Optical scanning device

A method of scanning a record carrier (22) having an outer face (24), said method comprising scanning said record carrier using an optical scanning device, wherein the optical scanning device comprises:

• a) a radiation source system (2) arranged to generate radiation;
• b) an objective system (20) having an exit face (76), said objective system being arranged between said radiation source system and said record carrier and providing for evanescent coupling of the radiation across a gap between the exit face of the objective system and the outer face of the record carrier;
• c) a radiation detector arrangement for detecting radiation after interaction with the record carrier, the radiation detector arrangement being arranged to produce a tilt error signal (α, β) representing a tilt misalignment between the exit face of the objective system and the outer face of the record carrier;
• and
• d) a tilt misalignment control system which is arranged to adjust the tilt misalignment between the exit face of the objective system and the outer face of the record carrier,
• wherein the method includes:
• irradiating said record carrier with said radiation generated by the radiation source system, wherein during said irradiation the radiation passes across the gap between the exit face of the objective system and the outer face of the record carrier by evanescent coupling;
• using said radiation detector arrangement to detect said radiation after interaction with the record carrier;
• using said radiation detector arrangement to produce a tilt error signal by detecting information in the detected radiation which is indicative of a variation in an efficiency of the evanescent coupling across the exit face;
• and
• using said tilt misalignment control system to adjust the tilt misalignment between the exit face of the objective system and the outer face of the record carrier, in accordance with the tilt error signal.