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technology. As Indians another degree of pride stringed to this new
photography and image processing technology is that the team researching
this at MIT is headed by an Indian namely Ramesh Raskar (interested souls
may know more by logging in to ted.com and searching for the video of
Ramesh).
We all have known reading that light travels the fastest; imagine tracking
light and tracing the splitting of light by increasing the frame speed of
the high-speed camera. This is possible only through the camera developed
by Raskar & his team which can generate a trillion frames per second. Going
forward, this technique is expected to be responsible for innovations in
medical and material management sciences. Imagine being able to see one's
body and internal parts without X-Rays. This weekend, I attach the original
abstract of the entire project written by the team; a photograph is also
attached which shows the normal propagation of light and the scattered beam
of light through the same medium.
Abstract
We have built an imaging solution that allows us to visualize propagation
of light. The effective exposure time of each frame is two trillionths of a
second and the resultant visualization depicts the movement of light at
roughly half a trillion frames per second. Direct recording of reflected or
scattered light at such a frame rate with sufficient brightness is nearly
impossible. We use an indirect 'stroboscopic' method that records millions
of repeated measurements by careful scanning in time and viewpoints. Then
we rearrange the data to create a 'movie' of a nanosecond long event.
The device has been developed by the MIT Media Lab’s Camera Culture group
in collaboration with Bawendi Lab in the Department of Chemistry at MIT. A
laser pulse that lasts less than one trillionth of a second is used as a
flash and the light returning from the scene is collected by a camera at a
rate equivalent to roughly half a trillion frames per second. However, due
to very short exposure times (roughly two trillionth of a second) and a
narrow field of view of the camera, the video is captured over several
minutes by repeated and periodic sampling.
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
starttime. 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.
Beyond the potential in artistic and educational visualization,
applications include industrial imaging to analyze faults and material
properties, scientific imaging for understanding ultrafast processes and
medical imaging to reconstruct sub-surface elements, i.e., 'ultrasound with
light'. In addition, the photon path analysis will allow new forms of
computational photography, e.g., to render and re-light photos using
computer graphics techniques.
Like I always say, brickbats and bouquets welcome!
-Sukhi
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