A random narrow-linewidth lasing at a wavelength of 976 nm was obtained in an ytterbium-doped germanophosphosilicate fiber with an array of weakly reflecting fiber Bragg gratings (FBGs). A random laser cavity was formed by implementing the standard phase mask method of FBG inscription directly during the fiber drawing process. The UV radiation pulses of a KrF excimer laser (248 nm wavelength) synchronized with the fiber drawing speed were used to fabricate the in-fiber array of hundreds of similar FBGs. The developed laser’s slope efficiency in the backward-pumping scheme was measured as high as 33%. The stable continuous-wave operation mode of the laser was detected. The magnitude of the laser power fluctuations depends linearly on the cavity length. The random laser cavity modified with a single highlyreflected (90%) FBG demonstrates significantly better power stability and higher slope efficiency than the same one without an FBG.

For the first time, radiation-induced absorption (RIA) of light is compared in two types of polarization-maintaining PANDA fibers having 1) undoped-silica core and F-doped-silica cladding, or 2) N-doped-silica core and undoped-silica cladding. RIA at λ=1.55 μm is compared under γ-irradiation and post-irradiation recovery at room temperature (RT) and -60°C. The post-irradiation RIA decay at RT is used to extrapolate RIA to the postulated end of the PANDA space mission (15 years) with the help of the “nth-order kinetic” model. The RIA extrapolation values for both PANDA types are found to be comparable. RIA spectra are measured in the PANDAs in the range ~0.5-4 eV in the process of γ-irradiation and recovery and Gaussian deconvolved. The RIA spectra of both Panda types are found to be composed of inherent and strain-assisted self-trapped holes (STHs), some undoped PANDAs demonstrating, in addition, a long-wavelength RIA tail affecting λ=1.55 μm. No N-related color centers are revealed. Finally, RIA at λ=1.55 μm is compared upon pulsed-X-ray irradiation. Undoped PANDAs are found to feature much smaller RIA at RT at post-pulse times larger than ~40-1000 μs, whereas at smaller times, an N-doped PANDA proved to be superior. At -60°C and at t>1 ms, both PANDA types demonstrate approximately equal RIAs. Thus, the experiments showed that the two PANDA types are quite comparable, each type having its own advantages and disadvantages.

Asingle-mode Yb-doped germanophosphosilicate fiber with ultra-low optical losses (less than 2 dB/km) was fabricated by means of the MCVD method utilizing an all-gas-phase deposition technique developed “in house”. The absorption and luminescent spectral properties of the fiber were thoroughly studied. The photosensitivity of the pristine (non-hydrogenated) fiber to 248 nm-laser radiation was confirmed by means of fiber Bragg grating (FBG) inscription directly during the drawing process. The random single-frequency lasing at the 1060-nm-wavelength obtained in the 21-m-long fiber with an array of weak FBG was reported. The developed laser slope efficiency in the backward-pumping scheme was measured as high as 32%.

All-fiber, polarization maintaining, narrow-bandwidth, Yb-doped fiber lasers with randomly distributed feedback operated near 976 nm were realized for the first time. It was shown that the laser operated in a single, longitudinal mode regime during intervals of a few seconds. At other times, the laser generated a few longitudinal modes, but its bandwidth was always below the resolution of the optical spectrum analyzer (0.02 nm). The linewidth of each single longitudinal mode of the laser was estimated to be below 20 kHz. The reasons for this observed laser behavior were discussed and methods for achieving stable, continuous wave operation in the single-longitudinal-mode regime were proposed.

In this study, we present results of development fiber picosecond laser by using an active ytterbium tapered double clad optical fiber with mode field diameter of 35 μm and low intrinsic birefringence (1.45 * 10⁻⁸ rad m⁻¹). We have demonstrated 1040 nm/50 ps optical source with tunable repetition rate (within range of 1–20 MHz) and an average power of 160 W (peak power 160 kW, 8 μJ per pulse) delivering Gaussian beam with excellent quality (M ² ∼ 1.11/1.22).