Light Beamer | Atmosphere

The atmosphere introduces two effects: absorption (or ‘reduction of transmission from unity’), and loss of beam quality (or ‘blurring of the beam spot’). The transmission of the atmosphere at a wavelength of 1 micron is extremely good, exceeding 90% at high altitude ground-based sites. Going to a high altitude site also significantly reduces atmospheric blurring, which would allow an adaptive optics system to achieve performance near to the diffraction limit.

The effects of atmospheric turbulence on the beam include a broadening of the beam footprint (equivalent to image blurring for telescope observations), random jitter of the beam spot, and intensity fluctuations (or ‘scintillations’). The blurring depends on turbulence and wind profile in the atmosphere. The turbulence amplitude is reduced by a factor of approximately 4 between sea level and an altitude of 5km.

The quality of an image is measured by the Strehl ratio, which reflects the ratio of the peak image intensity from a point source to the diffraction limit of an ideal optical system. The ratio measures phase deviations caused by lens aberrations and atmospheric turbulence. 10m-class telescopes, such as the Large Binocular Telescope (LBT), comprising two 8.4m telescopes, have demonstrated image resolution of 40 milliarcseconds and Strehl ratio of 80% at a wavelength of 1.6 microns.

Breakthrough Starshot aims to achieve the diffraction limit for an optical system of laser beams across 0.2-1km, which is 1-2 orders of magnitude beyond existing demonstrations. There are no fundamental physics limitations to achieving this improvement. A beacon on the nanocraft or near its launch point (for instance on the mothership) could be used to correct for phase variations in real time. The effect of the light beam on the atmosphere could be studied, and corrected for, by adaptive optics, again in real time. Additional beam focusing may also be explored to reduce the beam spot size using pulsed laser filamentation techniques.

Jul 05, 2020 08:50 Posted on: Breakthrough Initiatives

Would it be possible to build it on the far side of the moon? I realize that if we were to do this today it would cost an enormous amount of money, but say 30 years, or so, from now we have a lunar base set up and we’ve begun to make use of the moon’s resources, could that be a viable option?

Jul 29, 2020 18:37 Breakthrough Initiatives Posted on: Breakthrough Initiatives

Thanks for your comment, Daniel. The Breakthrough Starshot effort is designed to send a probe to Alpha Centauri at the lowest cost and highest reliability. The primary effort (and funding) is focused on the ability to coherently combine a near infinite number of lasers. This effort will benefit the program no matter where the installation is placed. Currently, our estimates of the economics of space flight suggest that the cost to place an installation on the far side of the moon is many trillions of dollars. However, if great advanced are made in lift and the price of lift drops to some very small fraction (1% ) of current costs we would consider the cost and risk dealing with the atmosphere versus of placing the installation beyond the atmosphere. But we have many years before this choice needs to be made.

Pete Klupar
Engineering Director
Breakthrough Initiatives

Aug 08, 2020 11:47 Sahil choudhary Posted on: Breakthrough Initiatives

We should set the sources of beam out in space just like we have hubble in space due atmospheric effects.......
Or we can set the beamers on moon in near future

Aug 26, 2020 19:08 Philip Lubin Posted on: Breakthrough Initiatives


Great question.

In the long term space would be preferable from the point of view of avoiding atmospheric perturbation issues. The Moon is a possibility we have discussed for the distant future but space is vastly more expensive to deploy that is an Earth based system. For example, currently the cost to place 1 kg (~2.2 pounds) on the lunar surface is about 1 million USD). This cost will come down as increased heavy lift capability arises but the costs are still daunting for large structures in space. At the moment we do not feel that space deployment is required. More data is needed (see below). Since we are based on an exponential technology (photonics), time is on our side as the system costs will drop dramatically with time and we still need many years to develop all the technology required.

If it turns out that we cannot mitigate the Earth's atmosphere well enough then space remains an option albeit a very expensive option. Before going to space it is important to work out the system issues and to find the limitations as much as possible on the Earth. As you no doubt know, ground based telescopes work remarkably well with modern adaptive optics in mitigating the Earth's atmosphere and though we do have space based observatories, including the HST and soon the JWST among many others, the largest telescopes are Earth based. For some astronomy applications space is essential (X-Ray, UV, far IR) but for visible and near IR the Earth's atmosphere is extremely transparent, though turbulent. Much of our effort on the laser array (photon engine) will focus on adaptive optics through the use of exo-atmospheric beacons to measure the phase on the Earth and correcting for it. Finding the limits of this are part of our future testing program.

If you are interested in a technical discussion of this point see one of our recent papers:
"Beam propagation simulation of large phased laser arrays"

Philip Lubin
UC Santa Barbara/ Starshot

Nov 15, 2020 00:43 John Weiss Posted on: Breakthrough Initiatives

Don't launch from the moon, just launch from a high-altitude earth satellite.

Feb 11, 2021 12:31 Posted on: Breakthrough Initiatives

There was a ''Science Alert'' article by Mike McRae a couple of weeks ago with the title "Groundbreaking New Laser system cuts through Earth's Atmosphere like it's nothing" . The article states that this is a French & Australian project with ''Lead author Ben-Dix Matthews, an electrical engineer with the International Centre for Radio Astronomy Research in Australia'' .

Would this make it possible to build another 100GW Phased Laser Array in outback Australia which has low altitude deserts instead of high altitude deserts like those in Chile ,etc?.

A forgotten source of potential power in Australia that could power the Laser , generate all of Australia's electrical power needs & probably use leftover electricity & seawater to produce Hydrogen fuel for export is tidal hydroelectric power generation in the Kimberley region of North West Australia. The Institution of Engineers (Australia) calculated in the 1970's that there is a potential 270 GW of power available (if you build the infrastructure) ,which at the time was 700% of Australia's electricity generating capacity.

I hope the Australian Government could fund ($10 Billion?) & own this project to help with Breakthrough Starshot and to do other things like Laser Ablation of space junk , deflection of meteors & asteroids . One function that nobody seems to mention but would be vitally important in defending Australia - Ballistic Missile Defense - existing missiles used in other countries such as Standard Missile 3 Block 2A or Arrow 3 are good but expensive & not 100% reliable - they need a good Laser backup .
Professor Hugh White wrote a book -''How to defend Australia'' & much of what he has written is good- an island continent nation surrounded by seas & oceans can protect itself from naval attacks with long range anti-ship missiles .
The bad or ugly part is the consideration of developing a British style Nuclear submarine fleet armed with Trident like Submarine Launched Ballistic missiles carrying Nuclear warheads . He explains in his book how the British had to plan in Dr Strangelove style for the death of tens of millions of Russians in order to deter a Soviet Nuclear attack on Britain. In addition to this Dr Strangelove nightmare ,it would cost a fortune ,perhaps $200 Billion or more & take a decade or longer to build . A much better way , I pray , is that we could vaporize or at least deflect ICBMs , multiple warheads , decoys , Hyper-sonic Glide Missiles, etc - like that other Doctor tried almost a century ago - Dr Tesla & his plans for a ''Teleforce'' directed energy weapon that would destroy aircraft in the air 200 miles away .

Mar 29, 2021 16:31 Wesley Green Posted on: Breakthrough Initiatives

Nov 15, 2020 00:43 John Weiss

As Klupar and Lubin have noted the cost required to launch such a system is prohibitively expensive for the time being, whether to the moon or to an orbit. Because of advancements in adaptive optics and phased array technology, avoiding the atmosphere is not necessary. Power reducing effects from scattering, absorption, focus anisoplanatism, and ordinary anisoplanatism can be limited by site selection and orbiting beacon designs, but some losses are still to be expected. Currently the cost of those losses pale in comparison to the cost of launch.

Wesley Green, Breakthrough Starshot

Apr 30, 2024 13:16 Michael Streeter Posted on: Breakthrough Initiatives

I read with interest the comments starting in 2016 to date and the number of times people have said "put it in space" and the response has been "we only have $10b - it's too expensive".

I just came to say now (2024) there's a British company (Oxfordshire-based Space Solar, probably many other companies around the world) that have concrete plans for space to ground power of 2GW. According to them, an independent techno-economic assessment by Frazer-Nash Consultancy (summary report available), concluded that a development programme would cost around £17Bn, including the first of a kind commercial power station in space. Production costs would not follow Moore's Law, they would follow Wright's Law (the more times a task has been performed, the less time -- and money -- is required on each subsequent iteration). After the first station they believe the capital cost of the subsequent production systems to be about £3.6 Bn for a 2GW system, so it hopefully won't be science fiction for much longer. If they can get the cost below £2Bn then maybe it won't be too expensive for Starshot any more either. I now think this is how things at SS will end up. Space Solar version 1 wants to go operational in the 2030s.

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