L. Pearson

Broadband Tm-doped superfluorescent fiber source with 11 W single-ended output power.

High-power operation of a cladding-pumped Tm-doped broadband superfluorescent fiber source in the two-micron wavelength regime is described. Predominately single-ended operation was achieved using a simple all-fiber geometry without the use of a high reflectivity mirror or fiber Bragg gratings. The source produced >11 W of single-ended amplified spontaneous emission output spanning the wavelength range from approximately 1930 nm to 1988 nm for a launched diode pump power of approximately 40 W at approximately 790 nm, corresponding to a slope efficiency of 38% with respect to launched pump power. The wavelength spectrum of the superfluorescent source spanned the range from approximately 1650 to 2100 nm with a bandwidth (FWHM) of > 100 nm for output power levels of < 20 mW.

High-power linearly-polarized single-frequency thulium-doped fiber master-oscillator power-amplifier

We report a high power narrow-linewidth source at approximately 2 microm based on a Tm-doped fiber distributed-feedback master-oscillator and three Tm fiber amplifier stages. The master-oscillator and first two amplifier stages were in-band pumped by Er,Yb fiber lasers operating at 1565 nm, and the final stage amplifier was cladding-pumped at 795 nm by two spatially-combined diode-stacks. The MOPA yielded 100 W of single frequency output at 1943 nm with a beam propagation factor (M(2)) of 1.25 and with a polarization extinction ratio of >94%. The output power was limited by thermally-induced damage in the final amplifier stage. The prospects for further power scaling are considered.

High power thulium doped fiber lasers

Thulium-doped silica fiber lasers and amplifiers offer a route to very high average power in the two-micron wavelength regime. This presentation reviews recent progress and considers the prospects for further improvement in performance.

Tm:fiber laser in-band pumping a cryogenically-cooled Ho:YAG laser

Cryogenically-cooled diode-pumped lasers have received significant interest in recent years for their demonstrated orders of magnitude improvement in output radiance using simple laser resonator configurations, with respect to their room temperature counterparts. Here we present a technique that offers the potential for a further order-of-magnitude radiance improvement utilising the in-band pumping hybrid-laser architecture, which employs high-power fiber lasers to excite cryogenically-cooled bulk gain media. The ability to exploit the quasi-four-level nature of a two-level laser system at very cold temperatures enables the operation of very low quantum defect transitions, thus providing reduction in the required thermal dissipation per unit power for the in-band pumped Ho:YAG laser, compared to diode-pumped Yb:YAG. Preliminary results will be discussed for a narrow linewidth Tm:fiber laser system operating in the 100W regime, pumping a cryogenically cooled Ho:YAG gain element, and employing a simple cavity configuration. Low quantum defect operation and power-scaling potential will be discussed.

High-power widely-tunable thulium-doped fiber master-oscillator power-amplifier around 2 mm

We report a high power, widely-tuneable Tm-doped fiber master-oscillator power-amplifier system generating over 100 W of linearly-polarized output with a >190 nm tuning range. The output power is limited only by the available pump power.

Cryogenically-cooled Ho:YAG laser in-band pumped by a Tm fibre laser

Scaling of laser power and brightness to meet the needs of ever-demanding applications is a demanding task which continues to preoccupy many within the laser community. In conventional “bulk” solid-state lasers the main obstacle is heat generation in the laser medium and its associated detrimental effects. Methods for combating these problems have been the focus of much research, resulting in many novel laser geometries with improved thermal management and reduced thermal lensing, but often at the expense of increased complexity and reduced flexibility. An alternative approach, which is beginning to attract a great deal of interest, is to operate the laser with the laser medium maintained at cryogenic temperatures (∼77 K), where the effects of heat loading are dramatically reduced due to a large increase in thermal conductivity and a large decrease in the temperature coefficient of refractive index (dn/dT) and expansion coefficient [1]. In host materials such as YAG the net reduction in thermal effects can be over 50 times compared to operation at room temperature. In the case of diode-pumped Yb:YAG lasers, the combined effect of a massive reduction in thermo-optic aberrations and lower re-absorption loss has allowed very impressive results to be achieved in terms of output power and beam quality from relatively simple laser resonator configurations [2]. In this paper we report on preliminary work ultimately aimed at achieving a further reduction in thermal effects by combining the advantages of cryogenic cooling with a very low quantum defect fibre-laser-pumping of bulk solid-state lasers. Here we describe preliminary results for a cryogenically-cooled Ho:YAG laser in-band pumped by a high-power Tm-doped silica fibre laser.

High power broadband tm-doped superfluorescent fibre source at 2 μm

In this paper, we report a highly-efficient double-ended broadband 2 can cladding-pumped Tm-doped superfluorescent fibre source with much higher output power. Over 15 W of combined output power was generated for a launched pump power of 50.3 W. The corresponding slope efficiency with respect the launched pump power was 42%. The bandwidth (FWHM) of the emission spectrum was ˜ 282 nm at an output power of 8 mW and ˜ 45nm at the highest output power of 15 W.

11W Broadband Amplified Spontaneous Emission Fiber Source at 2 μm

High-power operation of Tm-doped superfluorescent fiber source is described. Over 11W of single-ended output spanning the wavelength-range from 1940nm to 1976nm was obtained with a slope efficiency of 38% with respect to launched pump power.