Faraday isolator for a 100 J/10 Hz pulsed laser.

We report the first-ever, to the best of our knowledge, demonstration of the optical isolation of a kilowatt average power pulsed laser. A Faraday isolator capable of stable protection of the laser amplifier chain delivering 100 J nanosecond laser pulses at the repetition rate of 10 Hz has been developed and successfully tested. The isolator provided an isolation ratio of 30.46 dB in the course of an hour-long testing run at full power without any noticeable decrease due to the thermal effects. This is the first-ever, to the best of our knowledge, demonstration of a nonreciprocal optical device operated with such a powerful high-energy, high-repetition-rate laser beam, opening up the possibilities for this type of laser to be used for a number of industrial and scientific applications.

Thermal-stress-induced birefringence management of complex laser systems by means of polarimetry.

The novel method of the thermally-induced polarization changes driven power losses (TIPCL) analysis in the complex laser systems has been developed. The measurement has been tested on the amplifier chain of the 100 J / 10 Hz laser system 'Bivoj' operated at HiLASE Centre. By the usage of the measured non-uniform Mueller matrix of the amplifier chain, the optimization of the ideal input and output polarization state has been calculated numerically. The results of the optimization have been applied to the laser system, thus reducing the TIPCL from originally observed more than 33% to 7.9% for CW beam and to 9% for pulsed laser beam, respectively. To the best of our knowledge, this result represents the most efficient TIPCL suppression method for complex laser systems so far. The method also allows the definition of the ideal fully polarized non-uniform pre-compensation of input beam consequently suffering from zero TIPCL.

Investigation of the lasing performance of a crystalline-coated Yb:YAG thin-disk directly bonded onto a silicon carbide heatsink.

We investigated the use of crystalline coatings as the highly reflective coating of an Yb:YAG thin disk directly bonded onto a silicon carbide heatsink. Compared to commonly used ion-beam-sputtered coatings, it possesses lower optical losses and higher thermal conductivity, resulting in better heat management and laser outputs. We pumped the disk up to 1.15 kW at 969 nm and reached 665 W of average output power, and disk temperature of 107 °C with a highly multi-modal V-cavity. These promising results were reached with this novel design despite the adoption of a cheap silicon carbide substrate having more than 3 times lower thermal conductivity compared to frequently used CVD diamond.

Faraday Rotation of Dy2O3, CeF3 and Y3Fe5O12 at the Mid-Infrared Wavelengths.

The relatively narrow choice of magneto-active materials that could be used to construct Faraday devices (such as rotators or isolators) for the mid-infrared wavelengths arguably represents a pressing issue that is currently limiting the development of the mid-infrared lasers. Furthermore, the knowledge of the magneto-optical properties of the yet-reported mid-infrared magneto-active materials is usually restricted to a single wavelength only. To address this issue, we have dedicated this work to a comprehensive investigation of the magneto-optical properties of both the emerging (Dy2O3 ceramics and CeF3 crystal) and established (Y3Fe5O12 crystal) mid-infrared magneto-active materials. A broadband radiation source was used in a combination with an advanced polarization-stepping method, enabling an in-depth analysis of the wavelength dependence of the investigated materials' Faraday rotation. We were able to derive approximate models for the examined dependence, which, as we believe, may be conveniently used for designing the needed mid-infrared Faraday devices for lasers with the emission wavelengths in the 2-µm spectral region. In the case of Y3Fe5O12 crystal, the derived model may be used as a rough approximation of the material's saturated Faraday rotation even beyond the 2-µm wavelengths.

Worm-like appearance of Listeria monocytogenes brain abscess: presentation of three cases.

Brain abscess caused by Listeria monocytogenes (LM) is a rare, yet serious condition with high mortality if not recognized and treated timely. We present a series of three cases of LM brain abscesses and describe their characteristic radiological appearances which can be considered very typical. LM abscesses frequently present as markedly irregular formations, revealing characteristic worm-like tubular pattern of chaotic curvilinear arrangement. Knowledge of this imaging pattern can be very helpful in early recognition of LM abscesses whose initial differential diagnosis can often be misleading initially.

Verdet constant of potassium terbium fluoride crystal as a function of wavelength and temperature.

Potassium terbium fluoride KTb3F10 (KTF) crystal is a promising magneto-active material for creating multi-kilowatt average-power Faraday isolators operating at the visible and near-infrared wavelengths. Nevertheless, the key material's parameter needed for the design of any Faraday isolator-the Verdet constant, has not been comprehensively investigated yet. In this Letter, we report on measurement of the Verdet constant of the KTF crystal for wavelengths between 600 and 1500 nm and for temperatures ranging from 15 to 295 K. A suitable model for the Verdet constant as a function of wavelength and temperature has been developed and may be conveniently used for optimal design of KTF-based high-average-power Faraday isolators.

Radiological markers of idiopathic normal pressure hydrocephalus: Relative comparison of their diagnostic performance.

PURPOSE: Numerous radiological measures have been proposed as imaging biomarkers of idiopathic normal pressure hydrocephalus (iNPH), however, the number of studies systematically comparing their diagnostic values remains limited. The study objective was to compare the diagnostic performance of fifteen cross-sectional imaging iNPH biomarkers. MATERIALS AND METHODS: Eighty subjects were prospectively enrolled in the study: 35 subjects with clinically confirmed iNPH and 45 matched healthy controls (HC). Values of linear, angular and index measurements including three newly proposed biomarkers were obtained from 3T brain MRI studies by two independent readers. Diagnostic performance of biomarkers was studied by using receiver operating characteristic (ROC) analysis and t-statistic. RESULTS: All biomarkers studied were able to reliably differentiate iNPH subjects from HC (p < .001) except for cella media-to-temporal horn ratio. Z-Evans index, vertical cella media and vertical frontal horn diameters showed the highest discriminatory power between iNPH and HC groups (area under curve >0.99). Simple linear measurements of vertical (0.99) or horizontal (0.95) frontal horn diameters showed results comparable to calculated ratios, i.e. z-Evans (0.99) and Evans (0.96) indexes, respectively. CONCLUSION: The best diagnostic performance among fifteen radiological iNPH biomarkers was found in linear measurements referring to caudocranial alterations of the ventricular geometry, outweighing those referring to laterolateral ventricular enlargement (as e.g. commonly used Evans index). Simple linear measurements of vertical or horizontal frontal horn diameters showed comparable results to calculated, more time-consuming z-Evans or Evans indexes, respectively.

Percutaneous cholecystostomy in the management of acute cholecystitis - 10 years of experience.

INTRODUCTION: The preferred treatment for acute cholecystitis is cholecystectomy, but for patients with precluded general anesthesia due to critical illness or multiple medical comorbidities it is not suitable. Cholecystostomy could be a minimally invasive therapeutic alternative. AIM: To retrospectively evaluate the indications, technical features, efficacy, complications, patients' development and relationships among monitored parameters of percutaneous computed tomography (CT)-guided cholecystostomies in cases of acute cholecystitis and find the role of this procedure in appropriate treatment selection. MATERIAL AND METHODS: Over the course of 10 years, 75 percutaneous cholecystostomy procedures in 69 patients were performed in cases with diagnosed acute cholecystitis, precluded general anesthesia and contraindicated cholecystectomy by an experienced surgeon and anesthesiologist. These interventions were done using only local anesthesia. The patients were men in 39 cases and women in 33 cases, aged 33 to 91 years. RESULTS: Technical success was achieved in all cases. The indications were sepsis in 34 (45.3%) cases, bridging acute gallbladder inflammatory status in 15 (20%) interventions, serious medical comorbidities in 8 (10.7%) cases, disseminated malignancy and cardiac failure in 6 cases each (both 8%) and neurological affections in 5 (6.5%) cases. Cholecystostomy was frequently the final solution in acalculous cholecystitis (79.3%). The 30-day mortality rate was determined at 10.7% and the overall complication rate was 21.3%, but all of these complications were managed conservatively or using minimally invasive treatment. CONCLUSIONS: Percutaneous CT-guided cholecystostomy is reserved for patients with a serious medical status for various reasons that preclude surgical treatment and general anesthesia. Simultaneously, technical success and efficacy are high and the complication rate is acceptable.

Wavelength dependence of magneto-optic properties of terbium gallium garnet ceramics.

The wavelength dependence of magneto-optic properties of TGG ceramics, including the Verdet constant, has been investigated experimentally. The previously obtained Verdet constant of 36.4 rad/Tm for 1064 nm wavelength and 139.6 rad/Tm for 633 nm are in good agreement with presented white light measurements . The comparison with previously reported Verdet constant and absorption coefficient values for TGG single crystal has shown very similar results. These results lead to the conclusion that TGG ceramics is a very good alternative to TGG single crystal and is a powerful approach for realizing large-aperture optical isolators which are required in high-average-power laser systems.

Design and optimization of an adaptive optics system for a high-average-power multi-slab laser (HiLASE).

We report numerical and experimental results obtained with an optical setup that simulates the heating and cooling processes expected in a multi-slab high-average-power laser head. We have tested the performance of an adaptive optics system consisting of a photo-controlled deformable mirror (PCDM) and a Shack-Hartmann wavefront sensor for the effective correction of the generated wavefront aberrations. The performance of the adaptive optics system is characterized for different layouts of the actuator array and for different configurations of the heating mechanisms. The numerical results are benchmarked using a PCDM, which allowed us to experimentally compare the performances of different deformable mirrors.