The group expected to push fluid containing mitochondria through the device and to see very weak signals emanating from the tiny organelles. Had this been true, signal-averaging techniques would have been necessary to generate a generalized, necessarily less crisp estimate of responses.
"We were pleasantly surprised but puzzled to see very large signals from each mitochondrion," Gourley said. "A statistical average was unnecessary."
The researchers realized that each mitochondrion acted as a lens for light passing through it because the organelle had a higher index of refraction (1.42) than water (1.33). Light refracted into the mitochondria in effect emerged amplified. It was exactly analogous to a lens concentrating light passing through it.
"When a critical concentration of emitted photons is reached," says Gourley, "stimulated emission of additional photons occurs in the semiconductor."
These photons, as well as those reflected from the mirror, retrace their paths back through the mitochondria. "Wildly wayward photons are lost," Gourley says. "Only the photons that pass back through the tiny mitochondrion will arrive back at the semiconductor with the proper phase and location where the photon amplification (gain) can recur."
This discovery suggested the laser cavity be set up sensitively - like a gun on a hair-trigger - by carefully setting the power of an external pump laser that beams energy into the cavity. When a mitochondria cell is present, the light in the cavity reaches critical concentration to trigger the avalanche of photons necessary for laser action.
Thus the tiny organelle becomes the center of a lasing process that yields light signals as bright as that emitted by an entire cell several orders of magnitude larger, offering possibilities for analysis that light scatterin
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Contact: Neal Singer
nsinger@sandia.gov
505-845-7078
DOE/Sandia National Laboratories
23-Sep-2003