Yakup Midilli

Estimating the atmospheric turbulence strength (C _n ²) becomes significant in the research field of electromagnetic radiation transmission through the atmosphere, particularly optical waves. As turbulence strength increases, the quality and strength of these optical waves may decrease and cause much trouble as they pass through the atmosphere. Throughout the years, C _n ² has been formulated by different research groups for various geographical locations and seasons using macro-meteorological variables empirically and theoretically. However, since these models are based on the data collected from numerous places and conditions, such as deserts or coastal areas, they do not provide accurate C _n ² predictions for our experimental site, as demonstrated for three well-known models in the paper. In this study, a novel, to our knowledge, artificial neural network (ANN) model named as quadratic Fourier neural network (QFNN) is trained to estimate C _n ² from experimentally measured ground-based atmospheric turbulence strength and macro-meteorological variables during the winter season in a rural area. The trained model gives reliable estimations, achieving a value of R²=0.92 for experimental C _n ² values.

High-power fiber lasers have been applied in many areas due to their advantages such as high beam quality, compact structure, flexibility and high efficiency. However, the absorption of the pump light is limited and a residual pumped light keeps propagating in the cladding. This residual pumped light affects the beam quality and can damage the whole system. Therefore, an efficient removal of excess high-power cladding light is critical for the safe operation of the high-power fiber lasers and high beam quality [1]. Adding a new structure to the cladding of the fiber leading to interrupt total internal reflection in the clad and scatter away the unwanted pump light is the generalized approach for a cladding light stripper (CLS) device fabrication. Also, it is important to scatter all the unwanted light uniformly along the CLS. Etching the fiber for surface damage and recoating the fiber [2] are two general methods for stripping the cladding light [3–5].

We demonstrate a 1018 nm ytterbium-doped all-fiber laser pumped by tunable pump sources operating in the broad absorption spectrum around 915 nm. In the experiment, two different pump diodes were tested to pump over a wide spectrum ranging from 904 to 924 nm by altering the cooling temperature of the pump diodes. Across this so-called pump wavelength regime having a 20 nm wavelength span, the amplified stimulated emission (ASE) suppression of the resulting laser was generally around 35 dB, showing good suppression ratio. Comparisons to the conventional 976 nm-pumped 1018 nm ytterbium-doped fiber laser were also addressed in this study. Finally, we have tested this system for high power experimentation and obtained 67% maximum optical-to-optical efficiency at an approximately 110 W output power level. To the best of our knowledge, this is the first 1018 nm ytterbium-doped all-fiber laser pumped by tunable pump sources around 915 nm reported in detail.