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Liver diseases are known to influence the serum concentration of insulin-like growth factor I (IGF-I) in humans, but such an effect has rarely been investigated in dogs. The aim of this study was to investigate serum IGF-I concentrations in dogs with primary liver diseases, in comparison with levels in healthy dogs and dogs with non-hepatic diseases. For this purpose, IGF-I serum concentrations were measured (DSL-5600 kit) in 36 dogs with various liver diseases and compared with 22 healthy controls and 20 dogs with non-hepatic diseases. The results showed that dogs with liver diseases had significantly lower IGF-I serum concentrations (P < 0.001) than clinical healthy dogs or dogs with non-hepatic diseases. But the results also indicate that the aetiology of liver disease has no influence on IGF-I serum concentration.

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BACKGROUND: With the assistance of ultrashort laser pulses (ca. 200 fs pulse duration) it is possible to perform precise incisions inside the corneal stroma with a width of a few microns. The advantage of ultrashort pulses is that the required energy of a few microjoules is more than an order of magnitude lower compared with longer pulse durations, i.e. ps or ns pulses. Therefore, the secondary effects, such as thermal and mechanical damage to the surrounding tissue and the amount of radiation reaching the retina, are reduced. This method of intrastromal photodisruption allows a very well defined deposition of energy within the laser focus inside the corneal stroma, accompanied by minimal collateral damage. METHODS: The possibilities of performing intrastromal cuts using fs-laser pulses at a wavelength of 780 nm and pulse durations of 200 fs were studied using a titanium-sapphire laser system. The treated tissue samples were analysed by light and scanning electron microscopy to determine incision quality, reproducibility and achievable accuracy. The mechanical side effects of fs-photodisruption inside the surrounding tissue were analysed by pressure measurements using pyroelectric transducers. CONCLUSION: The thermal and mechanical side-effects of this method are very low and comparable to the effects during excimer treatment. Therefore an application of ultrashort laser pulses in refractive surgery appears to be a feasible alternative.

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BACKGROUND: Considerable problems occur in transscleral laser cyclophotocoagulation concerning energy dosage. We investigated the feasibility of localizing the ciliary body by the detection of thermoelastic pressure transients and of supervising on-line the degree of tissue damage during treatment. METHOD: We used a specially designed handpiece to apply short pulsed laser radiation with low energy levels to enucleated bulbs of rabbits. With an adjusted pressure transducer we examined acoustical transients generated in the area of absorption of the ciliary muscle or the pigmented epithelial layer and measured axial resolution of the method at various distances to the corneoscleral limbus. RESULTS: We detected acoustic transients that allowed rough localization of the target area. A marked change in signal was recorded with increasing level of ciliary destruction. CONCLUSION: This procedure can serve as an essential tool in the on-line supervision of the coagulation process. The laser parameters can thus be adjusted optimally to the progress of the treatment.

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We have demonstrated more than 3 W of average output power from a 2.94-mu;m quasi-cw diode-pumped total internal reflection (TIR) Er:YAG laser operating at 100 Hz with a 4% duty cycle. Moreover, repetition rates of up to 600 Hz at more than 1.2-W output power have been achieved. The cavity consists of a plane-mirror resonator of 40-mm length and uses three of five TIR regions within the laser crystal as pump facets to efficiently couple the pump energy into the resonant laser mode. Differential efficiencies of up to 18.3% have been achieved at an optimum pump pulse width in the range of 300 micros .

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BACKGROUND: Recently, laser systems have become available which generate ultrashort laser pulses with a duration of 100-200 femtoseconds (fs). By generating micro-plasmas inside the corneal stroma with fs pulses, it is possible to achieve a cutting effect inside the tissue while leaving the anterior layers intact. The energy threshold to generate a micro-plasma with fs pulses is some orders of magnitude lower than it is for picosecond or nanosecond pulses. This results in a strong reduction of the thermal and mechanical damage of the surrounding tissue. METHODS: With a titanium:sapphire fs laser system, the cutting effect on corneal tissue from freshly enucleated porcine eye globes was investigated with different pulse energies. The irradiated samples were examined by light and electron microscopy. The laser-induced pressure transients and the laser-induced bubble formation were analysed with a broadband acoustic transducer and by flash photography. RESULTS: With fs laser pulses, the extent of thermal and mechanical damage of the adjacent tissue is in the order of 1 microm or below and therefore comparable with the tissue alterations after ArF excimer laser ablation. Using pulse energies of approximately 1-2 microJ and a spot diameter of 5-10 microm, intrastromal cuts can be performed very precisely in order to prepare corneal flaps and lenticules. CONCLUSION: Femtosecond photodisruption has the potential to become an attractive tool for intrastromal refractive surgery.

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We demonstrate a master-oscillator fiber power-amplifier system consisting of a diode-pumped monolithic nonplanar ring oscillator as the master oscillator and a Nd:glass double-clad fiber as the power amplifier. The system emits up to 5.5 W of single-frequency radiation at a wavelength of 1064 nm with an M(2) value of ~1.1 . The optical emission spectrum is investigated with respect to the background of residual amplified spontaneous emission. Spectrally resolved amplitude-noise behavior is examined. Further power-scaling possibilities are discussed.

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Spatially localized femtosecond pulses have been produced by a combination of scanning near-field optical microscopy with ultrashort pulse lasers. With these pulses direct ablative writing on metal surfaces is demonstrated. Possible applications of this technique for nanostructuring, repair, and production of lithographic masks are discussed.

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PURPOSE: This study was designed to investigate the quality of a scanning and rotating slit delivery system of an ArF excimer laser (Nidek EC-5000). METHODS: The ablation patterns on polymethylmethacrylate (PMMA) wafers were examined by scanning electron microscopy. The influence of inhomogeneities in the beam profile was simulated on a computer and compared with a conventional large-area ablation system. The impairment of the ablation rate by radiation absorption of the ablation plume was measured as a function of the repetition rate and the application of a fixation ring. RESULTS: The scanning and rotating slit delivery system is tolerant of small-beam non-homogeneities. The ablation rate is sensitive to the dynamics of the ablation plume. CONCLUSIONS: Although the operating procedure takes less time with a large-area ablation system, a scanning and rotating delivery system has the advantage of reliable and homogeneous removal of corneal tissue.

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We have realized novel electrode configurations for efficient periodic poling of ferroelectric crystals by applying a simple patterning method based on laser-induced material ablation. The new geometries were theoretically investigated and compared with conventional configurations. A systematic optimization of the patterning according to the ablated profile led to high-quality quasi-phase-matched structures in lithium niobate with a grating period of 20 mum . The periodically poled samples were characterized by use of third-order second-harmonic generation of a Nd:YAG laser.

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A compact source of stable cw single-frequency radiation at 473 nm has been realized by second-harmonic generation of a diode-pumped miniature Nd:YAG ring laser operating on the (4)F(3/2) - (4)I(9/2) laser transition. By use of potassium niobate (KNbO(3)), single-longitudinal-mode output powers of 500 mW cw with high stability and maximum optical-to-optical conversion efficiencies >81% are achieved. An external semimonolithic cavity permits mode-hop-free frequency tuning of blue radiation over as much as 20 GHz.

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Applying Cr(4+):YAG saturable absorbers, we demonstrate efficient passively Q -switched operation of diode-pumped Nd:YAG lasers with a maximum average output power of more than 800 mW. Pulse durations below 3 ns, energies of 70 microJ, and peak powers of 30 kW are observed with kilohertz repetition rates. Single-frequency operation is accomplished for all output powers by a nonplanar ring geometry.

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A new external-cavity diode laser system based on an extended version of the Littman configuration is investigated. In our laser system the tuning mirror is replaced with a second grating mounted at the Littrow angle. This double-grating design provides a smaller passive bandwidth than the grating-mirror configuration, which is used to compensate for the large angle-of-incidence-dependent losses of the grazing-incidence grating. This results in a broader continuous tuning range with an improved mode stability. Because two laser diodes, emitting at 820 and 775 nm, respectively, are used, the external-cavity laser is continuously tunable without mode hops across 35 nm at 820 nm and 27 nm at 775 nm. Such a laser was used to measure the absorption lines of the oxygen A band around 762 nm. The complete R - and P -rotational branches of the b summation operator(g)(1) (+)(nu(??)=0)?X (3) summation operator(g)(-)(nu (?)=0) transition were recorded in a single-wavelength scan.

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This study was designed to investigate the quality of a scanning and rotating slit delivery system of an ArF-Excimer laser (Nidek EC 5000). The ablation patterns on PMMA samples were examined by REM. The influence of inhomogeneities in the beam profile was simulated on a computer and compared with a conventional large-area ablation system. The impairment of the ablation rate by radiation absorption of the ablation plume was measured as a function of the repetition rate and the application of a fixation ring. The scanning and rotating slit delivery system creates extremely smooth ablation patterns. The delivery system is very tolerant of small-beam inhomogeneities. The ablation rate is very sensitive to the dynamics of the ablation plume. Although the operating procedure takes less time with a large-area ablation system, a scanning and rotating delivery system has the advantage of reliable and homogeneous removal of corneal tissue.

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Amplitude and frequency noise of an injection-locked diode-pumped Nd:YAG ring laser operating at a singlefrequency output power of 20 W cw are investigated. This laser system will be used as a light source for an interferometric gravitational-wave detector.

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We report on a 9.2-W cw, two-times diffraction-limited, neodymium-doped fiber laser operating in the 1.06-microm region. For a silica-based double-clad fiber, slope efficiencies of more than 25% are observed for pumping by a diode-laser system operating near 810 nm.

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We report on the laser performance and power scaling properties of diode-laser side-pumped Nd:YAG rod lasers operating at high cw output powers. Applying a pump power of 1100 W cw in a ninefold pump geometry, we obtain an output power of more than 300 W in multimode operation. For a comparable pump scheme an output power of more than 45 W in TEM(00) mode operation is realized with an optical-to-optical efficiency of more than 11%.

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Several idiots savants who were able to identify prime numbers have been reported. This ability requires complex calculations, because no simple algorithms are known for determining primes. Many savants, however, who demonstrate this ability, do not possess the arithmetical skills to perform such calculations. Explanations offered for the feats of idiots savants are reviewed in the light of their applicability to the cases of prime identification. Existing models cannot fully explain prime number identification for savants with weak arithmetical skills. The author shows that through the natural tendency of visual perception to be organized symmetrically, a distinction between prime and nonprime numbers can be made. This process could both explain the origin of the interest and the ability to identify prime numbers in mathematically weak savants.

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Subpicosecond pulses at 193 nm, generated by a nonresonant difference-frequency mixing process in xenon, have been amplified in an ArF excimer gain module to output energies of as much as 10 mJ. Investigations on the gain characteristics of the ArF excimer amplifier yield a saturation energy density of 1.9 mJ/cm(2) and a maximum small-signal gain coefficient of 0.15 cm(-1). Gain recovery measurements have been performed. A dominant gain recovery time of ~3 ns with indications of a small fast contribution in the picosecond range have been observed.