Apparatus for and method of verifying etching of optical servo information on magnetic media

An apparatus for etching a point on the surface of a magnetic medium to reduce the reflectivity of said point and for verifying said etching, comprising:

• a light source for providing a collimated incident beam of light;
• a polarizer situated in the path of the incident beam for linearly polarizing the incident beam in a first polarizing direction;
• a beam separator situated in the path of the incident beam having means for transmitting light linearly polarized in the first polarizing direction and for deflecting light linearly polarized in a direction orthogonal to the first polarizing direction, the beam separator transmitting the incident beam;
• a first lens situated in the path of the transmitted incident beam for focusing the incident beam to a point on the magnetic medium, the focused incident beam reacting with the magnetic medium to reduce the reflectivity at that point, a portion of the focused incident beam being reflected, said first lens collimating the reflected beam and directing the reflected beam back toward the beam separator;
• means for altering the polarization of the reflected beam relative to the incident beam prior to passing back through the beam separator such that the reflected beam is linearly polarized in a direction orthogonal to the first polarizing direction of the incident beam thereby causing the beam separator to deflect the reflected beam;
• and
• detector means situated in the path of the deflected reflected beam for measuring the intensity of the reflected beam, and for comparing the measured intensity to a threshold value, whereby proper etching is verified if the intensity of the reflected beam is not less than the threshold value.

An apparatus for etching a plurality of concentric optical servo tracks about the rotational axis of a magnetic storage disc having concentric magnetic data tracks about said rotational axis, wherein each optical servo track comprises a plurality of equally spaced etched stitches, and for verifying the stitch count of each track, comprising:

• means for rotating the disc about the rotational axis thereof;
• a light source for providing a collimated incident beam of light;
• means for modulating the light source on and off for consecutively etching the plurality of equally spaced stitches in each optical servo track;
• a polarizer situated in the path of the incident beam for linearly polarizing the incident beam in a first polarizing direction;
• a beam separator situated in the path of the incident beam having means for transmitting light linearly polarized in the first polarizing direction and for deflecting light linearly polarized in a direction orthogonal to the first polarizing direction, the beam separator transmitting the incident beam;
• a first lens situated in the path of the transmitted incident beam for focusing the incident beam to a point on the magnetic disc, the first lens being positioned such that the disc lies substantially in the focal plane of the first lens, the focused incident beam reacting with the rotating magnetic medium to create a stitch on the medium having reduced reflectivity,
• a portion of the focused incident beam being reflected, said first lens collimating the reflected beam and directing the reflected beam back toward the beam separator;
• means for altering the polarization of the reflected beam relative to the incident beam prior to passing back through the beam separator such that the reflected beam is linearly polarized in a direction orthogonal to the first polarizing direction of the incident beam thereby causing the beam separator to deflect the reflected beam;
• detector means situated in the path of the deflected reflected beam for measuring the intensity of the reflected beam, and for comparing the measured intensity to a threshold value, and for incrementing a counter when the measured intensity is not less than the threshold value;
• means for moving the incident beam radially of the disc for etching each of the plurality of concentric optical servo tracks.

In an apparatus for etching a plurality of concentric optical servo tracks about the rotational axis of a magnetic storage disc having concentric magnetic data tracks about the rotational axis, wherein each optical servo track comprises a plurality of equally spaced stitches and wherein the stitches are consecutively etched by modulating on and off an incident beam of light focused on said disc by a lens as said disc rotates, and wherein a portion of said incident beam is reflected off the disk during the etching of each stitch, a method for verifying each stitch comprising the steps of:

• a) collimating the reflected portion of the incident beam to produce a reflected beam;
• b) separating the reflected beam from the incident beam;
• c) measuring the intensity of the reflected beam and comparing the measured intensity to a threshold value;
• and
• d) providing an indication of verification if the measured intensity is not less than the threshold value.

A method of etching a spot on the surface of a magnetic medium to reduce the reflectivity of the spot and of verifying said etching, comprising the steps of:

• a) providing an incident beam of light;
• b) focusing the incident beam to a spot on the magnetic medium, said incident beam reacting with the magnetic medium to reduce the reflectivity of the spot, a portion of the incident beam being reflected by the medium;
• c) collimating the reflected portion of the incident beam to produce a reflected beam;
• d) separating the reflected beam from the incident beam;
• e) measuring the intensity of the reflected beam and comparing the measured intensity to a threshold value;
• and
• f) providing an indication of verification if the measured intensity is not less than the threshold value.