Showing papers by "Lawrence Shah published in 2018"
TL;DR: In this article, the spectroscopic properties of Tm3+ -doped silica are first detailed, revealing complex processes and large variations among published measurements, with outputs ranging from 1908 to 2130 nm.
Abstract: Thulium-doped fiber lasers (TDFLs) have had the second highest growth in average output power next to ytterbium-doped fiber lasers. This has been enabled by access to high power, high brightness ∼790-nm pump diodes in conjunction with the cross-relaxation process that improves laser efficiency. While numerous high power TDFLs have been recently demonstrated, a 1-kW result from 2010 remains the highest output power system reported to date. This paper reviews these systems and the concepts behind high power TDFLs. The spectroscopic properties of Tm3+ -doped silica are first detailed, revealing complex processes and large variations among published measurements. Notable multi-100 W TDFLs are then summarized, with outputs ranging from 1908 to 2130 nm. Another route for power scaling is to in-band pump with another TDFL to enable >90% efficiencies. Both 790- and 1900-nm pumped TDFL architectures are theoretically modeled based on currently available systems. Hindered by high background losses and available pump sources, achieving >4 kW like ytterbium-fiber systems will be a substantial challenge.
62 citations
TL;DR: Results indicate that by improving the anti-reflection coatings and using a high beam quality mid-infrared source, chalcogenide fibers can reliably deliver ≥10 W in a single mode, potentially out to 6.5 µm.
Abstract: Mechanically robust and low loss single-mode arsenic sulfide fibers are used to deliver high power mid-infrared sources. Anti-reflection coatings were deposited on the fiber facets, enabling 90% transmission through 20 cm length fibers. 10.3 W was transmitted through an anti-reflection coated fiber at 2053 nm, and uncoated fibers sustained 12 MW/cm2 intensities on the facet without failure. A Cr:ZnSe laser transmitted >1 W at 2520 nm, and a Fe:ZnSe laser transmitted 0.5 W at 4102 nm. These results indicate that by improving the anti-reflection coatings and using a high beam quality mid-infrared source, chalcogenide fibers can reliably deliver ≥10 W in a single mode, potentially out to 6.5 µm.
34 citations
01 May 2018
TL;DR: In this paper, the authors describe an experimental investigation of thermal management in a high power, high repetition-rate, pulsed Thulium (Tm) fiber laser with a tunable nanosecond TDF laser system.
Abstract: Thulium silica doped fiber (TDF) lasers are becoming important laser sources in both research and applications in industry. A key element of all high-power lasers is thermal management and its impact on laser performance. This is particularly important in TDF lasers, which utilize an unusual cross-relation pumping scheme, and are optically less efficient than other types of fiber lasers. The present work describes an experimental investigation of thermal management in a high power, high repetition-rate, pulsed Thulium (Tm) fiber laser. A tunable nanosecond TDF laser system across the 1838 nm – 1948 nm wavelength range, has been built to propagate 2μm signal seed pulses into a TDF amplifier, comprising a polarized large mode area (PLMA) thulium fiber (TDF) with a 793nm laser diode pump source. The PLMA TDF amplifier is thermally managed by a separately controlled cooling system with a temperature varied from 12°C to 36°C. The maximum output energy (~400 μJ), of the system is achieved at 12°C at 1947 nm wavelength with ~32 W of absorbed pump power at 20 kHz with a pulse duration of ~ 74 ns.
01 Jan 2018
TL;DR: In this article, the authors present advances in laser-aided direct machining of wafer materials utilized in the electronics industry, primarily semiconductors such as silicon and gallium arsenide.
Abstract: This chapter covers recent research and development advances in laser-aided direct machining of wafer materials utilized in the electronics industry, primarily semiconductors such as silicon and gallium arsenide. In order to satisfy the steadily growing demand for smaller, faster, and more efficient consumer electronic devices, new fabrication methodologies involving novel laser sources and advanced laser-matter interaction regimes are needed. Successful development of these methods relies on a fundamental understanding of the optical properties of materials and materials' response to irradiation. Laser processing of semiconductor wafers in 2D and 3D is presented utilizing high-energy ultrafast lasers, as well as novel fiber lasers operating in the mid-infrared spectral range.
04 May 2018
TL;DR: In this paper, a 2 μm master oscillator power amplifier (MOPA) fiber laser system capable of producing 700 μJ pulse energies from a single 1.5 m long amplifier was presented.
Abstract: We report on a 2 μm master oscillator power amplifier (MOPA) fiber laser system capable of producing 700 μJ pulse energies from a single 1.5 m long amplifier. The oscillator is a single-mode, thulium-doped fiber that is Q-switched by an acousto-optic modulator. The oscillator seeds the amplifier with 1 W average power at 20 kHz repetition rate. The power amplifier is a polarization-maintaining, large mode area thulium-doped fiber cladding pumped by a 793 nm fiber-coupled diode. The fiber length is minimized to avoid nonlinearities during amplification while simultaneously enabling high energy extraction. The system delivers 700 μJ pulse energies with 114 ns pulse duration and 14 W average power at 1977 nm center wavelength.
04 May 2018
TL;DR: In this article, the performance of in-house drawn active fiber active optical fibers is investigated and the results on a highly multi-mode, high average power pulsed Raman fiber amplifier pumped by a thin disc laser are presented.
Abstract: To advance the science of high power fiber lasers, in-house drawn specialty optical fibers are investigated. Ongoing research involves the fabrication and testing of Yb- and Tm-doped fibers at 1μm and 2μm. Using specialized fiber and pump mixing geometries, dopant profiles and system configurations, the performance of our in-house drawn active fibers has been examined. Results on a highly multi-mode, high average power pulsed Raman fiber amplifier pumped by a thin disc laser are presented. The Raman fiber is a large mode-area graded index fiber, also drawn in house. Finally, the development of capabilities for kilometer range propagation experiments of kW-level CW and TW-level pulsed lasers at the TISTEF laser range is reported.
26 Feb 2018
TL;DR: In this article, the feasibility of passive cooling in high-power Yb amplifiers was investigated, and an all-glass airclad step-index (ACSI) amplifier was diode-pumped with 400W and provided 200W power levels.
Abstract: This work investigates the feasibility of passive cooling in high-power Yb amplifiers. Experimentally, an all-glass airclad step-index (ACSI) amplifier is diode-pumped with 400W and provides 200W power levels. With only natural convection to extract heat, core temperatures are estimated near 130°C with no degradation of performance relative to cooled architectures. Further, advanced analysis techniques allow for core temperature determination using thermal interferometry without the need for complicated stabilization or calibration.
20 Feb 2018
TL;DR: In this article, a custom optical system was constructed to efficiently couple the 0.8 NA QCL radiation into the chalcogenide glasses (ChGs) fiber, allowing for a maximum of 78% overlap between the quantum cascade radiation and fundamental mode of the fiber.
Abstract: Due to the intrinsic absorption edge in silica near 2.4 μm, more exotic materials are required to transmit laser power in the IR such as fluoride or chalcogenide glasses (ChGs). In particular, ChG fibers offer broad IR transmission with low losses 15 W, CW Tm:fiber laser. Power handling up to 10.2 W with single mode beam quality has been demonstrated, limited only by the available Tm:fiber output power. Anti-reflective coatings were successfully deposited on the ChG fiber facets, allowing up to 90.6% transmission with 12.2 MW/cm2 intensity on the facet. Single mode guidance at 4550 nm was also demonstrated using a quantum cascade laser (QCL). A custom optical system was constructed to efficiently couple the 0.8 NA QCL radiation into the 0.2 NA ChG fiber, allowing for a maximum of 78% overlap between the QCL radiation and fundamental mode of the fiber. With an AR-coated, 25 μm core diameter fiber, >50 mW transmission was demonstrated with > 87% transmission. Finally, we present results on fiber coupling from a free space Cr:ZnSe resonator at 2520 nm.