Search

Beam confinement or “no free-space optics” via fiber transmission can achieve improved reliability, lower cost, and reduced component count for active sensing systems. For midinfrared delivery, mechanically robust chalcogenide (arsenic sulfide) single-mode fibers are of interest. A 12-μm core diameter fiber is shown to transport >10 W at 2053 nm, and a 25-μm core diameter fiber enables single-mode beam transport from a 4550-nm quantum cascade laser. As midinfrared sources continue to increase their output power capabilities, chalcogenide fibers will eventually be limited in their power-handling capacity due to optical nonlinearities or thermal failure. These limitations are discussed and analyzed in the context of single-mode chalcogenide fibers in order to provide a framework for power transmission limitations in various operating regimes. [ABSTRACT FROM AUTHOR]

A self-developed nanosecond-pulsed thulium fiber laser operating at the wavelength λ = 2 μm was used to selectively modify the front and the back surfaces of various uncoated and metal-coated silicon and gallium arsenide wafers utilizing transparency of semiconductors at this wavelength. This novel processing regime was studied in terms of the process parameter variations, i.e., pulse energy and pulse duration, and the corresponding modification fluence thresholds were determined. The results revealed nearly debris-free back surface processing of wafers, in which modifications could be induced without affecting the front surfaces. The back surface modification threshold of Si was significantly higher than at the front surface due to non-linear absorption and aberration effects observed in experiments. A qualitative study of the underlying physical mechanisms responsible for material modification was performed, including basic analytical modeling and z-scan measurements. Multi-photon absorption, surface-enhanced absorption at nano- and microscopic defect sites, and damage accumulation effects are considered the main physical mechanisms accountable for consistent surface modifications. Applications of trans-wafer processing in removal of thin single- and multi-material layers from the back surface of Si wafers, both in single tracks and large areas, are presented. [ABSTRACT FROM AUTHOR]

• A narrow linewidth, tunable 80 W thulium fiber laser is presented. • Low doping concentration thulium fiber was used to avoid thermal degradation. • System performance was optimized to investigate thermal blooming. • Effects of thermal blooming on laser propagation have been investigated. We describe the design and characterization of a tunable narrow linewidth thulium-doped fiber laser source which combines a core-pumped preamplifier and high power cladding-pumped amplifier, providing >80 W average power. The single-frequency wavelength output from 1.92 um to 2.01 µm is digitally tunable to target specific atmospheric absorption and transmission windows for applications targeting atmospheric transmission at 2 µm. Results from preliminary thermal blooming studies are presented. [ABSTRACT FROM AUTHOR]