4 KudoZ points awarded for this answer. Comment: "Thanks, everyone, for your help. I finally went with "modulation theorem" based on Kim's and Johanna's references plus: http://www.formel-sammlung.de/ld-Laplace-Transformation-1182.html (German) and http://instruct.uwo.ca/engin-sc/ece233b/notes/ECE233b-Laplace_ch12.pdf (English, on p. 13) Further research shows that "damping factor" is 100% correct, also in connection with Laplace transformations and transforms, but in a slightly different context from the one I'm dealing with. I'm sorry I couldn't provide more detailed context, but I couldn't find a way to copy the relevant formula into the question box."