Alan B. Marchant

Laser marking of thin organic films

Laser marking of thin organic films on reflective substrates involves three general physical processes—optical absorption, heat flow, and mass motion—all of which can proceed on nanosecond time scales. We report observations of pit morphology and discuss the contributions of these processes to pit formation.

Focusing elliptical laser beams

The spot formed by focusing an elliptical laser beam through an ordinary objective lens can be optimized by properly filling the objective lens. Criteria are given for maximizing the central irradiance and the line-spread function. An optimized spot is much less elliptical than the incident laser beam. For beam ellipticities as high as 2:1, this spatial filtering reduces the central irradiance by <14%.

Cover Sheet Aberrations In Optical Recording

Optical recording systems include a transparent layer between the diffraction-limited objective and the recording surface, which prevents dust and dirt from obscuring the optical signal. A laser beam focused on the recording surface may be aberrated by thickness variations or birefringence in this cover sheet. This paper presents calculations of these aberrations and a discussion of the corresponding cover-sheet tolerances.

Optical disk readout: a model for coherent scanning

The design and evaluation of optical recording systems, media, and codes require both qualitative and quantitative understanding of the readout process. Scalar diffraction theory permits a simple formulation of the readout process, which provides a qualitative insight and also permits rapid, detailed, numerical solutions to a wide range of problems. Several examples demonstrate the application of the model to Laser Write and Read (LWR) optical recording media.

Digital Optical Recording In Infrared-Sensitive Organic Polymers

Recording and playback of digital signals in organic media designed to be written with diode lasers and read out with visible or diode lasers is discussed.

Polarization Considerations In Magnetooptical Recording

Reading of magnetooptically recorded data relies on the detection of light whose polarization state varies very slightly with the direction of magnetization of the sensitive layer of the disk. Because the change in polarization is so small, differential detection methods are used, and a number of features of the optical detection scheme can adversely affect the polarization and the signal levels. Among those features considered are the polarization of the laser itself, optical surfaces within the head, substrate birefringence, and optical feedback.

Index variations in cover sheets

When an optical system focuses light through a transparent cover sheet, refractive-index variations create spherical aberration which can be partially compensated by adjusting the cover-sheet thickness. In practice, a wide range of refractive index can be tolerated by a diffraction-limited objective lens given such thickness optimization. For example, a system with a numerical aperture of 0.6 and a nominal cover-sheet thickness of 1.2 mm can tolerate a refractive-index range from 1.45 to 1.60.