Top panel: Random laser emission spectra from different excited spots,and their average

Random Lasing in Human TissuePolson, Raikh, Vardeny , University of Utah

DMR 02-02790Random lasing from a healthy colon human tissue

Bottom panel:Fourier transform of the same spectra, and their average

Our FRG program deals with laser action in pi- conjugated organic systems, including films, solutions, single crystals and self assembled monolayers. There are basically four types of laser action phenomena known in the literature. These are: amplified spontaneous emission, super-radiance, super-fluoresence, and cavity lasing (or true laser). However we have discovered a new laser action type that we now study in detail; this is “random lasing”.

A random collection of scatterers in a gain medium can produce coherent laser emission lines dubbed “coherent random lasing”. We have studied random lasing in various media including films of pi-conjugated conducting polymers, pi-conjugated polymers and oligomers infiltrated into opals, and single crystals. We then extended the study of random lasing in other media including biological tissues. We have shown that biological tissues, such as vegetables and animal meat, can support coherent random lasing by infiltrating them with a concentrated laser dye, pi-conjugated polymer as well as pi-conjugated oligomer solutions. During our studies we have discovered that malignant tissues show many more laser modes in the emission spectrum compared to healthy tissues. We found that the narrow lines in the laser emission spectrum are in fact coherent laser modes and thus are formed in real cavities via the process of coherent feedback. Our findings therefore indicate that there are much more random cavities in malignant tissues compared to healthy tissues taken from the same organ in the body. To extract a typical random resonator size within the tissue, which may be used as a tag for the tissue, we average the Fourier transform of random laser emission spectra collected from many excitation locations in the tissue (see the animated Slide figure). Whereas the average random emission spectrum from the different spots gives a smooth curve that is proportional to the gain spectrum of the infiltrated medium, the average Fourier transform of the emission spectra does not give a smooth curve. In fact it averages to give the Fourier transform of a random laser based on a dominant cavity in the medium (see the animation). The average spectrum is typical of a Fourier transform of the emission spectrum from cavity-based lasers that show Fourier components at multiples of nL/ , where n is the refractive index and L is the cavity length. We verified this procedure by a computer simulation. From the average Fourier transform spectrum above we extracted a dominant cavity length of about 34 m. The obtained dominant random resonator length was found to be different for healthy and cancerous human tissues and this may lead to a novel technique of separating malignant from healthy tissues that may be used for diagnostic imaging. In fact so far we have achieved a resolution of 2mm2 for imaging malignant tissue within an otherwise healthy one. This work has been submitted to publication. In addition we have submitted a patent disclosure to the University of Utah Patent office, and made contact with the University Hospital here for further development of the imaging procedure.

The Slide figure demonstrates the averaging process of random laser emission spectra (upper panel) from different excited spots in the tissue, and Fourier transform of each spectrum (lower panel); these laser emission spectra were collected from a healthy human colon tissue. Whereas the average spectrum is smooth, the average Fourier transform spectrum shows features that do not average out. In fact these are Fourier components of the dominant cavity in this tissue, and can be used for diagnostic if compared to malignant tissue of the same colon.

FRG; Excitation Dynamics and Laser Action in Systems of -Conjugated Materials

Per Z. Valy Vardeny, University of Utah; DMR 0202790

Education:One undergraduate student (Alison Hatt), three graduate students (Minghong Tong, ChuanXiang Sheng, and Alex Ndobo Sosso), and three postdocs (Vlamir Burtman and Vadym Apalkov, and Randy Polson) contributed to this work. Dr. Polson is currently a senior Research Engineer at the Utah Laser Institute; Dr. Apalkov is a Research Assistant Professor in the Physics Department, at the University of Utah.

Outreach:We are in close contact with MD’s from the Huntsman Cancer Institute in Salt Lake City, for exploring the possibility to use the Random Laser in tissue phenomenon for cancer diagnostics imaging. During the summer the PI hosted gifted high school students from Skyline High, Salt Lake City in his laboratory.