I. Stuart McDermid

Laser ablation of human atherosclerotic plaque without adjacent tissue injury

Seventy samples of human cadaver atherosclerotic aorta were irradiated in vitro using a 308 nm xenon chloride excimer laser. Energy per pulse, pulse duration and frequency were varied. For comparison, 60 segments were also irradiated with an argon ion and an Nd:YAG (neodymium:yttrium aluminum garnet) laser operated in the continuous mode. Tissue was fixed in formalin, sectioned and examined microscopically. The Nd:YAG and argon ion-irradiated tissue exhibited a central crater with irregular edges and concentric zones of thermal and blast injury. In contrast, the excimer laser-irradiated tissue had narrow deep incisions with minimal or no thermal injury. These preliminary experiments indicate that the excimer laser vaporizes tissue in a manner different from that of the continuous wave Nd:YAG or argon ion laser. The sharp incision margins and minimal damage to adjacent normal tissue suggest that the excimer laser is more desirable for general surgical and intravascular uses than are the conventionally used medical lasers.

Radiative lifetimes and electronic quenching rate constants for single-photon-excited rotational levels of no (A2Σ+, ν′ = 0)☆

Abstract A narrow-band, frequency-doubled, tunable dye laser has been used to excite fluorescence from the A2Σ+, ν′ = 0 state of NO. Collision-free lifetimes were measured for 21 different K′ levels giving a mean radiative lifetime τ = 217 ± 4 ns. Electronic quenching rate constants of NO (A2Σ+, ν′ = 0) were measured for O2, N2, H2O, CO2 and Ar. No dependence of the quenching-rate constant on the initially excited rotational level was observed.

Radiative lifetimes and quenching rate coefficients for directly excited rotational levels of OH (A 2Σ+,v′=0)

A narrow bandwidth pulsed dye laser has been used to excite OH X 2Πi radicals to the A 2Σ+ state by pumping in the (0,0) vibrational band around 308 nm. The radiative lifetimes of specific (K′,J′) rotational levels in v′ = 0 were measured at low pressures ⩽1 mTorr which gave a mean lifetime τ0=0.721±0.009 μs (2σ). Electronic quenching rate constants for important atmospheric species N2, O2, H2O, and also for H2 were measured for a range of initially excited rotational levels. A strong dependence of this rate constant on the initially excited level was found for N2, and less markedly for O2, with the rate constant tending to increase for the lowest rotational levels K′⩽3. The implications of these measurements of radiative and quenching rates for state selected rotational levels of OH A, v′=0 to the laser‐induced fluorescence detection of atmospheric OH are discussed.

Effect of hematoporphyrin derivative and photodynamic therapy on atherosclerotic rabbits

This study was performed to demonstrate selective uptake of hematoporphyrin derivative (HPD) within actively developing atheroma, to localize the site of uptake of HPD within the atheroma, and to determine the potential for photodynamic therapy (PDT) of atherosclerosis in the rabbit model. Fifteen rabbits were rendered atherosclerotic. Five rabbits received neither HPD nor PDT and 2 rabbits received HPD, 10 mg/kg intravenously, without subsequent irradiation. Eight other rabbits received 5 to 20 mg of HPD intravenously and subsequent intravascular 636-nm laser radiation to either the thoracic aorta or the aortic arch. A total of 32 to 288 J of laser energy was delivered through a 300-mu quartz fiber. All rabbits that received in vivo HPD had red fluorescence of their aortas when placed under ultraviolet light. The pattern of fluorescence corresponded precisely to the pattern of atheroma. In segments that received PDT, light microscopic examination revealed an accumulation of smooth muscle cells at the intimal surface. Fluorescence microscopy revealed a diminishing concentration gradient of HPD from intimal surface layers towards the media. Assessment of treated thoracic aortic segments revealed quantitative and qualitative differences compared with control segments. In the arch-treated segments, however, no changes were seen. It is concluded that HPD localizes within rabbit atheroma, can be detected by fluorescence and is deposited in a diminishing concentration gradient from lumen toward media. Irradiation with 636-nm light may induce qualitative and quantitative changes in atheroma.

Temperature climatology of the middle atmosphere from long-term lidar measurements at middle and low latitudes

Long-term measurements from several lidar instruments (Rayleigh and sodium) located at 44.0°N, 40.6°N, 34.4°N, and 19.5°N have been used to develop a new climatology of the middle atmosphere temperature. For each instrument, the measurements on every individual day of the year over the entire long-term record were averaged to build a composite year of temperature profiles. These profiles were then interpolated to provide temperature values at 1-km altitude intervals so that the climatology comprises daily temperature values at integer altitudes between 15 and 110 km, depending on the instrument. The climatologies for each lidar were then compared to the CIRA-86 model and to each other. Large differences between the lidar temperatures and the CIRA-86 temperatures are identified and explained. When compared to all instruments, CIRA-86 appears systematically much too cold between 90 and 95 km, by 20 K or more, and possibly 6–8 K too warm around 80 km, making its use as a reference atmosphere model questionable at these altitudes. The annual and semiannual components of the seasonal variability and the 2- to 33-day period variability were investigated. An annual cycle with 6–7 K amplitude in the upper stratosphere, increasing to 15–20 K at 80 km, is observed at midlatitudes. This cycle is in phase with the solar flux in the stratosphere and in opposite phase in the mesosphere with a very cold summer mesopause at 85 km, in good agreement with previous climatologies. At lower latitudes, a semiannual oscillation propagates downward from 85 to 30 km and is characterized by a stronger first cycle than the second (4 and 2 K amplitude respectively). The 2- to 33-day variability at midlatitudes shows a maximum during winter around 40 km and in the mesosphere. The first peak is associated with planetary wave activity and stratospheric warmings and the second to the occurrence of mesospheric temperature inversions. Finally, sudden seasonal transitions, highly consistent between all instruments, have been observed. In particular, in the early winter midlatitudes a two-step warming of the winter mesosphere between 65 and 85 km as well as a cooling of the lower mesosphere appear to be real climatological events rather than some short-term geophysical or instrumental random variability.

Ozone differential absorption lidar algorithm intercomparison

An intercomparison of ozone differential absorption lidar algorithms was performed in 1996 within the framework of the Network for the Detection of Stratospheric Changes (NDSC) lidar working group. The objective of this research was mainly to test the differentiating techniques used by the various lidar teams involved in the NDSC for the calculation of the ozone number density from the lidar signals. The exercise consisted of processing synthetic lidar signals computed from simple Rayleigh scattering and three initial ozone profiles. Two of these profiles contained perturbations in the low and the high stratosphere to test the vertical resolution of the various algorithms. For the unperturbed profiles the results of the simulations show the correct behavior of the lidar processing methods in the low and the middle stratosphere with biases of less than 1% with respect to the initial profile to as high as 30 km in most cases. In the upper stratosphere, significant biases reaching 10% at 45 km for most of the algorithms are obtained. This bias is due to the decrease in the signal-to-noise ratio with altitude, which makes it necessary to increase the number of points of the derivative low-pass filter used for data processing. As a consequence the response of the various retrieval algorithms to perturbations in the ozone profile is much better in the lower stratosphere than in the higher range. These results show the necessity of limiting the vertical smoothing in the ozone lidar retrieval algorithm and questions the ability of current lidar systems to detect long-term ozone trends above 40 km. Otherwise the simulations show in general a correct estimation of the ozone profile random error and, as shown by the tests involving the perturbed ozone profiles, some inconsistency in the estimation of the vertical resolution among the lidar teams involved in this experiment.

Quantum-resolved dynamics of excited states. Part 4.—Radiative and predissociative lifetimes of IF B3Π(0+)

The kinetics of decay of excited IF B3Π(0+) molecules in defined ro-vibrational states (v′, J′) have been determined under collision-free conditions. Laser-induced fluorescence was used to directly determine the dynamics of excited IF(B); the laser bandwidth was 1 pm, using excitation wavelengths between 440 and 530 nm.Collision-free lifetimes τ0 were measured for all stable states of IF(B). The mean values text-decoration:overlineτ0(1σ) varied monotonically with v′ from (8.80 ± 0.89)µs (6 J′ 0) for v′= 9, down to (6.96 ± 0.47)µs (45 J′ 5) for v′= 0. The mean value of the electric dipole moment |Re|2 for the B–X transition was calculated to be (0.101 ± 0.010) D2.As for BrF(B), the higher-energy vibrational levels of IF(B) showed predissociation. This predissociation of IF in the states v′= 8, J′ 52 and v′= 9, J′ 7 was observed as a shortening of lifetime. All accessible rotational states in the (8,J′) and (9,J′) manifolds above the onset of predissociation had similar lifetimes near 1 µs. However, the (10,J′) manifold showed a rotationally dependent predissociation, with a nearly linear dependence of 1/τ0 upon J′(J′+ 1). The magnitudes of the predissociation energies in the (8,J′) and (9,J′) manifolds indicate that the predissociating state is a shallow, bound state [Herzberg case 1(b)]. Narrow limits for the (previously uncertain) dissociation energy of IF X1Σ+ can thus be obtained: D00(IF)=(22 333 ± 2) cm–1.The low-lying states of IF are considered in relation to the present and previous results. It is concluded that the predissociation of the (8,J′) and (9,J′) states is probably due to interaction of the B state with a weakly-bound 0+ state, designated here as C3Π(0+), which dissociates diabatically to I2P+ F2P½ atoms. Lifetime shortening is ascribed to interaction at long r-values of the bound C3Π(0+) state with a repulsive 0+ state, that correlates with I2P+ F2P atoms. The strong predissociation in IF(B) found previously at higher energies [in the (11, 45) and higher states] is due to direct interaction of the B state and the repulsive 0+ state. Similarities with BrF are indicated.

Redesign and improved performance of the tropospheric ozone lidar at the Jet Propulsion Laboratory Table Mountain Facility

Improvements to the tropospheric ozone lidar at the Jet Propulsion Laboratory Table Mountain Facility for measurements of ozone profiles in the troposphere and lower stratosphere, between approximately 5-and 20-km altitude, are described. The changes were primarily related to the receiver optical subsystems and the data-acquisition system. The original 40-cm Cassegrain telescope was replaced with a faster (f/3) 91-cm Newtonian mirror. In the focal plane of this mirror, the lidar signal is divided into two parts by use of two separate optical fibers as field stops corresponding to different but neighboring 0.6-mrad fields of view. We then separate the two received wavelengths by aligning each transmitted beam to one of the fibers. In addition, two 50-mm telescopes are used for the collection of near-range returns. The four optical signals are brought to a chopper wheel for independent signal selection in the time and range domain. For each channel, an interference filter is used for skylight rejection and additional cross-talk prevention. The signals are detected with miniature photomultiplier tubes and input to a fast photon-counting system. The goals of these modifications were to increase the spatial and temporal resolution of the lidar, to extend the altitude range covered, to improve the quality of the raw data, and to enable regular and routine operation of the system for long-term measurements.

Optical systems design for a stratospheric lidar system

The optical systems for the transmitter and receiver of a high-power lidar for stratospheric measurements have been designed and analyzed. The system requirements and design results are presented and explained. An important and driving factor of this design was the requirement for a small image diameter in the plane of an optical chopper to allow the high-intensity lidar returns from the lower atmosphere to be shielded from the detection system. Some results relevant to the optical performance of the system are presented. The resulting system has been constructed and is now in operation at the Mauna Loa Observatory, Hawaii, and is making regular measurements of stratospheric ozone, temperature, and aerosol profiles.

Ultranarrow linewidth, magnetically switched, long pulse, xenon chloride laser

A spectral linewidth of <7×10−4 A and diffraction‐limited beam divergence has been obtained from a long pulse, electric discharge xenon chloride laser with intracavity Fabry–Perot etalons. A gain duration of 100 ns provided for multipass operation of the etalons, significantly improving both contrast and finesse. The electrical discharge circuit required to produce this long gain duration was comprised of a pulse forming network, saturable inductor magnetic switch, and a tapered, constant impedance, interface transmission line.