Orthogonal coding methods for increasing the number of multiplexed channels in coherent beam combining.

We introduce orthogonally coded modulations for active coherent beam combining (CBC), and show how using Walsh codes enables the increase of the number of combined channels. Analytical, numerical, and experimental results are presented and compared to the standard multifrequency dithering technique, demonstrating that at least 5 times more fibers can be combined using the same modulation frequency. The modulation format excluded, no particular changes in the system need to be introduced and the benefits of active coherent beam combing, such as atmospheric turbulence compensation capability, are kept unchanged. Finally, we point out that this approach can be applied in partially CBC.

Coherent beam combination of narrow-linewidth 1.5 µm fiber amplifiers in a long-pulse regime.

We report what we believe to be the first experimental demonstration of coherent beam combining of two fiber amplifiers in a 100 ns pulse regime using a signal leak between the pulses. Pulses of ∼100 W stimulated-Brillouin-scattering limited peak power are combined with 95% efficiency, a residual phase error of λ/27, and no significant beam quality degradation.

Multifilament-core fibers for high energy pulse amplification at 1.5 microm with excellent beam quality.

We report on what we believe to be the first demonstration of an erbium-ytterbium-doped multifilament-core (MFC) fiber for single-mode amplification of narrow linewidth high peak power pulses. A master-oscillator-power-fiber-amplifier laser source has been demonstrated using a 37-filament MFC fiber in the last amplification stage. Pulses with 750 microJ (940 W peak power) and laser linewidth<1 MHz have beam generated with M2 approximately 1.3. This value is close to the theoretical value M2 approximately 1.5.

Spatial mode cleaning by femtosecond filamentation in air.

By studying the conical emission of a blue femtosecond laser filament in air, it is shown that self-improvement of the beams' spatial mode quality occurs for a self-guided laser pulse.

Degree of dependence on the ventilator according to sleep states in artificially ventilated premature infants.

Polygraphic recordings were performed in 14 sleeping premature infants receiving ventilation for respiratory distress syndrome. All were clinically stabilized, with normal EEG and neurologic status and differentiated sleep states (coded according to EEG and REM criteria). They all had two respiratory patterns: passive, completely dependent on the ventilator, and active, with autonomous respiratory movements and/or inspiratory diaphragmatic activity added to passive respiration. We found that in infants ventilated at the rate of 18-54/min, respiration was more active and autonomous in active REM sleep and more passive and dependent on the machine in quiet NREM sleep (P less than 0.005). Within the limits of the values observed in our study, differences between sleep states were not due to other factors that could possibly interfere with and modify the degree of respiratory autonomy. We found no significant correlation between the percentage of time passed with active respiration on one hand and age (gestational, postnatal, conceptional) or diagnostic or physical parameters of artificial ventilation and blood gas levels on the other hand. Our results suggest that in artificially ventilated but neurologically normal premature infants, differences between respiratory control in both sleep states exist as early as 28 weeks conceptional age (lower limit of our study).