Laser Recording

A DWL66 recording laser device manufactured past Heidelberg Instruments with the working light amplification by stimulated emission of radiation wavelength of 442nm was used for the formation of calculated structures on the positive photoresist AZ4562 (Hoechst).

From: Computer Pattern of Diffractive Optics , 2013

Consumer digital technology

Richard Brice , in Newnes Guide to Digital TV (Second Edition), 2003

DVD Recordable (DVD-R)

Like in concept to CD-R, DVD-R is a write-once medium that tin incorporate any type of information unremarkably stored on mass-produced DVD discs. Depending on the type of data recorded, DVD-R discs are usable on whatever DVD playback device, including DVD-ROM drives and DVD video players. A total of approximately 7.9 or 9.iv Gb can be stored on a ii-sided DVD-R disc. Data can be written to or read from a disc at 11.08 megabits per second (Mbit/s), which is roughly equivalent to nine times the transfer rate of CD-ROMs '1X' speed. DVD-R, like CD-R, uses a constant linear velocity rotation technique to maximize the storage density on the disc surface. This results in a variable number of revolutions per infinitesimal (RPM) as disc writing/reading progresses from one finish to the other. To achieve a sixfold increment in storage density over CD-R, ii key components of the writing hardware needed to exist altered: the wavelength of the recording light amplification by stimulated emission of radiation and the numerical aperture (n.a.) of the lens that focuses it. In the example of CD-R, an infrared laser with a wavelength of 780 nanometers (nm) is employed, while DVD-R uses a ruby laser with a wavelength of 635 nm. These factors allow DVD-R discs to record 'pits' equally small as 0.44 μm equally compared with the minimum 0.834 μm size with CD-R.

Recording on DVD-R discs is achieved through the apply of a dye polymer recording layer that is permanently transformed by a highly focused laser beam. This dye polymer substance is spin-coated onto a clear polycarbonate substrate that forms 1 side of the 'torso' of a complete disc. The substrate has a microscopic, 'pre-groove' spiral rails formed onto its surface. This groove is used by a DVD-R drive to guide the recording laser beam during the writing process. A thin layer of metal is and then sputtered onto the recording layer so that a reading light amplification by stimulated emission of radiation tin can be reflected off the disc during playback. The recording action takes place by momentarily exposing the recording layer to a loftier power (10 mW) laser beam that is tightly focused onto its surface. As the dye polymer layer is heated, it is permanently contradistinct such that microscopic marks are formed in the pre-groove. These recorded marks differ in length depending on how long the write laser is turned on and off, which is how data is stored on the disc. The light sensitivity of the recording layer has been tuned to an appropriate wavelength of low-cal so that exposure to ambient calorie-free or playback lasers will not harm a recording. Playback occurs by focusing a lower power laser of the same approximate wavelength (635 or 650 nm) onto the surface of the disc. The 'land' areas between marks are reflective, meaning that most of the calorie-free is returned to the histrion's optical head, whereas, recorded marks are not very reflective, significant that very little of the low-cal is returned. This 'on-off' pattern is thereby interpreted as the modulated signal, which is then decoded into the original user data by the playback device.

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Synthesis of DOE on polycrystalline diamond films

In Computer Blueprint of Diffractive Optics, 2013

11.8 Experimental report of the focuser into a circle

In [38,39] attention was paid to the construction of a stochastic genetic optimization procedure for the radially symmetric office of the quantized DOE.

In [45] performance testing of the approach developed past the field experiment was carried out. As a model problem was the synthesis of a four-level focuser of the Gaussian beam into a circle for the visible range.

The four-level relief was formed past laser lithography. A DWL66 recording laser device manufactured by Heidelberg Instruments with the working laser wavelength of 442   nm was used for the formation of calculated structures on the positive photoresist AZ4562 (Hoechst). Recording was carried out using a lens with a 4   mm focus and a spatial resolution of 640   nm. These options allow one to write lines with a width of about ane μm. The refractive index of the photoresist was n  =   1.628, which for the wavelength λ = 543   nm of laser radiation with the beam focused by the DOE, determines the maximum depth of etching as λ/(due north–1)   =   865   nm. The recorder tin operate in a binary or grayscale. In the binary mode, switching ON and OFF states decide the formation of a binary construction. The grayscale mode allows for immediate implementation of a multi-level (upwardly to 32 levels) profile with a height determined by the exposure conditions. In this case, the calculated relief must be presented at the input of the device as a standard DXF-file (the standard representation of information developed by Autodesk Inc).

The element, calculated by the modified procedure [39], as an add-on to the spherical lens has the following parameters: external lens focus f  =   300   mm, the wavelength of the illuminating beam λ = 543   nm, the radius of the aperture R  =   i.75   mm, the radius of the focal circle R 1  =   0.half dozen   mm, the radius of the illuminating Gaussian beam σ = 0.525   mm, the number of counts in the phase role along the radius North  =   50.

The element has a radially symmetric phase structure with 14 zones. Figure 11.31 shows the calculated relief (radial section) and the result of profilometric exam of the microrelief.

Fig. 11.31. Comparison of the calculated profile element (crosses) from realized (solid line) -the results measurements.

The radiation source was a He–Ne laser operating at a wavelength of 543   nm with a divergence of Thousand ii ≅ ane.2. Figure 11.32 shows the cantankerous section of the formed beam, obtained with a CCD-camera in the output plane of the lens and in the airplane, spaced at 20   mm behind the exit airplane of the lens. For comparison, Fig. 11.32 shows the cross section of the calculated intensity distribution in the focus of the lens for a diffraction-express beam (M 2  =   1). The resulting absolute value of intensity was normalized with respect to the distribution of energy in the focus of the same optical organisation, but in the absenteeism of the DOE. The calculated intensity obtained for a Gaussian axle One thousand 2  =   1, and the measurement issue (M ii ≅ i.2) were calibrated on the assumption that the maximum intensity of the Gaussian beam passing through an optical system in the absence of the DOE, is unity. The presence of higher modes in the illuminating axle explains the larger size of the formed intensity distribution every bit compared with the calculated ones.

Fig. eleven.32. Comparison of the calculated intensity distribution in the output aeroplane of the lens (point), the measured distribution intensity in the focus of the lens (solid line) and the measured distribution in the plane located at 20   mm behind the focal plane of the lens.

Figure 11.33 shows the ii-dimensional intensity distributions formed by the DOE and measured in the absenteeism of an optical chemical element. Note that for a four-element implemented for a given gear up of physical parameters, a aeroplane with less uneven distribution of intensity is beyond the output aeroplane of the lens.

Fig. 11.33. Intensity distribution measured in the output plane of the lens in the absenteeism of the DOE (a), in the presence of DOE (b), and in the aeroplane spaced at a distance of 20   mm backside the output aeroplane of the lens (c).

Numerical integration based on measurements taken with a CCD-photographic camera in the output plane of the lens, gave estimates of the diffraction efficiency of 77.6% and 79.half-dozen% for the radius of the focal range R 1  =   0.6   mm and R ane  =   0.66   mm, respectively. This agrees well with the estimates obtained in the numerical experiment (81.3% and 81.half dozen%, respectively). The diffraction efficiency in the field experiment is the ratio of energy, focused by the DOE in a focal circumvolve to the full energy of a light beam passing through the plate coated with the DOE microrelief.

Thus, the measured efficiency of a four-level chemical element was about 97% of the theoretical limit with a good uniformity of the generated intensity distribution. Notation that for practical applications, an important parameter is the depth of the focus of the DOE focusing the radiation in a radially symmetrical field. Figure 11.34 shows the calculated longitudinal section of the beam intensity, formed by the DOE, and restored using the results of optical measurements at a distance of 540 to 660   mm from the DOE (distance 600   mm from the DOE airplane corresponds to an output plane of the lens: 2f  =   600   mm).

Fig. 11.34. Estimated longitudinal section of the axle intensity, formed by the DOE (a) and restored on the results of optical measurements (b).

These results indicate the feasibility of the calculation of quantized DOEs using stochastic procedures of calculation.

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Information-Related Applications of Lasers

John F. Ready , in Industrial Applications of Lasers (Second Edition), 1997

D. Laser Graphics

A wide variety of light amplification by stimulated emission of radiation applications take developed in the fields of the graphic arts. These applications include methods to record, reproduce, and transmit graphic and textual information. There take been many applications of light amplification by stimulated emission of radiation graphics in the publishing industry, including phototypesetting and platemaking. In what follows, nosotros shall describe a few examples of such systems.

Laser printers, which convert pages of text or graphics stored in a reckoner to printed material, could also be considered as an instance of laser graphics. This application will be described in a later on section.

A generalized light amplification by stimulated emission of radiation graphic organization is illustrated in Figure 24-fifteen. The laser axle is scanned over a recording medium and records a pattern that may represent either printed or pictorial information. The modulator switches the beam on or off as the beam scans to course the desired pattern. The system is controlled by an input signal, which may derive from a variety of sources, according to the application. In a pasteup-to-plate awarding, it could derive from a detector viewing the reflection from a laser beam scanning a pasteup in synchronism with the scanning of the recording laser. In a direct-to-plate awarding, information technology could come direct from a calculator in which the information is stored.

Effigy 24-15. A generalized laser graphic system.

A variety of lasers have been employed in light amplification by stimulated emission of radiation graphic systems. Historically, helium–neon lasers and air-cooled argon lasers operating at 488 nm accept been employed. In more than recent times, semiconductor diode lasers, operating in the 700–900 nm range, have go widely used. In applications requiring college power, diode-pumped Nd:YAG lasers are sometimes used.

A number of different recording materials are used. Many systems utilise dry silver halide photographic films, which are developed past heat. Photopolymer materials are also common. Other materials have included polyesters, photoresists, and electrophotographic films. The sensitivity in terms of energy per unit area to betrayal the different materials varies over orders of magnitude. Their spectral response also varies. Thus, the choice of laser depends strongly on the recording medium chosen. The laser must exist able to supply acceptable free energy per unit of measurement surface area at the right wavelength.

1 of the first laser graphics applications in the 1970s allowed scanning of page pasteups in club to produce a printing plate direct. The plate was made right from the pasteup, eliminating intermediate steps and reducing costs. This pasteup-to-plate awarding has been used in the paper manufacture.

Another early on application was light amplification by stimulated emission of radiation phototypesetting. Phototypesetting involves photographing characters on film. Phototypesetting machines select, under command of a keyboard, a negative of a desired character. The paradigm of the character is projected onto the recording medium, which subsequently serves equally the basis for making the printing surface. The exchange of a laser as the light source in a phototypesetting operation also reduced costs. Sophisticated laser phototypesetting equipment has been used in the newspaper manufacture. As in nonlaser systems, an operator at a keyboard enters in a character. The electronic logic controls the light amplification by stimulated emission of radiation axle to project the image of the character onto the recording medium. Choices of different inputs, like magnetic record or directly computer control, are as well possible.

1 meaning reward that laser graphics provides is the power to deal with photographs, text, and line art simultaneously, on one piece of equipment. All these formats may exist projected on the recording medium without having to go through the stage of manual cutting and pasting. Because of this ability, laser graphic systems are sometimes chosen imagesetters. This adequacy is being utilized in modern direct-to-plate systems in which printing plates are exposed directly by the imagesetter to class the integrated pages of text and illustrations nether the control of the reckoner that has stored the information. This procedure eliminates several steps in the generation of printing plates and offers savings in both toll and time.

In a recent instance [2], a laser imagesetter immune the publishing, for the starting time fourth dimension, of a color magazine by direct writing of images on offset printing plates without use of movie. The imagesetter employed a 488 nm argon laser and exposed the press plates using a raster scan. Both polymer-based and silver halide plates were used. The direct-to-plate system offered toll reductions through elimination of the picture show and processing costs.

In another example, a computer-to-plate organization uses a series of laser diodes, 24 or 32, depending on the size of the plate. The laser light is brought to the plate by a fiber optic delivery organisation. The laser beams are scanned horizontally under the control of a computer to form the desired images on the plates.

Dry plates incorporate three layers, a peak layer that repels ink, a middle layer that absorbs low-cal, and a base layer that accepts ink. The laser light is absorbed in the center layer, causing it to ablate. The ablation procedure also removes the top layer. This exposes the base layer, in the form of the desired image. This procedure directly produces the plates for printing, with the epitome formed on an ink accepting layer.

The process is done without apply of photographic film, moving-picture show processing, or photographic chemicals. The system offers increased productivity and lowered costs compared with conventional platemaking processes.

Many different laser graphic systems have been developed, using different facets of laser technology and offering advantages for a variety of applications. The ability of laser-based systems to eliminate intermediate steps and to expose a press plate set up for press, straight from reckoner input, is an important accelerate for the printing industry. Applications for sophisticated laser graphic systems capable of reckoner-to-plate processing are continuing to develop.

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Sputtering Targets and Sputtered Films for the Microelectronic Manufacture

Jaydeep Sarkar , in Sputtering Materials for VLSI and Thin Film Devices, 2014

ane.6 Sputtering materials for optical storage media

While magnetic recording technologies are based on the switching of the magnetic polarity of magnetized domains, optical storage technologies utilise pocket-size areas (marks) on a media in the form of a circular disc with optical properties that are unlike from their surroundings [130–132]. In club to increase data storage chapters, the marking size in optical recording media has to be reduced the same as the written chip size in magnetic recording media. Common optical storage media are compact discs (CDs), digital video discs (DVDs) and Blu-ray discs (BD). Figure 1.60 shows the bones components of a CD histrion and the structure of the optical media [133].

Effigy i.60. Schematic diagram showing major components of a CD player. The bottom-most figure shows construction of a CD disc media including pits (raised bumps) and lands (flat area betwixt pits) [133].

Typically a CD media has 4 layers: a polycarbonate plastic substrate, a thin metallic reflection layer, a spin-coated lacquer layer and a screen-printed artwork layer. As shown, the media retains binary information (bits) in the grade of pits (raised bumps) separated past lands (the flat area between the pits). When a disc media is read, the pits stand for to 0 or off (due to the lack of reflection) and lands stand for to 1 or on (due to a reflection). Optical discs tin exist divided into iii categories, namely pre-recorded, recordable (write once; R) and re-recordable (writable; RW). Tabular array 1.20 lists the various types of optical discs under these categories. All of them take fairly simple construction in terms of layers used. Effigy 1.61 (p. 69) shows the evolution of various optical storage technologies in the data rate–storage capacity space and Table 1.21 (p. 69). Lists key parameters for three generations of optical storage technologies [134]. Table 1.22 (p. seventy) lists major inventions that took place in the optical storage manufacture.

Table 1.20. Examples of Optical Discs

Optical Media Type Example
Pre-recorded CD, CD-ROM, DVD, HD-DVD, BD-ROM
Recordable CD-R, DVD-R, BD-R
Re-writable CD-RW, DVD-RW, DVD-RAM, BD-RE

Figure i.61. Development of optical recording technologies in terms of storage chapters and data rate [134].

Table one.21. Primal Parameters for 3 Generations of Optical Storage Technologies [134]

Parameters 1st Generation 2nd Generation 3rd Generation
CD DVD HD-DVD BD
Laser wavelength (nm) 780   nm 658   nm 405   nm 405   nm
Capacity (unmarried-layer disc) 650   Mb 4.7   Gb xv–20   Gb 25   Gb

Table 1.22. Major Inventions in the Optical Storage Manufacture

Twelvemonth Inventions
1958 Optical disc for video recording using pits (David Paul Gregg)
1972 Laser disc
1976 Sony demonstrated optical digital audio disc
1982 Meaty disc (CD), digital audio
1985 CD-ROM (read only memory)
1988 CD-MO (magneto-optical re-writable)
1989 CD-R (write one time)
1991 CD-R (recordable)
1995 CD-RW (read-write)
1996 DVD
1997 DVD-ROM & DVD-Video
2000 - Blu-ray disc (BD) and and so forth

Figure 1.62 (p. 70) shows a CD manufacturing flow chart and typical unit processes. In the beginning, a polished glass disc of diameter 240   mm and thickness 6   mm is spin-coated with a photoresist layer (150   μm thick) that is hardened by baking at nigh lxxx°C for thirty   minutes. Then a light amplification by stimulated emission of radiation beam recorder is used to generate pulses of blue/violet laser to expose and soften portions of the photoresist layer on the glass (known every bit the drinking glass master). This is called laser recording [99].

Figure ane.62. A representative flow chart for CD manufacturing.

In the adjacent steps, i.e., master evolution, a sodium hydroxide solution is spun over the glass principal. This is washed to dissolve the areas exposed to the laser, i.e., etch pits in the photoresist. Side by side, in the electroforming pace, a nickel alloy layer is used to coat the glass master. This develops a metallic principal chosen the begetter. Then, the metallic master father is separated from the glass main, which tin be used for stamping discs. In the disc-stamping step, one disc of polycarbonate can be pressed every 2–3   seconds in a mod stamping machine to press the data prototype (pits and lands). Approximately, xviii   gm of molten polycarbonate at 350°C is used for this purpose.

Next, in the metallization stride, polycarbonate disc base is sputter coated with aluminum (50–100   nm thick) to make it reflective. In the protective coating step, metalized disc is spin-coated (six–vii   µm thick) with an acrylic lacquer followed by curing with ultra-violet light. This layer prevents oxidation of aluminum reflective layer.

Finally, a label is screen-printed on the disc and again cured with ultra-violet calorie-free. About common CDs are 1.2   mm thick and 120   mm in diameter. The dimensions of each pit are 100   nm deep, 500   nm wide and length 850   nm to 3.v   µm. The distance between the tracks, the pitch, is usually 1.6   µm. The plan surface area in a CD is 86.05   cm² and the length of the recordable screw is (86.05   cm2/i.half-dozen   µm)=5.38   km. Scanning velocity is ordinarily betwixt 1.2 and 1.iv   m/s, which is equivalent to approximately 500   rpm at the inside of the disc and approximately 200   rpm at the exterior edge.

Sony offset demonstrated an optical digital audio disc in September 1976 and then Phillips demonstrated a CD sound thespian in March 1979. Its superior digital sound quality and large storage chapters (650   Mb and more) led to the complete replacement of vinyl records and audiocassettes. In playback mode, a light amplification by stimulated emission of radiation of wavelength 780   nm (infrared) is used to read a CD through the bottom of the polycarbonate layer. When the laser hits a country on the track, the light is reflected back. In dissimilarity, when the laser hits a pit, no calorie-free is reflected back. Therefore, in playback style the laser axle reads the modulation of the calorie-free reflected by these pits and lands from the disc media.

Figure 1.63 shows typical configurations of CD-R (write once) and CD-RW (re-writable) [99]. In CD-R (write in one case), on the pre-groove side the polycarbonate disc is coated with a very thin layer (110–120   nm) of organic dye. So, the dye is coated with a thin (60–lxx   nm) reflecting layer (e.chiliad., silver, silvery blend or gold). Finally, a protective coating of a photo-polymerizable lacquer is practical on top of the metal reflector and cured with UV-light. Note that in the example of CD-R (write once) optical discs, the organic dye (east.g., Cyanine, Phthalocyanine, Azo and then forth) layer acts every bit an information storage layer. CD-Rs based on cyanine dye are mostly green in color. Phthalocyanine dye based CD-Rs are commonly silver, gold or light green in color. Azo dye based CD-Rs are dark bluish in color. A CD-R recorder writes information to a media past using a laser in which it heats areas of the organic dye layer.

Figure 1.63. Representative layered structures of CD-R (write once) and CD-RW (re-writable) optical media [99].

The writing process does not produce pits and instead the heat permanently changes the optical properties of the dye leading to modify in the reflectivity of those areas. A CD-R can exist recorded in multiple sessions. Once a department of a CD-R is written, it cannot be erased or rewritten, unlike a CD-RW. Using a relatively low laser power, then as not to further change the dye, the disc media is read back in the same manner as a CD-ROM. The reflected light is non modulated past the alternate regions of heated and unaltered dye. In the reading process, the change of the intensity of the reflected laser radiation is transformed into an electrical betoken, from which the digital information is decoded. In CD-R media, the dye itself can dethrone over fourth dimension, causing data to get unreadable.

For re-writable discs (eastward.g., CD-RW, DVD-RW, BD-RE), a metallic blend layer fabricated of phase change materials (e.g., AgInSbTe, GeInSbTe, GeInSbSn) is the information storage layer [131,132]. In a CD-RW disc media, typically the recording layer is made of AgInSbTe alloy. In its as-deposited land AgInSbTe alloy film is polycrystalline in nature and has a certain degree of reflectivity. In the writing process, the laser beam heats the AgInSbTe alloy layer to 500–700°C. On cooling, the AgInSbTe alloy layer loses its polycrystalline structure and assumes an amorphous state. The baggy material has reduced reflectivity. The lost reflectivity serves the same part every bit pits in a CD and the opaque spots in a CD-R. To erase the information from the disc media, the write beam heats the amorphous regions of the AgInSbTe layer with low power that raises the temperature to almost 200°C. Every bit a event, the AgInSbTe alloy film is non melted, but returns to the polycrystalline land and thus becomes reflective once more. Re-writable media with a suitable optical drive can be re-written up to 100,000   times.

In the next stages of development, DVDs with two-disc structure emerged. Two 0.6   mm thick polycarbonate discs coated with thin metallic layers were used in DVDs, which tin can be read independently and from one or both sides. Every bit compared to CDs, DVDs have a smaller feature size and short wave-length (658   nm) readout light amplification by stimulated emission of radiation. This lead to initial storage capacity of single-sided and single-layer DVDs equally large as 4.7   Gb. Effigy i.64 shows the materials typically used in a DVD-RW disc media. The choices of stage change material are manufacturer dependent.

Figure 1.64. A schematic analogy of films typically used in a DVD-RW disc media.

In the quest for greater storage capacity (fifteen–25   Gb) in a DVD, smaller information bits and shorter wavelength (405   nm) lasers are being used – as is the case of BDs and Hard disk-DVDs. Note that the majority of the layers in re-writable discs are sputter deposited (Tabular array ane.23). With the exception of single crystal silicon targets for semi-reflective layer applications, about sputtering targets are polycrystalline in nature. Reactive sputtering in a nitrogen temper is used for Ge and GeCr targets to grade their nitride films for protective/capping layer applications. The common sputtering tools used for depositing such films include Balzers ARQ tools, Singulus II, Iii and Smart, Shibaura Stella, M2 Unisource, ODME Nova Focus, ODME Miniliner, 4M Phoenix and so forth.

Tabular array 1.23. Films that are Sputtered Deposited on Optical Disc Media

Role Thin Films Deposition Method
Reflective layer Al, Al alloy, Ag, Ag alloy, Cu blend Sputtering
Semi-cogitating layer Ag alloy, Si Sputtering (reactive sputtering for Si)
Dielectric layer/protective (capping) layer ZnS-SiO2/GeNx, GeCrNx, Si3N4 Reactive sputtering of Ge & GeCr
Recording layer Phase modify materials (e.g., AgInSbTe, GeInSbTe, GeInSbSn) Sputtering

Before CD-RW technology emerged, a standard for magneto-optical recordable and erasable CDs, chosen CD-MO, was introduced in the early 1990s. CD-MO was essentially a CD with a magneto-optical recording layer. Information recording (and erasing) was accomplished by heating the magneto-optical layer made of alloys such as DyFeCo, TbFeCo and GdFeCo up to their Curie signal. This resulted in erasing all previous information then using a magnetic field to write the new data. The details of magneto-optical recording can be found elsewhere [135].

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Diamond-like carbon for information and beer storage

Cinzia Casiraghi , ... Andrea C. Ferrari , in Materials Today, 2007

The flying applied science requires the use of a blanket in order to protect slider and disk during offset-finish and crashes. In the instance of optical applied science, the protective coating must:

1.

Accept practiced adhesion to drinking glass or plastic sliders and the upper layer of the disk;

two.

Be transparent at the laser recording wavelength (i.e. 400 nm);

3.

Have low stress in social club to avoid high waviness of the plastic substrate;

four.

Be relatively dumbo and difficult in order to provide protection against crashes;

five.

Exist resistant to the estrus from the recording laser spot; and

6.

Be compatible with the lubricant.

All these requirements can be satisfied by ta-C:H 83 . Notation that the need for transparency at 400 nm would require films with a bandgap of at least 3 eV, which is larger than the typical ta-C:H bandgap. Nonetheless, since the target is to permit the bluish light amplification by stimulated emission of radiation line become through the carbon coating, what actually matters is the film transmittance rather than its optical gap. One style to increase the transmittance for a lower gap is to decrease the pic thickness 10,83 . Indeed, ta-C:H less than ∼40 nm thick is transparent, relatively dense, hard, and can be deposited apace and uniformly (70-80%) on the optical disk substrates 83 .

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