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Bigrating Laser Beam-Riding Light Sail Is Self-Correcting

A light sail consisting of a bigrating (two opposing diffraction gratings) has been experimentally demonstrated for the first time. The designed prototype is self-correcting.


(Bigrating solar sail)

A technology for propelling spacecraft using a “sail” pushed by light has passed an initial test, with the prototype device staying centered in a laser beam.

An optical beam rider making use of a light sail comprising two opposing diffraction gratings is experimentally demonstrated for the first time. We verify that the illuminated space-variant grating structure provides an optical restoring force, exhibiting stable oscillations when the bigrating is displaced from equilibrium. We further demonstrate parametric cooling by illuminating the sail with synchronized light pulses. This experiment enhances the technical feasibility of a laser-driven light sail based on diffractive radiation pressure.

(Experimental Verification of a Bigrating Beam Rider)

The basic idea for the laser beam/light sail propulsion system belongs to Robert L. Forward, who published a short paper Ground-Based Lasers For Propulsion In Space in 1961. (Read a short autobiography of Robert Forward.) Dr. Forward gives a more detailed version of the idea in his 1985 novel Rocheworld; see the entry for Interstellar Laser Propulsion System.

The idea of using a laser beam to power a light sail spacecraft was famously used in Niven/Pournelle 1974 classic Mote in God's Eye:

"Captain, look," he said, and threw a plot of the local stellar region on the screen. "The intruder came from here. Whoever launched it fired a laser cannon, or a set of laser cannon - probably a whole mess of them on asteroids, with mirrors to focus them - for about forty-five years, so the intruder would have a beam to travel on. The beam and the intruder both came straight in from the Mote.

(Read more about laser cannon)

The earliest use of a light sail was probably in The Lady Who Sailed The Soul (1960), by Cordwainer Smith; see the entry for Starlight Sail (Light Sail).

Thanks to @nyrath (Winchell Chung) for tweeting this item.

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