Photonic Crystals Could Be Exactly What Breakthrough Starshot is Looking For. Light sail technology is a fascinating concept and a step change in rocket propulsion.

photonic crystals could be exactly what Breakthrough Starshot is looking for. Breakthrough Starshot is a space exploration initiative that aims to send a spacecraft to the habitable zone of the planet Proxima Centauri b. 

Photonic crystals are optical nanostructures that can be used to manipulate light. They have a periodic structure that can create a photonic bandgap, which is a range of “forbidden” frequencies. Photons with energies in the bandgap cannot pass through the medium.

Photonic crystals (PCs) are highly ordered materials that can control the propagation of light. They are optical nanostructures with a periodically changing refractive index

PCs have a photonic band gap (PBG), which is a range of frequencies where light propagation is forbidden. Electromagnetic waves with frequencies in the PBGs cannot propagate in the structure. 

PCs can confine light in a small area and improve the interaction between light and material. They can achieve high propagation speed and high frequency with no interaction. This has advantages in sensors, solar cells, filters, and infrared stealth applications. 

Opals and the wings of the Blue Morpho butterfly are examples of naturally occurring photonic crystals

Lightsail technology, also known as solar sails and photon sails, uses radiation pressure from sunlight to propel spacecraft

Light sail technology is a concept that uses sunlight to propel spacecraft. It involves deploying large, reflective sails that capture the momentum of photons from the sun

Light sails have several advantages over traditional propulsion systems: 

• Endless propellant: Light sails don’t rely on limited fuel reserves. 
• High speed and efficiency: Once accelerated, light sail spacecraft can reach high velocities, making interstellar travel possible within human lifetimes. 

Light sails are also known as solar sails and photon sails. Since the 1980s, several spaceflight missions have been proposed to test solar propulsion and navigation. 

In 2010, the Planetary Society’s LightSail program was initiated to advance solar sail technology. In 2019, LightSail 2 was launched and demonstrated the first controlled solar sailing in Earth’s orbit using a CubeSat. It remained in orbit until late 2022.

Breakthrough Starshot is a research and engineering project by Breakthrough Initiatives. The project aims to develop a fleet of light sail interstellar probes called Starchip. The probes are designed to be ultra-lightweight, light-sail, and capable of traveling tens of trillions of kilometers at speeds approaching the speed of light. The probes are expected to reach the Alpha Centauri star system in 20 years

The project’s steps are as follows: 

1. A “mothership” releases tiny probes one at a time 
2. The probes ride the beams of a ground-based laser array 
3. The laser beam accelerates the probes’ sails up to one hundred kilometers per second 

The project also aims to establish whether nanocrafts can fly over a thousand times faster

Here are some reasons why photonic crystals are important: 

• Optical communications Photonic crystals could address many problems that currently constrain the integration technology of optical device and system. 
• Infrared stealth technology A photonic crystal structure can achieve a high propagation speed and high frequency with no interaction. This has advantages in sensors, solar cells, filters, and infrared stealth applications. 
• Light science applications Researchers have produced photonic time crystals in the near-visible spectrum, potentially revolutionizing light science applications. 
• Structural coloration The surfaces of morpho butterflies, jewel beetles, and opals also have fine periodic structures, and these exhibit unique brilliance, which is referred to as structural coloration. 

Photonic crystals manipulate material properties in space, creating band gaps in the frequency domain. This manipulation has led to various applications such as optical cavities, waveguides, and control of spontaneous emission

Eli Yablonovitch, a professor of electrical engineering and computer sciences at the University of California, Berkeley, proposed and created photonic crystals in the 1980s. He is also known as the “father of photonic band engineering”. 

Yablonovitch and Sajeev John introduced the term “photonic crystals” in 1987. They are engineered nanostructures that have a periodic arrangement of materials with different refractive indices. They can have a period in one, two, or three dimensions. 

Yablonovitch worked with microwaves to create photonic crystals because their longer wavelengths allowed him to develop periodic designs with spacings on the scale of a few millimeters

Here are some examples of photonic crystals: 

• Opal A naturally occurring gemstone that exhibits opalescence, which is a photonic crystal phenomenon. 
• Dielectric mirrors One-dimensional photonic crystals that can create ultra-high reflectivity mirrors at a specific wavelength. 
• Photonic-crystal fibers Two-dimensional photonic crystals used for fiber-optic communication. 
• Dielectric rods Periodically arranged in air, they are a common example of a two-dimensional photonic crystal. 
• Air holes Spaced in a dielectric block, they are a common example of a two-dimensional photonic crystal. 

Photonic crystals can also be found in nature, such as in the feathers of domestic pigeons, the wings of Morpho butterflies, and the barbules of male peacocks.

Photonic crystals are widely used in solar cells to improve their efficiency. This is because they can manipulate photon transmission and optimize the propagation and distribution of light. 

Photonic crystals are used in dye-sensitive and quantum-dot-sensitive solar cells, but less so in perovskite solar cells. 

Photonic crystals are also attractive optical materials for controlling and manipulating light flow. One-dimensional photonic crystals are already used in thin-film optics, such as low and high reflection coatings on lenses and mirrors, and color-changing paints and inks.

Breakthrough Starshot is looking for photonic crystals to help create a solar-sail-like structure that could be attached to an asteroid to block sunlight and reduce climate change

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