tough. It may be possible theoretically (not even sure of that), but in practice it just can't be done. --- End quote --- <=1 Hz linewidth lasers are built quite routinely now in many many groups around the world working on optical clocks or other precision experiments. Most of these lasers are stabilized to a Fabry-Perot cavity made from a low thermal expansion material (Zerodur, ULE glass, single crystal silicon). The cavity is put in a vacuum chamber with thermal shields and good thermal control. Thermal time-constant of days or weeks. Choose a material with parabolic thermal expansion and operate it where the slope is zero. When all other technical noise sources are suppressed what remains is thermal noise, mostly from the multilayer mirror coatings. The latest development is crystalline mirrors (instead of conventional multilayer dielectric mirrors) which have low thermal noise. Here is a fun video, from the Hänsch (2005 Nobel prize) lab AFAIK: |
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