### •The Rochester cloak is a system of lenses that can bend light around an object, rendering it invisible under certain conditions. •A team of researchers from the University of the Philippines improved the design using a mathematical approach to tracing light’s path. •Now, even students can obtain the necessary items and conduct their own invisibility experiments in their schools’ laboratories.

From S.H.I.E.L.D.’s hellicarrier and the Avengers’ quinjet to Harry Potter’s invisibility cloak, pop culture and fantasy have illustrated humanity’s fascination with turning invisible.

In 2014, the University of Rochester in New York, U.S.A. made fiction real with a Rochester cloak. It is a system of four lenses using geometric optics which can make anything placed between two lenses “disappear.” The lenses bend light around an object, making it invisible when viewed from a certain angle.

However, the original configuration required two pairs of lenses with the same focal length (the distance from which the lenses can focus on a subject).

Now, a team of physicists from the University of the Philippines (UP) have made laboratory invisibility possible by improving on the Rochester cloak’s design.

In fact, they’ve managed to simplify the method to a point where even students can put it together in their school labs.

## Uncovering the science

“(The Rochester cloak) is made of four lenses, the same thing you’d find in your glasses. The lenses are specially arranged on a line and you view the background from one end,” said Miguel Revilla, researcher and lead author of the study.

“You can put objects inside this lens system without blocking your view of the background.”

To achieve this, Revilla, together with fellow undergraduate student JC Lorenzo and Dr. Nathaniel Hermosa, used a method called analytical ray tracing.

Analytical ray tracing uses math to trace the path of light and simulate how it affects objects.

With this method, they were able to recalculate the separation distances of lenses, even with different focal lengths.

This allowed them to create a Rochester cloak that did not specifically require lenses with the same focal length.

Interestingly, the team started solving the problem by hand two years ago for a local physics conference.

“I trusted the science. Based on my physical intuition, it will work,” Hermosa told FlipScience.

“The real lightbulb moment would have been if the equations and my intuition are wrong upon doing the experiment.”

## In plain sight

Meanwhile, the “Aha!” moment for Revilla was when they used plain old lenses–“The ones you’d buy from a bookstore,” he said–to test their theory.

“After assembling the lenses, we tested it with a metal rod as our object,” shared Revilla. “We were amazed that the rod was hidden from our view.”

The partially invisible rod is in the image posted on the UP Office of the Vice President for Academic Affairs (UPOVPAA)’s Facebook page.

For many years, scientists have proposed, developed and mounted different optical systems to achieve the effect of…

In an academic setting, this update on the invisibility cloak makes it a fitting introduction of the analytical ray tracing method to students — an invisible gateway to physics, so to speak.

It’s worth noting that we’re still a ways off from simulating the powers of the Fantastic Four’s Invisible Woman. Outside the classroom, though, Revilla believes that the surgical and manufacturing fields can benefit from a more compact version of the cloak.

“I am thinking of a more compact camera or imaging system,” added Hermosa. “Imagine putting more electrical and/or optical component at the cloaking regions. You can save on space.”

## Blind spots?

But just like any technology, invisibility has its downsides.

“After all, if you’ll be hiding something from view, it can be motivated by illegal reasons,” warned Revilla. For instance, smugglers of illegal substances may appropriate the technology to get contraband items through the usual security measures.

Hermosa, however, is optimistic that they can devise ways to stop would-be criminals in their “invisible” tracks.

“The nice thing about knowing the system is that you also know how to crack it,” said Hermosa.

“People may apply it to illegal activities but because we how it works, we can design how to spot them.”

Their paper is slated for publication in the European Journal of Physics.–MF

#### References

• Miguel Lao Revilla et al 2019 Eur. J. Phys. in press https://doi.org/10.1088/1361-6404/ab0e52

#### Author: Ronin Bautista

Ronin is a Christmas-loving wandering scribe who wanted to be a doctor, until he learned it meant cutting dead bodies open. He is currently finishing his MA in Asian Studies (major in Japanese Studies), while teaching journalism classes at UP Diliman’s College of Mass Communication.