Yes, it's his second wife, and the photo was taken in 1972 when he was visiting Mstislav Rostropovich. There is another photo from the same series here: https://rg.ru/2019/12/10/vospominaniia-solzhenicyna-o-tom-ka...

the caption says it is "his wife, Natalia"

However, Wikipedia says both his wives were called Natalia. He married the second one after receiving the Nobel.