Near-field recording with a 266 nm laser for disc mastering process

A near-field mastering process was realized with a 266 nm laser and a solid immersion lens (SIL) of 1.35 numerical aperture (NA). The air gap was detected with a 532 nm laser and it was servo-controlled at about 100 nm by driving the SIL with an air-suspended pad and a piezoelectric transducer (PZT) actuator. A residual fluctuation of the air gap was constrained within 10 nmPP. For a rear converging lens, one of the molded lenses with a wave front error (WFE) of below 70 mλrms was selected. It was assembled with a supersphere SIL of about 10 mλrms WFE. As a result of read-only memory (ROM) recording in a density corresponding to 40 gigabytes (GB) in compact disc (CD) size, a clear pit pattern was fabricated. As for 25 GB ROM recording, acceptable signal quality was obtained.