Astigmatizer for laser recording and reproducing system

Details Astigmatizer for laser recording and reproducing system Astigmatizer for laser recording and reproducing system

1974-12-09

1976-09-28

Canney, Vincent P.

Telegraphy

Systems

Simplex-reversing periodic

178 67A, 1791003V, 1791003G, 350190, 350271, 340173LM, 178 66DD, G11B 718, H04N 576

Patent

active

039833178

ABSTRACT:
In a laser recording system, a high energy intensity laser beam is focused to form a circular write-spot on a rotating thermoplastic disc. This spot creates tracks of grooves and flat areas or lands in accordance with input data. To read the data from the disc a reduced energy beam is focused on the previously recorded track, and the pattern of grooves and lands is determined from the reflected energy. The optics associated with the reading process include an astigmatizer which elongates the read-spot in a direction transverse to the track. This reduces mechanical tolerances required to insure that the read-spot will impinge upon the desired track. The astigmatizer may also serve to reduce the beam spot energy intensity so that the same laser, without the astigmatizer, can be used for the recording process.
In one embodiment, the astigmatizer is a movable plate having a single slit. For reading, the astigmatizer is positioned in the beam path and the slit creates an orthogonal diffraction pattern which provides the elongated read-spot of reduced energy intensity.

REFERENCES:
patent: 3314075 (1967-04-01), Becker
patent: 3567855 (1971-03-01), Hamisch
patent: 3623024 (1971-11-01), Hamilton
patent: 3825323 (1974-07-01), Landwer
patent: 3829622 (1974-08-01), Elliot
patent: 3913076 (1975-10-01), Lehureau
"The Optical Scanning System of the Philips `VLP` Record Player", Philips Tech. Rev. 33, pp. 186-189, 1973, No. 7, by G. Bouwhuis et al.

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