3 ms·

That is partly true, there is no way a chip based laser can achieve the divergence even for a 1,860 million mile path. Chip geometry is intrinsically too diverg

That is partly true, there is no way a chip based laser can achieve the divergence even for a 1,860 million mile path. Chip geometry is intrinsically too divergent. A pumped self collimating fiber 1/1000 light second long = 186 miles, coiled in a large loop might not do it. I would have to look up the limits of self collimation? That said, we do not progress with leaps in thought and technique.

ben_w 5y ago
Why do you even want self collimation? Can’t it just focus the laser light with a (very) big mirror on the sending side? (Genuine question; my physics isn’t at that level).
- aurizon 5y ago
  This is commonly used in fibers, a gradual gradient in the refractive index from the center to the edge automatically steers the beam to the core path. Focus has limits, you can focus the sun to an image but not to a zero dimension point, although you can not focus stars to an image, they are so far away they are essentially parallel = many many light years so they appear to be a point and for most uses they are..
  - ben_w 5y ago
    That doesn’t really tell me why you are suggesting this in this case. Naturally all things have limits, but the question is which is limited least? As the goal here is to get as much power as possible on a very small thing up to 3 million km away, surely you can just work backwards from the wavelength to the mirror size you need to get that focus. I think they’re planning to use a phased array of laser light here because no single mirror is big enough, but the same principle applies. Isn’t the limiting factor the aperture anyway?
    - aurizon 5y ago
      I hope an optics person can weigh in here for a detailed tech response. In essence if the laser was perfectly parallel it could then be focussed down to a point image as small as the source. How to get a true point - the fiber gradient is all I can think of - and that might have limits. Then adding power - at some point there will be a limit. Even a beam 10 seconds long is a long way in terms of a small beam spread. True, you can waste power, amplify the beam to 100x the power needed might work. Then can the chip withstand this power level at the start? Strange things happen at the atomic level at these power levels - some people feel it may be able to change how atoms decay = accelerate the decay of nuclear waste if the waste is first fractionated to pure radionucleotides first - of course if we did that the storage needs would shrink dramatically, obviating a lot of the problem - my guess is $$ is one barrier?

ben_w 5y ago

Why do you even want self collimation? Can’t it just focus the laser light with a (very) big mirror on the sending side? (Genuine question; my physics isn’t at that level).

aurizon 5y ago
This is commonly used in fibers, a gradual gradient in the refractive index from the center to the edge automatically steers the beam to the core path. Focus has limits, you can focus the sun to an image but not to a zero dimension point, although you can not focus stars to an image, they are so far away they are essentially parallel = many many light years so they appear to be a point and for most uses they are..
- ben_w 5y ago
  That doesn’t really tell me why you are suggesting this in this case. Naturally all things have limits, but the question is which is limited least? As the goal here is to get as much power as possible on a very small thing up to 3 million km away, surely you can just work backwards from the wavelength to the mirror size you need to get that focus. I think they’re planning to use a phased array of laser light here because no single mirror is big enough, but the same principle applies. Isn’t the limiting factor the aperture anyway?
  - aurizon 5y ago
    I hope an optics person can weigh in here for a detailed tech response. In essence if the laser was perfectly parallel it could then be focussed down to a point image as small as the source. How to get a true point - the fiber gradient is all I can think of - and that might have limits. Then adding power - at some point there will be a limit. Even a beam 10 seconds long is a long way in terms of a small beam spread. True, you can waste power, amplify the beam to 100x the power needed might work. Then can the chip withstand this power level at the start? Strange things happen at the atomic level at these power levels - some people feel it may be able to change how atoms decay = accelerate the decay of nuclear waste if the waste is first fractionated to pure radionucleotides first - of course if we did that the storage needs would shrink dramatically, obviating a lot of the problem - my guess is $$ is one barrier?