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Optical Device for Online Assessment of Magnetic Tape Surface Quality

IP.com Disclosure Number: IPCOM000060141D
Original Publication Date: 1986-Mar-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Booth, RA: AUTHOR [+4]

Abstract

An optical device for online assessment of magnetic tape surface quality uses a cylindrical lens and quadrant detector in a schlieren arrangement. The device provides extremely fast and reliable on-the- spool assessment of acceptable quality for the magnetic tape. In Fig. 1, a gallium arsenide laser 1 is located at the focus of a lens 2. A shutter 3 and polarizer 4 is located immediately after 2. An optional half-wave plate 5 can be included after the polarizer 4. The beam emanating from laser 1 is now collimated and enters a polarizing cube beam-splitter 6. Since the beam is of the appropriate polarization, it traverses splitter 6 without losses. Upon exiting from splitter 6, the beam which was linearly polarized goes through a suitably oriented quarter-wave plate 7 and becomes circularly polarized.

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Optical Device for Online Assessment of Magnetic Tape Surface Quality

An optical device for online assessment of magnetic tape surface quality uses a cylindrical lens and quadrant detector in a schlieren arrangement. The device provides extremely fast and reliable on-the- spool assessment of acceptable quality for the magnetic tape. In Fig. 1, a gallium arsenide laser 1 is located at the focus of a lens 2. A shutter 3 and polarizer 4 is located immediately after 2. An optional half-wave plate 5 can be included after the polarizer 4. The beam emanating from laser 1 is now collimated and enters a polarizing cube beam- splitter 6. Since the beam is of the appropriate polarization, it traverses splitter 6 without losses. Upon exiting from splitter 6, the beam which was linearly polarized goes through a suitably oriented quarter-wave plate 7 and becomes circularly polarized. The beam now enters the cylindrical lens 8 which focuses it along a line. This line is coincident with the axis of rotation of a spool 9 on which the tape is being wound. Thus the beam emanating from lens 8 is now at all times perpendicular to the surface of the tape irregardless of the state of winding. For the incident beam which is reflected by the tape, a condition of retro- reflection now exists and the beam retraces its path. After going through lens 8 and plate 7, linear polarization and collimation are restored. However, reflection at the surface of the tape changed the handedness of the circularly polarized beam and the linear polarization that now exists is perpendicular to that of the input beam. Accordingly, the beam will now be reflected by splitter 6. After its exit from splitter 6, the beam is brought to a focus by the lens 10. If the tape is defect-free, the optics perfectly aligned and the components in the correct geometric relationship, only diffraction and the aberrations of the system will impose a lower limit on th...