The invention relates to an optical cell for a separation chamber of a density centrifuge blood processing system for separating fluid components comprising an extraction chamber having a first external optical surface for transmitting at least a portion of an incident optical beam; and an extraction port having an axial bore for passing fluid components and a first external optical surface for transmitting at least a portion of the incident optical beam; wherein said first external optical surface of said extraction chamber and said first external optical surface of said extraction port are both positioned within the depth of field of a light collection element.