Christina C. C. Willis

Bio: Christina C. C. Willis is an academic researcher from University of Central Florida. The author has contributed to research in topics: Fiber laser & Laser linewidth. The author has an hindex of 8, co-authored 32 publications receiving 316 citations.

High-power widely tunable thulium fiber lasers

Abstract: 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 >150W of average power, >50% slope efficiency, narrow output linewidth, and >100nm tunability in the wavelength range around 2μm.

Laser-induced breakdown spectroscopy of copper with a 2 μm thulium fiber laser

Abstract: We report the first implementation of a 2 μm thulium fiber laser in a Laser-Induced Breakdown Spectroscopy system. Emission from plasma on copper samples was analyzed from 200 to 900 nm. The low ablation fluence (<100 J.cm−2) and 200 ns pulse duration lead to a plasma with neither continuum emission, nor air emission in the near-infrared region.

Spectral narrowing and stabilization of thulium fiber lasers using guided-mode resonance filters

Abstract: We used guided-mode resonance filters (GMRFs), fabricated using thin-film deposition and chemical etching, as intracavity feedback elements to stabilize and narrow the output spectrum in thulium-doped fiber oscillators operating in the 2 μm wavelength regime, producing linewidths of <700 pm up to 10 W power levels. A Tm fiber-based amplified spontaneous emission source was used to characterize the reflective properties of the GMRFs. Linewidths of 500 pm and a 7.3 dB reduction in transmission were measured on resonances.

Integrated Tm:fiber MOPA with polarized output and narrow linewidth with 100 W average power

Abstract: We report on a Tm:fiber master oscillator power amplifier (MOPA) system producing 109 W CW output power, with >15 dB polarization extinction ratio, sub-nm spectral linewidth, and M2 <1.25. The system consists of polarization maintaining (PM) fiber and PM-fiber components including tapered fiber bundle pump combiners, a single-mode to large mode area mode field adapter, and a fiber-coupled isolator. The laser components ultimately determine the system architecture and the limits of laser performance, particularly considering the immature and rapidly developing state of fiber components in the 2 μm wavelength regime.

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

Abstract: 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 laser's performance as an ablation source for LIBS experiments on copper.

Fiber lasers and their applications [Invited]

Abstract: Fiber lasers have seen progressive developments in terms of spectral coverage and linewidth, output power, pulse energy, and ultrashort pulse width since the first demonstration of a glass fiber laser in 1964. Their applications have extended into a variety of fields accordingly. In this paper, the milestones of glass fiber laser development are briefly reviewed and recent advances of high-power continuous wave, Q-switched, mode-locked, and single-frequency fiber lasers in the 1, 1.5, 2, and 3 μm regions and their applications in such areas as industry, medicine, research, defense, and security are addressed in detail.

Welding of polymers using a 2 μm thulium fiber laser

Abstract: Absorber-free transmission and butt-welding of different polymers were performed using thulium fiber laser radiation at the wavelength 2 μm. The relations between the laser process conditions and the dimensions and quality of the seam were investigated by means of optical and phase-contrast microscopy. Mechanical properties of the weld joints were studied in tensile strength tests. Laser-welded polyethylene samples revealed a tensile strength of greater than 80% of the bulk material strength. Transmission welding of different polymer combinations featured the formation of different joint classes depending on the spectral properties. The experiments demonstrate new application areas of mid-IR fiber laser sources for materials processing.

Recent Advances in Resonant Waveguide Gratings

Abstract: Resonant waveguide gratings (RWGs), also known as guided mode resonant (GMR) gratings or waveguide-mode resonant gratings, are dielectric structures where these resonant diffractive elements benefit from lateral leaky guided modes from UV to microwave frequencies in many different configurations. A broad range of optical effects are obtained using RWGs such as waveguide coupling, filtering, focusing, field enhancement and nonlinear effects, magneto-optical Kerr effect, or electromagnetically induced transparency. Thanks to their high degree of optical tunability (wavelength, phase, polarization, intensity) and the variety of fabrication processes and materials available, RWGs have been implemented in a broad scope of applications in research and industry: refractive index and fluorescence biosensors, solar cells and photodetectors, signal processing, polarizers and wave plates, spectrometers, active tunable filters, mirrors for lasers and optical security features. The aim of this review is to discuss the latest developments in the field including numerical modeling, manufacturing, the physics, and applications of RWGs. Scientists and engineers interested in using RWGs for their application will also find links to the standard tools and references in modeling and fabrication according to their needs.

Materials for optical fiber lasers: A review

Abstract: Over the past two decades, fiber laser technologies have matured to such an extent that they have captured a large portion of the commercial laser marketplace. Yet, there still is a seemingly unquenchable thirst for ever greater optical power to levels where certain deleterious light-matter interactions that limit continued power scaling become significant. In the past decade or so, the industry has focused mainly on waveguide engineering to overcome many of these hurdles. However, there is an emerging body of work emphasizing the enabling role of the material. In an effort to underpin these developments, this paper reviews the relevance of the material in high power fiber laser technologies. As the durable material-of-choice for the application, the discussion will mainly be limited to silicate host glasses. The discussion presented herein follows an outward path, starting with the trivalent rare earth ions and their spectroscopic properties. The ion then is placed into a host, whose impact on the spectroscopy is reviewed. Finally, adverse interactions between the laser lightwave and the host are discussed, and novel composition glass fiber design and fabrication methodologies are presented. With deference to the symbiosis required between material and waveguide engineering in active fiber development, this review will emphasize the former. Specifically, where appropriate, materials-based paths to the enhancement of laser performance will be underscored.