Gavin Frith

Tm-Doped Fiber Lasers: Fundamentals and Power Scaling

We describe fundamental measurements of the properties of thulium (Tm)-doped silica and power scaling studies of fiber lasers based on the material. Data on the high-lying Tm:silica energy levels, the first taken to our knowledge, indicate that pumping at 790 nm is unlikely to lead to fiber darkening via multiphoton excitation. Measurement of the cross-relaxation dynamics produces an estimate that, at the doping levels used, as much as 80% of the decay of the Tm level pumped is due to cross relaxation. Using a fiber having a 25-mum-diameter, 0.08 numerical aperture (NA) core, we observed fiber laser efficiencies as high as 64.5% and output powers of 300 W (around 2040 nm) for 500 W of launched pump power, with a nearly diffraction-limited beam. At these efficiencies, the cross-relaxation process was producing 1.8 laser photons per pump photon. We generated 885 W from a multimode laser using a 35-mum, 0.2-NA core fiber and set a new record for Tm-doped fiber laser continuous-wave power.

Efficient, High-Power, Tm-Doped Silica Fiber Laser

We report on a Tm-doped silica fiber laser that generates 263 W of cw power with a launched pump conversion efficiency of 52% and a slope efficiency of 59%.

Design considerations for short-wavelength operation of 790-nm-pumped Tm-doped fibers.

Tm-doped 790-nm-pumped silica fiber lasers are excellent candidates for producing emission at <1.95 microm, but achieving efficient operation at these wavelengths requires careful attention to fiber design because of the characteristic three-level reabsorption effects. We present a discussion of methods for mitigation of these effects and two high-efficiency systems that are capable of producing up to 70 W at <1.92 microm.

High power pulse amplification in Tm-doped fiber

We report >20 W of average output power at 1.995 mum from a pulsed Tm-doped fiber amplifier system operating at 100 kHz. Pulse energies of >325 muJ have been generated at 50 kHz with 13 ns pulses in the same amplifier.

Mitigation of photodegradation in 790nm-pumped Tm-doped fibers

The capability of Tm-doped silica fibers pumped at 790nm to efficiently produce high power emission in the 1.9~2.1μm region has been well documented to date but little has been presented on the reliability of this technology. Early experiments highlighted that photodarkening can be a significant concern when Tm-doped silica fibers are exposed to high intensity blue light. We present a discussion of the processes responsible for the production of blue light in Tmdoped fibers pumped at 790nm and how fiber composition influences these processes. Through optimization of fiber composition we have demonstrated highly efficient lasers exhibiting less than 1% output power degradation per thousand hours.

Frequency Doubling of Tm-Doped Fiber Lasers for Efficient 950nm Generation

We demonstrate a robust, highly efficient pulsed Tm-doped fiber laser systems operating at 1908nm and producing 6W average power. Using PPLN crystal we demonstrate 60% conversion efficiency to 954nm.

Thulium-doped fiber lasers: Providing eye-safer high power output

Thulium-doped fiber lasers are beginning to demonstrate their potential for high power operation, and for many applications are emerging as the preferred technology. An overview of the technology is presented.

Diode pump requirements for high power fiber lasers

The single most important factor in the recent power scaling of CW fiber lasers has been the continuing improvement in fiber coupled, high brightness pump diodes. As the available power/brightness per module has increased, the cost associated with pumping a fiber laser has decreased and in turn the available CW power from a single fiber laser has increased exponentially over the last five or so years. Here we review some of the unique requirements associated with pumping high power fiber lasers in various architectures, the roadmap on power scaling and wavelength requirements for next generation eye-safe fiber lasers.The single most important factor in the recent power scaling of CW fiber lasers has been the continuing improvement in fiber coupled, high brightness pump diodes. As the available power/brightness per module has increased, the cost associated with pumping a fiber laser has decreased and in turn the available CW power from a single fiber laser has increased exponentially over the last five or so years. Here we review some of the unique requirements associated with pumping high power fiber lasers in various architectures, the roadmap on power scaling and wavelength requirements for next generation eye-safe fiber lasers.

Amplification of Picosecond Pulses Generated in a Carbon Nanotube Modelocked Thulium Fiber Laser

Generation of 5ps, 32pJ pulses from a carbon nanotube modelocked thulium fiber oscillator and their amplification to 0.6W average power, 2.6kW peak power, 13nJ pulses by an LMA thulium fiber amplifier is discussed.

High Efficiency 20W Single Frequency PM Fiber Amplifier at 2037nm

We demonstrate a high efficiency PM fiber amplifier delivering 20W output power and operating in conjunction with an external single frequency, seed source at 2037nm (linewidth ~100kHz). The system is not limited by SBS.