Limits of Femtosecond Fiber Amplification by Parabolic Pre-Shaping.

We explore parabolic pre-shaping as a means of generating and amplifying ultrashort pulses. We develop a theoretical framework for modeling the technique and use its conclusions to design a femtosecond fiber amplifier. Starting from 9 ps pulses, we obtain 4.3 µJ, nearly transform-limited pulses 275 fs in duration, simultaneously achieving over 40 dB gain and 33-fold compression. Finally, we show that this amplification scheme is limited by Raman scattering, and outline a method by which the pulse duration and energy may be further improved and tailored for a given application.

Coherent combining of pulsed fiber amplifiers in the nonlinear chirp regime with intra-pulse phase control.

Two high pulse contrast (> 95 dB) polarization maintaining all-fiber amplifier chains were coherently combined to generate 0.42 mJ, 1 ns 25 kHz pulses with 79% efficiency despite 38 radians of intra-pulse phase distortion. A recursive intra-pulse phase compensation method was utilized to correct for the large nonlinear chirp providing a path for improved coherent waveform control of nanosecond pulse trains.

High density spectral beam combination with spatial chirp precompensation.

A method for spectral combination of lasers with extremely high spectral density is introduced, enabling greater than 80% and theoretically approaching 100% spectral density utilization with no degradation in beam quality. Experiments demonstrating the utility of our method are described, cumulating in a demonstration of a compact, packaged laser with photonic-crystal-fiber-rod amplifiers at 0.5-MW peak power and 0.15-nm wavelength spacing. Our method is potentially scalable to many 100's of channels within the gain bandwidth of high average power or peak power rare earth doped fiber lasers at any wavelength in a compact footprint and uses only reflective optics and gratings.

Spectral narrowing and stabilization of thulium fiber lasers using guided-mode resonance filters.

We used guided-mode resonance filters (GMRFs), fabricated using thin-film deposition and chemical etching, as intracavity feedback elements to stabilize and narrow the output spectrum in thulium-doped fiber oscillators operating in the 2 µm wavelength regime, producing linewidths of <700 pm up to 10 W power levels. A Tm fiber-based amplified spontaneous emission source was used to characterize the reflective properties of the GMRFs. Linewidths of 500 pm and a 7.3 dB reduction in transmission were measured on resonances.

High-power widely tunable thulium fiber lasers.

Applications requiring long-range atmospheric propagation are driving the development of high-power thulium fiber lasers. We report on the performance of two different laser configurations for high-power tunable thulium fiber lasers: one is a single oscillator utilizing a volume Bragg grating for wavelength stabilization; the other is a master oscillator power amplifier system with the oscillator stabilized and made tunable by a diffraction grating. Each configuration provides >150 W of average power, >50% slope efficiency, narrow output linewidth, and >100 nm tunability in the wavelength range around 2 µm.

An investigation of blood selenium concentrations of goats in New York State.

The goal of the current study was to determine the range of blood selenium concentrations in goats in New York State that were fed adequately supplemented diets. Blood samples from mature, juvenile, and neonatal goats from commercial farms, 2 dairy and 2 meat producers, were analyzed via graphite-furnace atomic absorption spectroscopy. Feed samples were analyzed by using inductively coupled argon plasma optical emission spectroscopy to confirm that dietary selenium concentrations were adequate. The ranges of blood selenium concentration obtained were 9.1-49.9 microg/dl for mature goats, 7.6-37.5 microg/dl for juveniles, and 9.7-40.7 microg/dl for neonates.

Active phase and polarization locking of a 1.4 kW fiber amplifier.

A three-stage Yb-fiber amplifier emitted 1.43 kW of single-mode power when seeded with a 25 GHz linewidth master oscillator (MO). The amplified output was polarization stabilized and phase locked using active heterodyne phase control. A low-power sample of the output beam was coherently combined to a second fiber amplifier with 90% visibility. The measured combining efficiency agreed with estimated decoherence effects from fiber nonlinearity, linewidth, and phase-locking accuracy. This is the highest-power fiber laser that has been coherently locked using any method that allows brightness scaling.

Volume Bragg grating stabilized spectrally narrow Tm fiber laser.

A Tm-doped large mode area (LMA) silica fiber laser has been locked to a stable wavelength of 2,053.9 nm using a volume Bragg grating (VBG). The measured spectral width of the laser output was <300 pm, limited by the spectrometer resolution. Although this laser had modest output (approximately 5W) and slope efficiency (41%), this new approach to spectrally limiting the output of LMA fiber lasers is inherently extendable to kilowatt powers, opening up several applications including high-power pulsed fiber lasers and spectral beam combining. Performance characteristics of the laser compared to one using a dielectric mirror as a high reflector are described, and the results imply low VBG losses.

Very large-core, single-mode, gain-guided, index-antiguided fiber lasers.

Lowest-order, single-mode laser oscillation is reported in gain-guided index-antiguided fiber lasers having core diameters from 100 to 400 microm. A model is presented explaining how to select resonator mirrors to assure single-mode operation.

Associations with home hemodialysis modality failure and mortality.

BACKGROUND: Limited data exist on risk factors for home hemodialysis (HH) failure and mortality. We sought to determine whether age, helper status, or ethnicity was associated with home dialysis failure or mortality. METHODS: We conducted a retrospective cohort study of all prevalent and incident patients from a regional dialysis unit who initiated HH training from December 2000 to September 2002. Baseline demographics, program entry and exit dates, and mortality were ascertained. Characteristics of those more likely to remain in the program were assessed using logistic regression; survival was determined using Cox proportional hazards models. RESULTS: Of the 1117 patients enrolled for dialysis, 116 patients were trained in the HH program (6.8%). Of those, 45.7% remained in the program, 10.3% received a transplant, 10.3% returned to in-center dialysis, 1.7% were lost to follow-up, and 31.7% expired. Compared to patients who returned to center or received a transplant, patients who remained on HH were more likely to be older, to have been on dialysis longer, and to have diabetes as their primary renal disease. Ethnicity, sex, or type of helper did not affect home program status. Among those who remained in the HH program, those with hypertension or other renal diseases had better survival than those with diabetes, as did those who had related helpers compared to those with unrelated helpers. CONCLUSIONS: Older and younger ages, but not ethnicity, helper status, or sex, were associated with home dialysis failure. Diabetes remained an independent risk factor for increased mortality. HH remains a viable option for many patients.