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Infections due to carbapenem-resistant Enterobacteriaceae (CRE) represent a growing problem nationally, are difficult to treat, and are associated with high mortality rates. Features of CRE infection within Connecticut, a nonendemic area, have not been described in the medical literature. We report a case series of five patients with CRE isolates who were treated at Hartford Hospital in Hartford, Connecticut from 2011-2013. CRE isolates included three Klebsiella pneumoniae, one Klebsiella oxytoca, and two E. coli. Three isolates were obtained from urine cultures, one from respiratory culture, and one from blood and wound cultures. Four patients survived the hospital course, including three patients who had a hospital stay of100 days. In this nonendemic hospital, CRE infections were identified mainly in patients with multiple comorbidities who underwent catheter placement and surgical procedures, had contact with the health care system in the preceding 90 days, and tended to have prolonged, complicated hospital courses.

We have investigated the somatic activity of the maize Activator (Ac) element in haploid and diploid aspen with the objective of developing an efficient transposon-based system for gene isolation in the model tree species Populus. It was shown that Ac is reinserted, frequently into or near coding regions in aspen, and therefore can be used for gene tagging studies. A number of phenotypic variants were also found following transformation of constructs harbouring the rolC gene. Comparative analyses of T-DNA flanking regions of variants and wild type lines indicate that T-DNA insertion has occurred in or near coding regions. However, the frequency of T-DNA insertion into genes is about one half of the frequency of Ac insertion hitting coding sequences. The results obtained give a proof-of-concept for transposon tagging in a tree system. Given the long generation cycles in tree species, gene tagging strategies are practical only to obtain dominant gain-of-function mutants that do not require selfing or test crossing. In order to obtain recessive loss-of-function mutants, we have regenerated haploid lines from immature pollen. These lines were successfully transformed with a construct containing the rolC transgene from Agrobacterium rhizogenes and Ac element from maize. The results indicate that Ac is also active in haploid aspen and hence can be used in general for gene tagging in trees.

In this study, the results of four different field experiments concerning the speciation of iron and the concentrations of some other chemical compounds in cloudwater samples are compared to one-another. Hydrogen peroxide concentrations were higher during campaigns, conducted at sites not much influenced by anthropogenic emissions as compared to those conducted at more polluted areas. In contrast, percentages of S(IV) in the cloudwater were lowest at the rural sites and highest at the sites polluted by human activities, indicating a consumption of hydrogen peroxide in the oxidation reaction with S(IV). The concentration of dissolved iron was observed to correlate with the percentage of S(IV), which may be an essential point for the reductive dissolution of oxidic iron compounds of the aerosol particles. As far as the speciation of the dissolved iron is concerned, it became obvious that the percentage of Fe(III) is anticorrelated to the concentration of dissolved iron. This clearly shows the important effect of the chemical and/or photo reductive ways of dissolving the iron(III)-compounds from the aerosol particles. However, a correlation between the pH-value and hydrogen peroxide was observed.

We study a special dual form of a convex minimization problem in a Hilbert space, which is formally suggested by Fenchel dualityand is useful for the Dykstra algorithm. For this special duality problem, we prove that strong duality holds if and only if the collection of underlying constraint sets {C1,...,Cm} has the strong conical hull intersection property. That is, $$\left( {\mathop \cap \limits_1^m C_i - x)^ \circ = \sum\limits_1^m {(C_1 - x} } \right)^ \circ {\text{, for each }}x \in \mathop \cap \limits_1^m C_1$$ where D° denotes the dual cone of D. In general, we can establish weak duality for a convex minimization problem in a Hilbert space by perturbing the constraint sets so that the perturbed sets have the strong conical hull intersection property. This generalizes a result of Gaffke and Mathar.

The placebo effect will have a growing importance in the field of nuclear medicine as the potentials for palliative therapy with internal sources are realized. It is important for nuclear medicine physicians and their colleagues to be familiar with the role of placebo responses in clinical trials, especially when such trials involve the subjective assessment of pain. A summary of the literature on the placebo effect in pain studies is presented in which traditional values for placebo responses are contrasted with more current thinking in the field. The few published double-blind studies of pain relief after treatment with radiotherapeutic agents are summarized specifically with respect to their cited placebo response.

Background and Objective Surgical reconstruction of bony defects in the maxillofacial region involves fixation of bony fragments with mini and micro plates. Bone stabilization during hole drilling is often challenging due to the need to apply pressure when using a conventional mechanical Hall drill. In addition, fragmentation of the fragile bones may occur and complicate the reconstruction. The pulsed Er:YAG laser offers an attractive alternative drilling modality because it does not require physical contact with the bone in order to drill holes, cuts bone with minimal thermal damage, and allows precise control of bone cutting. The objective of this study was to investigate the pulsed Er:YAG laser as an alternative to the mechanical bur by comparing bone healing using both modalities. Study Design/Materials and Methods Bone healing in an inferior border defect of the rat mandible was examined using either an Er:YAG laser or a mechanical but for drilling. The healing of osteotomies in facial bones and of screw holes for plate stabilization of free bone fragments was studied. Results All defects healed by 4 weeks postoperatively. Histologic evaluation demonstrated no difference in the amount of newly formed woven bone at the osteotomy site or screw holes made by either the laser or the drill. The extent of thermal damage at the osteotomy sites was comparable in laser and mechanically cut bone fragments. Conclusions On the basis of this study we suggest that the Er:YAG laser can be used clinically in thin, fragile bones in the maxillofacial region. © 1996 Wiley-Liss, Inc.

Background and Objective To determine the survival of in vitro retinal pigment epithelium (RPE) cells subjected to laser-generated stress transients (shock waves) and compare it to that of other cell lines. Study Design/Materials and Methods Normal and transformed human retinal pigment epithelium cell lines were used. The cells were imbedded in a gel to prevent motion and cavitation and located in a thin layer at the bottom of a pipette tube closed at one end by a polyimide film. Stress transients were generated by pulsed excimer laser (193 nm and 248 nm wavelength) ablation of the polyimide film. Cell survival, compared to that of unirradiated cells, was assessed by counting surviving cells. The stress was varied from 300 to 740 bars and the number of shock wave pulses applied varied from 5 to 150. Results Cell survival decreased sharply at the higher stresses but some cells always survived. The lowest survival rate was 50%. Increasing the number of shock wave pulses did not increase cell killing after 20 pulses, demonstrating a saturation effect. In contrast to the transformed cell line, normal cells could not be killed at the highest stress available to us. Conclusion The susceptibility of RPE cells to damage by stress waves varies with cell line. Transformed retinal pigment epithelium cells are more susceptible than normal ones. Saturation of the damage versus number of pulses is observed and a threshold-like behavior for cell killing versus stress is found. Because at least 50% of the cells survived, normal cell growth can serve to replenish damaged cells. © 1996 Wiley-Liss, Inc.

Massive cortical autografts and allografts have been found to incorporate into host bone very slowly and thus are subject to complications such as fatigue fracture and infection. In order to understand and improve the process of osteogenesis in these types of bone grafts, a new experimental model was developed using bone discs from rat calvaria prepared by demineralization and drilling of 0.5 mm diameter holes with a pulsed, 2.94 microns wavelength Erbium:Yttrium-Aluminum-Garnet laser. Four types of bone discs were analyzed: untreated (Type I), demineralized (Type II), laser-ablated (Type III), and laser-ablated then demineralized (Type IV). The discs were transplanted into a subcutaneous site in adult Sprague-Dawley rats and followed for as long as 6 weeks. Histologic analysis of the discs at weekly intervals with use of hematoxylin and eosin staining confirmed the presence of new bone growth in Type-II and Type-IV discs. The amount of new bone growth in each disc was estimated by determining the mineral x-ray attenuation coefficient, which is proportional to mineral density, from digitized radiographs of the discs. The results showed that the processes of demineralization (P < 0.001) and laser ablation with demineralization (p < 0.05) were both significant in enhancing new bone growth in this model. This study demonstrated that osteoinduction can be fostered in cortical bone through the processes of demineralization and laser ablation. To the extent that laser ablation may allow maintenance of structural integrity while altering the surface geometry in such a way as to promote ingrowth of new bone, this experimental model represents an advance in understanding how osteogenesis in cortical bone grafts might be improved.

Stress transients are generated in polyimide by irradiation with excimer‐laser pulses at radiant exposures between 3×10−3 and 102 J/cm2. The duration and peak stress of these transients are measured using piezoelectric film transducers. For all the wavelengths tested (193, 248, 308, 351 nm) we determine three ranges of radiant exposure within which different physical mechanisms govern the stress generation. The scaling of stress with radiant exposure depends on wavelength only in the low fluence regime. In this regime the stresses observed are attributed to subsurface thermal decomposition at 351 and 308 nm and to photodecomposition at 248 and 193 nm. At higher radiant exposure the stress generation is governed either by the thermal expansion of the gaseous ablation products or by the formation and expansion of a dense plasma. The boundary between these two regimes is identified from the variation of the mechanical coupling coefficient with radiant exposure. The results also indicate that heat conduction contributes significantly to the coupling of energy into the target, leading to a reduction in the stresses generated and to an increase in etch depth when ablation is achieved.

The kinetics of pyridine exchange on trans-[MO2(py)4]+ have been followed by 1H-NMR in CD3NO2 for M = Re, Tc: k298S−1 = (5.5 ± 0.1) × 10−6, 0.04 ± 0.02; ΔH≠/kJmol−1 = 111 ± 3, 101 ± 9; ΔS≠/JK−1mol−1 = +28 ± 10, +68 ± 35. For the Rev complex, pyridine and oxygen exchanges have been measured simultaneously by 1H- and 17O-NMR in deuterated water: k298/s−1 = (8.6 ± 0.2) × 10−6 (py), (14.5 ± 0.3) × 10−6 (oxygen); ΔH≠/kJmol−1 = 111 ± 1, 91 ± 1; ΔS /JK−1mol−1 = +32 ± 3, −32 ± 4. For both complexes, the rate law for pyridine exchange is first-order in complex and zero-order in pyridine; together with the activation parameter values, and the fact that the rate does not depend significantly on the nature of the solvent, this strongly implies the operation of a dissociative mechanism. The ratio of pyridine exchange rates for the Tc and Re complexes at room temperature is ca. 8000. The consequences of these observations for radiopharmaceutical synthesis are discussed.

We investigate shock waves generated by excimer laser ablation of sheet polyimide confined in water. The velocities of the ablation-induced pressure waves in the water are determined by an optical probe system. We measure supersonic velocities up to a few hundred microns away from the irradiated surface, indicating the formation of shock waves. We use these velocities to calculate the corresponding pressures. They are already in the kbar range at fluences comparable to the threshold of ablation. The shock pressure varies as the square root of the incident laser fluence, a behavior that is explained by the rapid heating of the confined gaseous products of ablation. The initially planar shock waves propagate, become spherical, and decay within a few hundred microns in the surrounding water to acoustic waves. During spherical expansion the shock pressure drops as the inverse of the square of the propagation distance. The shock waves generated may be relevant in explaining photoacoustic damage observed in biological tissue after excimer-ablation at corresponding irradiances. They may also be important in material processing applications of excimer laser ablation of polymers as they can lead to plastic deformation.

The dynamics of tissue ablation using an Er:YAG laser were studied using flash photography and optical pump-probe techniques. Both normal-spiking-mode and Q-switched Er:YAG laser radiation were used to study the ablation of skin and bone. Time-resolved photographs of the ablation plume were obtained using a microscope-mounted camera together with pulsed illumination from an excimer-pumped dye laser. The velocity of the plume front, obtained from the photographs, was approximately 1400 m/s. The same velocity was also measured using an optical pump-probe technique. Both techniques indicate that material removal occurred after the end of the 90-ns-long Q-switched laser pulse and that each micropulse in the normal-spiking-mode pulse train was capable of ablating and rapidly ejecting tissue.

The 355-nm transient absorption of polyimide thin films has been measured following excitation withsubablative, 24-ps long, 355-nm laser pulses. The 355-nm absorption increases by 25% following 355-nm, 20 mJ/cm2 excitation and recovers with a fast time constant ≈34 ps, and a slow time constant which is much longer than 6 ns. The data are fitted by a three-level rate equation model incorporating the temperature dependence of the ground state absorption coefficient. The fast component is attributed to the decay ofS 1 and the slow component results from increased ground state absorption caused by a laser-induced temperature rise. The nonlinear intensity dependence is attributed to excited state (S 1) absorption. These results indicate the importance of considering the dynamic absorption in modelling ablation.

Thermal damage produced by continuous wave (cw) CO2 laser ablation of tissue in vitro was measured for irradiances ranging from 360 W/cm2 to 740 kW/cm2 in order to investigate the extent to which ablative cooling can limit tissue damage. Damage zones thinner than 100 microns were readily produced using single pulses to cut guinea pig skin as well as bovine cornea, aorta, and myocardium. Multiple pulses can lead to increased damage. However, a systematic decrease in damage with irradiance, predicted theoretically by an evaporation model of ablation, was not observed. The damage-zone thickness was approximately constant around the periphery of the cut, consistent with the existence of a liquid layer which stores heat and leads to tissue damage, and with a model of damage and ablation recently proposed by Zweig et al.

Objective. Previous studies have suggested that 5-aminolevulinic acid (ALA) may be used topically on the cervix to allow optical detection of cervical dysplasia, based on the fluorescence of protoporphyrin IX (PpIX) synthesized in situ from ALA. However, the uniformity of distribution of topically applied PpIX and the sensitivity and specificity of detection are not optimal. The current study was undertaken to demonstrate the feasibility of administering ALA by mouth (po) with the hypothesis that systemic administration might provide a more reliable diagnostic tool. Methods. Oral ALA was administered to 14 patients with abnormal Pap smears in a dose- and time-intensity design. Institutional review board approval was obtained. A starting dose of 10 mg/kg of po ALA was administered and colposcopy was performed in 3 patients at 1 h, 3 patients at 2 h, 6 patients at 3 h, and 2 patients at 4 h. The study was written with the intent to increase the dose in 10 mg/kg increments if fluorescence was not detected; however, fluorescence was detected at the first dose level. Liver function tests were checked pre and post ALA and follow-up telephone calls were made regarding possible side effects. Both white and blue light colposcopy examinations were performed by two blinded clinicians and biopsies of all abnormal areas were performed. Results. All patients tolerated po ALA well, with no systemic side effects. At the 10 mg/kg dose there was no reported nausea or photosensitivity. Optimal fluorescence was achieved at the 3-h time point, with quenching noted at the 4-h time point. Excellent absorption was documented with fluorescence of the lip demonstrated with Wood's lamp. In some cases fluorescence correlated with dysplasia on biopsy. Conclusion. 5-ALA given via the po route and at the dose and time period studied is well tolerated and affords fluorescence of the cervix. Future study is needed to demonstrate the successful identification of dysplastic lesions, with the ultimate goal of treating dysplasia of the lower genital tract with 5-ALA and light therapy.

To report the results of a clinical study investigating the diagnosis of malignant and dysplastic bladder lesions by protoporphyrin IX (PPIX) fluorescence and to compare them with those from earlier studies.The study included 55 patients with suspected bladder carcinoma (at initial diagnosis or at tumour follow-up visits); 130 bladder biopsies from 49 patients were classified by pathological analysis. All patients received an intravesical instillation of 50 mL of a 3% 5-aminolaevulinic acid (ALA) solution a mean of 135 min before cystoscopy, which was then performed under white and blue light. Malignant/dysplastic lesions showing red fluorescence under blue-light excitation were noted and the increase in detection rate calculated.There were 63 benign and 67 malignant/dysplastic areas biopsied; 10 malignant/dysplastic lesions (four transitional cell carcinoma, two carcinoma in situ, four dysplasia) were not detected during routine white-light cystoscopy but were identified under blue light. Fluorescence cystoscopy improved the overall diagnosis of malignant/dysplastic bladder lesions by 18% over standard white-light cystoscopy. The improvement was greater for dysplastic lesions and carcinoma in situ (50%). However, the improvement over standard cystoscopy was less than that found by other groups.The ALA-based fluorescence detection system significantly enhanced the diagnosis of malignant/dysplastic bladder lesions. However, determining the optimum drug exposure time requires further investigation using well-characterized instrumentation and study protocols, which would then allow comparison of the results from different groups.

Overexpression of the multidrug resistance (MDR1) P-glycoprotein (Pgp) correlates with cancer chemotherapeutic failure. Lipophilic cationic radiopharmaceuticals such as 99mTc-sestamibi, 99mTc-tetrofosmin and 99Tc-furifosmin (Tc-Q12) have been validated as transport substrates for the MDR1 Pgp and may enable functional imaging of the MDR phenotype in cancer by observing enhanced washout rates of the tracers in those tumor areas expressing Pgp. To further explore and optimize the Pgp recognition properties of Schiff base phosphine mixed-ligand complexes of the Tc-Q series of nonreducible (Tc(III) cations, a variety of Tc-Q complexes were synthesized and tested in vitro for recognition as transport substrates by the human MDR1 Pgp.Tracer assays with human drug-sensitive KB-3-1 epidermal carcinoma and MDR KB-8-5 cells expressing nonimmunodetectable and modest levels of MDR1 Pgp, respectively, were used to screen and pharmacologically characterize 37 novel 99mTc-Q analogs.The ideal agent should have low nonspecific binding, high distinction in net uptake between drug-sensitive cells and MDR tumor cells, and high enhancement of uptake in resistant cells after treatment with an MDR modulator, indicating selective blockade of Pgp-mediated efflux of the radiotracer. Three analogs, trans-[5,5'-(1,2-ethanediyldiimino)bis(2-OEt-2-Me-4-penten-3 -one)]bis[dimethyl(3-OMe-1-propyl)phosphine]99mTc(III) (99mTc-Q63) and two trans-[bis(methyl-bis(3-OMe-1-propyl)phosphine)] analogs (99mTc-Q57 and 99mTc-Q58) displayed transport distinctions between drug-sensitive and MDR cell lines that were equal to or greater than all previously available agents. Cyclosporin A, an MDR modulator, had no significant effect in KB-3-1 cells for these 99mTc-complexes but enhanced tracer accumulations in KB-8-5 cells with IC50 values of approximately 1 microM. In contrast, the non-MDR agents methotrexate and cisplatin had no effect on accumulation of 99mTc-Q complexes and 99mTc-sestamibi in KB-8-5 cells.Technetium-99m-Q57, 99mTc-Q58 and 99mTc-Q63 are avid transport substrates recognized by the human MDR1 Pgp, and have enhanced in vitro properties that may enable functional imaging of Pgp in vivo with improved signal-to-noise ratios and tissue contrast compared to currently available agents.

Surgical reconstruction of bony defects in the maxillofacial region involves fixation of bony fragments with mini and micro plates. Bone stabilization during hole drilling is often challenging due to the need to apply pressure when using a conventional mechanical Hall drill. In addition, fragmentation of the fragile bones may occur and complicate the reconstruction. The pulsed Er:YAG laser offers an attractive alternative drilling modality because it does not require physical contact with the bone in order to drill holes, cuts bone with minimal thermal damage, and allows precise control of bone cutting. The objective of this study was to investigate the pulsed Er:YAG laser as an alternative to the mechanical bur by comparing bone healing using both modalities.Bone healing in an inferior border defect of the rat mandible was examined using either an Er:YAG laser or a mechanical bur for drilling. The healing of osteotomies in facial bones and of screw holes for plate stabilization of free bone fragments was studied.All defects healed by 4 weeks postoperatively. Histologic evaluation demonstrated no difference in the amount of newly formed woven bone at the osteotomy site or screw holes made by either the laser or the drill. The extent of thermal damage at the osteotomy sites was comparable in laser and mechanically cut bone fragments.On the basis of this study we suggest that the Er: YAG laser can be used clinically in thin, fragile bones in the maxillofacial region.

Hydroxyapatite (HA), a natural constituent of bone, was studied as a particulate carrier for beta-emitting radionuclides in radiation synovectomy. Particles were radiolabeled with 153Sm or 186Re and their in vivo safety was investigated following intra-articular injection into knees of normal rabbits and rabbits with antigen-induced arthritis (AIA). Radiolabeling efficiency was greater than 95%; in vitro studies showed minimal (or = 1%) loss of activity from particles over a 6-day period with 153Sm-labeled HA and about 5% loss of activity over a 5-day period with 186Re-labeled HA. The total cumulative extra-articular leakage of 153Sm over 6 days was 0.28% in normal rabbits and 0.09% in AIA rabbits. Leakage of 186Re from the joint was 3.05% over a 4-day period with 80% of extra-articular activity found in the urine. Histopathological evaluation of treated knees showed that HA particles are distributed throughout the synovium, embedded in the synovial fat pad. The ease and efficiency with which this HA carrier is labeled, coupled with observed extremely low leakage rates from the joint, make radiolabeled HA particles an attractive candidate as a radiation synovectomy agent for evaluation in rheumatoid arthritis patients.

Spatially resolved (∼1 μm) Raman scattering measurements of the Si optical phonon spectrum have been used to map the stress in silicon‐on‐sapphire device structures. Devices defined by an isolated island etch technique exhibit a stress relaxation extending about 1.5 μm from the edges of a 6‐μm‐wide Si stripe. Devices defined by a local oxidation of the Si exhibit a more uniform stress profile.

The 10.6‐μm absorption in most KCl is shown to be dominated by a broad absorption band near 9.7 μm. The integrated absorption of this band decreases with increasing temperature. The temperature dependence is consistent with that to be expected from the dissociation of an absorbing pair. A KCl crystal has been measured whose 10.6‐μm absorption, 6.6±2×10−5 cm−1, is at the intrinsic multiphonon level.

The effects of picosecond laser-induced optical breakdown on tissue were investigated using high-intensity 40 ps Nd:YAG laser pulses at 1.06 microns. Tissue damage was evaluated using the corneal endothelium in vitro as a model system. Systematic studies were performed to determine the scaling of the tissue damage and damage range with pulse energy. For suprathreshold lesions, the radius of the damage zone varies as the cube root of the pulse energy, in agreement with simple physical scaling laws. A minimum damage range of less than 100 microns was observed for pulse energies of 8 muJ. Damage morphology was investigated by scanning electron microscopy. Three different damage patterns were observed; cell damage, cell removal, and rupture of Descemet's membrane. Different irradiation geometries were used to study damage mediated by either the shock wave or the cavitation bubble. Comparative studies using 10 ns pulses demonstrated that picosecond pulses yielded a significant reduction in collateral tissue damage.

Laser endarterectomy, a promising new method of reopening stenotic or occluded arteries, has been limited by difficulties in ablating calcified plaque. This study demonstrates that pulsed, visible laser radiation (482 nm, 1 μs duration, 40-80 mJ/pulse) can ablate calcified plaque at intensities (50 MW/cm2) that are readily transmit, ted down flexible (320 μm diameter) optical fibers and at fluences which are below the threshold for ablating normal artery. The ablative process is characterized by a loud snapping sound, a luminescent plume, ejection of fine debris, and an ablation efficiency as high as 10 mg/J, suggesting that removal of material occurs primarily by formation of a plasma and fracturing of the plaque, rather than by thermal vaporization. The presence of a plasma associated with ablation of calcified plaque was documented by emission spectrum measurements.

Picosecond optical breakdown was investigated in order to assess its potential for performing highly localized incisions for laser surgery. Measurements of breakdown were performed using single 40-ps Nd: YAG laser pulses in distilled water. Novel optical pump-probe techniques were developed to characterize the transient spatial and temporal dynamics of the plasma, shock wave, and cavitation phenomena which are associated with the breakdown. The maximum cavity radius and the shock wave zone are shown to scale as the cube root of the pump pulse energy over almost three orders of magnitude. For pulse energies close to the threshold energy of 8 μJ, the shock range was ∼100–200 μm and the cavity radius was 140 μm. Complementary experiments were performed with 10-ns pulse durations. Since picosecond pulses have high peak intensities with low pulse energies, a significant enhancement in localizability may be achieved. The implications for ophthalmic microsurgery are discussed.

A focused, ultraviolet (UV) laser beam has been used to produce micrometer-sized chemical processes on solid surfaces. These processes are initiated by the photodissociatlon of a molecular gas in the vicinity of the gas-solid interface. Depending on whether the active photofragment reacts with or is adsorbed on the solid, microetching or microdeposition occurs. Both the surface properties of the solid and the gas-phase kinetics contribute to the process localization. Metal alkyls and methyl halides have been used as parent molecules for deposition and etching, respectively. A focused, 3 mW UV laser is sufficiently intense to produce satisfactory rates for both processes. Several applications of this small-scale photochemistry to microelectronics have been investigated.

The fragmentation of gallstones and kidney stones using pulsed visible laser radiation has recently been demonstrated; however, the fragmentation mechanism is not well understood. The temporal and spectral characteristics of the bright flash of light accompanying fragmentation of gallstones were studied using 0.8 and 360-μs-long, 690-nm-wavelength, dye-laser pulses. Time-resolved visible emission spectra show a broad continuum upon which line spectra are superimposed. The continuum emission is due to free-free and free-bound electron transitions indicative of a plasma and the line spectra are due to neutral and ionized calcium. Initiation of this plasma is fluence rather than intensity dependent. A model is proposed in which laser energy is coupled to the plasma, which then impulsively expands, generating intense acoustic transients which fracture the stone.

Several experiments were performed to understand the increased efficiency of microsecond-domain pulsed visible laser fragmentation of urinary and biliary stones produced by immersion in water. An optoacoustic sensor and a piezoelectric transducer were used to measure the effect of water immersion on the stress wave traveling through a stone during laser-induced ablation. The stress wave signal increased by a factor of 10 with immersion and was proportional to the square root of laser fluence. The temporal and spatial behavior of the stress wave and cavity (bubble) generated in the surrounding water were examined using pump-probe and microsecond-flash photographic techniques. The results suggest that improved fragmentation efficiency can be explained by confinement of a plasma by water.

The use of lasers in medicine began soon after the first ruby laser was invented in 1960. In recent years the number and variety of applications of lasers to biology and medicine has been increasing rapidly. I will review some of these applications, with emphasis on the physical mechanisms and the technology. After an overview of the various types of laser‐tissue interactions, I give some examples of how these interactions are exploited in medicine.

High-speed flash photographs of laser-induced fragmentation of biliary and renal calculi under water were obtained using one-microsecond-long dye-laser pulses for both illumination and ablation. The photographs show the presence of a bubble with irregularities on the surface that suggest the early presence of debris or microbubbles. Fragmentation occurs before the bubble collapses, suggesting that fragmentation is due to laser-induced acoustic transients rather than to collapse of a laser-induced cavitation bubble.

Infrared–infrared double resonance measurements of the SF6 ν3 mode spectral region for excitation levels of up to 1.2 J/cm2 are reported. Immediately following the pump laser excitation, the induced absorption spectrum of the ν3 mode shows a pronounced red shift. The spectrum then shifts to shorter wavelengths on a time scale of several microseconds, showing a cooling of the ν3 mode. At an excitation level of 3 photons/molecule the measured spectra approach the thermal spectrum expected for complete vibrational energy thermalization among all of the vibrational degrees of freedom on a time scale of 3±2 μsec. At higher excitation levels (∼10 photons/molecule) the induced spectrum still shifts on a comparable time scale but is broader than a thermal spectrum. At the lower fluence levels (∼3 photons/molecule), a ν3 mode temperature can be assigned to the spectra. The time evolution of this temperature exhibits only a weak pressure dependence. A much broader induced absorption band, approximately a factor of ...

The laser window problem is reviewed with emphasis on failure mechanisms, absorption processes, and material evaluation. Failure by thermal fracture and by optical distortion is discussed and the material parameters needed to calculate figures of merit for these failure modes are tabulated for a variety of materials. The exponential dependence of absorption coefficient on wavenumber for intrinsic multi-phonon processes is discussed and its use in discriminating extrinsic from intrinsic absorption emphasized. Laser calorimeter absorption measurements at 10. 6 Μm and 5. 25 Μm are described and the measured values tabulated. The use of internal reflection spectroscopy to examine the effect of various surface treatments on

The performance of N2–CO2–He lasers operating at pressures in the 10–120‐Torr range and with nitrogen flow rates of 20–90 standard liters per minute is discussed. A 10‐cm‐long, 13.5‐mm‐i.d. discharge tube produced 140‐W output power. These lasers operate as in‐line mixing lasers, producing about one photon per excited nitrogen molecule. Cooling is provided by rapid removal of hot gas from the discharge region.

Dye solution lasers are observed to lase at shorter wavelengths when laser pumped than when flashlamp excited. A comparison of the computed frequency‐ and time‐dependent gains for the two pumping methods explains this behavior and the observed Q dependence of the lasing frequency. This treatment also suggests a new technique for frequency tuning dye lasers.

The direct doping of InP with variable Cd concentrations has been demonstrated in a maskless process with micrometer‐scale spatial control. The process makes use of cw UV‐laser photodeposition of the dopant on a laser‐heated surface.

Metal deposits with features smaller than 2 μm have been produced by the uv laser‐induced photodissociation of organometallic compounds. Such laser‐induced heterogeneous photochemical processes may have application in several areas of microelectronics including metallization, etching, and growth of semiconductor films.

Time‐resolved detection of the surface acoustic waves (SAW) generated upon relaxation of energy optically absorbed in surface films has been used to measure surface absorption spectra and laser‐induced desorption cross sections. This new background‐free spectroscopic technique is shown to be highly sensitive to the details of the film/substrate bonding. Minimum detectable molecular surface densities of 2×1011 cm−2 over an area of 10−3 cm2 have been demonstrated for rhodamine‐590 dye on a crystal quartz substrate using a pulsed laser source and an edge‐bonded SAW detector.

Ultraviolet laser photolysis of methyl‐halides has been used to produce localized photoetching of GaAs and InP. A spatial resolution of ≃1μm has been achieved and an etch rate ≳104 times that of the dark reaction demonstrated. A chemical mechanism is proposed and the observed resolution is explained by a simple physical model.

ArF excimer laser radiation has been used to deposit W films on silicon and on SiO2 by initiating the gas phase reaction of WF6 with H2. Deposition rates >100 nm/min and film resistivities as low as two times the bulk value have been obtained at deposition temperatures of 440 °C. The properties of the laser‐deposited films are compared with those of fims obtained using conventional thermal deposition techniques. Film resistivity correlates with the microstructure which in turn depends on the deposition temperature; above 350 °C the low‐resistivity α‐W phase dominates.

Photodissociation of a thin surface layer of metal‐alkyl molecules with a UV laser is shown to be an effective technique for predisposing the irradiated region to subsequent film growth. The efficacy of this technique, termed ’’prenucleation,’’ can be understood using a simple mathematical model for the early stages of thin‐film formation. The technique has applications in direct writing of microstructures.

An Ar‐ion laser has been used to activate surface pyrolytic deposition of polycrystalline Si in a several micrometer reaction zone. Controlled doping with boron during deposition allows one‐step direct writing of highly conducting Si lines with linewidths as small as 1 μm. An unexpectedly fast deposition rate is associated with changes in the reaction kinetics as the dimensions of the reaction volume are reduced to microscopic lengths.

High‐resolution etching of single‐crystal and polycrystalline silicon has been demonstrated using an argon‐ion laser to control microscopic chemical reactions. Gas‐phase Cl2 or HCl is used in reactions initiated both by surface heating and by molecular photolysis. Features smaller than 5 μm and etch rates greater than 6 μm/s have been obtained. The process seems immediately suitable for a variety of problems in integrated‐circuit fabrication.

Laser-beam profile is an important laser parameter that is frequently ignored because conventional measurement techniques are cumbersome. A technique for accurately and rapidly measuring laser-beam profile with a commercial video camera and oscilloscope is described. Both two-dimensional pictures of the beam and quantitative, one-dimensional beam profiles can be obtained. The technique is particularly well suited for biomedical applications because it is compatible with most pulsed and continuous wave visible lasers, it uses readily available and relatively inexpensive components, and it is easy to implement.

Nitrocellulose films have been shown to function as self‐developing resist layers that are sensitive to both low‐energy ( 25:1 have been demonstrated using a stencil mask and an argon ion beam; the resolution obtained was mask limited. The sensitivity of the resist to 2‐keV Ar+ ions is 36 μm/min at beam currents of 1 mA/cm2, allowing exposure times of 1 s for 0.5 μm of resist. The material is capable of functioning as a mask material for typical semiconductor dry etching processes.

The electrical properties of single‐crystal and amorphous Si, doped using a pulsed UV laser, have been studied as a function of laser wavelength and fluence and of UV dose. BCl3 or PCl3 parent gases were used to provide B or P dopant atoms. Dissociation of molecules adsorbed on the Si surface can supplement photolysis of gas‐phase molecules as a source of doping atoms.