A new camera developed by MIT has now achieved the amazing, being fast enough to capture photons of light as they propagate. Check out the videos below, then stick around for the science.
ABOVE—The advancing spherical front of light intersects the surfaces of table, the shape of the fruit and the back wall.
And how about a “bullet” of photons moving through a soda bottle?
ABOVE—The pulse of light is less than a millimeter long. Between each frame, the pulse travels less than half a millimeter. Light travels a foot in a nanosecond and the duration of travel through a one foot long bottle is barely one nanosecond (one billionth of a second).
Pretty amazing, right? You are actually witnessing the propagation of light waves. Keep in mind that because of the minuscule exposure times (two trillionth of a second) that the video is a composite of multiple light pulses over a few minutes.
I’ll let the developers explain (long but thorough):
The new technique, which we call Femto Photography, consists of femtosecond laser illumination, picosecond-accurate detectors and mathematical reconstruction techniques. Our light source is a Titanium Sapphire laser that emits pulses at regular intervals every ~13 nanoseconds. These pulses illuminate the scene, and also trigger our picosecond accurate streak tube which captures the light returned from the scene.
The streak camera has a reasonable field of view in horizontal direction but very narrow (roughly equivalent to one scan line) in vertical dimension. At every recording, we can only record a ’1D movie’ of this narrow field of view. In the movie, we record roughly 480 frames and each frame has a roughly 1.71 picosecond exposure time. Through a system of mirrors, we orient the view of the camera towards different parts of the object and capture a movie for each view. We maintain a fixed delay between the laser pulse and our movie start time. Finally, our algorithm uses this captured data to compose a single 2D movie of roughly 480 frames each with an effective exposure time of 1.71 picoseconds.
So, what we are seeing is the composite images of multiple laser pulses as they propagate in a spherical wave and interact with objects. To fully capture these events, millions of lasers pulses have to be shot (like capturing a bullet on video) and compiled via mathematical algorithms. The end result is nothing short of fascinating.
Beyond future scientific and artistic applications, experiments like these bring the magic of nature squarely into view. Taking something basically invisible to us (the movement of light) and making it uniquely visible is the best part of research. It’s not a mystery anymore, it’s science.
You can find more picture, videos, and information directly from the researchers here.