Spectrally Tailored Pulsed Thulium Fiber Laser System for Broadband Lidar CO2 Sensing

Thulium doped pulsed fiber lasers are capable of meeting the spectral, temporal, efficiency, size and weight demands of defense and civil applications for pulsed lasers in the eye-safe spectral regime due to inherent mechanical stability, compact "all-fiber" master oscillator power amplifier (MOPA) architectures, high beam quality and efficiency. Thulium fiber's longer operating wavelength allows use of larger fiber cores without compromising beam quality, increasing potential single aperture pulse energies. Applications of these lasers include eye-safe laser ranging, frequency conversion to longer or shorter wavelengths for IR countermeasures and sensing applications with otherwise tough to achieve wavelengths and detection of atmospheric species including CO2 and water vapor. Performance of a portable thulium fiber laser system developed for CO2 sensing via a broadband lidar technique with an etalon based sensor will be discussed. The fielded laser operates with approximately 280 J pulse energy in 90-150ns pulses over a tunable 110nm spectral range and has a uniquely tailored broadband spectral output allowing the sensing of multiple CO2 lines simultaneously, simplifying future potentially space based CO2 sensing instruments by reducing the number and complexity of lasers required to carry out high precision sensing missions. Power scaling and future "all fiber" system configurations for a number of ranging, sensing, countermeasures and other yet to be defined applications by use of flexible spectral and temporal performance master oscillators will be discussed. The compact, low mass, robust, efficient and readily power scalable nature of "all-fiber" thulium lasers makes them ideal candidates for use in future space based sensing applications

Temporal Relationships Exist Between Cecum, Ileum, and Litter Bacterial Microbiomes in a Commercial Turkey Flock, and Subtherapeutic Penicillin Treatment Impacts Ileum Bacterial Community Establishment

Gut health is paramount for commercial poultry production, and improved methods to assess gut health are critically needed to better understand how the avian gastrointestinal tract matures over time. One important aspect of gut health is the totality of bacterial populations inhabiting different sites of the avian gastrointestinal tract, and associations of these populations with the poultry farm environment, since these bacteria are thought to drive metabolism and prime the developing host immune system. In this study, a single flock of commercial turkeys was followed over the course of twelve weeks to examine bacterial microbiome inhabiting the ceca, ileum, and corresponding poultry litter. Furthermore, the effects of low-dose, growth-promoting penicillin treatment (50 g/ton) in feed on the ileum bacterial microbiome were also examined during the early brood period. The cecum and ileum bacterial communities of turkeys were distinct, yet shifted in parallel to one another over time during bird maturation. Corresponding poultry litter was also distinct yet more closely represented the ileal bacterial populations than cecal bacterial populations, and also changed parallel to ileum bacterial populations over time. Penicillin applied at low dose in feed significantly enhanced early weight gain in commercial poults, and this correlated with predictable shifts in the ileum bacterial populations in control versus treatment groups. Overall, this study identified the dynamics of the turkey gastrointestinal microbiome during development, correlations between bacterial populations in the gastrointestinal tract and the litter environment, and the impact of low-dose penicillin on modulation of bacterial communities in the ileum. Such modulations provide a target for alternatives to low-dose antibiotics

The Effect Stacking Fault Segregation and Phase Transformations have on Creep Strength in Ni-based Superalloys

In this study, two commercially similar polycrystalline Ni-based disk superalloys (LSHR and ME3) were creep tested at 760C and 552MPa to approximately 0.3% plastic strain. LSHR consistently displayed superior creep properties at this stress/temperature regime even though the microstructural characteristics between the two alloys were comparable. High resolution structural and chemical analysis, however, revealed significant differences between the two alloys among active gamma prime shearing modes involving superlattice intrinsic and extrinsic stacking faults. In ME3, Co and Cr segregation and Ni and Al depletion were observed along the intrinsic faults - revealing a gamma prime -to- gamma phase transformation. Conversely in LSHR, an alloy with a higher W content, Co and W segregation was observed along the intrinsic faults. This observation combined with scanning transmission electron microscopy (STEM) simulations confirm a gamma prime-to-D019 phase transformation along the intrinsic faults in LSHR. Using experimental observations and density functional theory calculations, a novel local phase transformation strengthening mechanism is proposed that could be further utilized to improve the high temperature creep capabilities of Ni-base disk alloys

Investigation Of The Thermal Characteristics Of A Gain-Guided, Index-Anti-Guided Fiber

We investigate the thermal characteristics of a, gain guided, index anti-guided (GG+IAG) fiber. We find the minimum of the heat transfer coefficient of the coolant to reduce the temperature of the core to below the transformation point of the GG+IAG fiber material

High power tunable thulium fiber laser with volume Bragg grating spectral control

A volume Bragg grating is used in two different configurations to control the output spectrum of a thulium doped silica fiber laser. When used in a direct feedback configuration on the end of a bidirectionally pumped resonator, a power of up to 159 W with 54% slope efficiency is produced with a narrow output spectrum centered at 2052.5 nm with \u3c1.5 nm full-width at 10 dB down from spectral peak. Maximum laser linewidth is limited by the VBG reflectivity width. The VBG based laser is compared to a laser resonator based on a standard HR mirror and is able to maintain stable spectrally narrow operation while the HR mirror laser has a wide and varied spectral output over 20-30 nm. Both lasers have similar slope efficiency, threshold and power performance with any difference attributed to lack of AR coatings on the VBG. In a second cavity, the VBG is used in a tunable configuration by rotating the VBG away from normal incidence. Tuning range was found to be \u3e100 nm from 1947 nm to 2052.5 nm with output powers as high as 48 W and up to 52% slope efficiency. Tuning range is determined by VBG center wavelength on the long wavelength end and by the VBG aperture size on the short end. In both system configurations, M2 is maintained at less than 1.2 at all power levels and long term operating stability at full power is demonstrated. © 2010 Copyright SPIE - The International Society for Optical Engineering

Spectral Narrowing And Stabilization Of Thulium Fiber Lasers Using Guided-Mode Resonance Filters

Guided mode resonance filters (GMRF) were used to spectrally-stabilize and line-narrow the output spectrum from Tm fiber lasers operating in the 2 μm wavelength regime. The GMRFs were placed in the output path of an amplified spontaneous emission (ASE) light source and the transmitted light was measured as a notch in the spectrum on resonance. The GMRFs were characterized to determine their peak reflectivity, resonance wavelength, and spectral linewidth of each element. These measurements showed various resonance wavelengths and linewidths varying from 0.50-1.5 nm depending on the individual GMRF parameters. Using GMRFs as feedback elements in Tm fiber laser oscillators resulted in output powers up to 10 W and slope efficiencies of 30-45% with respect to launched 790 nm pump power. In order to scale to higher powers and maintain narrow linewidths, a master oscillator power amplifier (MOPA) setup was employed with a GMRF stabilized master oscillator. In addition to the laser and amplifier characteristics, thermal and damage testing of the GMRFs is reported. © 2010 Copyright SPIE - The International Society for Optical Engineering

High-Energy Q-Switched Tm\u3csup\u3e3+\u3c/sup\u3e-Doped Polarization Maintaining Silica Fiber Laser

We report the performance of an actively Q-switched Tm fiber laser system. The laser was stabilized to sub-nanometer spectral width using each of two feedback elements: a blazed reflection grating and a volume Bragg grating. Maximum pulse energy using the reflection grating was 325 μJ pulses at 1992 nm (\u3c 200 pm width) with a 125 ns duration at a 20 kHz repetition rate. Maximum pulse energy using the volume Bragg grating was 225 μJ pulses at 2052 nm (\u3c200 pm width) with a 200 ns duration also at 20 kHz. We also report the laser\u27s performance as an ablation source for LIBS experiments on copper. © 2010 Copyright SPIE - The International Society for Optical Engineering

High Power Tunable Thulium Fiber Laser With Volume Bragg Grating Spectral Control

A volume Bragg grating is used in two different configurations to control the output spectrum of a thulium doped silica fiber laser. When used in a direct feedback configuration on the end of a bidirectionally pumped resonator, a power of up to 159 W with 54% slope efficiency is produced with a narrow output spectrum centered at 2052.5 nm with \u3c1.5 nm full-width at 10 dB down from spectral peak. Maximum laser linewidth is limited by the VBG reflectivity width. The VBG based laser is compared to a laser resonator based on a standard HR mirror and is able to maintain stable spectrally narrow operation while the HR mirror laser has a wide and varied spectral output over 20-30 nm. Both lasers have similar slope efficiency, threshold and power performance with any difference attributed to lack of AR coatings on the VBG. In a second cavity, the VBG is used in a tunable configuration by rotating the VBG away from normal incidence. Tuning range was found to be \u3e100 nm from 1947 nm to 2052.5 nm with output powers as high as 48 W and up to 52% slope efficiency. Tuning range is determined by VBG center wavelength on the long wavelength end and by the VBG aperture size on the short end. In both system configurations, M2 is maintained at less than 1.2 at all power levels and long term operating stability at full power is demonstrated. © 2010 Copyright SPIE - The International Society for Optical Engineering

Amplification Of Picosecond Pulses Generated In A Carbon Nanotube Modelocked Thulium Fiber Laser

Generation of 5ps, 32pJ pulses from a carbon nanotube modelocked thulium fiber oscillator and their amplification to 0.6W average power, 2.6kW peak power, 13nJ pulses by an LMA thulium fiber amplifier is discussed. © 2010 Optical Society of America

Widely-Tunable (≪100 Nm) Continuous-Wave Narrow-Linewidth Highpower Thulium Fiber Laser

Eye-safe, high power, tunable, narrow linewidth lasers are key technologies for a number of applications, including atmospheric propagation measurements. Since the atmosphere has narrow line transmission windows it is important to have a tunable linewidth source which can be matched to the transmission window. We have developed a stable narrowlinewidth (0.3 nm), tunable (from 1947 nm to 2108 nm) large mode area thulium doped fiber laser. Using this as a seed source, a master oscillator power amplifier with ̃100 W output power will be presented. © 2009 SPIE