Experimental investigation of a high-power 1018 nm fiber laser using a 20/400 µm ytterbium-doped fiber.

A 472 W monolithic fiber laser, operating at 1018 nm by employing an active fiber with a low core/cladding diameter ratio of 20/400 µm, is reported in this paper. The slope efficiency and beam quality factor (M2) of the fiber laser are, respectively, 49.4% and 1.17. To realize the setup, the effects of the characteristics of the experimental elements-reflectivity of the output coupling fiber Bragg grating, length of the active fiber, etc.-on the output behavior of the system have been investigated. These are the highest recorded output signal power, efficiency, and beam quality factor in monolithic 1018 nm ytterbium-doped fiber lasers using fibers with a core/cladding diameter ratio of 20/400 µm.

Simultaneous measurement of temperature and refractive index using focused ion beam milled Fabry-Perot cavities in optical fiber micro-tips.

Optical fiber micro-tips are promising devices for sensing applications in small volume and difficult to access locations, such as biological and biomedical settings. The tapered fiber tips are prepared by dynamic chemical etching, reducing the size from 125 µm to just a few µm. Focused ion beam milling is then used to create cavity structures on the tapered fiber tips. Two different Fabry-Perot micro-cavities have been prepared and characterized: a solid silica cavity created by milling two thin slots and a gap cavity. A third multi-cavity structure is fabricated by combining the concepts of solid silica cavity and gap cavity. This micro-tip structure is analyzed using a fast Fourier transform method to demultiplex the signals of each cavity. Simultaneous measurement of temperature and external refractive index is then demonstrated, presenting sensitivities of - 15.8 pm/K and -1316 nm/RIU, respectively.

Simulation, fabrication, and characterization of a tunable electrowetting-based lens with a wedge-shaped PDMS dielectric layer.

Microlenses with tunable focal length have wide applications in optofluidic devices. This work presents a numerical and experimental investigation on a tunable electrowetting-based concave lens. Optical properties such as focal length of the lens and visibility of images were investigated numerically and experimentally. A finite element analysis and a ZEMAX simulation were used for determination of surface profile and focal length of the lens. The results show that the theoretical surface profile and focal length of the lens are in good agreement with the experimental ones. The lens has a wide tuning focal length equal to 6.5 (cm). Because the polydimethylsiloxane (PDMS) layer is wedge shaped (as both the dielectric and hydrophobic layers), lower applied voltage is needed. A commercial program was used to find the focal length of the lens from maximum visibility value by tuning the applied voltage.

Prevalence of different kinds of maxillofacial fractures and their associated factors are surveyed in patients.

INTRODUCTION: Nowadays maxillofacial fractures have increased. In this study prevalence of different kinds of maxillofacial fractures and their associated factors are surveyed in patients referred to Imam Khomeini Hospital, Urmia in 2011. METHODS: The study was across-sectional observational study. 637 cases of patients with a confirmed diagnosis of maxillofacial fractures in 2011 referred to Imam Khomeini Hospital, Urmia and their data records were analyzed using SPSS software and chi-square tests. RESULTS: In this study, 457 patients were male and 178 were female and the mean age was 14.47 ± 26.68 years. Falling was the most common cause of fractures after accidents and assaults were the most common causes. The most common site of nasal fractures was about 66.4% and then fractures in several places about 14.9% and mandibular 7.1%. CONCLUSION: Based on the results obtained in the present study with other studies in this area it is concluded that maxillofacial fractures in males and in 20 to 30 years of age is prevalent and is mostly due to falling and road accidents and are further seen in nasal bone and mandible.

Methylene blue based device for pathogen reduction in human plasma.

BACKGROUND: Despite improvement in safety of plasma transfusion some virus transmission still remains a problem. So as World Health Organization (WHO) recommends, many countries developed Pathogen Reduction Technologies (PRT) to inactivate pathogens, in plasma components. The Methylene Blue (MB) based methods is one of the most universal one. The purpose of this research was, produce a device that can inactivate viruses in MB environment. MATERIALS AND METHODS: In this interventional study, each Plasma Sample was illuminated by 70Pieces (PCs) of 1 w red Light Emitting Diodes (LEDs) from one side. These LEDs emit light at central wavelength of 627 nm with 20 nm Full Width at Half Maximum (FWHM). Two model viruses Herpes Simplex Virus (HSV) and Vesicular Stomatitis Virus (VSV) were used and Tissue Culture 50% Infection Dose (TCID50) was used to calculate virus Log reduction. Two concentration of MB and 5 different illumination times were used. RESULTS: In 10 µm concentration of MB, HSV had 6.00±0.2 maximum log reduction that obtain after 60 minutes illumination and VSV had 5.50± 0.3 maximum log reduction after 75 minutes illumination. In 1 µM concentration of MB, HSV had 5.20±0.3 maximum log reduction that obtain after 60 minutes illumination and VSV had 4.90± 0.2 maximum log reduction after 75 minutes illumination. CONCLUSION: Results of virus inactivation in this method were similar to other methods (P-value<0.05 in comparison with Spring method, and P-value>0.05 in comparison with Theraflex), and it showed this device could inactivate viruses according to WHO recommendation.

Modal interferometer based on hollow-core photonic crystal fiber for strain and temperature measurement.

In this work, sensitivity to strain and temperature of a sensor relying on modal interferometry in hollow-core photonic crystal fibers is studied. The sensing structure is simply a piece of hollow-core fiber connected in both ends to standard single mode fiber. An interference pattern that is associated to the interference of light that propagates in the hollow core fundamental mode with light that propagates in other modes is observed. The phase of this interference pattern changes with the measurand interaction, which is the basis for considering this structure for sensing. The phase recovery is performed using a white light interferometric technique. Resolutions of +/- 1.4 microepsilon and +/- 0.2 degrees C were achieved for strain and temperature, respectively. It was also found that the fiber structure is not sensitive to curvature.

Color Doppler flow imaging of pediatric soft tissue masses.

The blood flow pattern within and around soft tissue tumors was analyzed to determine if color Doppler images could aid in the differential diagnosis. The study comprised 49 children with 50 masses: 24 inflammatory lesions, eight malformations, six neoplasms, five cysts, and seven traumatic lesions. A peripheral pattern (flow around the mass) was noted in eight of 50 lesions (16%). A mixed pattern (flow within and around the lesion) was noted in eight of 50 lesions (16%), and a central pattern (flow in the central region of the mass) was noted in 10 of 50 lesions (20%). Flow was absent in 24 lesions (48%). The peripheral pattern was observed only in abscesses. The other patterns were seen most frequently in lymphadenitis but were not specific for that diagnosis. Our experience suggests that color Doppler imaging is useful only in the diagnosis of abscess. In other lesions, color Doppler imaging alone is insufficient for diagnosis.

Diffuse neonatal hemangiomatosis: CT findings in an adult.

Diffuse neonatal hemangiomatosis (DNH) is a rare disorder that usually presents in infancy and has a high mortality rate. We report a long-term adult survivor of DNH who presented with multiple calcifications in the bowel wall, liver, spleen, and adrenal glands on CT. Diffuse neonatal hemangiomatosis needs to be added to the causes of visceral calcifications.

Imaging rounds. Bilateral condensing osteitis of the clavicles.

The following case illustrates the roentgenographic and clinical findings of a condition of interest to the orthopaedic surgeon. The initial history, physical findings, and roentgenographic examinations are found on the first two pages. The following pages present the final clinical and roentgenographic differential diagnosis.

CT of inflammatory abdominal aortic aneurysm: development from an uncomplicated atherosclerotic aneurysm.

The etiology and natural history of inflammatory abdominal aortic aneurysm are poorly understood. We report a case of inflammatory abdominal aortic aneurysm that developed from an uncomplicated aneurysm over a period of 6 1/2 months.

High-spectral-resolution fluorescence light detection and ranging for mesospheric sodium temperature measurements.

The principle and practice of narrow-band light detection and ranging (lidar) for temperature measurements are discussed, with emphasis on a new two-frequency technique for measuring mesospheric Na temperature and density profiles. The uniqueness of this narrow-band lidar lies in the transmitter whose line-shape function can be measured directly. The frequency of the laser output can be monitored simultaneously during data acquisition with Doppler-free fluorescence spectroscopy by using a laboratory Na cell. These measurement techniques along with the procedures for data analysis are described in detail. At present the absolute temperature accuracy at the Na layer peak is +/-3 K (+/-4 K) with a vertical resolution of 1 km and an integration period of 5 min (2.5 min). Potential applications and furtherimprovements in this lidar technique are also discussed.

Multiple superheating thresholds of micrometer-sized droplets irradiated by pulsed CO(2) lasers.

Two distinct superheating fluence thresholds have been measured for micrometer-sized droplets of liquids irradiated by pulsed CO(2) lasers. The lower, deformation, threshold results in minimal droplet mass loss, whereas the higher, disintegration, threshold (which is well defined only if observed several tens of microseconds after the heating laser pulse) leads to droplet fragmentation into many microparticles and vapor. Deformation thresholds are nearly coincident for either long (10-micros) or short (0.4-micros) laser pulses. Disintegration thresholds are higher for long-pulse irradiation and increase with decreasing absorption. A qualitative explanation is given for these phenomena based on the effects of surface tension, thermal conduction, and thermally induced optical inhomogeneities.

Childhood cerebellar astrocytomas: is there a role for postoperative irradiation?

Eighty children with astrocytomas of the cerebellum were treated at Washington University Medical Center in St. Louis, Missouri from 1928-1980. The most important predictor of recurrence was completeness of surgical removal. Of 40 patients whose tumors were totally removed, only one recurred (2.5%). Forty cases were subtotally removed and 14 subsequently recurred (35%). Postoperative irradiation did not significantly improve survival in the patients with incompletely excised tumors; however, there was lack of uniformity in the radiation therapy. Although a survival advantage could not be demonstrated, there was a trend toward a lowering of the recurrence rates in patients with subtotally excised solid tumors who received radiation therapy.

Lasing and stimulated Raman scattering in spherical liquid droplets: time, irradiance, and wavelength dependence.

Measurement of lasing from dye doped micron sized ethanol droplets irradiated by a pulsed Nd:YAG laser shows evidence of lifetime broadening and relaxation oscillations. Observations of stimulated Raman scattering (SRS) and lasing generated by the same laser pulse in a dye doped ethanol droplet and coupled to the same morphology dependent resonance exhibit longer delays in the initiation of SRS than for pure ethanol droplets where lasing is absent. SRS emission above the plasma breakdown threshold is not measurably delayed and is quenched by the developing plasma.

Astrocytomas of the cerebellum in children.

Between 1928 and 1980, 84 children (aged 19 years or younger) with an astrocytoma of the cerebellum were managed at Washington University Medical Center-Barnes Hospital. Fifty-eight children were treated with surgery only and 26 received surgery and postoperative irradiation. The 5-, 10-, and 25-year actuarial disease-free survival rates for the entire group were 92%, 88%, and 88%, respectively. Age at diagnosis and extent of surgery were prognostic factors, but no correlation with survival times was found for gross appearance of the tumor or postoperative irradiation. Posttreatment neurological function was excellent in the 58 patients alive at the end of the study; 92% were completely normal or had only a mild neurological deficit and 75% were employed or attending school.

Time-resolved spectroscopy of laser emission from dye-doped droplets.

Micrometer-sized droplets of Rhodamine 6G solution in water and ethanol are irradiated by high-intensity nanosecond pulses from a frequency-doubled Nd:YAG laser. Coupling of the spontaneous fluorescence emission with natural resonant modes of the spherical droplets results in stimulated emission, with each droplet behaving like a laser cavity. Spectral observations suggest that droplet lasing emission is supported by resonances of a single mode order. The emission exhibits faster rise times and is shorter lived than corresponding bulk-liquid fluorescence. Lasing in droplets is generally initiated almost simultaneously with elastic scattering, unlike stimulated Raman scattering, which is significantly delayed.

Stimulated Raman scattering in micrometer-sized droplets: time-resolved measurements.

Time-resolved measurements of elastic scattering and stimulated Raman scattering (SRS) in micrometer-sized water and carbon tetrachloride droplets irradiated with a pulsed, frequency-doubled Nd:YAG laser (pulse width 8 nsec, lambda = 532 nm, peak intensity ~1 GW cm(-2)) are reported. Elastic scattering of light is instantaneous within our measurement error, estimated to be <+/-3 nsec. On the other hand, the first Stokes shift in water and multiple-order (through ninth-order) Stokes shifts in carbon tetrachloride are delayed from the elastically scattered light by 5-7 nsec. The delay in SRS is apparently a consequence of structure resonances within the droplet, which acts as an optical cavity with relatively high Q. Quasi-periodic peaks in SRS spectra of water droplets are shown to be associated with elastic-scattering structure resonances having the same mode order.

Stimulated Raman scattering in micrometer-sized droplets: measurements of angular scattering characteristics.

Measurements of the angular scattering characteristics of elastic and stimulated Raman scattering (SRS) in single (nominal 20-microm-radius) water, ethanol, and CC1(4) droplets irradiated with 0.532-microm-wavelength radiation from a pulsed laser demonstrate that SRS is more isotropic than elastic scattering yet qualitatively mimics angularly smoothed elastic scattering patterns. The angular fine structure characteristic of the coherent elastic scattering process is lacking in SRS, regardless of whether the SRS derives from multiple orders of Stokes shifts, multiple resonances within a single Stokes shift, or single resonances within a single Stokes shift.