Continuous-wave broadly tunable intracavity frequency-doubled Cr4+: forsterite laser

Continuous-wave (CW) power performance of a room-temperature, broadly tunable intracavity frequency-doubled Cr⁴⁺: forsterite laser is described. Intracavity doubling was achieved by using a 2-cm-long periodically poled lithium niobate (PPLN) crystal. At the PPLN crystal temperature of 188°C, orange-red radiation could be obtained between 613 and 655 nm by using gratings with different poling periods. Experimentally measured temperature tuning data of the PPLN crystal was further found to be in very good agreement with theoretical predictions based on temperature-dependent Sellmeier data. With an incident pump power of 6.8 W at 1064 nm, the Cr⁴⁺: forsterite laser produced 245 mW of CW output power at 1260 nm and intracavity doubling yielded 45 mW of second harmonic output at 630 nm     

Erbium(III)‐doped polyurethaneureas: Novel broadband ultraviolet‐to‐visible converters

Novel, polymeric UV‐to‐visible converters were prepared by doping elastomeric poly(ether‐urethaneurea) copolymers with 5–25% by weight of ErCl₃ 6H₂O, corresponding to Er³⁺ concentrations of 2.19 to 10.86% by weight. When excited in the UV at 355 nm, the doped films generated a very broad, continuous visible luminescence between 400 and 750 nm. Preparation and spectroscopic characterization of the samples are discussed in detail. The color coordinates, color temperature, color rendering index of the samples, and the degree of overlap of their emission bands with the spectral response of the eye were determined. The color rendering index of samples is in the 57–70 range. The sample containing 2.19% by weight of Er³⁺ was found to give the color coordinates closest to the white‐source region and the highest color rendering index. The color temperatures of the samples were in the 5093–5540 K range. Overlap between the emission bands and the spectral response of the eye improved with increasing erbium concentration. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Comparative experimental investigation of thermal loading in continuous-wave cr(4 +):forsterite lasers

Results of a detailed experimental study aimed at reducing the thermal loading effects in room-temperature continuous-wave Cr(4+):forsterite lasers are presented. By using a Nd:YAG pump laser operated at 1.06 mum, the effect of the absorption coefficient and crystal cross-sectional area on the power performance of three crystals was compared between 12 and 36 degrees C. Experiments indicated that a low differential absorption coefficient significantly reduces the pump-induced thermal effects and cavity losses that would otherwise give rise to inefficient operation and increased temperature sensitivity. In particular, a Cr(4+):forsterite crystal with an absorption coefficient of 0.57 cm(-1) yielded as much as 900 mW of output power at 1.26 mum and a crystal temperature of 15 degrees C with an incident pump power of only 7.6 W. To the author's knowledge, the demonstrated slope efficiency of 30% represents the highest continuous-wave power performance reported to date from this laser system at elevated temperatures.     

Influence of doping concentration on the power performance of diode-pumped continuous-wave Tm/sup 3+/:YAlO/sub 3/ lasers

We investigated the effect of thulium ion concentration on the continuous-wave (CW) power performance of diode single-end-pumped thulium-doped YAlO/sub 3/ (Tm:YAP) lasers. Three samples with 1.5%, 3%, and 4% Tm/sup 3+/ concentration were examined at 18/spl deg/C. Lifetime and fluorescence measurements were further performed to assess the strength of cross relaxation and nonradiative decay. Our results showed that in single-end-pumped configurations, the best CW power performance was obtained with the 1.5% Tm:YAP sample, and laser performance of the samples degraded monotonically with increasing Tm/sup 3+/ concentration. By using 9.5 W of incident pump power at 797 nm, a maximum of 1430 mW of output power was obtained with the 1.5% Tm:YAP sample and 2% output coupler. We discuss how the effects of cross relaxation, reabsorption, nonradiative decay, and internal heating vary with increasing concentration. Spectroscopic measurements and rate-equation analysis suggest that cross relaxation should already be effective in samples with 1.5% Tm/sup 3+/ ion concentration and doping concentrations larger than 4% will lead to degradation in power performance due to higher nonradiative decay rates and larger reabsorption losses.     

MR imaging in squamous cell carcinoma of the head and neck with no palpable lymph nodes

PURPOSE: To assess the efficacy of MR imaging in the detection of lymph node metastasis in patients with no palpable lymph nodes ("N0 neck") who have squamous cell carcinoma of the head and neck region. MATERIAL AND METHODS: MR neck imagings in 18 patients who underwent neck dissection (bilaterally in 2) for squamous cell carcinoma of the head and neck region were examined preoperatively for the purpose of detecting lymph node metastases. The imaging features taken into consideration were: size (cutoff point 10 mm), grouping, presence of central necrosis, and appearance of extracapsular spread. The MR examinations comprised spin-echo T1- and T2-weighted sequences. The MR findings were compared with those of surgery and histopathological examination. RESULTS: MR suggested metastatic lymph node involvement in 5 necks. In 2 of these, central necrosis was seen in the enlarged lymph nodes. In a third, a grouping of the lymph nodes was noted. Extracapsular spread was not present. Histopathological examination revealed metastatic lymph nodes in 7 of the 20 necks, the rate of clinically occult disease being 35%, and 4 of them had been accurately graded by MR. There was one false-positive MR examination. The MR sensitivity was 57.1% and specificity 92.3%. CONCLUSION: MR may reveal metastatic lymph nodes in patients with no clinical evidence of metastasis. However, conventional MR techniques are not always sufficient for decision-making on surgery in cases of "N0 neck".     

Efficient continuous-wave radiatively cooled cr(4+):forsterite lasers at room temperature

Results of a detailed experimental investigation aimed at reducing the thermal loading problem in a cw Cr(4+):forsterite laser at elevated temperatures are presented. From a Cr(4+):forsterite crystal with a differential absorption coefficient of 0.57 cm(-1), as much as 900 mW of cw output power has been obtained at 1.26 mum and at a crystal boundary temperature of 15 degrees C with an absorbed pump power of only 4.5 W at 1.06 mum. No chopping of the pump beam was necessary. An efficient radiative cooling technique was further employed to cool the laser and no subsequent power fading was observed. To the author's knowledge, the measured absorbed power slope efficiency of 29.5% represents the highest cw power performance reported to date from a Cr(4+):forsterite laser pumped by a Nd:YAG laser around room temperature. The role of the low differential absorption coefficient in the reduction of thermal loading is further elucidated by presenting comparative cw power performance data with a second Cr(4+):forsterite crystal having a differential absorption coefficient of 1.78 cm(-1) in the temperature range between 12 and 35 degrees C. Finally, some interesting multipulse effects of the laser observed in the millisecond regime during quasi-cw operation at 50% duty cycle are described.     

Co‐Culture of Keratinocyte‐Staphylococcus aureus on Cu‐Ag‐Zn/CuO and Cu‐Ag‐W Nanoparticle Loaded Bacterial Cellulose:PMMA Bandages

Pressurized gyration and its sister processes are novel methods to produce polymeric fibers. Potential applications for such fibers include wound dressings, tissue engineering scaffolds, and filters. This study reports on a pressurized gyration technique that employs pressured N₂ gas to prepare biocompatible wound dressing bandages from bacterial cellulose and poly (methylmethacrylate) polymer blended with alloyed antimicrobial nanoparticles. Resulting bandages are manufactured with high product yield and characterized for their chemical, physical, and mechanical properties. Increased density in solutions with additional antimicrobial nanoparticles results in increased fiber diameters. Also, addition of antimicrobial nanoparticles enhances ultimate tensile strength and Young's modulus of the bandages. Typical molecular bonding in the bandages is confirmed by Fourier‐transform infrared spectroscopy, with peaks that have higher intensity and narrowing points being caused by additional antimicrobial nanoparticles. More so, the cellular response to the bandages and the accompanying antimicrobial activity are studied in detail by in vitro co‐culture of Staphylococcus aureus and keratinocytes. Antimicrobial nanoparticle‐loaded bandage samples show increased cell viability and bacteria inhibition during co‐culture and are found to have a promising future as epidermal wound dressing materials.