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The Breakthrough Starshot initiative aims to accelerate a swarm of 16m$^2$-area solar sails to 15% of $c$ using Earth-based lasers in the order of 100GW power in 10 minute bursts. Considering loses from various medium densities and temperatures of the atmosphere they estimate the sails to receive 60 times the amount light that the Sun provides.
Sunlight in Space is abundant, 8% of its spectrum is ultra-violet light which is more energetic, and has an intensity of around 1000 W/m$^2$.

Could the gigawatt lasers be replaced entirely with an apparatus, in Space, that would be some arrangement of Fresnel lenses, lenses, mirrors and crystalline materials so as to forward and beam pumped sunlight to the sails, possibly for longer exposition times?
If yes, what would be the size and composition of such an apparatus, roughly?

Somewhat of a follow up question: what kind of heat would such a beam of sunlight-turned-coherent carry in relation to distance from the spacecraft?

fenollp
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Because of its angular width (low spatial coherence), the sun's light cannot be focused to a small (meter-sized) spot at large distances. Any kind of lens arrangement can at best form an image of the sun.

However, large arrays of photovoltaic cells could certainly be used to power a laser array for Starshot. A laser beam with a large (kilometer-scale) aperture can be focused to the requisite meter-scale spot at interplanetary distances because it has very high spatial coherence.

S. McGrew
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