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Cancerous tissue forms laser cavity

25 Aug 2004

A pair of US scientists reveals that cancerous tissue can lase.

Malignant tissues doped with Rhodamine 6G emit more laser lines compared with healthy tissue from the same organ say Randal Polson and Valy Vardeny of the University of Utah, US. The duo says this finding may lead to a way to identify the different tissues for cancer diagnostics. (Applied Physics Letters 85 1289)

In a random laser, multiple random scattering replaces the mirrored cavity found in standard lasers. When the system produces a set of narrow spectral lines, it is known as a coherent random laser.

"There are more laser resonators in the cancerous tissue due to more scatterers as well as excess disorder," explained Vardeny. "To penetrate the biological world with random lasing - which was originally discovered by our group and another at Northwestern - was quite an event."

Having originally produced random lasing in potatoes, the researchers moved on to study samples of human colon and kidney tissue and chicken meat. Each sample was soaked in the laser dye Rhodamine 6G and then pumped with 100 ps, 50µJ pulses from a Nd:YAG operating at 532 nm and a repetition rate of 100 Hz.

The pump beam passes through a cylindrical lens to form a 100 µm x 2mm stripe which is translated across the tissue.

To analyse the emission spectra, the researchers make use of a function called the power Fourier transform (PFT). "By averaging the PFT of the emission spectra across the samples we could distinguish malignant and non-malignant human tissues within about a 2-mm spatial resolution," say the duo.

Polson and Vardeny now plan to work with other laser dyes. "The next steps are to get random lasing from dyes that have large two-photon fluorescence properties using lasers in the near infrared," Vardeny told Optics.org. "We then want to try and get laser action in human tissue infiltrated with such a dye and then try 3D mapping."

Jacqueline Hewett is technology editor on Optics.org and Opto & Laser Europe magazine.

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