A blue laser was used to illuminate the ruby cube from the side while a high-power green laser was focused through it for the experiment. In order to produce a matched region in the illuminating light and a darker area that looks as a shadow of the green laser beam, the green laser increases the optical absorption of the blue illuminating laser beam.

Is it possible for light to cast a shadow? Researchers have discovered that, in some circumstances, a laser beam can behave like an opaque object and cast a shadow, which may sound like a philosophical conundrum. The finding casts doubt on the conventional wisdom regarding shadows and creates new opportunities for devices that could manipulate another laser beam with a laser beam.

“Laser light casting a shadow was previously thought impossible since light usually passes through other light without interacting,” said Raphael A. Abrahao, the leader of the study team from Brookhaven National Laboratory, formerly at the University of Ottawa. “Our demonstration of a very counter-intuitive optical effect invites us to reconsider our notion of shadow.”

In Optica, scientists explain how they demonstrated that a laser beam could block light and produce a visible shadow because of a nonlinear optical process using a ruby crystal and particular laser wavelengths. Light can affect another optical field when it interacts with a material in an intensity-dependent manner.

“Our understanding of shadows has developed hand-in-hand with our understanding of light and optics,” Abrahao stated. “This new finding could prove useful in various applications such as optical switching, devices in which light controls the presence of another light, or technologies that require precise control of light transmission, like high-power lasers.”

The new study is a part of a broader investigation of nonlinear optical processes and the interaction of two light beams under specific conditions.

Some experimental drawings created with 3D visualization software portray the shadow of a laser beam because they interpret it as a cylinder without taking into account the physics of a laser beam. This idea was first raised during a lunch chat. Could this be done in a lab? asked some of the scientists.

“What started as a funny discussion over lunch led to a conversation on the physics of lasers and the nonlinear optical response of materials,” Abrahao remarked. “From there, we decided to conduct an experiment to demonstrate the shadow of a laser beam.”

The researchers accomplished this by shining a blue laser sideways on a cube of regular ruby crystal and passing a high-power green laser through it. The material’s reaction to the blue wavelength is locally altered when the green laser enters the ruby. Whereas the blue laser behaves like illumination, the green laser behaves like a regular object.

On a screen, the interaction of the two light sources produced a shadow that could be seen as a dark spot where the blue light was blocked by the green laser. Because it was visible to the unaided eye, followed the outlines of the surface it fell on, and followed the location and form of the laser beam, which functioned as an object, it satisfied all the requirements for a shadow.

The ruby’s optical nonlinear absorption is what causes the laser shadow effect. The green laser produces a corresponding region in the illuminating light with reduced optical intensity by increasing the blue illuminating laser beam’s optical absorption. As a result, the green laser beam appears as a shadow in a darker area.

One of the most enduring mysteries of vertebrate evolution is how the distinct brains and intellect of contemporary birds developed, and a “one of a kind” fossil discovery could revolutionize our knowledge of this process.

An exceptionally well-preserved fossil bird from the Mesozoic Era, around the size of a starling, has been discovered by researchers. This is one of the most important discoveries of its kind since the entire skull has been preserved nearly intact, which is uncommon for any fossil bird but especially for one so old.

The researchers, lead by the Natural History Museum of Los Angeles County and the University of Cambridge, were able to digitally rebuild the bird’s brain, which they have called Navaornis hestiae, thanks to the remarkable three-dimensional preservation of the skull. Before the catastrophic extinction catastrophe that wiped off all non-avian dinosaurs, Navaornis thrived in what is now Brazil around 80 million years ago.

According to the researchers, their finding, which was published in the journal Nature, may serve as a kind of “Rosetta Stone” for figuring out the evolutionary history of the contemporary bird brain. The fossil closes a 70-million-year gap in our knowledge of the evolution of bird brains between the 150-million-year-old Archaeopteryx, the first known dinosaur that resembled a bird, and modern birds.

Given that its cerebrum was larger than Archaeopteryx’s, Navaornis may have possessed more sophisticated cognitive abilities than the first dinosaurs that resembled birds. But the majority of its brain regions, such as the cerebellum, were underdeveloped, indicating that it had not yet developed the sophisticated flight control systems found in contemporary birds.

According to co-lead author Dr. Guillermo Navalón of Cambridge’s Department of Earth Sciences, “the brain structure of Navaornis is almost exactly intermediate between Archaeopteryx and modern birds – it was one of these moments in which the missing piece fits absolutely perfectly.”

The fossil was found in 2016 at a location in the nearby neighborhood of Presidente Prudente, and Navaornis is named for William Nava, director of the Museu de Paleontologia de Marília in São Paolo State, Brazil. This location was probably a dry region with slowly moving creeks tens of millions of years ago, which allowed for the fossil’s remarkable preservation. Because of its preservation, the researchers were able to recreate the bird’s brain and skull in remarkably detailed detail using cutting-edge micro-CT scanning technology.

“This fossil is truly so one-of-a-kind that I was awestruck from the moment I first saw it to the moment I finished assembling all the skull bones and the brain, which lets us fully appreciate the anatomy of this early bird,” Navalón said.

According to the study’s principal author, Professor Daniel Field of Cambridge’s Department of Earth Sciences, “modern birds have some of the most advanced cognitive capabilities in the animal kingdom, comparable only with mammals.” “But scientists have struggled to understand how and when the unique brains and remarkable intelligence of birds evolved—the field has been awaiting the discovery of a fossil exactly like this one.”

The evolutionary transition between the brains of Archaeopteryx and modern birds was essentially unknown prior to this finding. “This represents nearly 70 million years of avian evolution in which all the major lineages of Mesozoic birds originated – including the first representatives of the birds that live today,”  Navalón said. “Navaornis sits right in the middle of this 70-million-year gap and informs us about what happened between these two evolutionary points.”

Even though Navaornis’s head initially looks a lot like that of a little pigeon, a closer look shows that it is actually a member of an ancient bird species known as enantiornithines, or the “opposite birds.”

Although “opposite birds” split from contemporary birds about 130 million years ago, they probably had sophisticated feathers and could fly just as well as modern birds. The Navaornis’s brain structure raises a new puzzle, though:how did opposite birds control their flight without the full suite of brain features observed in living birds, including an expanded cerebellum, which is a living bird’s spatial control centre?

Field, who is also the Strickland Curator of Ornithology at Cambridge’s Museum of Zoology, stated, “This fossil represents a species at the midpoint along the evolutionary journey of bird cognition.” “Its cognitive abilities may have given Navaornis an advantage when it came to finding food or shelter, and it may have been capable of elaborate mating displays or other complex social behaviour.”

Despite being a major accomplishment, the researchers claim the discovery is just the beginning of their understanding of how avian intelligence evolved. How Navaornis interacts with its surroundings may be revealed by future research, which could assist address more general queries regarding the historical development of bird cognition.

Field’s research team has been describing four Mesozoic fossil birds since 2018, including Janavis, Ichthyornis, and Asteriornis (the “Wonderchicken”). Navaornis is the most recent of these birds. By combining cutting-edge visualization and analytical techniques with new fossil findings, the team has uncovered important new information about the origins of birds, the most varied group of vertebrate animals still in existence.

The study was partially funded by UKRI, or UK Research and Innovation. Daniel Field attends Cambridge’s Christ’s College as a Fellow.

The announcement by civilian supersonic startup Exosonic that it is going out of business due to its inability to acquire necessary funding is another illustration of the huge upheaval occurring in the cutting-edge aerospace industry.

Any technological field that experiences a boom goes through several stages, some of which can be quite unpleasant for individuals engaged. I had the good fortune to be writing contracts in Seattle, Washington, which was the core of the internet explosion in the late 1990s.

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In those days, businesses would appear like mushrooms in a park during an autumn rainstorm. Suddenly, a new firm would occupy every available office space, furnishing it with expensive furniture and paying even more to hire employees. It was highly intoxicating, akin to seeing a gold rush. But by 2000, the boom had turned to crash, with the startups disappearing as fast as the figurative mushrooms, leaving just the most resilient.

As the competitors to profit from new developments are pushed aside, a similar shakedown is presently taking place in the more inventive sectors of the aircraft industry. Exosonic, situated in Torrance, California, has joined the ranks of hypersonic engine manufacturer Reaction Engines and eVTOL taxi startup Lilium that have already filed for bankruptcy.

After the collapse of the Concorde, aerospace engineer Norris Tie founded Exospace in 2019 with the goal of creating the next generation of civilian supersonic aircraft. Tie had previously worked at Lockheed Martin and Northrop Grumman. They were somewhat successful, obtaining contracts with the US Air Force to develop supersonic training drones and raising US$6.5 million in finance.

As the competitors to profit from new developments are pushed aside, a similar shakedown is presently taking place in the more inventive sectors of the aircraft industry. Exosonic, situated in Torrance, California, has joined the ranks of hypersonic engine manufacturer Reaction Engines and eVTOL taxi startup Lilium that have already filed for bankruptcy.

After the collapse of the Concorde, aerospace engineer Norris Tie founded Exospace in 2019 with the goal of creating the next generation of civilian supersonic aircraft. Tie had previously worked at Lockheed Martin and Northrop Grumman. They were somewhat successful, obtaining contracts with the US Air Force to develop supersonic training drones and raising US$6.5 million in finance.

“To all that stayed updated on our journey, we thank you for your support and shared love for our company’s vision and mission,” stated Exosonic in a statement. “For those that continue to be in the race, such as Boom Supersonic, Hermeus, Destinus, Venus Aerospace, Spectre Aerospace, and others, we wish you the best on your super/hypersonic campaigns. We will be rooting for you from the sidelines.”