Harry Potter's invisibility cloak could soon become a reality
What's the story
In what would seem like a blurring of lines between Harry Potter-esque fantasy and reality, scientists from Canada have now taken us a step closer towards invisibility cloaks. Researchers from Montreal's National Institute of Scientific Research (INRS) recently published a study wherein they describe something called a 'spectral cloaking device' that can make objects fully invisible, even in natural light. Here are the details.
Details
The device works by manipulating frequency of light waves
In the breakthrough study, published in the journal Optica, the scientists found a novel way to turn something invisible. Unlike earlier approaches, the spectral cloaking device manipulates the color (or frequency) of light waves that interact with an object, thereby rendering it invisible. If that sounds too complicated, here's a simple break down of what it actually does.
Light and colors
Back-to-basics: Light, the electromagnetic spectrum, and colours
Light has something called the electromagnetic spectrum, which contains different frequencies of electromagnetic radiation - X-rays, gamma rays, etc. all fall somewhere on this spectrum. Our eyes can only see a small range of frequencies on this spectrum, commonly called 'visible light'. Visible light is a range of frequencies, what we perceive as 'colors', starting with violet, and ending with red (remember VIBGYOR?).
Seeing
Back-to-basics: The phenomenon of 'sight'
Some light sources, called broadband sources, contain more than one frequency (like sunlight). When we 'see' an object we essentially see the interaction of these light frequencies with the object. For example, when sunlight shines on a red car, the car primarily reflects the red frequency, while other color frequencies pass through it. Our eyes pick up the reflected red light, thus enabling 'sight'.
Invisibility
How the INRS cloaking device manipulates light frequencies
Using commercially available electro-optical components, the researchers created a filter which shifts colors toward regions of the electromagnetic spectrum that are not affected when light propagates through an object. For instance, if light is passing through a green object, light in the green portion of the spectrum might be shifted to blue so that there's no green light for the object to reflect.
Experiment
How the researchers made an object invisible
For the experiment, these filters were placed on two sides of a green object. The first filter shifted green color frequency of the light (broadband source) shining on the object to blue, and the second filter shifted the frequency back to green when the light wave exited the object. Thus, the object couldn't reflect green light, thereby rendering it invisible to the human eye.
Do you know?
Previous attempts made it apparent that something was amiss
Previous attempts at invisibility involved altering the path of light waves around an object, or manipulating the propagation speed of light to achieve temporary invisibility. These approaches, by altering a light wave's temporal profile, made it apparent to an observer that something was amiss.
Limitations
Currently, the device only works from one direction
However, there's still some way to go before we have invisibility cloaks like Harry Potter. Currently, the cloaking device only works from one direction i.e. a viewer's gaze will have to follow the path of the light and view the object facing the first filter. Yet, theoretically, the scientists believe that this approach can be replicated to make an object invisible from any direction.