Timothy S. McComb

High-power widely tunable thulium fiber lasers

Applications requiring long-range atmospheric propagation are driving the development of high-power thulium fiber lasers. We report on the performance of two different laser configurations for high-power tunable thulium fiber lasers: one is a single oscillator utilizing a volume Bragg grating for wavelength stabilization; the other is a master oscillator power amplifier system with the oscillator stabilized and made tunable by a diffraction grating. Each configuration provides >150 W of average power, >50% slope efficiency, narrow output linewidth, and >100 nm tunability in the wavelength range around 2 μm.

Very large-core, single-mode, gain-guided, index-antiguided fiber lasers

Lowest-order, single-mode laser oscillation is reported in gain-guided index-antiguided fiber lasers having core diameters from 100 to 400 microm. A model is presented explaining how to select resonator mirrors to assure single-mode operation.

Lasing in a gain-guided index antiguided fiber

Experimental demonstration is presented of lasing in a gain-guided index antiguided Nd3+-doped phosphate glass core fiber. This type of lasing remains in its lowest-order mode even when pumped well above threshold, leading to excellent beam quality.

Volume Bragg grating stabilized spectrally narrow Tm fiber laser

A Tm-doped large mode area (LMA) silica fiber laser has been locked to a stable wavelength of 2,053.9 nm using a volume Bragg grating (VBG). The measured spectral width of the laser output was <300 pm, limited by the spectrometer resolution. Although this laser had modest output (approximately 5W) and slope efficiency (41%), this new approach to spectrally limiting the output of LMA fiber lasers is inherently extendable to kilowatt powers, opening up several applications including high-power pulsed fiber lasers and spectral beam combining. Performance characteristics of the laser compared to one using a dielectric mirror as a high reflector are described, and the results imply low VBG losses.

High-energy Q-switched Tm3+-doped polarization maintaining silica fiber laser

We report the performance of an actively Q-switched Tm fiber laser system. The laser was stabilized to sub-nanometer spectral width using each of two feedback elements: a blazed reflection grating and a volume Bragg grating. Maximum pulse energy using the reflection grating was 325 μJ pulses at 1992 nm (< 200 pm width) with a 125 ns duration at a 20 kHz repetition rate. Maximum pulse energy using the volume Bragg grating was 225 μJ pulses at 2052 nm (<200 pm width) with a 200 ns duration also at 20 kHz. We also report the lasers performance as an ablation source for LIBS experiments on copper.

Atmospheric propagation testing with a high power, tunable thulium fiber laser system

A tunable master oscillator power amplifier (MOPA) fiber laser system based on thulium doped silica fiber designed for investigation of multi-kilometer propagation through atmospheric transmission windows existing from ~2030 nm to ~2050 nm and from ~2080 nm to beyond 2100 nm is demonstrated. The system includes a master oscillator tunable over >200 nm of bandwidth from 1902 nm to beyond 2106 nm producing up to 10 W of linearly polarized, stable, narrow linewidth output power with near diffraction limited beam quality. Output from the seed laser is amplified in a power amplifier stage designed for operation at up to 200 W CW over a tuning range from 1927 - 2097 nm. Initial field tests of this system at the Innovative Science & Technology Experimental Facility (ISTEF) laser range on Cape Canaveral Air Force Station, Florida will be discussed. Results presented will include investigation of transmission versus wavelength both in and out of atmospheric windows, at a variety of distances. Investigations of beam quality degradation at ranges up to 1 km at a variety of wavelengths both in and out of atmospheric transmission windows will be also presented. Available theoretical models of atmospheric transmission are compared to the experimental results.

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.

Diode-Pumped Very Large Core, Gain Guided, Index Antiguided Single Mode Fiber Laser

Single-mode laser action, up to 4-times the threshold power, in a diode-pumped Nd-doped phosphate glass fiber having a 300-μm core is demonstrated. Subtle differences associated with the effectiveness of diode-pumping gain-guided, index-antiguided fibers are discussed.

Tunable high power thulium fiber lasers

Two thulium fiber laser configurations are described providing widely tunable and narrow linewidth output. We show that such systems can produce average powers greater than 100 W.

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.