Latkin, K.P., A.S. Smirnov, Yu.A. Konstantinov, and V.V. Burdin. 2018. “The Erbium Ions Absolute Concentration Measuring Technique in Active Fiber Preform”. Perm Federal Research Centre Journal, no. 4 (November): 21-26. https://doi.org/10.7242/1998-2097/2018.4.3.