All-fiber laser source at 1645 nm for lidar measurement of methane concentration and wind velocity.

We report on the realization of an all-fiber laser source that delivers single-frequency pulses at 1645 nm, on a linearly polarized single-mode beam, based on stimulated Raman scattering in passive fibers. The pulse energy reaches 14 µJ for a repetition rate of 20 kHz, and the spectral linewidth is 9.5 MHz for 100 ns square pulses. To the best of our knowledge, this energy is the highest reported at 1645 nm in an all-fiber laser source. Our method consists of reducing the stimulated Brillouin scattering (SBS) gain for the pump and signal pulses, respectively, by sweeping the optical frequency of the pump beam, and by applying a strain gradient on the amplification fiber. This compact laser source is now used in a transportable lidar system to measure simultaneously wind velocity and methane (CH4) concentration.

Low Osteoporosis Treatment Initiation Rate in Women after Distal Forearm or Proximal Humerus Fracture: A Healthcare Database Nested Cohort Study.

Treatment initiation rates following fragility fractures have often been reported to be low and in recent years numerous programs have been implemented worldwide to increase them. This study aimed at describing osteoporosis (OP) treatment initiation in a representative sample of women who were hospitalized for a distal forearm fracture (DFF) or proximal humerus fracture (PHF) in 2009-2011 in France. The data source was a nationwide sample of 600,000 individuals, extracted from the French National Insurance Healthcare System database. All women aged 50 years and older who were hospitalized for a DFF or PHF between 2009 and 2011 and who had not received any OP treatment in the preceding 12 months were included in a retrospective cohort study. OP treatments initiated during the year following the fracture were analyzed. From 2009 to 2011, 729 women were hospitalized for a DFF or a PHF and 284 were on OP treatment at the time of the fracture occurrence. Among the 445 women who had no prevalent OP treatment, 131 (29.4%) received supplementation treatment only (vitamin D and/or calcium) and 42 (9.4%) received a pharmacologic OP treatment in the year following their fracture. Pharmacological OP treatments included bisphosphonates (n = 21), strontium ranelate (n = 14), hormone replacement therapy (n = 4), or raloxifene (n = 3). General practitioners prescribed 75% of initial OP treatments. Despite the guidelines published in 2006 and the numerous initiatives to promote post-fracture OP treatment, OP treatment initiation rate in women who were hospitalized for a fragility fracture remained low in 2009-2011 in France.

1 kW peak power, 110 ns single-frequency thulium doped fiber amplifier at 2050 nm.

We report a high power, single frequency, linearly polarized master oscillator power amplifier emitting 110 ns, 1 kW peak power pulses at 2050 nm. A 20% slope efficiency and a beam quality of M2=1.21 are achieved with three-stage double-clad Tm(3+)-doped fiber architecture. Various pump schemes are compared leading to the conclusion that 793 nm pump wavelength is the most efficient for amplification at 2050 nm. Based on numerical simulations, the Brillouin gain coefficient around 2 µm in Tm(3+) highly doped silica fiber is estimated to 1.2×10(-11) m/W. Output peak power is limited by stimulated Brillouin scattering to 535 W without mitigation and to 1 kW with application of a strain distribution along the doped fiber.

Spatially resolved modal spectroscopy of Er:Yb doped multifilament-core fiber amplifier.

The spatially resolved spectral (S2) imaging method is applied on an active microstructured fiber, with a multi-filament core (MFC). This type of fiber has been designed to be the last amplifying stage of a source for a long range coherent lidar. Studying the influence of the bending radius on the modal content with or without gain, we demonstrate that an upper-bound of the high-order modes content can be found by performing the S2 imaging on the bleached fiber. S2 imaging is then used to verify that the output beam of the MFC fiber can be made effectively single-mode. We also show that it can be simply adapted for measuring the fiber birefringence. Finally, a comparison of the MFC fiber mode area with that of a standard large mode area Erbium doped step index fiber illustrates the interest of the MFC structure for high power amplifiers.

26 nJ picosecond solitons from thulium-doped single-mode master oscillator power fiber amplifier.

We report on an all single-mode master oscillator power fiber amplifier delivering high energy picosecond solitons at 1960 nm. The Bragg stabilized and self-starting oscillator delivers 62 pJ transform-limited pulses at 11.2 MHz pulse repetition frequency. Solitons are amplified in a core-pumped single-mode heavily thulium-doped fiber up to 26 nJ. The average and peak power are 291 mW and 7.4 kW, respectively. Pulses remain transform limited without significant self-phase-modulation distortion. We discuss the limitations of picosecond pulse amplification in a core-pumped single-mode fiber amplifier.

Analysis of the multifilament core fiber using the effective index theory.

Multifilament core (MFC) fibers are a new type of microstructured fiber recently introduced. We investigate their properties using finite element modeling and show that the equivalent step index fiber based on moments theory does not provide similar properties. We propose an effective index theory based on the fundamental space filling mode which allows to predict the MFC properties using a semi-analytical modeling. Good resistance to bending is thus attributed to increased core effective index due to the high index filaments.

Evidence of thermal effects in a high-power Er3+-Yb3+ fiber laser.

We analyze the influence of heat generation caused by nonradiative transitions in a high-power 1.55 microm double-clad erbium-ytterbium fiber laser on the Stark level population. At strong pumping rates, 1 microm lasing can start as a result of parasitic reflections. We present a model that allows us to simulate the effect of self-generated heat on the Stark level population by using the MacCumber relation. Heat generation plays a significant role and improves the 1.5 microm laser's efficiency by increasing the 1 microm lasing threshold.