Coherent beam combination of four holmium amplifiers with phase control via a direct digital synthesizer chip.

We present the coherent beam combination of four 2100 nm holmium amplifiers with their phase controlled through acousto-optic modulators driven by the RF output of direct digital synthesizer chips. Phase alignment was achieved through the use of a field programmable gate array based stochastic parallel gradient descent algorithm.

High power cryogenic Ho:YAG laser.

We have improved significantly the brightness of cryogenic Ho:YAG, reporting up to 65 W output power with a beam quality of M <1.3 and a slope efficiency of 71%. The laser emission was ~2 nm wide and centered at 2097.

Nanoparticle doping for high power fiber lasers at eye-safer wavelengths.

A nanoparticle (NP) doping technique was developed for fabricating erbium (Er)- and holmium (Ho)-doped silica-based optical fibers for high energy lasers. Slope efficiencies in excess of 74% were realized for Er NP doping in a single mode fiber based master oscillator power amplifier (MOPA) and 53% with multi-Watt-level output in a resonantly cladding-pumped power oscillator laser configuration based on a double-clad fiber. Cores comprising Ho doped LaF and LuO nanoparticles exhibited slope efficiencies as high as 85% at 2.

Metal clad active fibres for power scaling and thermal management at kW power levels.

We present a new approach to high power fibre laser design, consisting of a polymer-free all-glass optical fibre waveguide directly overclad with a high thermal conductivity metal coating. This metal clad active fibre allows a significant reduction in thermal resistance between the active fibre and the laser heat-sink as well as a significant increase in the operating temperature range. In this paper we show the results of a detailed thermal analysis of both polymer and metal coated active fibres under thermal loads typical of kW fibre laser systems.

Efficient, low threshold, cryogenic Ho:YAG laser.

We report the development of an efficient, liquid-nitrogen conduction cooled Ho:YAG slab laser with good beam quality. Detailed measurements resolving the structure of the 1900-1911 nm absorption band in Ho:YAG at 77 K are presented. Stress-free conduction cooled mounting of the Ho:YAG slab was demonstrated and the resulting laser operated with a large mode volume of 42 mm, a slope efficiency of 75% and a threshold of 0.

CO laser-fabricated cladding light strippers for high-power fiber lasers and amplifiers.

We present and characterize a simple CO laser processing technique for the fabrication of compact all-glass optical fiber cladding light strippers. We investigate the cladding light loss as a function of radiation angle of incidence and demonstrate devices in a 400 μm diameter fiber with cladding losses of greater than 20 dB for a 7 cm device length. The core losses are also measured giving a loss of <0.

High precision 9.6 µm CO(2) laser end-face processing of optical fibres.

Reproducible, precise cleaving of optical fibres is of great importance to the fibre laser and telecommunications industries. We present a novel approach to the end-face processing of optical fibres using a 9.6 µm CO laser to produce flat, smooth and symmetric fibre end-face profiles with no rounding or melting at the edges of the fibre.

Design and experimental demonstration of a large pedestal thulium-doped fibre.

We present a novel large-mode-area thulium-doped fibre with a large pedestal design. We discuss the advantages of this large pedestal fibre in the context of overcoming limitations imposed by cleaving and splicing tolerances. Finally we demonstrate the use of such a fibre in constructing monolithic fibre lasers operating at 1.

Pulsed operation of a resonantly pumped, linearly polarised, large mode area holmium-doped fibre amplifier.

We present the design of a polarisation maintaining, resonantly and cladding pumped, large mode area holmium-doped fibre. We describe the operation of this fibre in a pulsed amplifier configuration. The amplifier produced pulses with energy of 2.

A cladding-pumped, tunable holmium doped fiber laser.

We present a tunable, high power cladding-pumped holmium doped fiber laser. The laser generated >15 W CW average power across a wavelength range of 2.043 - 2.

99 W mid-IR operation of a ZGP OPO at 25% duty cycle.

We have demonstrated the highest reported output power from a mid-IR ZGP OPO. The laser is a cascaded hybrid system consisting of a thulium fibre laser, Ho:YAG solid state laser and a Zinc Germanium Phosphide parametric oscillator. The system produces 27 W of output power in the 3-5 μm wavelength range with an M(2) = 4.

High power operation of cladding pumped holmium-doped silica fibre lasers.

We report the highest power operation of a resonantly cladding-pumped, holmium-doped silica fibre laser. The cladding pumped all-glass fibre utilises a fluorine doped glass layer to provide low loss cladding guidance of the 1.95 µm pump radiation.

Efficient, polarised, gain-switched operation of a Tm-doped fibre laser.

We present a monolithic, robustly polarised thulium fibre laser which produces pulses with 25 ns duration and energy of up to 35 µJ. A pulsed 1.55 μm source was used to gain switch the laser at repetition rates of up to 300 kHz, producing average powers of up to 8 W at 2.