Disclosed herein is an apparatus for spectroscopic ellipsometry, preferably for infrared spectroscopic ellipsometry, and a method for spectroscopic ellipsometry employing the apparatus. In some embodiments, the apparatus may comprise a light source (12), a detector (30), a polarizer (40), an analyzer (41), and a measuring probe (10). In one embodiment, the measuring probe may comprise an ATR prism (50) having at least one first surface having at least one measuring portion (M) configured to be brought in optical contact with a measured object (72), and at least one second surface having at least one reflective portion (RX).