J.A. Alvarez-Chavez

High-energy, high-power ytterbium-doped Q-switched fiber laser

We report on a Q -switched, cladding-pumped, ytterbium-doped large-mode-area fiber laser operating at 1090 nm that is capable of generating 2.3 mJ of output pulse energy at a 500-Hz repetition rate and more than 5 W of average output power at higher repetition rates in a high-brightness beam (M(2) = 3) . Using a similar fiber with a smaller core, we generated >0.5-mJ pulses in a diffraction-limited beam. Our results represent a threefold increase in pulse energy over previously published values for Q-switched fiber lasers and firmly establish fiber lasers as compact, multiwatt, multimillijoule pulse sources with large scope for both industrial and scientific applications.

Characteristics of Q-switched cladding-pumped ytterbium-doped fiber lasers with different high-energy fiber designs

We theoretically and experimentally analyze Q-switched cladding pumped ytterbium-doped fiber lasers designed for high pulse energies. We compare the extractable energy from two high-energy fiber designs: (1) single- or few-moded low-NA large mode area (LMA) fibers and (2) large-core multimode fibers, which may incorporate a fiber taper for brightness enhancement. Our results show that the pulse energy is proportional to the effective core area and, therefore, LMA fibers and multimode fibers of comparable core size give comparable results. However, the energy storage in multimode fibers is mostly limited by strong losses due to amplified spontaneous emission (ASE) or even spurious lasing between pulses. The ASE power increases with the number of modes in a fiber. Furthermore, spurious feedback is more difficult to suppress with a higher NA, and Rayleigh back-scattering increases with higher NA, too. These effects are smaller in low-NA LMA fibers, allowing for somewhat higher energy storage. For the LMA fibers, we found that facet damage was a more severe restriction than ASE losses or spurious lasing. With a modified laser cavity, we could avoid facet damage in the LMA fiber, and reached output pulse energies as high as 2.3 mJ, limited by ASE. Theoretical estimates suggest that output pulse energies around 10 mJ are feasible with a larger core fiber, while maintaining a good beam quality.

High-power and tunable operation of erbium-ytterbium Co-doped cladding-pumped fiber lasers

We describe erbium-ytterbium co-doped fiber lasers in different free-running and tunable configurations. The lasers were cladding-pumped by high-power multimode diode sources. We compare pumping at 915 and 980 nm. With a free-running laser, we obtained slope efficiencies of up to 50% with 915-nm pumping and 38% with 980-nm pumping, with respect to absorbed pump power. We reached a double-ended output power of 16.8 W from the free-running laser. Thanks to a high rare-earth concentration and a small inner cladding area (possible with the high-brightness pump sources we used), the operating pump absorption of the fiber reached 8 dB/m. With such high absorption, short fibers with high nonlinear thresholds are possible even with cladding pumping. The tunable fiber laser had a tuning range from 1533 to 1600 nm and emitted 6.7 W of output power at 1550nm in a high-brightness, single-polarization, narrow linewidth beam.

Mode selection in high power cladding pumped fibre lasers with tapered section

Summary form only given. Cladding pumped fibre lasers are undoubtedly becoming the most attractive source of high power radiation in the near IR region. The small overlap between the pump and the rare-earth-doped core leads to a small pump absorption, e.g., 1 dB/m. Larger core and absorption is often desirable, especially if (transversally) single-mode operation can be maintained. Thus, single-mode operation following selective excitation of the fundamental mode of large-core multimode fiber amplifiers was recently demonstrated in short fibres. In this paper, we use a simple fiber taper inside a laser cavity with a multimode gain fibre to suppress higher-order modes.

83-W single-frequency narrow-linewidth MOPA using large-core erbium-ytterbium Co-doped fiber

We demonstrate a continuous-wave (CW) single-frequency narrow-linewidth laser at 1552 nm with an output power of 83 W using a master-oscillator power amplifier configuration. A seed from an all-fiber distributed feedback-laser with a linewidth of 13 kHz was polarization scrambled and boosted through a chain of amplifiers in an all-fiber configuration. The last amplification stage consisted of a highly efficient cladding-pumped large-core erbium-ytterbium co-doped fiber which helped increase nonlinear thresholds.

Kilowatt-class single-frequency fiber sources

We discuss the dramatic development of high-power fiber laser technology in recent years and the prospects of kilowattclass single-frequency fiber sources. We describe experimental results from an ytterbium-doped fiber-based multihundred-watt single-frequency, single-mode, plane-polarized master-oscillator power amplifier (MOPA) operating at 1060 nm and a similar source with 0.5 kW of output power, albeit with a degraded beam quality (M2 = 1.6) and not linearly polarized. Experiments and simulations aimed at predicting the Brillouin limit of single-frequency system with a thermally broadened Brillouin gain are presented. These suggest that single-frequency MOPAs with over 1 kW of output power are possible. In addition, the power scalability of a simple single-strand fiber laser to 10 kW is discussed.

Multi-mJ, multi-watt Q-switched fiber laser

Using a large mode area, ytterbium-doped cladding-pumped fiber and a novel cavity configuration we obtain 2.3 mJ Q-switched pulses, a record pulse energy for a fiber laser. Average powers in excess of 5 W were achieved.

7.7 mJ pulses from a large core Yb-doped cladding pumped Q-switched fibre laser

Summary form only given. Double-clad rare-earth doped fibre lasers pumped by high brightness laser diodes are very efficient and compact sources of cw and pulsed radiation. For Q-switching, fibre lasers are limited by the build-up of amplified spontaneous emission (ASE) between pulses. Rayleigh backscattering and fibre facet damage are other important issues that need to be considered. The ASE limit is relaxed if large-core fibres are used, however, at some point the fibre becomes multimoded. This is often undesirable. We have previously studied Q-switching of large-core Yb-doped fibre lasers, including those with special core designs for enhancement of the beam quality (so-called large mode area fibres). We also investigate Q-switching of a large-core cladding-pumped Yb-doped fibre laser, but here, we focus on maximizing the pulse energy and pay less attention to beam quality. We used a fibre with a 60 /spl mu/m core.

Broad-band diode-pumped ytterbium-doped fiber amplifier with 34-dBm output power

We investigate a high-power diode-pumped double-clad ytterbium-doped fiber amplifier with 34-dBm average output power and 1050-1095-nm bandwidth. A multidiode concentrator pumps the amplifier at 980 nm, with /spl sim/6 W of power launched into the inner cladding. Besides CW-signals, we amplify pulses from a mode-locked laser to 1 kW of peak power with only minor nonlinear distortions as well as pulses from a Q-switched laser to 50 /spl mu/J of energy. Reflections and backscatter limit the gain of the amplifier to 40 dB for a pump power of 2.5 W. For higher pump-powers than this, the amplifier started to self-Q-switch. The results are important for the development of cladding-pumped high-power fiber amplifiers.

High-power cladding pumped erbium-ytterbium co-doped fiber laser

Cladding pumped erbium-ytterbium fiber lasers (EYDFL) in different free-running configurations have been described. We obtained slope efficiency of up to 50% with respect to absorbed pump power and an output power of 16.8 W.We study the influence of fiber length and pump wavelength in cladding-pumped erbium-ytterbium doped fiber lasers. We reached up to 16.8 W of output power from an EYDFL pumped through both ends at 915 nm. We believe this to be the highest-power EYDFL described in the literature. The slope efficiency was up to 50% with 915 nm pumping and 38% with 980 nm pumping,, both with respect to absorbed pump power.