Video Captures Laser Pulses at ‘1 Billion FPS’
WARSAW, Poland — Hollywood laser blasts give off bright colors and are easy to track with the eye. In real life, laser pulses flash by faster than the eye — or even the fastest camera — can follow.
To visualize the propagation of a roughly 12-fs pulse, researchers from the Polish Academy of Sciences and the University of Warsaw used a clever trick to approximate a frame rate of 1 billion fps.
The researchers set their laser to fire roughly 10 pulses per second, then synchronized a camera to take 5-ns exposures. Each successive pulse was captured at a slightly later moment in its propagation, allowing the researchers to produce a composite movie of a single pulse travelling down a long hallway.
At the heart of the experiment was a roughly 10-TW laser emitting in the near-infrared spectrum. The tabletop system utilizes a noncollinear optical parametric chirped-pulse amplifier with 30 percent efficiency that has been under development by professor Dr. Czeslaw Radzewicz and his team since 2005.
The pulses ionize the air they pass through, forming plasma filaments.
“It is worth noting that although the light we are shooting from the laser is in the near-infrared range, a laser beam like this travelling through the air changes color to white,” said Dr. Yuriy Stepanenko, who led the team that built the laser. “This happens since the interaction of the pulse with the plasma generates light of many different wavelengths. Received simultaneously, these waves give the impression of white.”
A 10-TW laser pulse disperses into water vapor. The other colors arise from the ionization of matter as the pulse propagates through the air. Courtesy of the Institute of Physical Chemistry of the Polish Academy of Sciences.
In the video, the pulse appears to give off bright flashes at various points along its trajectory, an effect of it passing through clouds of water vapor and scattering off other particles in the air.
“On the film one can observe all the effects associated with the movement of the laser pulse in space,” said Dr. Pawel Wnuk, “in particular, the changes in ambient light depending on the position of the pulse, and the formation of flares on the walls when the light passes through the dispersing cloud of condensed water vapor.”
Not only do the plasma filaments formed by the pulses glow white, they also allow the pulses to self-focus and travel farther without dispersing. This makes the laser potentially useful for long-range lidar applications, Stepanenko said, including gathering spectroscopic data from clouds and quantifying atmospheric pollution.
Other possible applications include accelerating protons for cancer therapy and generating picosecond x-ray pulses, Stepanenko said.
For more information, visit www.english.pan.pl.
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