Ancient photosynthetic eukaryote biofilms in an Atacama Desert coastal cave.

Caves offer a stable and protected environment from harsh and changing outside prevailing conditions. Hence, they represent an interesting habitat for studying life in extreme environments. Here, we report the presence of a member of the ancient eukaryote red algae Cyanidium group in a coastal cave of the hyperarid Atacama Desert. This microorganism was found to form a seemingly monospecific biofilm growing under extremely low photon flux levels. Our work suggests that this species, Cyanidium sp. Atacama, is a new member of a recently proposed novel monophyletic lineage of mesophilic "cave" Cyanidium sp., distinct from the remaining three other lineages which are all thermo-acidophilic. The cave described in this work may represent an evolutionary island for life in the midst of the Atacama Desert.

Laser-induced fluorescence detection of atherosclerotic plaque with hematoporphyrin derivative used as an exogenous probe.

Clinical use of laser angioplasty is limited by the lack of an adequate guidance system. As a first step toward developing a reliable guidance system, laser-induced surface fluorescence and a fluorescent probe were used to differentiate plaque from normal arterial wall. The aortas from four normal New Zealand white rabbits and six atherosclerotic rabbits were studied in vitro. Rabbits from each group received 2.5 mg/kg of hematoporphyrin derivative intravenously 24 hours before death. Segments of the aortas were irradiated with a helium-cadmium laser, and the tissue surface fluorescence spectra were recorded with an optical multichannel analyzer. A plaque index, based on the resulting spectra, was calculated for each specimen of aorta. The spectra from normal aorta without hematoporphyrin derivative, normal aorta with hematoporphyrin derivative, and from plaque of atherosclerotic rabbits without hematoporphyrin derivative showed the same wavelength dependence. The plaque index values were not significantly different from one another. However, in plaque from atherosclerotic rabbits given hematoporphyrin derivative, the spectrum was markedly different, showing a broad spectral peak at 632 nm. This spectral peak corresponds to the spectral peak of hematoporphyrin derivative and was only seen in the plaque of atherosclerotic rabbits given hematoporphyrin derivative. The plaque index for these specimens was significantly different from all other specimens (p less than 0.001). This difference in fluorescence spectra and plaque index could be incorporated into a guidance system for laser angioplasty.

Ultraviolet laser ablation of skin: healing studies and a thermal model.

We have followed the course of healing of incisions made with the krypton-fluoride excimer laser. Incisions were made in guinea pig skin, in vivo, under identical conditions of irradiation. The progressive healing of these incisions was followed over the course of 3 weeks. We noted excellent healing with re-epithelialization, and the re-formation of collagen fibers with minimal fibrosis. We present a simple thermal model for ablation of tissue by a short pulse of strongly absorbed laser radiation.

Ultraviolet-laser ablation of skin.

We report on the use of pulsed ultraviolet-laser irradiation at 193 nm from an argon-fluoride laser and at 248 nm from a krypton-fluoride laser to ablate skin. In vitro, both wavelengths performed comparably, removing tissue precisely and cleanly, and leaving minimal thermal damage to the surrounding tissue. In vivo, the 193-nm laser radiation failed to remove tissue after bleeding began. The 248-nm radiation, however, continued to remove tissue despite bleeding and left a clean incision with only minimal thermal damage. The krypton-fluoride excimer laser beam at 248 nm, which should be deliverable through a quartz optical fiber, has great potential as a surgical instrument.

Far-ultraviolet laser ablation of atherosclerotic lesions.

Far-ultraviolet (far-UV) (193 nm) laser radiation ablates arterial wall tissue, including noncalcified atherosclerotic lesions, with no apparent thermal damage to remaining tissue. This effect contrasts sharply with the thermal damage produced by visible-wavelength laser irradiation. The mechanism by which far-UV radiation interacts with tissue is predominantly photochemical rather than photothermal. Potential clinical applications include those in which geometrically precise removal of tissue, without thermal damage to the remaining substrate, is desired. Ultraviolet laser catheterization appears practical with respect to the availability of fiberoptic materials and high-pulse-rate excimer lasers.

Atomic Rydberg-state spectroscopy of Ca I using pulsed colorcenter lasers.

The utility of using color-center lasers for atomic spectroscopy is demonstrated. Pulsed, color-center lasers are used in conjunction with pulsed dye lasers for multiphoton ionization spectroscopy studies of Ca I. The 4s6d(1)D(2)-4snf(1)F( masculine)(3) spectrum for n = 11-16 is observed. Two other series of lines are identified as 4s5f(1)F( masculine)(3)-4sng(1)G(4) and X-4sng(1)G(4) transitions.

Ionization studies in laser-excited alkaline-earth vapors.

We report on the time behavior of ionization signals produced by laser excitation of Ca and Ba atomic vapor to high-Rydberg states. A space-charge-limited thermionic diode detector shows a long-lived (>I-msec) ionization signal. However, optical detection of atomic ions (Ca+, Ba+) shows that these species live for much shorter times (<100 microsec). These results, in conjunction with published results on mass-spectrometric studies of high-density atomic beams, suggest that our ionization signal is primarily due to molecular species (Ca2+, Ba2+). We also observed optically pumped amplified spontaneous emission and stimulated electronic Raman scattering in Ca+ and Ba+.

Spectroscopy of even-parity autoionizing levels in Ba.

Using multiphoton ionization spectroscopy, we have observed transitions in Ba from the 6s(2)(1)S(0) ground state to even-parity autoionizing states. We have seen extended series with J = 0, 1, and 2 of the type 5dnd and 5dns, converging on the 5d(2)D(3/2) and (2)D(5/2) ionization limits. A multichannel quantum-defect theory analysis of the J = 0 spectrum is presented.