Tech Briefs

"LaserMan" is a tool for assessing damage from laser exposure.

Lasers are an integral part of the modern battlefield, used for applications as diverse as point-to-point communications and ballistic missile defense. Their widespread use increases the warfighter's likelihood of being exposed to laser hazards, and damage to an individual's eyes and skin can be serious. AFRL has served as a leading authority on laser-induced damage thresholds for many years.

Scientists assigned to AFRL's Advanced Laser Bioeffects Team, under the direction of Dr. Benjamin A. Rockwell, recently demonstrated a tissue substitute suitable for use in laser damage experiments. The goal of the team's project, dubbed "LaserMan," was to develop synthetic materials that could effectively mimic the properties of human skin, bone, muscle, and fat. Scientists have traditionally relied upon medical subjects and excised tissue samples in conducting laser damage experiments. While tissue samples are helpful, however, they lack the ability to adequately mimic healthy human tissue, can be quite costly, and require a great deal of preparation and a strictly controlled environment. These limitations ultimately prompted the search for an optical material phantom: a synthetic replacement for human tissue in laser damage experiments.

ImageResearchers have used phantom tissue for many years, primarily in the capacity of structural models used for medical applications dealing with energy. Phantoms are also popular mechanisms among military and civilian groups that train medical clinicians on the use of ultrasound techniques and diagnoses. While these phantoms are useful for highly specific medical purposes, they do not exhibit the parameters necessary for optical studies and are therefore not suitable as tissue substitutes for laser testing.

In order to synthesize a material that would match the desired properties, the AFRL researchers acquired over a dozen possible constituent materials. They characterized each sample according to its thermal, optical, and physical properties and then compared this data to values obtained from the available literature for human tissue. The team's main interest was the materials' refractive index, as well as their light absorption and scattering characteristics. The scientists then examined the results of laser tests incorporating the different materials and compared these outcomes with previously collected data assessing measured laser interactions with human tissue. By combining several different materials in just the right proportions, the team created a promising substitute material for replacing human tissue in studies of laser-induced damage. The LaserMan prototype material is a combination of agar, ballistic media, India ink, and Intralipid (see Figure 1). The properties of the agar and ballistic media closely resemble the optical characteristics of human muscle and fat, whereas the added proportions of India ink and Intralipid correct differences in optical scattering and absorption rates (see Figure 2).