This is the pastel portrait of Paul Helleu by John Singer Sargent from 1880, and it is his only pastel painting I could find on the net. If you know for some more please let us know in the comments.
Fogg Museum of Art (USA)
Width: 44.8 cm (17.64″) Height: 49.5 cm (19.49″).
To see it in the better resolution click on the image.