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  • This Is Your Garden-Variety Laser

Photonics Spectra
Dec 1999
MORIOKA, Japan -- Next time you go shopping for a lasing medium, forget about rubies or sapphires or gases. Just go to the local supermarket and pick up some carrots, potatoes or peppers.

Researchers at Iwate University are studying the use of vegetable cells as resonating chambers to make lasers. Scientist Hiroshi Taniguchi slices his veggies, dips them in rhodamine 6-G fluorescent dye and then zaps them with a frequency-doubled Nd:YAG laser, causing the vegetable cells to glow. He believes that this glow is an effect known as multiple light scattering -- alias a random laser.

Taniguchi explained that when a photon enters a vegetable cell, it is absorbed by the dye and re-emitted as fluorescence inside the cell. Some of these fluorescing photons follow repetitive paths; if they are amplified as they ricochet within the cell walls and if their wavelength matches that of the incoming light, they lock their wavelengths and phases together. In short, he thinks they become coherent and in phase: lasers.

There is one difference, however. Vegetable cells have heterogeneous and continuously disordered structures, with different refractive and reflective indices in the cellular structure. This means that the photons within the cell emerge in all directions, resulting in an unfocused laser.

Taniguchi said the work on random lasers produced by organic cells is similar in principle to a study on lasing in inorganic cells, written by researchers Robert P.H. Chang and Hui Cao at Northwestern University in Evanston, Ill. (See Photonics Spectra, February 1999, p. 28.) They found that highly disordered powders, such as ZnO, can function as a lasing medium when individual grain sizes measure between 50 and 150 nm.

Taniguchi has tested his method on a variety of organic matter in this cell size, including radishes, algae, rice and paper. Articles on his work have appeared in journals such as Applied Optics and Electronics Letters.

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