H. Zellmer

High-power air-clad large-mode-area photonic crystal fiber laser

We report on a 2.3 m long air-clad ytterbium-doped large-mode-area photonic crystal fiber laser generating up to 80 W output power with a slope efficiency of 78%. Single transverse mode operation is achieved with a mode-field area of 350 /spl mu/m/sup 2/. No thermo-optical limitations are observed at the extracted /spl sim/35 W/m, therefore such fibers allow scaling to even higher powers.

Low-nonlinearity single-transverse-mode ytterbium-doped photonic crystal fiber amplifier

We report on an air-clad large-core single-transverse-mode ytterbium-doped photonic crystal fiber with a mode-field-diameter of 35 microm, corresponding to a mode-field-area of ~1000 microm(2). In a first experiment this fiber is used to amplify 10-ps pulses to a peak power of 60 kW without significant spectral broadening due to self-phase modulation allowing for the frequency up-conversion of these pulses using narrow-bandwidth phase matched nonlinear crystals.

High-power rod-type photonic crystal fiber laser

We report on a novel ytterbium-doped fiber design that combines the advantages of rod and fiber gain media. The fiber design has outer dimensions of a rod laser, meaning a diameter in the range of a few millimeters and a length of just a few tens of centimeters, and includes two important waveguide structures, one for pump radiation and one for laser radiation. We obtained 120-W output power in single-mode beam quality from a 48-cm-long fiber cane that corresponds to an extracted power of 250 W/m. The fiber has significantly reduced nonlinearity, which therefore allows for scalability in the performance of a high-peak-power fiber laser and amplifier system.

High-power femtosecond Yb-doped fiber amplifier.

We report on the generation of linearly chirped parabolic pulses with 17-W average power at 75 MHz repetition rate and diffraction-limited beam quality in a large-mode-area ytterbium-doped fiber amplifier. Highly efficient transmission gratings in fused silica are applied to recompress these pulses down to 80-fs with an efficiency of 60%, resulting in a peak power of 1.7 MW. Power scaling limitations given by the amplifier bandwidth are discussed.

100-W single-frequency master-oscillator fiber power amplifier

We report the efficient generation of 100-W single-frequency radiation with diffraction-limited beam quality at the 1064-nm wavelength by use of a master-oscillator fiber power-amplifier system, consisting of a diode-pumped monolithic nonplanar ring laser as the master oscillator and an Yb-doped large-mode-area fiber as the power amplifier. The emission spectrum, the intensity noise behavior, and further power-scaling possibilities to the >200-W level, which are determined by the threshold of stimulated Brillouin scattering in the fiber amplifier, are discussed.

All fiber chirped-pulse amplification system based on compression in air-guiding photonic bandgap fiber.

We report on the experimental demonstration of an all fiber CPA system based on a step-index fiber stretcher and an air-guiding photonic crystal fiber compressor. The ultrafast fiber laser system producing an average power of 6.0 W with 100-fs pulses at 73 MHz, what corresponds to a peak power out of the compressor fiber of 0.82 MW. This completely fiber integrated approach has the potential to be scaled to significantly higher peak powers.

The renaissance and bright future of fibre lasers

The first rare-earth-doped fibre lasers were operated in the early 1960s and produced a few milliwatts at a wavelength around 1 µm. For the next several decades, fibre lasers were little more than a low-power laboratory curiosity. Recently, however, fibre lasers have entered the realm of kilowatt powers with diffraction-limited beam quality. In this paper we review the reasons for this power evolution. Beyond this, we will discuss how the next generation of fibres, so-called photonic crystal fibres, enable upward power scaling and therefore open up the avenue to new performance levels of solid-state lasers.

Highly efficient transmission gratings in fused silica for chirped-pulse amplification systems

We report on highly efficient transmission gratings in fused silica with a grating period of 800 nm generated by electron-beam lithography. At a wavelength of 1060 nm, 95% diffraction efficiency is achieved under Littrow conditions. The damage threshold, extremely enhanced compared with conventional gold-coated diffraction gratings, makes these gratings the key elements in high average power (>100 W) femtosecond fiber chirped-pulse amplification systems.

High-power cw neodymium-doped fiber laser operating at 9.2 W with high beam quality

We report on a 9.2-W cw, two-times diffraction-limited, neodymium-doped fiber laser operating in the 1.06-microm region. For a silica-based double-clad fiber, slope efficiencies of more than 25% are observed for pumping by a diode-laser system operating near 810 nm.

Thermo-optical properties of air-clad photonic crystal fiber lasers in high power operation.

We report on the investigation of the thermo-optical behavior of air-clad ytterbium-doped large-mode-area photonic crystal fiber lasers. Analytical and numerical models are applied to calculate the heat distribution and induced stresses in a microstructured fiber. The results are compared to conventional double-clad fiber lasers and design guidelines are provided to ensure maximum heat dissipation and scalability to power levels of several kWs.