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...

Thank you!

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.

The woman in the photo is his second wife, Natalia née Svetlova.