Dennis C. Jones

200 W self-organized coherent fiber arrays

We report producing 200 W coherent fiber laser arrays without active control. This outcome is obtained via self-organization using a non-fiber coupler for two- to ten-laser arrays.

Stimulated Brillouin scattering gain variation and transient effects in a CH 4 : He binary gas mixture

Experimental measurements are presented that show that the stimulated Brillouin scattering gain of methane, and hence the nature of the competition between stimulated Brillouin scattering and stimulated Raman scattering, can be systematically varied by the addition of helium. The gain variation is explained in terms of a transient gain model in which the dominant effect of the helium is to increase the Brillouin linewidth (acoustic attenuation). Broadening mechanisms are discussed. At methane and helium partial pressures of 19 and 41.8 kTorr (25 and 55 atm), respectively, backward stimulated Raman scattering dominates stimulated Brillouin scattering when the 532-nm pump energy exceeds 160 mJ.

An 8.2 J phase-conjugate solid-state laser coherently combining eight parallel amplifiers

We describe a phase-conjugate master oscillator-power amplifier configuration in which as many as eight parallel flashlamp-pumped Cr:Nd:GSGG amplifiers and four parallel CD*A frequency doubling crystals were coherently combined. Operating at a pulse repetition frequency of 1.25 Hz, we demonstrated an output energy of 8.2 J at 1 /spl mu/m and 4.4 J at 530 nm for a 54% frequency-doubling efficiency. This effort represents the highest reported output energy achieved using coherent coupling via phase conjugation. In subsequent experiments at a pulse repetition frequency of 5 Hz, we produced /spl sim/22 W of 1.06 /spl mu/m average power with a beam quality that was /spl sim/2.5 times diffraction-limited. The observed far-field intensity profile indicates that we achieved effective and consistent compensation of optical-path length differences among the multiple parallel amplifiers and frequency-doubling crystals. >

Coherent combining of fiber lasers

It seems straightforward to combine the latest high power fiber lasers together to scale up power. Yet every approach, including HRLs self-organization architecture, has proved more challenging than expected at high power. In practice power scaling elicits several undesirable phenomena whose consequences inhibit coherent combining. Stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS), for example, can together turn the relatively benign power fluctuations associated with mode beating into fiber-damaging pulses. Coherence and polarization integrity are inevitably impaired by glass-related nonlinear index changes (n2). HRL has demonstrated two to four lasers coherently combined to the 200 Watt level, using free space coupling with beamsplitters. In addition, nine independent lasers were locked in an all-fiber coupler

Real-time atmospheric compensation using stimulated Brillouin scattering phase conjugation

We review what is, to our knowledge, the first successful demonstration of atmospheric compensation employing a phase-conjugate mirror (PCM) based on ordinary stimulated Brillouin scattering (SBS). The principal challenge in using SBS in this application is to reach SBS threshold despite the significant losses inherent in the atmospheric propagation. In our system, the required gain of 95 dB is provided by backward-Raman amplifiers.<<ETX>>

Self-organized coherence in fiber lasers

We have combined multiple 100 W fiber lasers in a self organized manner so that they produce a coherent, high brightness output beam. We use lasers designed to avoid SBS, SRS and FWM limitations and use proper coupling between fibers to ensure in-phase output.

An 8.2 J solid-state laser using phase-conjugation to coherently combine eight parallel amplifiers

Coherent coupling, or beam combining, offers a significant benefit to designers of practical high-power lasers. Unlimited by volume availability, the medium selection trade-offs can be based on many other important material parameters including stimulated-emission cross section and saturation fluence, compatibility with diode pumping, available optical quality, resistance to radiation damage, and thermo-mechanical properties. In our flashlamp-pumped laser, we chose Cr-sensitized, Nd-doped gadolinium scandium gallium garnet (Cr:Nd:GSGG), which is significantly more efficient than Nd:YAG and has thermo-mechanical properties that are vastly superior to those of Nd:glass.<<ETX>>