Note: Descriptions are shown in the official language in which they were submitted.
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` ~43~75
1LASER PYROGRAP~IlC REFLEGllIVE l'.EC~ORDIN(~ MEDIUM
3_oss Refe~ ence to Related Application
4This is a continuation-in-part of application S.N. 921,723 filed August 17,
51978, now abandoned
6Background of the Invention
7 a. Field of the Invention. The inventicn relates to dat~ storage media,
8 and more particularly to a storage medium useflll for directly reading laser writing
9 immediately after laser writing.
b. Prior Art. Previously, many t~Tpes of opticnl recording media have
11 been developed for laser writin~. For example, an article in Optical En~neerin~,
12 Vol. 15, No. 2, Mnrch-April, 1976, p. ~9 discusses properties of a large.number of
13 media. Some of these media require post write processing before they can be read,
14 ¦ and some can be read immediately after laser writing. The media of interest herein
15 ¦ are for "direct read after write" capability, commonl~7 known as "DRAW" media~
16 ¦ Presently l~nown laser D~AW media are thin metal films in which holes may be
~7 melted~ composite shiny films whose reflectivity at a spot may be reduced by
18 evaporation, thin films of dyes or other coatings which can be ablated at a spot,
19 and dielectric materials whose refractive-index may be changed at a point~ causing
~O a scattering of light when scanned with fl read laser.
21 Today, these media are generally manufactured by means of vacuurn
22 deposition on a batch basis rather than cortimlous-flow basis and are therefore
23 expensive ancl it is difficult to achieve a uniformity of quality for large production
24 quantities of the product since many batches would be involved. Refractive-iadeY.-
change materials which have been proposed for futllre manufacture on a continuous
~e6 basis have the disadvantage that in order for these media to be read by reflection,
27 a metal ùndercoating must be applied, thereby introducing a batch type production
28 process with the above ment;oned disadvantages.
29
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32
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1 Tlle most commoll VRAW media are thin metal films, usually on a glass
2 substrate. Thin metal films have several advantages: Pirst, they can be producec1
3 easily in small quantities with commerciaUy available sputtering equipment. Second,
4 they can be read either by reflection or by transmission. Third, films of tellurium
and bismuth have relatively high recording sensitivities.
6 Ii ortunately, for all of these reasons, metal films have enabled a large
7 amount of research to be conducted and progress to be made in the design of optical
8 data storage systems. To date, tellurium has evolved as the most widely used of~
9 the metal films. However, tellurium must be mam~factured by an expensive,
batch-type, vacuum sputtering technique; it does not form a tenacious coating; and
~11 it introduces manufacturing and environmental complications because of its toxicity.
12 In ll.S. patent 3,911,444 I,ou, Watson, and Willens disclose a vacuum-
13 deposited metal film recording media ~or laser writing incorporating a separately
14 deposited plnstic film undercoat between the rnetal film and a flexible transparent
substrate in order to re~uire less energy to write with a laser and to prevent impurity
transfer between the substrate and the radiation absorbing film.
17 In Example I of U.S. patent 3,567,447 Chand diseloses that upon heating
18 a processed silver-halide emulsion coated photoplate, the non-image areas, clear
19 gelatin, darkened to a transparent reddish color and the image areas assumed a
reflective metallic sheen. Chand used the reddish color to delineate nonimage areas
21 to be removed chemically, therehy leaving hardened opaque image areas7 with clear
non-image areas.
23 In U.S. patent 3,893,~ 29 Endo discloses exposed and partially developed
24 film for recording laser writing hy means of heating the film to cause local
deformation which scatter light.
26 In U.S. patent 3,fi89,894 1,a~lra and Eng disclose exposed and developed
27 microfilm to record data by optically writing transparent bits of data with black
28 areas of the microfilm by burning holes through the black silver-halide emulsion.
29
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Many other patents reveal light absorptive media for
recording laser writing. My objactive was to devise a moderate-
ly reflective DRAW laser recording material which may be manu-
factured without the use of a vacuum system and on a continuous
basis and which may be used to record non-reflective spots in
a reflective field with relatively low energy laser pulses.
Another objective was to devise a laser recording medium which
permits the pre-recording of control indicia and certain data
base data by normal photographic means to facilitate the use of
discs or plates in both the recording apparatus and the playback
apparatus.
Temperatures between 280C and 340C are preferred to
produce the reflective coating during a time cycle on the order
of one-half minute to 20 minutes. Heating methods include the
use of a convection oven, a contacting hot source, or radiant
heating. A resulting shiny reflective emulsion coated trans-
parent or absorptive substrate is a DRAW laser pyrographic
reflective recording medium.
An advantage of the recording medium of the present
invention is that it may be made on a continuous flow basis.
The emulsion coating is tenacious with respect to its substrate
and is not toxic when laser writing ablates portions of the
coating. Another advantage is that the emulsion coating may be
previously exposed to desired patterns by normal photographic
means to provide control indicia for the recording apparatus
and/or playback apparatus and for replication of master disc
recordings.
According to a broad aspect, the present invention
provides an information storage medium for pyrographically
recording laser writing comprising a sheet substrate and a
refle~tive surface coating disposed on the sheet substrate, the
reflective coating comprising reflective silver particles which
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~347~5
are characterized by a gold color and are distributed within a
gelatin matrix.
The information storage medium may be made by photo-
graphically processing a silver-halide emuls.ion coating on a
substrate to blackness, and thermally converting said black
photographically processed silver-halide emulsion coating by
heating at least to 250C in an atmosphere having a substantial
percentage of oxygen at least until a gold colored reflective
component appears on the emulsion coating surface.
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2 Brief Descril-tion of the D~@
Figure 1 is a top plan view of the recording medium of the present
invention.
6 Figure 2 is a side sectional view of l:he recording medium of
7 Figure 1.
8 Figures 3-7 are detail views of the recordmg medium of Figure 1 showi~g--
9 sequential processing steps for making the finished recording medium.
~igure 8 is a side sectional view of the recording medium of Figure 1
11 showing laser writing.
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13 Description of the Preferred Embodiment
. . .
Fi,gllre 1 shows a d-sc lt having an inner periphery 13 and an outer
16 periphery 15. The interior of the inner periphery 13 is ~oid so that a centering
collar may be used to hold dise 11 on a splndle for high spee~ rotntion. Wbile the
- ~ ~ 18 recordm~ medlum o~ the present invention is described as a disc, a disc configur~tion
;~ ~ is not essential for operating of the recording medium. l~or exarnple, the recording
medium may be a flat sheet-lilce material which could be squa~re and with a central
21 hub rather than a hole. It could also be a non rotating rectangulal plate. However,
22 rotating discs are preferred for fnst random access to medium amounts of data and
23 non-rotating rectangular plates in stacks are preferred to provide intermediate speed
29 random access to large amounls of data by mechanically selecting a plate and
scanning it by rnechanical and eleetro-optical means.
~6 The disc of ~igure 1 is photographically partitioned into reeording and
27 non-recording arefls. For example~ a first annular recording zone 17 could be spaced
28 ~ ~ from r sec d annular recordin zone 13 by an nnnular guard zone 2l. The function
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1 OI the guar(l 7.0ne may be to separ ate different recording fields, to carry control
2 information, such as timing signals and to provide space for data read-write trans-
3 ducers to reside when not over recording areas. While such guard bands are preferable,
4 they are not essential to the operation of the present invention. It should be noted
~ that the recording fields are for data and control signal recording, while the guard
6 band is not for data recording, but may have control signal recording thereon. The
7 recording field l9 is shown to have a plurality of concentric, circumferentially-spaced
8 servo tracks 23 thereon. Such servo tracks are thin lines which define the spaces
9 between circular paths wherein data are written. The pattern for such lines is
10 applied photographicRlly as explainecl below with reference to Figures 3--7.
11 ~igure 2 shows a side sectional view of the recording medium of Figure
12 1. The medium consists of a substrate 27 which is a sheet-like layer which is
transparent, translucent, or opaque; preferably a high temperature, dimensionally
14 stable material, like glass, ceramic, and thermoset and thermoplastic polyimide
~15 plastics. One of the requirements of the substrate material is that it withstand
:L6 temperatures to at least 280C and most likely 320C but up to 34ûC, without
17 thermal deformation. Transparency or absorptivity of the substrate is desired so
:L8 that when the light beam of the reflective playback apparatus impinges upon a
19 recorded spot, It either paæes through the substrate or is absorbed by it with
20 minimum reflection. If the substrate is absorptive, it may be absorptive at the
2~ wavelengths of the recording beam or the reading beam, or both. Thus, not all
common photographic substrates may be used. For example, the most common
23 photo~,rraphic film bases are polyester polyterephfllate, polycarbonate, or eellulose
2a, triacetate--which normally have maximum continuous operating temperatures of
~6 145C, 132C, and 205C, respectively. Further, in order to coat a photographic
emulsion on a substrate, it must be etchable, dimensionally stable, non-destructible
28 by slmlight, h~ve ~ood mechanical strength, and should also be relatively inexpensive
29 and currently available in adequate quantities. Further, when lata recordings are
to be read only in reflection rather than transmission, the substrate may be a
non-reflectirlg, opaque material. There is one plastic--polymide--that meets
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32 ~ _5_
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1 nll of these conditions. It is available as a thermo-plastic and a thermoset plastic,
2 can operate at 320C for mimltes7 an-l is etchable with alkalines.
3 E~or the case where the substrate is transparent, the recording medium
4 may be read in a transmissive mode, for example as in U. S. patent application
serial No. ~45,332, entitled Error Checking Method and Apparatus for Digital Data
6 in Optical Recording Systems, assigned to the assignee of the present invention.
7 The thickness of the substrate is not critical when the lnser beam is
B directed onto the surface as shown in Figure 8, but it should have sufficient thickness
9 to provide strength for resistance against breakage. If the laser beam is directed
through a transparent substrate, then in order to maintain focus of the beam the11 thickness of the transparent substrate would have to be very uniform (for example,
12 as obtainable from float glass or selected high quality drawn glass). Also, the
13 thicknes~s of the sul~strate may depend on the overall size of the recording medium
14 being used. ~or a 1~-inch disc, a thickness of 1/8 inch may be suitable.lS The purpose of substrate 27 is to support a sîlver-halide emulsion coating
16 29, which is uniformly applied to the substrate in a conventional manner and which
1~ i9 converted subsequently to layers 32 and 33 in Figure 8. Currently availaMe
18 silver-halide emulsions from 3 to B microns thick are adequate, provided they are
characterized by very fine silver-halide grain size, i.e., only a small percentage of
the grains are larger than 0.07 microns. This grain size ap~ears to be important21 because when grain sizes becorne larger than approximately 0.06 microns the con-
22 version from Maclc to reddish coloration, which subsequently becomes metallic, appears
23 to be less complete. Emulsion coated glass plates having these characteristics are
2a~ commercially available and are Icnown as photoplates which are used to make
photomasks for the manufacture of semiconductor integrated circuits. ~or example,
~!6 emulsion coated photoplates suitable for use herein are manufactured by Ag~a-
27 Gaevaert of Belgium, Konishiroku Photo Industries of Japan and the Eastman Kodak
28 Company.
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1~3475
1 The shiny reflective component 32 in Figure 8 results from the thermal
2 processing describe-3 herein and reflectivity does not initially exist in the emulsion.
3 At the inception the material of reflective component 32 is mostly, excepting oxygen,
4 all found in the photographic emulsion ~,which is ImiIorm in its composition. A
~ subbing layer, not shown, is usual]y used to attnch the substrate 27 to the emulsion
6 29. Fo~lowing the thermal conversion of the present invention the emulsion 29 of
7 Figure 2 produces a reflective component 32 at the emulsion surface shown in Figure
8 8, with a non-reflective underlayer 33 beneath it~ The reflective component 32 is
9 not well defined in thickness, but exhibits a silver concentration gradient, with most
10 of the silver near the surface, and less extending downwardly. Thus, althou~h ~iguré
11 8 depicts a sharp boundary for refleetive component 32, actually such is not the
12 case and is only pictured in this manner to explain the contrast which exists between
13 the surface of the material and the urlderlying emulsion. The presence of more
14 silver particles at the surface and less below after heating is surprising and not
15 completely understood. It is believed that heat causes breakup of filamentary silver
16 particles into much more mobile, smaller particles which, in the presence of oxygen
17 at the surface concentrate and become reflective.
18 Underlayer 33, while not completely depleted of silver, contains less silver
19 than reflective component 32. Optically, underlayer 33 is pflrtially transmissive to
20 red light having wavelengths of 630 nanometers and longer, so that once craters are
2~ created penetrating reflective component 32, the craters may be detected by trans-
22 mission of red light through the underlayer 33, provided that the opacity of the
23 reflective layer is sufficiently great at the selected wavelength to permit detection
24 of the craters through differences in light transmission. The data contained in the
25 craters may nlso be read by changes in reflectivity of the shiny reflective component
~6 throughout the visible spectrum and into the near infrared where it is ultimately
limited in its usability &lS it becomes more and more transparent and therefore less
28 reflective in the non-data areas.
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1 It should be noted that both the recording areas 17, l 9 and the non-
2 recording guard band 21 of Figure l have silver-halide emulsion covering a glass
3 substrate. Thus, the designation of recording and non-recording areas is arbitrary
4 and the entire surface could be used for recording if desired. However, as a matter
5 of convenience, it is preferable to designate areas as non-recording areas. The
6 boundaries between recording and non-recording areas may be defined by concentric
7 lines, just as the servo trac1cs 23 of Figure l, wl ich have been greatly enlarged in-
8 the Figure, may be defined by lines. Typically, servo traclcs are closely spaced
9 concentric circles or adjacent lines of a spiral, with data bein~ written on or between
10 the lines. Such servo track lines, as well as line boundaries for non-recording areas,
11 may be photographically recorded on the recording medium prior to any data recording.
12 Moreover, other nlphanumeric information or data base information which is to be
13 a permanent parl: of the recording medium also may be applied to the recording
medium at an earIy time in the processing cycle since it becomes a permanent part
15 of the recording medium.
1 6 One of the advanta~es of the present invention is that the permanent
17 information to be recorded on the recording medium of the present invention may
18 be applied by photographic techniques since the starting material for the recording
19 medium is an unexposed commercially available photoplate used in the manufacture
of semiconductor integrated circl1its. After thermal conversion this information may
2~ be read in reflection since the blaclc image areas will become highly reflective and
22 the clear non-image areas will be onl~ slightly reflective.
23 The photographic techniques whic}) may be used to pre-record data base
2a~ and control information are well known in the semi-conductor industry. Lines having
a thiclcness of one micron thiclcness may be made. The typical procedure for creating
~G a line pattern is illustrated in Figures 3-6. With reference to Figure 3, the medium
27 ll is exposed to a line pattern consisting of the circular lines 23a, 23b and 23c.
28 ï`he line pattern exists as a latent image in the silver-halide emulsion, the remainc3er
29 of which is unexposed to light.
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1 Figure 4 illustrntes the processing of the plate 11 through a well known
2 commercially available developer which c~luses the image pattern of lines 23a, 23b,
3 23c to become black, characteristic of black silver, the remainder of the material
4 being transparent.
In Figure 5, the developed silver areas 23a~ 23b, 23c are bleached out so
6 that they are clear. The bleach does not afPect the unexposed æones of the recording
7 material 11.
8 In Figure 6, the entire rec~rding medium is now strongly exposed to~
9 actinic radiation, such as by a mercury arc lamp, incandescent lamp or xenon flash
lamp, and developed for maximum blackness (fixing is optional). The object OI this
11 step is ta provide black zones for conversion into the reflective data recording ~ields.
12 Of course, the guard zone 21 in ~igure 1 between recording fields will also have
13 the same black char~cter~ only its use is different. This exposure, development and
14 fixing step would be the only processirig procedure taken, prior to heating, if there
were no information to be pre-recorded, such as the servo tracks 23a, 23b, 23c and
16 there were no other pre-recorded alphanumeric or control indicia. In fact if no
17 images are to be photog~raphically recorded a fogging developer could be used in
18 some eases to avoid the need for the exposure step. Fogging developers are known
19 for use in reversal processing where it is desired to develop all remaining silver in
a silver-halide emulsion. See "The Theory of the Photographic Processl', 4th Ed.,
~IcMillan (1977~ p. 4~2. The min~mum extent of blackness opacity must be such
22 that the reflective component 32 subsequently produced by thermal conversion is
23 adequately reflective to the wavelength o light used in reflective playhack. A thin
24 reflective component with adequate reflectivity, less than 0.5 micron thick is preferred
in order to minimize energy needed to punch through the coating for laser pyrographic
26 writing.
27 As an alternative to wet chemical development for creating blacl~ emulsion,
28 dry thermal developmenl may also be used. In thermal development, a latent image
29 is developed by henting an e~posed photosensitive thermographic material. Various
types of materials exist, but in each case very miid heating causes development.
32 Eleating to about 11 5C lor five seconds causes development in typionl
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1 thermographic materials. One type of material which may he thermally developed
2 contains a developer composition together Witll silver-halide grains. Heating causes
3 the developer to become activated, sometimes using moisture derived from the
4 emulsion carrier. In either instance, whether a chemical developer or a dry developer
is used~ the photographic emulsion is processed for maximum blackness.
6 Once the recording medium has achieved the described level of blackness,
~ with or without pre-recorded indicia thereon, thermal conversion into a reflectiYe
8 medium may commence by heating the emulsion coating to a temperature of-
9 approximately 280C to 340C in air, or 250C to 340C in oxygen, until a shiny
reflective component 32 in Figure 8 appears. The coating initially is first converted
11 to a dark eherry red transmissive medium. This conversion, indicated in Figure 7,
12 begins to occur at temperatures as low as 200C. At higher temperatures, specifically
13 at about 3û0C the coating starts to becom0 reflective in less than a minute. After
14 further heating, reflectivity is clearly evident at the upper surface and the material
1S 11 has a characteristic gold color. Electrlcal resistance measurements on the shiny
16 component 32 in Figure 8 indicate no measureable conductivity. Heating methods
17 include the use of a convection oven, contacting hot source or radiant heating.
18 R;adiant heating is preferred because it heats the emulsion fast and uniformly and
19 ean be progr~mmed easily to minimize thermal shock to the substrate.
The shiny component 32 also has low thermal conductivity. It is be]ieved
2' that silver grains which form the Siliny component .,2 are indlvidually separated from
22 each other by gelatin. In other words, the rmild temperatures used in thermally
23 converting the emulsion coating into a shiny component 32 are low enough to preserve
2~ the insulative properties of the ~elatin. Higher temperatures would char or burn
the gelatin, perhaps removing it by ablation. It appears that the mild temperatures
26 used herein are adequate to stimulate silver grain brealcup, and cause a dispersion
27 of the grains which appears to be necessary for the creation of the reflective layer.
~8 The oXvgen component of the heating atmosphere is preferably maximized
29 because it lowers both the temperature and tlle time required for processing. Although
heating in air will work, fl pure oxygen environment is better. A minimum percentage
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1 of oxygen, at lcast a few percent and preferably much more, such as the substantial
2 percent of oxygen found in air, is necessary to create the shiny silver component
3 32 by thermal conversion.
4 At a minimum, the shiny reflective component must be visible on the
surface OI the material to be usefall for reading the data by differential reflectivity.
6 How&ver, in some instances it may be desirable to have a thicker coatîng of tlle
7 shiny material; in this instance longer heating would be required. For example, in~
13 the instance of therma~ly converting the entire thiclcness of the coating~ heating for
above 2û mim~tes is needed. Conversion may oceur at temperatures between 280 C
:LO and 340C. The higher the conversion temperature, the faster the reaction and the
11 more complete conversion; however, 320C is selected as a preEerred maximum~
12 temperature so as to minimize the charring of the gelatin in the emulsion coating
13 and to minimize possible thermal damage to the substrate. Charring in gelatin is
14 noted by an amber color in the material. Note that the shiny component 32 only
occurs where black silver previously existed. The shiny component is thus derived
16 from the silver in the developed silver -halidc emulsion. While the silver appears
17 at the surface and is concentrated there, the thickness of the shiny component is
18 not well defined because of a silver concentration gradient diminishing toward the
19 direction away from tlle exposed surface. It was shown above that certain black
:~0 ¦ silver areas could be removed by bleaching in order to leave control indicia Ol line
21 boundaries. Clear indicia markings c e simple types can also be introduced by a
22 negative processing procedure in which a mask or an intermittent beam is used to
23 create the black images Y~hich outline the clear indicia.
24 While a silver-halide emulsion is the~ starting material for the recording
medium of the present invention, the finished product is considered to be a silver
26 gelatin complex, the halides being substantially removed in the exposure and develop-
2q ment process. The finished product is characterized by a reflective silver component
28 at the surface thereof having a silver g~adient with more silver at the surface and
29 less below, but with some silver throughout the gelatin.
To use the recording medium of the present invention laser light is focused
31 on a spot at the surface of the coating of the recording medium. Enou~h laser
32 energy is delivered to the spot to remove the shiny reflective material. The shiny
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1 mnterial is plimarily at the surace and since a re~lective read proeedure is usecl,
2 for example as described in U.S. patent 3,657,707, the recorclin~ laser beam need
3 only penetrate and remove the shiny coating--not tlle fu11 depth of the emulsion
4 coating. Transmissive type reading can be nccomplished to a limited extent i~ a
5 red or very near infrared laser beam is used such that the opas~ity o~ the coatin~
6 blocks 90% of the light and the recor ded craters permit transmission of at least
q 50% of the light. -
Figure 8 shows emulsion coating 29 on substrate 27 covered by shiny
9 component 32 having a crater 30 damaging the shiny component created by means
10 OI laser light indicated by the rays 31. The size of the craters is kept at a minimum~
ïl preferably slightly under one micron in diameter but no larger than a few microns
12 in diameter to achieve high data densities. Data written by means of lflser light
13 are recorded in the recording areas 17, 19 shown in Figure 1, designated by the
14 letter R. As mentioned previously, these recording areas may also contain pre-
15 recorded data base data and control indicia whieh may be disposed over essentially
16 the entire area OI the medium. No data is recorded in the guard band 2l, designated
17 by the letter G, although this region may have control indicia written therein.
18 Control indicia in either of the areas may be written by means of photographic
19 techniques or by pyrographic methods such as laser writing.
20 ` Thus, the recording medium of the present inve11tion may contain R mix
2~ of pre-recorded data and control indicia which has been applied to the recording~
22 medium by photogrAphic techniques, as well as subseguently ~vritten data applied to
23 the recolc1ing medium by laser pyrographic writing. There is no data storage
2~ distinction between pre-recorded non-reElective spots and non-reflective spots made
25 by laser writing. In the read mode, data base data and control inormation are
26 accessible on the same disc as data, while in the record mode the control information
27 is used.
;~!8 The table below lists the relative contrast measurements obtained from
29 1aser writing and reading as shown in Figure 8 on a sample of this laser pyrographic
3V reflective recording mediurn on a glass substrate. Measurements were made by
31
32
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1 recording and reading 32 spots at each of L6 power levels, or a total of 512 spots,
2 with an argon laser generating the green 5l4 nanometer line~ Electron micro~raphs
3 ancl optical microscope photographs were taken of the holes created. These photos
4 confirmed that the depth of the holes at rated power levels is considerably le~ss
5 than the 0.8 micron hole diameter itsel~; also, that at the lower power levels the
6 holes are reduced in size. The ta~le illustrates that the contrast is almost unchanged
7 from power levels oE 28 milliwatts down to 6.9 milliwatts, indicating that as long
8 ¦ as the power is above the required level, the material performs well. There is no-
g ¦ apparent "overpower" effect. Note that there is little further degrac3ation in contrast
10 ¦ down to 4.6 milliwatts. Finally note that the usable contrast (when the median
:ll ¦ contrast is much larger than the 1 Sigma distribution value) is as low as 2.2 milliwatts.
12 Frorn these data it can be concluded that the medium could be rated at 5 milliwatts
13 for 0.8 micron beam recording with 100 nanosecond pulses. This is sligrhtly less than
14 that required to record on a thin layer o~ vacuum-deposited tellurium--fl metal which
~5 is one of the more popular lase.r recording ma-terials.
16 The above clescribed reflective recording medium reqllires much less laser
lr~ energy and creates considerably less recording debris than prior media in which holes
18 were burned through an entire 6 microns thick black silver-halide emulsion.
19 The method herein described results in melting and removal o~ less than
O.S micron of the thermally converted emulsion. Thus, the laser energy required
and the debris gen~rated are reduced by more than one order Oe magnitude ~ my
22 proposed recordin~ method and medium.
23 Note that the thermally converted processed silver-halicle emlllsion Imder
24 the reflective coating, 33, plays a thermal insulating role in improving recording
sensitivity similar to what is accomplished by the plastic film undercoat of the prior
26 art. However, the present coating metilod does not require the added step OI a
27 batch-type vacllum cleposition procedure. A continuous flow manufacturing process
28 may be used to produce the reflective coating.
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TA~LE
LASEl~ Wl~ITING AND READING ON
PYROGRAPIlIC REE~LECTIVE RECORDING MEDIUM
Laser Beam: 514 Nanometers Wavelengtl
0.8 Micron Diameter
100 Nanosecond Pulses
Statistical Distribution
Pulsed Power at SurfaceRelative Contrastof Contrast Ratios
of Recording Medium Ratio Avera~edof the 32 Spots
(in Milliwat~s) Over 32 Spots (+ 1 Si~ma)
2~ 2~L~7 + 276
24.3 2361 ~ 442 - -
21 : 2518 . + 267
18 2700 ~ 296
15.4 2690 -~ 314
12.8 ~ 2804 + 267
10.4 2634 + 270
8.7 265~ + 325
6.9 249~ ~ + 336
5.7 2221 . + 459
4.6 2156 + 432
3.6 186U + 624
.8 1725 +-380
2.2 ~ 1217 . + 250
: 1 ~7 654 + 188
1.3 279 . + 145
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