Dimethyl formamide-free, urea-NaCl fluorescence in situ hybridization assay for Staphylococcus aureus.

AIMS: To test the feasibility of identifying Staphylococcus aureus with a fluorescence in situ hybridization (FISH) assay that uses a single hot-plate and urea-NaCl reagents. METHODS AND RESULTS: Slides spotted with S. aureus and treated with methanol and lysozyme were incubated with urea-NaCl reagents on a hot-plate with a precise temperature control and identified with specific DNA probes. CONCLUSIONS: Staphylococcus aureus was detected and differentiated from Staphylococcus epidermidis in 1 h with a novel FISH method that used a single hot-plate and in the absence of dimethyl formamide. SIGNIFICANCE AND IMPACT OF STUDY: A rapid hot-plate FISH assay with urea-NaCl and without toxic dimethyl formamide might be useful if FISH is run infrequently or where resources are limited.

High efficiency, multi-Watt CW yellow emission from an intracavity-doubled self-Raman laser using Nd:GdVO4.

Efficient multi-Watt continuous-wave (CW) yellow emission at 586.5 nm is demonstrated through intracavity frequency-doubling of a Nd:GdVO(4) self-Raman laser pumped at 880 nm. 2.51 W of CW yellow emission with an overall diode-to-yellow conversion efficiency of 12.2% is achieved through the use of a 20 mm long Nd:GdVO(4) self-Raman crystal and an intracavity mirror which facilitates collection of yellow emission generated within the resonator, and reduces thermal loading of the laser crystal.

Increased wavelength options in the visible and ultraviolet for Raman lasers operating on dual Raman modes.

We report increased wavelength options from Raman lasers for Raman media having two Raman modes of similar gain coefficient. For an external-cavity potassium gadolinium tungstate Raman laser pumped at 532 nm, we show that two sets of Stokes orders are generated simultaneously by appropriate orientation of the Raman crystal, and also wavelengths that correspond to sums of the two Raman modes. Up to 14 visible Stokes lines were observed in the wavelength range 555-675 nm. The increase in Stokes wavelengths also enables a much greater selection of wavelengths to be accessed via intracavity nonlinear sum frequency and difference frequency mixing. For example, we demonstrate 30 output wavelength options for a wavelength-selectable 271-321 nm Raman laser with intracavity sum frequency mixing in BBO. We also present a theoretical analysis that enables prediction of wavelength options for dual Raman mode systems.

High average power, all-solid-state external resonator Raman laser.

As much as 3 W of average power at 1064 nm from a diode-pumped Nd:YAG laser, Q switched at 4 kHz, was used to pump an external-resonator, crystalline Ba(NO3)2 Raman laser generating a maximum of 1.3-W output at the first Stokes wavelength of 1197 nm. The slope efficiency was 63% with respect to the fundamental power incident on the Ba(NO3)2 crystal. A reduction in the beam quality of the Stokes output from M2 approximately 1.4 at lower Stokes powers to M2 approximately 3.4 at higher powers is attributed to thermal loading of the Raman-active crystal.

Characterizing output beams for lasers that use high-magnification unstable resonators.

Laser beams generated from high-magnification on-axis unstable resonators by use of hard-edged optics typically have a doughnut-shaped distribution in the near field (i.e., a flat-top profile with a hole in the middle for an axially coupled beam). We derive analytical expressions describing this distribution by using the flattened Gaussian beams concept. The superposition of two flattened Gaussian beams whose flatness and steepness of edges are controlled by defined parameters (i.e., the beam width and the order) is used to analyze the output beam intensity along the propagation axis. Finally, experimental measurements of beam propagation from a copper-vapor laser fitted with a high-magnification unstable resonator show excellent agreement with theoretical predictions.

Efficient continuous-wave self-frequency-doubling green diode-pumped Yb:YAl(3)(BO(3))(4) lasers.

Efficient cw self-frequency-doubled green laser output of 160 mW has been obtained from Yb:YAl(3)(BO(3))(4) crystal pumped by 1.4-W incident power from a fiber-coupled 976-nm laser diode. The incident-pump-power-green-output-power conversion efficiency is greater than 11.3%, and the electrical-input-green conversion efficiency is 3.9%. Tunable green output from 513.0 to 545.8 nm is also demonstrated with a quartz birefringent filter.

Sutureless microvascular anastomoses by a biodegradable laser-activated solid protein solder.

A new sutureless technique to successfully anastomose the abdominal aorta of rats (1.3 mm in diameter) by using a fully biodegradable, laser-activated protein solder is presented. A total of 90 rats were divided into two groups randomly. In group one, the anastomoses were performed by using conventional microsuturing technique, whereas in group two, the anastomoses were performed by using a new laser welding technique. In addition, each of the two groups were divided into five subgroups and evaluated at different follow-up periods (10 minutes, 1 hour, 1 day, 1 week, and 6 weeks). At these intervals, the anastomoses were evaluated for patency and tensile strength. Three anastomoses in each subgroup were processed for light and electron microscopy. All anastomoses were found to be patent. The mean clamp time of the anastomoses performed with conventional suturing was 20.6 minutes compared with 7.2 minutes for the laser-activated welded anastomoses (p < 0.001). The strain measurements showed a stronger mechanical bond of the sutured anastomoses in the initial phase. However, at 6 weeks the tensile strength of the laser-welded anastomoses was higher compared with the conventional suture technique. Histologic evaluations revealed a near complete resorption of the solder after 6 weeks. The junction site of the vessel ends cannot be determined on the luminal side of the artery. In conclusion, a resorbable protein used as a solder, activated by a diode laser, can provide a reliable, safe, and rapid arterial anastomosis, which could be performed by any microsurgeon faster than conventional suturing after a short learning curve.

Efficient all-solid-state yellow laser source producing 1.2-W average power.

We report a practical and efficient all-solid-state laser source operating at 578 nm. The source comprises a diode-pumped Nd:YAG laser gain medium producing fundamental output at 1064 nm, an intracavity LiIO (3) Raman-active crystal that generates first-Stokes output at 1155 nm, and an intracavity LiB(3)O(5) frequency-doubling crystal, which frequency doubles the first-Stokes output to 578 nm. Q -switched output with as much as 1.2-W average power has been obtained; conversion efficiencies from the fundamental to the yellow as high as 33% have been obtained.

Laser nerve repair by solid protein band technique. I: identification of optimal laser dose, power, and solder surface area.

Thirty-four tibial nerves in 17 adult male wistar rats were repaired by applying protein bands longitudinally across the nerve join. The bands were then irradiated with a fibre-coupled diode laser (lambda = 810 nm). The relations among the laser weld breaking force, the power, and the solder surface area were investigated, while maintaining a consistent ratio between the total mass of protein solder in a band and total laser energy delivered (the laser energy dose). When this laser energy dose was held constant, the average breaking force of the laser welds irradiated by 72 mW laser output power was weaker than that reached after 90 mW laser radiation. There is a linear relation between the solder breaking force and the solder surface area when band thickness, laser power, and laser dose are unvaried.

Laser nerve repair by solid protein band technique. II: assessment of long-term nerve regeneration.

A total of 18 adult male Wistar rats had left tibial nerve repaired by either the laser-solder technique or a more conventional microsuture technique. The diode laser power was 90 mW and the radiation dose 16 J/mg. Three months postoperatively electrophysiology showed that the average compound muscle action potential (CMAP) of the laser repair group was not significantly different from the CMAP of the sutured nerves. Light microscopy confirmed regeneration of myelinated axons in both groups of animals. The laser-solder technique, when used with such parameters, proved to be a reliable method to achieve satisfactory peripheral nerve anastomosis and nerve regeneration.

Enhanced performance of elemental copper-vapor lasers by use of H(2)-HCl-Ne buffer-gas mixtures.

The output power from a 25-mm-diameter (volume, 0.49 L) and a 40-mm-diameter (volume, 1.9 L) copper-vapor laser (nominally 20- and 65-W devices, respectively) was approximately doubled to >50 and >100 W , respectively, by addition of small partial pressures of both H(2) and HCl to the neon buffer gas. The specific output powers of these lasers are believed to be records for any copper-vapor lasers of this size.

Repetition-rate scaling of a kinetically enhanced copper-vapor laser.

The output power of a kinetically enhanced Cu-vapor laser is shown to increase linearly with pulse repetition frequency to an experimental limit of 22 kHz. Output power of >150 W has been produced by a medium-scale (38-mm diameter, 1.55-m long) device operating at 22 kHz.

Pulse-stacking technique for enhanced performance of a solid-state laser pumped by a high-pulse-rate source.

We report on a pulse-stacking technique in which a Cr, Nd:GSGG laser pumped by a high-pulse-rate (25 kHz) source is Q switched at lower pulse rates (submultiples of the pump rate) to achieve higher-output pulse energies and shorter pulse durations. For six pump pulses stacked, the output peak power increased by a factor of 10 compared with gain-switched output.

A common strategic language for clinicians and senior managers.

Effective strategic analysis of existing and potential services requires a framework which is relevant and understandable to both clinicians and senior managers. Our work with NHS trusts has developed a framework based on analysis of services into four principal service streams--emergency general hospital, non-emergency general hospital, specialist general hospital and tertiary. Relating service streams to clinical specialties provides a matrix which can provide a basis for an initial analysis of the current and prospective clinical services portfolio, allowing drilling down into the detail and back up to the overall picture. Portfolio effectiveness is assessed by considering overall viability consisting of three interrelated elements--clinical, market and financial viability. The interrelationship of service streams, clinical specialties and viability allows the trust board and key clinicians to share insights into the current and potential systemic linkages between these three elements and to develop a vision of future strategic direction.

Observation of single-cell fluorescence spectra in laser flow cytometry.

We report the first demonstration of directly recording fluorescence spectra of single cells in flow cytometry. An intensified, 512-element photodiode array was used in conjunction with a dispersing prism to capture the fluorescence emission spectra of Coulter ImmunoCheck calibration beads and Dictyostelium discoideum spores stained with the indocarbocyanine derivative CY3, fluorescein isothiocyanate, or R-phycoerythrin. The demonstration was made feasible by enhancing the signal-to-noise ratio of the detection process by using a fast gating technique applied to the detector. Results show that the complete fluorescence spectra of individual stained cells contain information that is normally not captured by conventional flow cytometers. By using the spectrographic flow cytometer, all this information is recorded, allowing small features and shifts in the fluorescence spectra of labelled particles to be studied.

Thermally induced strain and birefringence calculations for a Nd:YAG rod encapsulated in a solid pump light collector.

Calculations and experimental measurements of the thermally induced strain and birefringence are presented for a diode-pumped Nd:YAG rod that is encapsulated in a prismatic pump light collector. A numerical model is developed to determine the spatiotemporal stress-induced strain distribution across the prism, index-matching fixant, and laser rod, and the birefringence that arises from the stress-induced strain within the laser rod. Calculations of the birefringence are compared with polarscopic measurements and display good agreement. Support for the rod on all sides is provided by the prism and fixant, and the distribution and degree of the stress-induced strain (and birefringence) within the laser rod are therefore influenced by the geometry and composition of the prism and fixant. These strains are thermomechanical in origin and are primarily a function of the elastic modulus of the fixant and the temperature of the system. Such stress-induced strains are additional to those strains that are produced from temperature gradients across the laser rod and result from the laser rod being constrained from expanding. Collectors utilizing index-matching fluid as the encapsulant display the smallest measure of birefringence relating to the temperature gradients in the rod. However, for collectors utilizing solid fixants (with significant elastic modulus), an increase in the birefringence results. In this case collector designs that have the laser rod located in a symmetrically shaped prism are effective in reducing the nonuniform pressures on the sides of the rod and therefore the birefringence.

Encapsulated rod for efficient thermal management in diode-side-pumped Nd:YAG lasers.

Theoretical calculations of energy deposition, temperature, and thermally induced birefringence are presented for a diode-side-pumped Nd:YAG laser that has the laser rod optically fixed into a right-rectangular prism with a square cross section. The design provides uniform cooling of the rod and allows for a number of conduction-cooling techniques to be used. Average output powers >5 W are feasible at optical-to-optical efficiencies of ~20% for long-pulse operation and ~10% for Q-switched operation for quite simple and convenient cooling arrangements (e.g., Peltier cooling).

Thermal modeling of solid nonfocusing pump-light collectors used for diode-pumped Nd:YAG lasers.

We have developed a thermal model for the determination of the temperature distribution of a diode side-pumped Nd:YAG laser in which the laser rod is fixed in a solid nonfocusing (prismatic) pump-light collector. The model permits the temperature to be determined as a function of both spatial and temporal parameters for a wide range of boundary conditions and different collector materials. Interferometric measurements were carried out to obtain the averaged rod temperatures for comparison with results from the model and to fix a convective-cooling rate for ambient air that best fits the experimental results. Two cases were studied both theoretically and experimentally with artificial sapphire and BK7 as prism materials, and good agreement was achieved between model and experimental results. The use of artificial sapphire as the prism material reduces by a factor of ~7 both the rod temperature and the warm-up time compared with BK7 glass. Peltier cooling of the underside of the BK7 glass prism yields thermal Characteristics of the device that are similar to those devices with sapphire prisms. Calculations also show that the thermal properties of the fixant are not critical for moderate fixant thermal diffusivities (i.e., k(f) > 10(-8)-10(-7) m(2) s(-1)), thus the choice of an appropriate fixant can be based on its mechanical and index-matching properties alone.

Fixed-wavelength operation of a copper-laser-pumped dye laser injection seeded by low-power He-Ne lasers.

The design and operating characteristics of a dye laser pumped by a 3-W copper-vapor laser (CVL) and injection seeded by low-power (1-5 mW) He-Ne lasers at 633 nm are reported. An extremely simple optical arrangement is used wherein the output mirror of the He-Ne laser and a third mirror form the dye laser cavity. Laser efficiency in fixed-wavelength operation has been investigated for variable CVL pump power, He-Ne injection power and polarization, and cavity output coupling for a standard Rhodamine 590/Rhodamine 640 dye solution. Over 90% of free-running (unseeded) laser power is obtained in fixed-wavelength (seeded) operation at low CVL pump powers (≤1 W), dropping to approximately 60% at 3-W pump power. Maximum CVL pump to dye laser optical conversion efficiency in narrow-band, fixed-wavelength operation at 633 nm was 12%.

Theoretical modeling of a diode-pumped Nd:YAG laser with a solid nonfocusing pump light collector.

We report theoretical modeling for a diode-side-pumped Nd:YAG laser in which the laser rod is fixed in a solid nonfocusing (prismatic) light collector. The geometry provides for pumping the rod from four sides, which gives a relatively uniform gain profile across the transverse section of the rod and enables a high tolerance of the laser output to resonator and pump diode misalignment. The numerical model is developed to illustrate how the pumping uniformity and the transfer efficiency are affected when changes in the collector and lasing materials are made. We use small-signal gain measurements to test the predictions of the model and to examine the extent to which surface scattering from the rough rod barrel further spatially averages the deposited pump energy. The effects of the different refractive indices of the rod, collector, and fixant and the absorption properties of the laser material on optical transfer efficiencies are discussed.