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High-Power Fiber Lasers
Published in Johan Meyer, Justice Sompo, Suné von Solms, Fiber Lasers, 2022
Johan Meyer, Justice Sompo, Sune von Solms
Optical power losses in a medium can grow when the medium is irradiated with light at certain wavelengths. This phenomenon known as photodarkening (PD) can lead to serious performance degradation of high-power fiber lasers. The optical loss in the event of PD is the result of colour centre formation in the glass matrix. The exact origin of the colour centre is still not clearly understood. Reported studies tend to prove that there is a connection between the PD rate and the Ytterbium inversion (Jetschke et al. 2007; Koponen et al. 2007). This order of inversion was quantified and reported to be in the range between 3.5 (Jetschke et al. 2007) and 7 (Koponen et al. 2007). Also, the PD-induced loss distribution is not uniform along the active fiber length. This loss variation is proportional to the square of the Ytterbium inversion. It has also been reported that the output power of the laser is inversely proportional to the operating temperature variation (Zervas et al. 2011). Finally, the PD entirely depends on the core material. By carefully choosing the Ytterbium concentration and other dopants such as Phosphorous (Engholm and Norin 2008), Aluminium (Jetschke et al. 2012; Morasse et al. 2007), or Cerium (Engholm et al. 2009), the PD can be critically reduced or even eliminated. PD has also been reported in Thulium-doped fibers (Broer et al. 1993; Brocklesby et al. 1993).
Reliability and Flight Qualification
Published in Hamid Hemmati, Near-Earth Laser Communications, 2020
Proton-induced displacement damage is the primary radiation damage mechanism in injection laser diodes (Barnes et al., 2002). Total ionizing dose and displacement damage reflected as an increased dark current for detectors is also a primary degradation mechanism for photodiodes. Increased attenuation due to photodarkening is a common effect of radiation on optical fibers.
Reliability and Flight Qualification
Published in Hamid Hemmati, Near-Earth Laser Communications, 2018
Proton-induced displacement damage is the primary radiation damage mechanism in injection laser diodes (Barnes et al., 2002). Displacement damage reflected as increased dark current for detectors is also a primary degradation mechanism for photodiodes. Increased attenuation due to photodarkening is a common effect of radiation on optical fibers.
Laser irradiation-induced structural, microstructural and optical properties change in Bi-doped As40Se60 thin films
Published in Phase Transitions, 2020
Mukta Behera, N. C. Mishra, R. Naik
In the present paper, the laser irradiation-induced changes in structural, microstructural and optical properties of both as-prepared and illuminated thin films of As40Se55Bi5 and As40Se45Bi15 were investigated. The indirect allowed optical band gap is decreased with laser irradiation showing the photodarkening phenomena. The reduction is due to the increase in density of defect states in the gap. The absorption coefficient and extinction coefficient showed change upon illumination. The small crystallite is noticed from the FESEM images. The XRD pattern shows the small crystallinity with increase in intensity. The Raman data support the observed changes in the illuminated films. As the optical constants like energy band gap, absorption coefficient and refractive index play a vital role in the optical devices, the change in these properties by laser irradiation in As40Se60 − xBix films will be useful for creation of optical mirrors, integrated optical elements, which need high local changes of optical parameters. The photo-induced crystallization property in this As40Se60 − xBix amorphous chalcogenides film is useful in erasable phase-change memories.