A field deployable hyperspectral imager utilizing chromotomography (CT), with a direct vision prism (DVP)
as the dispersive element, has been constructed at the Air Force Institute of Technology (AFIT). A "shift and
add" reconstruction algorithm was used to resolve spectral and spatial content of the collected data. The AFIT
instrument is currently the fastest known imaging DVP based hyperspectral CT instrument of its type and is
a prototype for a space-based system. The imager captured images at rates up to 900 frames per second (fps)
and acquired data cube information in 55 ms, during testing. This instrument has the ability to capture spatial
and spectral data of static and transient scenes. During testing, the imager captured spectral data of a rapidly
evolving scene (a firecracker detonation) lasting approximately 0.12 s. Spectral results included potassium and
sodium emission lines present during the explosion and an absorption feature as the fireball extinguishes. Spatial
and spectral reconstruction of a scene in which an explosion occurs during the middle of the collection period
is also presented in this paper. The instrument is capable of acquiring data required to identify, classify and
characterize transient battlespace events, such as explosions.
The aim of this study was to determine the histopathologic effect on the skin of 2.0 &mgr;m wavelength laser with various
exposure conditions 48 hours after irradiation.
Histological sections of lesions were created at, below and beyond the threshold for grossly apparent thermal lesions.
These lesions were studied to 1)identify and define the microscopically apparent threshold lesions, 2)determine the
mechanisms producing the gross and microscopic threshold lesions in the skin, and 3)map the extent and severity of the
Grossly apparent threshold lesion were defined as persistent surface redness at 48 hours. Histologically, these lesions
showed relatively severe thermal damage in both the epidermis and the dermis. Damage included death and necrosis of
the epidermal cells and endothelial necrosis, intravascular thrombosis as well as perivascular edema and inflammation
in dermal blood vessels. The collagen bundles below the epidermis were slightly swollen but there was no change in
birefringence image intensity. For each threshold lesion, three quantitative parameters were measured to map the extent
of thermal damage: 1) the width of necrotic epidermis, 2) the depth measured from the epidermal/dermal junction to the
deepest extent of thrombosis, and 3) the depth measured from the epidermal/dermal junction to the deepest extent of
perivascular inflammation and edema. Birefringence change of dermal collagen which occurred at powers above
threshold was another measurable damage marker which indicated coagulation of collagen bundles.
These quantitative histopathologic data for skin damage associated with the transient temperature profiles and
irradiation parameters provided important information to mathematically derive rate process coefficients for thermal
damage and formulate mathematical tissue damage models for each cutaneous damage effect.
A series of experiments were conducted <i>in vivo</i> on female Yucatan mini-pigs to determine the ED<sub>50</sub> damage thresholds for 2000 nm continuous wave laser irradiation. These results provide new information for refinement of Maximum Permissible Exposure (MPE). The study employed Gaussian laser beam exposures with spot diameters (1/e<sup>2</sup>) of 4.83 mm, 9.65 mm and 14.65 mm and exposure durations of 0.25 s, 0.5 s, 1.0 s and 2.5 seconds as a function of laser power. The effect of each irradiation was evaluated within one minute after irradiation and the final determination was made at 48 hours post exposure. Probit analysis was conducted to estimate the dose for 50% probability of laser-induced damage (ED<sub>50</sub>) defined as persistent redness at the site of irradiation for the mini-pig skin after 48 hours. Histopathologic procedures were used to determine the mechanisms of the laser effects in the skin and map the extent and severity of the lesions. The thresholds study shows that consideration for lowering the current Maximum Permissible Exposure (MPE) limits should be explored as the laser beam diameter becomes larger than 3.5 mm. Based on the limited experimental data, the duration and size dependences of the ED<sub>50</sub> damage thresholds could be described by an empirical equation: (Equation available in manuscript.)