fix Raman gain estimation during design #260

Job	Run time
Tests on paywalled platforms	0s
Tox test (py38)	1m 50s
Tests on other platforms (windows-2019, 3.10)	2m 39s
Tox test (py39)	1m 49s
Tests on other platforms (windows-2022, 3.11)	2m 43s
Tox test (py310)	1m 51s
Tests on other platforms (windows-2022, 3.12)	2m 46s
Tox test (py311)	1m 47s
Tests on other platforms (macos-12, 3.11)	1m 21s
Tox test (py312-cover)	2m 49s
Tests on other platforms (macos-13, 3.12)	1m 36s
Tox test (docs, graphviz)	2m 13s
PyPI packaging	0s
Docker image	0s
	23m 24s

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