birefringence vs double refraction

birefringence and double refraction both are nouns.

Word	Noun	Adjective	Verb	Adverb
birefringence	Yes	No	No	No
double refraction	Yes	No	No	No

As nouns, birefringence and double refraction are synonyms defined as:

birefringence and double refraction: splitting a ray into two parallel rays polarized perpendicularly

birefringence (noun)	double refraction (noun)
splitting a ray into two parallel rays polarized perpendicularly	splitting a ray into two parallel rays polarized perpendicularly