KR100378496B1 - Laser texturing of magnetic recording medium using multiple lens focusing - Google Patents

Abstract

A magnetic recording medium is disclosed that is textured with a pulsed laser light beam through a multilens focusing system. The use of such a multilens focusing system makes it possible to form a relatively even plurality of projections smaller than that obtained with a single lens focusing system. In one embodiment, the laser light beam is split by offsetting the lens to obtain a plurality of pairs of protrusions smaller than that obtained with a laser light beam having a centralized energy profile. The pulsed, multilens focused laser light beam is used to texture the substrate, the underlayer and the magnetic layer. The final lazy textured magnetic recording medium exhibits improved flight stability, glide performance and reliability.

Description

A magnetic recording medium having a textured surface using a multi-lens focusing system and a method of manufacturing the same {LASER TEXTURING OF MAGNETIC RECORDING MEDIUM USING MULTIPLE LENS FOCUSING}

Magnetic disks and disk drives are typically used to store data in magnetized form. Typically, one or more discs are rotated and axially moved about a central axis in combination with a data conversion head located in close proximity to the recording surface of the disc. Magnetic disks are generally housed in a magnetic disk unit and a stationary magnetic disk unit with a specific load that is elastically contacted and pressed against the surface of the disk.

In operation, the magnetic disk is generally driven by the contact start stop (CSS) method, where the head begins to slide about the surface of the disk as the disk begins to rotate. As the predetermined high rotational speed is reached, the head floats in the air at predetermined intervals from the surface of the disk due to the dynamic pressure effect caused by the airflow between the disk and the sliding surface of the head. During read and write operations, the transducer head is held at a controlled distance from the recording surface, supporting it on the bearing of air as the disk rotates. The magnetic head unit is arranged such that the magnetic head can be freely moved in the circumferential and axial directions of the disc in the floating state, allowing data to be retrieved or written from the surface of the disc at the desired position.

At the end of operation of the disc drive, the rotational speed of the disc decreases and the head starts to slide again against the surface of the disc and ultimately contacts and stops to apply pressure to the disc. Thus, the transducer head contacts the recording surface when the disc is at rest, when it is accelerated from the standstill and every deceleration just before it comes to a complete stop. Each time the head and disk assembly is driven, the sliding surface of the head repeats a cycle operation consisting of a stop, a slide on the disk surface, floating in air, and a stop.

It is considered desirable to keep each transducer head as close as possible to the associated recording surface during read and write operations, ie to minimize the flying height of the head. This purpose is particularly important as the area recording density increases. The local recording density (Mbits / inch ² ) is the recording density per unit area, linear density (BPI) in terms of bits per inch, and track density (TPI) in terms of tracks per inch. Thus, a flat recording surface and a flat opposing surface of the associated transducer head are preferred, thereby allowing the head and disk to be positioned closer to the existing increases in the consistent action and predictability of the air bearings supporting the head. . However, other factors work for this purpose. If the head surface and the recording surface are too flat, a precise match of these surfaces causes excessive settling and friction during the start and stop phases, thereby wearing the head and recording surface to a state called "head compression". . Accordingly, the present invention aims to reduce head / disk friction and minimize transducer flight height.

To meet this purpose, the recording surface of the magnetic disk is provided with a rough surface to reduce head / disk friction with a technique generally referred to as "texturing". Conventional texturing techniques polish the surface of a disk substrate to provide a texture thereon prior to subsequent layer deposition, such as a lower layer, magnetic layer, protective overcoat comprising carbon and lubricity topcoat, typically chromium or chromium-alloy. Wherein the textured surface on the substrate is intended to be substantially replicated on the surface of the magnetic disk.

A typical magnetic recording medium is shown in FIG. 1 and includes a substrate 10 which is typically an aluminum (Al) -based alloy, such as an aluminum-magnesium (Al-Mg) alloy, plated with an amorphous nickel-phosphorus (NiP) layer. do. Substrate 10 is generally a chromium (Cr) sublayer 11 deposited sequentially thereon, a magnetic layer 12, typically a cobalt (Co) -based alloy, a protective overcoat (13) generally comprising carbon and lubricity Topcoat 14. The chromium (Cr) underlayer 11, the magnetic layer 12, typically a cobalt (Co) -based alloy, the protective overcoat 13, typically comprising carbon, and the lubricity topcoat 14 are generally deposited by sputtering techniques. do. Conventional Al-alloy substrates are provided with NiP plating to increase the strength of the Al substrate, which serves as a suitable surface for polishing to provide the necessary surface roughness or texture substantially reproduced on the disk surface. .

Increasing requirements for high local recording densities impose greater requirements in terms of coercivity, stiction squareness, small media noise and narrow track recording performance. In addition, increasing high density and large capacity magnetic disks require increasingly smaller flight heights, i.e., the spacing of the heads on the disk's surface in CSS drives. This requirement is particularly difficult to meet the requirement for controlled texturing to prevent head breakage, as the requirement for further reducing the head's flight height imposed by increasingly high recording densities and capacities. .

Conventional texturing techniques include mechanical operations such as polishing. See, eg, US Pat. No. 5,202,810 by Nakamura. However, conventional mechanical texturing techniques have several disadvantages. As an example, it is difficult to provide a clean textured surface due to debris created by mechanical wear. Moreover, textured surfaces are inevitable to scratch during mechanical operation, resulting in poor sliding properties and large drawbacks. In addition, it is difficult to process various desirable substrates by conventional mechanical texturing techniques. This undesirably limits facets by mechanical texturing techniques and substantially eliminates the use of multiple substrates and conductive graphite substrates that promote the achievement of substantially high coercive forces.

Co-pending application number 08 / 608,072, filed February 28, 1996, discloses sputter texturing technology. The disclosed sputter texturing method can be advantageously applied to many different substrates.

Other alternatives to mechanical texturing techniques include laser texturing techniques by impinging a pulsed focused laser light beam onto a layer of magnetic recording medium, such as an upper surface of a nonmagnetic substrate. Examples include polishing a NiP plated Al substrate at the specular end, and rotating the substrate while directing pulsed laser energy for a portion of the radius, thereby leaving a data zone specular. See US Pat. No. 5,062,021 (European Patent Application 0 447 025 A1) by Ranjan, which provides a textured landing zone. The landing zone includes a number of individual laser spots characterized by a central depletion surrounded by a substantially circular raised rim.

Another laser texturing technique is described in Baumgart et al. "A New Laser Texturing Technique for High Performance Magnetic Disk Drives," IEEE Transactions on Magnetics, Vol. 31, No. 6, pp. 2946-2951, November 1995. Laser texturing techniques disclosed by Baumgart et al. Include impinging a pulsed laser light beam on a substrate surface through a single lens focusing system. Baumgart et al. Disclosed that the shape of the final protrusion is changed by adjusting the pulse energy. At low pulse energy, the bump or protrusion shape includes a central depression and a circumferential rim, similar to that reported by Ranjan et al. As the pulse energy increases, the bottom of the depression flattens into a circular flat central dome resembling a "sombrero". The higher the power, the wider and lower the central dome will eventually be the same or lower than the rim.

As reported by Ranjan et al., The profile of the protrusion formed by the laser texturing technique is shown in FIG. 2, with a substantially circular rim 23 extending over the surface 21 surrounding the central depression 20. It includes. The depth d of the depression 20 below the upper surface 21 has been reported by Ranjan et al. And is typically twice the height h of the rim.

The deformation of the protrusion shape reported by Baumgart et al. Is shown in FIG. 3, which shows a sequence of atomic force microscope (ATM) cross-sections of the protrusions created with different incident laser pulse energies, which are the microphone joules (μj).

Laser surface texturing provides desirable control that is not available with mechanical texturing. Moreover, the accuracy of the laser light beam provides a precise contour of the textured area boundary, thereby maximizing the area available for data storage while enabling the accurate and reproducible formation of the textured landing area. Rounded protrusions reported by Ranjan et al. Have been reported, allowing control of the head / disk while reducing friction and wear. The generally circular depressions and peripheral rims reported by Ranjan et al. Further reduce frictional wear by acting as a gathering area for lubrication and debris coated on the disc.

However, conventional laser texturing techniques as disclosed by Ranjan et al. Baumgart et al. Have various disadvantages. The topographical configuration of the topological projections formed by such a conventional laser texturing technique using a single lens focusing system is the result of thermal degradation and high speed centralized melting from the center of the focused laser spot to the edge of the spot. . This single lens focusing system forms a textured area with relatively large topological projections and is characterized by a sharp local profile change that adversely affects the sliding performance and flight stability of the magnetic recording head, Adversely affects reliability. This problematic local profile change requires greater precision in texturing magnetic recording media by providing an even pattern of protrusions that are smaller than those obtained by conventional laser texturing techniques.

In a series of co-pending application No. 08 / 647,407, a method of texturing a magnetic recording medium is disclosed wherein the focused laser light beam is spaced and interposed between the lens focusing system surfaces to which laser texturing is applied. Pass through the crystal material. The use of optical crystalline materials makes it possible to form a texture comprising a plurality of controlled and precisely spaced protrusions.

US Pat. No. 4,060,306 to Swaminathan discloses the use of multiple lens systems including spherical aberration-free meniscus lenses and companion doublet lenses for use in a microscope. The use of multiple lens systems for recording and reading disc drive data is disclosed in US Pat. No. 5,402,407 to Euguchi, US Pat. No. 5,128,914 to Kurata, and US Pat. No. 5,416,755 to Endo.

Thus, there is a need for a texturing system, such as a laser texturing system, which can provide a structure that includes a large number of controlled, even height, relatively small protrusions, thereby resulting in improved flight stability, sliding performance, and reliability. give.

The present invention relates to the recording, storage and reading of magnetic data, and more particularly to a rotatable magnetic recording medium such as a thin film magnetic disk having a textured surface for contacting with a cooperating magnetic conversion head. The present invention relates to a high density magnetic recording medium with low noise and improved flying stability, glide performance and head-to-media interface reliability.

1 is a diagram showing a structure of a conventional magnetic recording medium.

2 is a schematic representation of a profile of a protrusion formed by conventional laser texturing techniques.

3 shows a change in protrusion geometry as a function of laser pulse energy in accordance with conventional laser texturing techniques.

4 schematically illustrates a conventional single lens laser focusing system.

5 schematically illustrates a multi-lens laser focusing system of the present invention.

6 shows schematically a protrusion formed according to the invention;

It is an object of the present invention to provide a textured magnetic recording medium exhibiting low noise and improved flight stability, sliding performance and head-medium interface reliability.

Another object of the present invention is to provide a method of laser texturing a non-magnetic substrate to provide a textured magnetic recording medium exhibiting low noise and improved flight stability, sliding performance and head-medium interface reliability.

Additional objects, advantages and other features of the invention will be set forth in part in the description which follows, and will be apparent to those skilled in the art upon examination of the description and will be learned by practice of the invention. The objects and advantages of the invention may be achieved and obtained in particular as indicated in the appended claims.

In accordance with the present invention, the above and other objects include: a nonmagnetic substrate having a textured top surface; And a magnetic layer formed on the upper surface, wherein the textured upper surface extends over the upper surface to a height of about 7.5 nm (75 kPa) to about 30 nm (300 kPa) and extends around the central hole extending into the upper surface. In part, by a magnetic recording medium comprising a plurality of protrusions, having a substantially circular rim with a diameter of about 3 μm to about 15 μm.

Another aspect of the invention is to provide a top surface to a pulsed laser light beam through a multi-lens focusing system comprising a first lens and a second lens located between the top surface of the substrate and a first lens and spaced apart from each other. A method of manufacturing a magnetic recording medium comprising texturing an upper surface of a nonmagnetic substrate by exposing.

Another aspect of the present invention is directed to a top surface of a laser light beam pulsed through a multi-lens focusing system comprising a first lens and a second lens located between the top surface of the substrate and a first lens and spaced apart from each other. Exposing the upper surface of the non-magnetic substrate by exposing, wherein the laser light beam exposes the upper surface to a laser light beam having an energy profile where each of the protrusions is centered substantially at a single energy peak. Have an energy profile with at least two energy peaks forming on the upper surface at least two protrusions having substantially circular rims extending above the upper surface at a height less than the height of the substantially single protrusion generated.

Further objects and advantages of the invention will be readily apparent to those skilled in the art from the following detailed description, wherein the embodiments of the invention are briefly illustrated by best contemplated examples for practicing the invention. As will be realized, the invention is capable of other and different embodiments, and its details may be modified in various obvious respects, all without departing from the scope of the invention. Accordingly, the drawings and detailed description are exemplary and should not be regarded as limiting of the invention.

Conventional laser texturing techniques change the topography of a non-magnetic substrate by forming a plurality of protrusions having substantially circular rims surrounding a central hole or central bump. After extensive research and experiments, it has been found that such laser formed textures including protrusions are characterized by rapid profile changes, thus adversely affecting flight stability, glide performance and head-medium interface reliability. After a more extensive search for such rapid profile changes, the tolerances associated with conventional laser texturing systems have been found to be inadequate to meet the requirements of high area density magnetic recording media. Rapid profile changes are believed to result from a variety of causes due to surface irregularities. Basically, the substrate surface essentially contains a certain degree of meandering due to manufacturing techniques. Moreover, as the magnetic recording disc rotates, an unavoidable amount of shaking occurs due to the associated disc drive. In addition, the lack of surface uniformity results from disk clamping during rotation. These factors adversely affect surface uniformity and thus require a high degree of utility and tolerance during laser texturing, which cannot be achieved with conventional texturing technology systems.

The present invention overcomes these problems with a laser texturing technique that can provide a magnetic recording medium with topography that includes a number of precisely controlled protrusions smaller than those formed by conventional laser texturing techniques. In accordance with the present invention, the laser texturing system is equipped with a focusing system having a deeper depth of focus than conventionally used, providing the necessary tolerances and usefulness for accommodating the inherent surface unevenness. Magnetic recording media formed in accordance with the present invention include textured topography that includes a plurality of uniformly controlled protrusions with very reduced sharp profile changes. The final textured magnetic recording medium exhibits low noise, improved flight stability, sliding performance and head-medium interface reliability and consequently reduced air turbulence. Laser-generated protrusions formed in accordance with the present invention are generally smaller than those formed by conventional laser texturing techniques, thus improving the head-medium interface reliability by providing a larger number of contact points, and thus smaller loads per contact. And wear occurs. Moreover, the laser textured surface formed in accordance with the present invention comprises a larger number of protrusions per unit area, thus enabling beneficial use by small head sliders.

The laser texturing technique according to the present invention comprises a multi-lens focusing system having a deeper depth of focus than that used in conventional laser texturing techniques, and thus is smaller in size than the protrusions formed by conventional laser texturing techniques. It allows for the formation of more protrusions in terms of numbers. The multi-lens focusing system of the present invention is designed to have a smaller number of f than the number of conventional single lens focusing systems, thereby providing greater depth of focus, thus allowing greater tolerance to accommodate inherent surface unevenness. to provide.

In one embodiment of the present invention, the multi-laser focusing system comprises a first lens and a second lens positioned and spaced between the first lens and the upper surface of the rotating substrate to be textured, thus multi-lens focusing. The system has a larger depth of focus than that of the first lens. The first lens of the multi-lens focusing system of the present invention may comprise a companion doublet lens, and the second lens may comprise a meniscus lens without spherical aberration. The depth of focus of the multi-lens focusing system of the present invention may range from about 30 to about 150 μm. In one embodiment of the present invention, the first lens is a companion doublet lens and the second lens is a meniscus lens without spherical aberration, and the depth of focus is about 50 μm.

The laser texturing method according to the present invention includes conventional equipment, including conventional laser sources. For example, a multimode Q-switched and pulsed laser can be employed when texturing NiP plated Al-alloy substrates. One skilled in the art can easily optimize the pulse period and power input in certain situations. As an example, about 30,000 to 70,000 pulses per second are sufficient to form the desired texture.

The multi-lens laser focusing system of the present invention can be advantageously employed for texturing a variety of conventional substrates used in the manufacture of magnetic recording media. The textured surface of the substrate is substantially replicated in sequentially deposited layers such as underlayers, magnetic layers, protective overcoats and lubricity topcoats. In one embodiment of the invention, selected portions of the substrate surface are laser textured to provide a landing zone. Thus, by confining the laser texturing area to a particular landing area, the recording area or data area can be maximized and provided with a very flat or mirror-like circular surface, thereby increasing the recording density and increasing the head flight height. Reduce even more.

A portion of a conventional laser texturing apparatus that includes a single lens focusing system is schematically illustrated in FIG. 4 and includes a single lens 40. The laser light beam 41 is focused at point 42 on the upper surface of the nonmagnetic substrate 43 and the surface topography of the relatively large protrusions is characterized by a sharp profile change due to the inherent surface unevenness. This drastic local profile change adversely affects flight stability, sliding performance and head-medium interface reliability.

A portion of the multi-lens focusing system according to the present invention is schematically illustrated in FIG. 5 and includes a first lens 50 as companion doublet rams and a second lens 51 as an aspheric aberration meniscus lens. The second lens 51 is separated and positioned between the first lens 50 and the substrate 54. However, the depth of focus of the multi-lens focusing system extends to point 55 by the second lens 51. The increased depth of focus provides the desired index of refraction and enables the formation of protrusions with small heights and diameters with great precision and uniform uniformity with the prior art single lens focus system shown in FIG. Clearly, providing increased depth of focus facilitates adjustment and maintenance of the focus, thereby providing tolerance for accommodating the inherent surface uniformity not obtainable in prior art single lens focus systems. Thus, the present invention overcomes abrupt profile changes and consequently overcomes air turbulence, a characteristic of laser textured surfaces for conventional magnetic recording media.

A representative protrusion in accordance with the present invention is shown in FIG. 6 and is characterized by a rim 60 having a radius of curvature rB and a rim diameter ψ. The head slider 61 contacts the protrusion 60 at the rim height Hb.

The protrusions formed in accordance with the present invention generally have a rim height of about 7.5 nm (75 mm 3) to about 30 nm (300 mm 3). In one embodiment of the present invention, protrusions are formed having a rim height of about 15 nm (150 mm 3) to about 22.5 nm (225 mm 3). The rim diameter of the protrusions formed in accordance with the present invention may range from about 3 μm to 15 μm. In one embodiment of the invention, protrusions are formed having a rim diameter of about 5 μm to 8 μm. The protrusion formed according to the present invention has a rim with a radius of curvature that can range from about 5 μm to 200 μm. In one embodiment of the present invention, the rim has a radius of curvature of about 50 μm to 70 μm.

The laser textured topography of the present invention includes protrusions having a substantially circular rim around a central hole that does not extend into the substrate by the depth of the central hole of a conventional laser textured topography. According to the invention, the ratio of distance to rim height of the central hole extending into the substrate is in the range of less than 1: 1 to less than 3: 1. The present invention readily achieves a ratio of distance to rim height of the central hole extending into the substrate, including 1: 1, which is less than 2: 1. In conventional laser textured topography, the distance of the central hole extending into the substrate is considerably longer than the rim height. Final conventional laser textured topography provides undesirable stress profiles when subsequent layers, such as underlying layers and / or magnetic layers, are deposited by sputtering at elevated temperatures. As a result, the topography formed on the upper surface of the substrate is not accurately reproduced in subsequent deposited layers. However, in accordance with the present invention, the textured topography exhibits a symmetrical configuration, thereby allowing the textured topography to be reproduced substantially accurately in subsequently deposited sputtering layers.

The size and geometry of the laser textured topography formed in accordance with the present invention is functionally important for improved flight stability, sliding performance and head-medium interface reliability. The size and specific geometry of the topography according to the present invention allows for optimization of tribology and wear characteristics.

In one embodiment of the present invention described above, the substrate is exposed to a pulsed laser light beam through a multiple lens focusing system while the substrate is rotating. The impinging laser light beam has a centralized energy profile that substantially produces a single protrusion. In another embodiment of the present invention, the substrate is exposed to a pulsed laser light beam through a multi-lens focusing system, but the original centralized beam energy distribution for the impact area is modified to obtain at least one week small energy peak. In accordance with this embodiment of the present invention, at least two protrusions are formed that are smaller in size than a single protrusion formed by an unmodified laser light beam having a centralized energy profile that produces a substantially single protrusion. In this way, tribological performance and reliability are further improved by providing laser textured topography with a larger number of small protrusions.

According to one aspect of the modified energy embodiment, the first lens and the second lens are offset relative to each other to produce at least two small energy peaks that create two or more protrusions on the substrate surface. Final laser textured topography with a larger number of small protrusions provides head reliability due to smaller air turbulence, in addition to providing individualized reliability due to less load and wear per contact between the head and media surface. Better tribological performance in terms of Advantageously, when generating a laser light beam with multiple energy peaks, high refresh rate laser pulses make it possible to form small spots with much greater precision. Multiple protrusion formation may be obtained by techniques such as changing the mode of the multi-mode Q-switched pulsed laser, or changing the optical train by interposing a mask between the laser light source and the first lens.

The laser texturing technique of the present invention can be employed on a textured magnetic recording medium by colliding the laser beam focused on any layer of the magnetic recording medium as well as on the rotating substrate as in the above embodiment. Thus, according to the present invention, a magnetic layer such as a Co-alloy magnetic layer applied directly to a substrate or substrate, or a lower layer such as Cr or Cr-alloy can be laser textured with a pulsed laser light beam through a multiple lens focusing system. have. The laser texture of the present invention may also be provided on an Al or Al-alloy substrate prior to plating with NiP. The laser textured surface provided according to the invention is substantially regenerated in a subsequently deposited layer.

The magnetic recording medium formed according to the present invention may include any of various conventional substrates employed in the magnetic recording medium. Such conventional substrates include NiP plated Al or Al-alloys such as Al-Mg-alloys.

The magnetic layer deposited in accordance with the present invention may be any conventional one employed in the manufacture of a magnetic recording medium. Such conventional magnetic alloys include cobalt-chromium (CoCr), cobalt-samarium (CoSm), cobalt-chromium-tantalum (CoCrTa), cobalt-nickel-chromium (CoNiCr), cobalt-chromium-samarium (CoCrSm), cobalt-chromium Such as -platinum-titanium (CoCrPtTa), cobalt-chromium-platinum (CoCrPt), cobalt-nickel-platinum (CoNiPt), cobalt-nickel-chromium-platinum (CoNiCrPt) and cobalt-chromium-platinum-boron (CoCrPtB) Cobalt (Co) -based alloys include, but are not limited to. The thickness of the magnetic layer is compatible with the conventional practice and in the magnetic recording medium. Cobalt-based alloys having a thickness of about 10 nm (100 mm 3) to 100 nm (1000 mm 3), such as about 20 nm (200 mm 3) to 50 nm (500 mm 3), are known to be suitable.

In a conventional implementation, the underlying layer may be deposited on a textured substrate prior to depositing the magnetic layer. The underlayer may comprise Cr alloys such as chromium-vanadium or chromium-titanium, oxygen-doped Cr or Cr, tungsten or tungsten alloys.

In addition, a protective overcoat, such as carbon overcoat, may be deposited on the magnetic layer, and a lubricious topcoat is deposited on the protective overcoat. The underlayer, magnetic layer and protective overcoat can be employed in conventional methods by any of the various sputtering techniques employed in the manufacture of magnetic recording media.

The present invention can be employed to produce any of various types of magnetic recording media including thin film discs, with improvements shown in flight stability, sliding performance and head-medium interface reliability. Moreover, the precise way in which the landing zone can be laser textured allows for a reduction in the size of the head slider and an increase in recording density.

Some embodiments and various examples of the invention have been shown and described herein. The present invention can be used in various combinations and environments and can be changed and modified within the scope of the spirit of the invention shown herein.

Claims (17)

A nonmagnetic substrate having a textured top surface; And It includes a magnetic layer formed on the upper surface, The textured top surface includes a plurality of protrusions having a circular rim having a diameter of about 3 μm to about 15 μm above a central hole extending from about 7.5 nm to about 30 nm above the top surface and extending to the top surface. And a magnetic recording medium. The method of claim 1, The rim has a radius of curvature of about 5 μm to about 200 μm; The rim has a diameter of about 5 μm to about 8 μm; And the height of the rim is about 15 nm to 22.5 nm. The method of claim 1, And the ratio of the height of the rim to the spacing of the central holes extending to the substrate is about 1: 1 or less to about 3: 1 or less. The method of claim 1, The textured surface includes a first companion doublet lens and a second lens located between the substrate and the first companion doublet lens, the textured surface having a depth of focus greater than the focus depth of the first companion doublet lens. Magnetic exposure medium formed by exposing a top surface of the substrate to a laser light beam pulsed through a plurality of lens focusing systems. The method of claim 4, wherein And the second lens comprises a non-surface gradient meniscus lens. The method of claim 5, And a depth of focus of the plurality of lens systems from about 30 μm to about 150 μm. The surface of the non-magnetic substrate on a laser light beam pulsed through a multi-lens focusing system comprising a first lens and a second lens positioned between the first lens and an upper surface of the non-magnetic substrate and spaced from the first lens. And texturing the non-magnetic substrate by exposing the plurality of lens focusing systems, wherein the multi-lens focusing system has a focus depth of a first companion doublet lens and the multi-lens focusing from about 50 to about 150 micrometers relative to the substrate surface. And a second lens selected to have a depth of focus greater than the depth of focus of the first companion doublet lens. The method of claim 7, wherein And the second lens comprises an aspherical aberration meniscus lens. The method of claim 7, wherein Depositing an underlying layer on the textured substrate; And depositing a magnetic layer on the lower layer. The method of claim 7, wherein And wherein the laser light beam comprises a centrally focused energy profile having a single energy peak forming a single protrusion on the upper surface of the substrate. The method of claim 7, wherein Exposing a top surface of the substrate to a pulsed laser light beam having an energy profile that appears at at least two energy peaks forming at least two protrusions on the surface of the substrate. The method of claim 11, Forming a laser light beam comprising an energy profile having at least two energy peaks by offsetting said first and / or second lenses relative to each other. The method of claim 11, Forming a laser light beam comprising an energy profile having at least two energy peaks by changing the laser mode. The method of claim 11, Forming a laser light beam comprising an energy profile having at least two energy peaks by altering the light train. The method of claim 14, And changing the optical train by interposing a mask between a laser light source and the first lens. The method of claim 7, wherein Rotating the disc while exposing the upper surface to a pulsed laser light beam. The method of claim 7, wherein Pulsing the laser light beam at a rate of about 30,000 to 70,000 pulses per second.