KR20070022713A - Graphic-arts laser imaging with reduced-length laser cavities and improved performance - Google Patents

Abstract

Cavity lasers exhibit relatively high beam quality despite relatively small cavity lengths (eg 50-53 mm) for high power (eg ≥10 watt) power devices. This allows for physically smaller laser and optical assembly configurations without sacrificing performance. Reduction of optical photon interference, which can impair image forming performance, is also facilitated. The laser and optical assembly may utilize an opening formed in the optical shielding element to reduce the divergence of the light beam emitted from the diode pumped laser.

Cavity Laser, Pump Laser, RF Driver

Description

GRAPHIC-ARTS LASER IMAGING WITH REDUCED-LENGTH LASER CAVITIES AND IMPROVED PERFORMANCE}

This application claims the priority and advantages of US Provisional Application No. 60 / 568,343, filed May 5, 2004, which disclosure is incorporated herein by reference.

FIELD OF THE INVENTION The present invention relates generally to graphic arts image formation, and more particularly to cavity laser optimization used for lithographic image formation.

In offset lithography, a printable image is present on the printing member as a pattern of ink acceptable (lipophilic) and ink repellent (oleophilic) surface regions. Once applied to these areas, the ink can be effectively delivered to the recording medium in substantially the same imaging pattern. Dry printing systems utilize a printing member that avoids ink sufficiently to allow the ink repellent to allow direct application of the ink. Ink uniformly applied to the printing member is transferred to the recording medium in an imaging pattern. Typically, the printing member first comes into contact with a soft intermediate surface called a blanket cylinder, which in turn applies an image onto paper or other recording media. In a typical paper feed press system, the recording medium is pinned to an impression cylinder that makes contact with the blanket cylinder.

In wet lithographic systems, the non-imaging region is hydrophilic and the requisite ink repellency is provided by initial application of a humidifying (or “water fountain”) solution to the plate before using the ink. The ink-adhesive source solution prevents the ink from adhering to the non-image areas, but does not affect the lipophilic properties of the image areas.

If the press prints in more than one color, a separate printing member corresponding to each color is required. The original image is decomposed into an imaging pattern or "split", each of which reflects the contribution of the corresponding printable color. The position of the printing member is adjusted so that the color components printed by the other member remain in registration on the printed copy. Each printing rich is typically mounted on a "plate" cylinder, and the set of cylinders associated with a particular color on the press is usually referred to as a printing station.

In most conventional presses, the print stations are arranged in a straight or "serial" configuration. Each such station typically includes an impression cylinder, a blanket cylinder, a plate cylinder, and the requisite ink (and humidification in a wet system) assembly. The recording medium is transferred sequentially between print stations, each station applying a different ink color to the material to produce a mixed multicolor image. Another configuration disclosed in US Pat. No. 4,936,211 relies on a central impression cylinder that carries sheets of recording material to each previous print station, thereby eliminating the need for mechanical delivery of media to each print station. With either type of press, the recording medium can be fed to the print station in the form of a continuous "mesh" of material when in the form of a cut sheet.

To circumvent cumbersome photography development, plate-mounting and plate-matching operations that represent traditional printing techniques, practitioners have developed electronic alternatives that store imaging patterns in digital form and press the patterns directly onto the plates. Computer-modifiable plate-imaging devices include various types of lasers (eg, cavity lasers). For example, US Pat. Nos. 5,339,737, 5,351,617, 5,385,092, 5,822,345, and 5,990,925 are all incorporated herein by reference, which are intended to remove one or more layers of lithographic printed blanks in an imaging pattern. Disclosed is an ablative / sub-ablative recording system that creates an instant ink print member without the need for photography development by using laser emission. According to such a system, the laser output is directed from the diode to the printing surface and focused on the surface (or on the layer which is most likely beneath the surface layer, where laser removal is easiest). Other systems use laser energy as a pointwise alternative to the entire exposure, either through the donor to the acceptor sheet and for non-removable recording, or through photomasks or negatives.

The challenge in designing a laser based imaging system is to obtain a beam with a high degree of symmetry and energy concentration while minimizing cost and equipment space. In general, the output is circular in nature and is characterized by a single dominant peak. The degree to which the actual output approaches the outlier of the diffraction-limited source can be quantified and this amount can be used to obtain the quality of the output. In particular, the widely used M factor correlates beam resolution with the outlier of the diffraction limit source (ie M ² = 1). The beam quality of the cavity laser unfortunately tends to change with the cavity length (for a given output power level), and the closer M ² is to 1, the better the beam as a result. What is required is therefore a design that combines a relatively high beam quality with a relatively short cavity length.

According to the present invention, cavity lasers exhibit relatively high beam quality despite relatively small cavity lengths (eg 50-53 mm) for high power (eg ≥10 watt) power devices. This enables physically smaller laser and optical assembly configurations without sacrificing performance. In addition, the present invention facilitates the reduction of optical photon interference, which can impair image forming performance. In one embodiment, the laser and optical assembly utilize an opening formed in the optical shielding element to reduce the divergence of the light beam emitted from the diode pumped laser. This divergent reduced light beam has a “host” laser crystal (eg Nd: YVO ₄ , Nd: GdVO ₄ ,) with a relatively reduced dopant level (eg 0.2-0.5%) to reduce the amount of bulk lens generated therein. Nd: YLF, Nd: YAG) are further focused. This reduced doping level allows absorption of pump energy to occur over longer lengths of crystals, resulting in more uniform crystal heating. The size of the opening associated with the reduced crystal doping level reduces the effective opening of the host crystal; This facilitates the use of an output coupler / lens with a moderate curvature which in turn reduces the length of the laser cavity. In addition, the length of the crystal can be reduced (e.g., 12mm to 10mm) so that the characteristics of the light beam radiating onto the recording medium can be controlled by selecting a specific output coupler in addition to the specific crystal. The second opening is preferably disposed between the crystal and output coupler to reduce the amount of cavity noise and to improve the mode quality (eg, M ² ).

When used in a recording system, the light beam emitted from the laser system is responsible for the amount of back reflection (which may damage the laser and / or cause undesirable over or under exposure of the recording medium) and / or operation of the laser. To reduce other undesirable interferences (eg, ionized gas plasma and debris plume that may be caused by thermal decomposition within the recording medium) that may adversely affect and degrade desired image quality, the recording medium may be vertically Rather than hitting, it may be guided to the recording medium according to a predetermined angle of incidence. In one particular useful embodiment, the light beam emitting from the laser system onto the recording medium may range from about 7.5 ° to about 10.0 ° (infrared (IR) or near IR) in addition to the very typical 2 ° incidence angle; This range can vary with respect to ultraviolet light or other wavelengths]. A relatively larger angle of incidence not only protects the laser from undesirable back reflections but also reduces the effects of plume and plasma interference with the beam; It also improves image quality and reduces required image forming power and obtained radiation. As will be apparent to those skilled in the art, plasma / plum shielding using relatively large angles of incidence can be advantageously applied to a wide range of implementations such as laser marking, laser engraving, laser milling and the like.

The use of large offset angles is not suitable for standard practice. For example, in a system for positioning a laser beam using a spinning mirror, the increase in the offset angle is the distance from the center of the spinning mirror to the point at which the beam strikes the cylinder (ie, the distance multiplied by the tangent angle) of the inner cylinder imager. Increase the overall width and distort the optical spot so it is no longer rounded. In addition, the larger angle of incidence reduces the energy absorbed into the layer of the recording medium by, for example, increasing the reflected energy. For this reason, the offset angle is typically minimized. However, the present technology has found that unexpected advantages outweigh conventional disadvantages.

In one embodiment, the disclosed technique utilizes a diode-pumped solid-state laser. In such a system, a multi-mode semiconductor laser (eg with a peak wavelength of 808 nm) pumps host crystals, which may be, for example, Nd: YVO ₄ , ND: GdVO ₄ , Nd: YLF or Nd: YAG. The host crystals in turn convert the highly divergent multimode pump energy into a very low divergence single mode laser beam. The laser resonator cavity is formed by an optical coating on opposite sides of the host crystal and output coupler. Some form of heat treatment is usually provided for host determination. The laser system can be used, for example, to image a removable / semi-removable print member or a transfer type print member.

In accordance with at least some aspects of the disclosed technology, the output of the pumping source is provided to the laser crystal via an optical assembly that includes a beam divergence reduction aperture through the focus lens device and the optical shield. The assembly may also include a second beam divergence reduction opening between the crystal and output coupler. The second opening reduces pump noise due to power supply line variation and mode disturbance, and also stabilizes the cavity. The beam emanating from the second aperture is provided to an acoustic optical modulator (“AOM”), which is then collimated with a primary (and / or zero) beam that is deflected onto the recording medium and a discarded secondary beam. do. The AOM modulates the beam to image on the print medium to create a "dot-on-demand" where the beam hits only the print medium that is required according to the image data. The placement of the beam on the print medium is achieved by a polygon mirror rotating at a fixed speed based on the image forming resolution.

In a removable system, the beam is focused on a "removal layer" of the recording medium designed to volatilize in response to laser radiation. In a delivery system, the beam is focused on the delivery layer. In other cases, the depth of focus of the laser beam provides some tolerance deviation. The depth of focus is then improved by using a high quality (ie low M ² ) single mode laser beam. Therefore, focal depth is important in commercial plate image forming systems, and the present invention provides the focal depth and beam quality essential for small laser packages.

The optical components of the disclosed technology can be mounted in a recording head that can include such multiple assemblies at equally spaced intervals. The controller generates relative movement between the recording head and the recording medium, effectively scans the laser or lasers on the surface, and activates them in the image direction at a suitable point or position adjacent to the area of the recording medium. The controller indexes the recording head after completion of each passage of the printing member by a distance determined by the number of beams emitted from the head and the desired resolution (i.e., the number of pixels per unit length). The pattern of laser activity is determined by the image signal corresponding to the original document or picture that is provided to the controller and copied onto the recording medium to produce a precise negative image or a positive image of the original image. The image signal is stored in the computer as a bitmap data file. Such files may be generated by a raster image processor (RIP) or other suitable means. For example, the RIP may accept input data in a page-description language that defines all the features required to be delivered on the recording medium, or in a combination of the page description language and one or more image data files. The bitmap is configured to form the screen frequency and angle as well as the hue of the color. The components of the disclosed technology can be placed on a press if the imaged plates are ready to print immediately, or a stand-alone CtP plate maker when the imaged plates are removed and transferred to the press. It can be placed on a plate-maker (or "platesetter").

As used herein, the term “plate” or “member” refers to any kind of recording medium or surface capable of recording an image formed by a region exhibiting differential affinity for ink and / or water solution. and; Suitable forms include traditional planar or curved (eg, concave or convex) lithographic plates mounted on a plate cylinder or off-press computer-to-plate (CtP) image forming apparatus of a printing press, but also include a seamless cylinder ( For example, roll surfaces of plate cylinders), endless belts or other devices.

In general, in one aspect, the invention features an apparatus for image forming a laser response recording medium. The apparatus includes an optical shielding element having an opening formed through a source that emits a radiation beam. The opening makes it possible to deliver only a portion of the beam, indicating a reduced dispersion compared to the beam where the delivered portion has entered the opening. The apparatus further includes a crystal for receiving radiation exiting the opening. The crystal forms a single mode radiation beam having an effective aperture based at least in part on the size of the aperture and the level of doping of the crystal. The apparatus further includes an output coupler that receives the single mode light beam formed by the crystal and forms a resonator cavity.

In various embodiments of the present invention, the radiation beam has a substantially infrared wavelength. In addition, the opening may have a diameter in the range of about 5.0 to 6.5 mm. In addition, the crystals may correspond to Nd: YVO ₄ crystals, Nd: GdVO ₄ crystals, Nd: YLF crystals and / or Nd: YAG crystals, as well as dopant levels in the range of about 0.2% to 0.5% with a length of about 10 mm. It may also indicate. The resonator cavity may have a length in the range of 50-53 mm. In some embodiments, the single mode light beam exiting the output coupler is focused onto the recording medium at an angle of incidence in the range of about 7.5 to 10.0 °.

In one embodiment of this aspect of the invention, the apparatus includes a second optical shielding element having a second opening formed therethrough, the opening resonator cavity to reduce modal power disturbance and block unwanted modes. Is located within. The second opening has a diameter in the range of about 0.02 to 0.05 inches (0.508 to 1.27 mm).

Generally, in another aspect of the present invention, the present invention provides a method of forming a single mode light beam and focusing the single mode light beam on a predetermined position of the recording medium at an angle of incidence in the range of about 7.5 to 10.0 °. A method of image forming a laser responsive recording medium comprising a.

In another aspect of the present invention, the present invention includes the steps of emitting a radiation beam and guiding the beam through an optical shielding element having an aperture formed therethrough, the beam being partially adapted to reduce beam divergence. And a method of transmitting laser radiation to transmit only the beam of light. The method further includes guiding the transmitted portion of the beam forming a single mode spinning beam having an effective opening based at least in part on the size of the opening and the level of doping of the crystal. The method further includes forming a resonator cavity using a single mode light beam formed by the crystal to produce a laser output. In various embodiments, the method further includes interposing a second optical shielding element having a second opening formed through the resonator cavity to reduce modal power disturbance and block unwanted modes.

The disclosed technique can be advantageously applied to environments other than printing. Indeed, any application requiring a high quality modulated laser beam may benefit from the approach described herein. Such applications include cutting, engraving, marking, soldering, medical treatment, and the like.

The foregoing discussion may be more readily understood from the following detailed description of the disclosed technology, taken in connection with one drawing, which schematically illustrates the basic components of the disclosed technology of a representative embodiment.

Unless otherwise specified, the illustrated embodiments may be understood to provide representative features that vary in detail in any embodiment, and therefore unless otherwise specified, features, components, processes, modules, data elements, and / or drawings in the figures. Or aspects may be combined, interconnected, arranged in succession, separated, interchanged, and / or rearranged in another manner without departing from the disclosed system or method. In addition, the shape and size of the components are also exemplary and may be changed without affecting the disclosed technology unless otherwise specified.

For the purposes of this disclosure, the term “substantially” is intended to the extent that it does not significantly affect the disclosed methods and systems, as well as precise relationships, conditions, arrangements, orientations and / or other properties, and is commonly used in the art. It is also interpreted broadly to dictate the deviations of those understood by those with knowledge of.

In one embodiment with reference to FIG. 1, a laser-removed / semi-removable recording system 100 incorporating in at least some aspects of the disclosed techniques may be combined with lithographic plate blankets or other graphic art constructs that may be secured to a support during image formation. It can be used for forming an image on the same recording medium 102. In the illustrated embodiment, this support is a cylinder 104 or other suitable configuration, such as a typical planar or curved support (eg, concave or convex cylinder) in which the recording medium 102 is disposed around and inside. If desired, the cylinder 104 may be directly included in the design of a conventional lithographic press or CtP freestanding device that serves as a plate cylinder. The cylinder 104 is supported within the frame and may be rotated by standard electric motors or other conventional means, although not required. As the cylinder rotates, each position of the cylinder 104 is monitored by a shaft encoder coupled with the detector 106. All or part of the optical components of the disclosed technology described below may be mounted in the recording head to move on a lead screw and guide-bar assembly (not shown) across the recording medium 102. The axial movement of the recording head is due to the rotation of a motor (not shown) which rotates the lead screw and indexes the recording head after each pass over the cylinder 104. If desired, the printing member may instead be mounted inside the stationary cylinder.

The imaging shaping radiation striking the recording medium 102 to affect the image direction scanning may include one or more diode-pumped solid state laser systems (“DPSS”) comprising a pump laser 112 and a host laser crystal 115. Start at The optical components described below are compact features that concentrate the entire laser output onto the recording medium 102 resulting in high efficiency power density. The DPSS operates at a constant power when in the image forming mode. Image data source (eg, computer) 120 provides image forming data to control electronics 122 operating RF modulator driver 125 to generate an image forming burst. The RF driver 125 controls an acousto-optic modulator (AOM) 130 which in turn modulates the laser beam to transfer image information onto the recording medium 102. In particular, when the image forming data instructs recording on the recording medium, the AOM 130 deflects the laser beam with an optical path leading to the recording medium 130; When the laser 110 is inversely adjacent to the point of imaging, the AOM 130 is not activated and the beam is guided through the reflective beam block 134 to the laser power detector 132. Additional optical elements, not shown, such as a lens between the AOM 130 and the beam block 134 may be employed as appropriate.

The controller 122 receives data from three sources. Each position of the cylinder 140 relative to the laser output is always monitored by a detector 106 that provides a signal indicative of the position to the controller 122. In addition, the image data source 120 also provides a data signal to the controller 122. The image data forms points on the recording medium 102 in which the image spot is recorded. Therefore, the controller 122 reports the instantaneous relative position of the laser 110 and the recording medium 102 (by the detector 106) to operate the RF driver 125 at an appropriate time during the scanning of the recording medium 102. Correlate with image data. The controller 122 also governs the rotation of the mirror 136 to determine the final placement of the beam on the recording medium 102 and the angle of incidence thereto. The drivers and control circuits required to implement this configuration are known in scanner and plotter technology; Suitable designs are described in '092 Patent and US Pat. No. 5,174,205, which is incorporated herein by reference in its entirety. The controller 122 also receives feedback from the laser power detector 132. The power detector 132 monitors the output power of the DPSS laser 110 and supplies this information to the controller 122 via the feedback circuit 140. The controller 122 then steers the current to the pump laser 112 to maintain a constant laser output power. The laser beam attenuator / shutter 142 may be located in an optical path leading to the recording medium 102. The laser beam will thereby be prevented from reaching the recording medium 102 while allowing the DPSS laser 110 to maintain optical and thermal stability for a quick response to an "on-demand" image forming signal. This increases the throughput of the on-press image forming apparatus as well as the throughput of the CtP offset-press image forming apparatus.

The output of the laser 112 (which emits directly or through the fiber bundle 145) pumps the laser crystal 115, which is actually the radiation of the crystal 115 reaching the recording medium 102. Various types of laser crystals can serve as the host 115 in accordance with the present invention as long as the laser emits with a suitable conversion efficiency and a given beam quality at a given imaging wavelength. Preferred crystals are doped with rare earth elements, mostly neodymium (Nd), and include Nd: YVO ₄ , Nd: GdVO ₄ , Nd: YLF and Nd: YAG crystals.

One or more lenses 150 concentrate the laser 112 output onto the pump face 152 of the crystal 115; For example, the diameter of the beam striking the pump surface 152 may be 500 μm. The radiation diverges when exiting the fiber bundle 145 or the laser source 112. In general, divergence along the short or “fast” axis shown in FIG. 1 (expressed as “open number” or NA) is primarily considered; This divergence can be reduced using divergence diminishing lenses located where the beam exits the fiber bundle 145, and / or at least a portion of the light beam emitted from the pumping laser 112 is exposed to the optical shield 156. By passing through an opening 154 formed therein. For example, if a divergence reducing lens is used, the divergence reducing lens may be a glass rod segment of essentially proper diameter in a cylinder lens, but other optical devices, such as lenses with hemispherical cross sections or that correct both fast and slow axes, are also advantageous. Can be used. The optical shield 156 may include a highly reflective and / or reflective surface 158 that guides unwanted light away from the crystal 115.

Lens 150 may focus radiation emitted from aperture 154 (and / or divergence diminishing lens) onto pump face 152 of laser crystal 115. The opening 154 serves to reduce M ² of the laser output beam when using short cavity lengths. In general, the pump surface 152 of the crystal 115 has a mirror coating that allows the incidence of radiation from the pumping source 112 of a predetermined wavelength and reflects the laser radiation wavelength of the host crystal inwards. The other axial surface has an AR coating 160 that allows maximum transmission of the laser radiation wavelength through the output face of crystal 115.

The output of the crystal 115 strikes the curved surface 162 of the output coupler 165, which may be a convex device (as shown) or may assume other geometry. Similar to face 152 of crystal 115, face 162 accommodates a mirror coating that reflects a portion of the laser radiation wavelength, and the two coatings facilitate internal reflection that characterizes laser amplification. The other emitting surface 168 of the output coupler 165 has an AR coating that limits surface power loss. In one embodiment, the pump face 152 receives an HR / HT coating while the coupler face 162 receives a PR / HR coating. For example, the coating can strongly reflect the output radiation, thereby confining it to form the resonator cavity 170, during which the input radiation is transmitted from the pumping laser 112.

Other focal elements not shown convey the output of the host decision 115 to the recording medium 102 via the rotating mirror 136. The rotating mirror may or may not be part of the translating recording head, and its rotation (and consequently on the beam guided medium 102) is governed by the controller 122 as described above. . When the beam strikes the recording medium 102, it causes removal of the image forming layer or transfers material from the donor to the acceptor sheet. The power output of the host crystal 115 can be quite large, for example 10 watts or more.

The function of the host laser crystal 115 is to generate a low-NA laser beam from the energy provided by the pump laser 112. In general, crystal 115 is preferably (but not necessarily) a planar-planar monolithic structure of "thermal lensing" material. Optical power delivered to the pump face 152 deforms the opposing faces 152, 160 to a convex surface. As already noted, to produce a well formed image forming spot, it has an output divergence as close as possible to the divergence of the diffraction limit source (i.e., M ² = 1), and a single transverse mode of operation (preferably Lowest order, basic TEM ₀₀ mode).

An important problem addressed by the present invention is the fact that beam quality is likely to degrade when the cavity length becomes short. Short cavity lengths reduce the space of the laser image forming assembly, but at the same time the beam quality is likely to deteriorate. High beam quality (eg, M ² ≦ 1.25) and long focal depth are important for the quality of image forming to accommodate the tolerance sums that characterize commercial image forming systems. The first piece used to improve beam quality at short cavity lengths is the optical shield 156 and aperture 154 described above. The diameter of the opening 154 may be in the range of 5.0 to 6.5 mm depending on the degree of divergence of light exiting the pump laser 112, for example. The second method is a decrease in the dopant level of crystal 115. Typical dopant levels are on the order of 1%. However, according to the present technology, the dopant level is in the range of about 0.1-0.75%, preferably about 0.2-0.5%. This reduces the amount of thermal lenses in the crystal 115 and readily uses shorter cavity lengths through the use of optical couplers 165 with increased curvature and reduced reflective coatings. A third factor in improving beam quality is the opening 172 formed in the laser cavity 170. In particular, an optical shield 174 with a penetrating opening 172 is disposed between the host crystal 115 and the output coupler 165. The opening 172 is large enough to pass through the basic (primary) mode of the laser, but blocks a higher order mode that degrades beam quality. In particular, the effective opening of the crystal 115 is a function of the opening 154 formed in the optical shield 126 and the dopant level of the crystal 115 and the internal cavity opening 172. In one embodiment, DPSS 110 has an aperture 154 of 6.5 mm (selected to accommodate high numerical aperture of light from the laser pump source), a dopant level of about 0.5%, and a diameter of 0.031 in (0.7874 mm). Having an internal cavity opening 172. These parameters facilitate the use of 53mm cavities and power levels above 10watt at M ² ≤1.25.

The length l of the crystal 115 can also be reduced so that selecting a particular output coupler in addition to the particular crystal can control the characteristics of the light beam that scans the recording medium 102 (eg, from standard 12 mm to 10 mm). At least 6 mm). The minimum crystal length is based on the need to remove heat from the crystal during operation. The crystals are metallized or soldered to the housing on an unpumped surface to promote thermal conductivity (and heat removal) by direct contact. This reduces the volume or thermal lens, thereby improving the quality of the laser beam. Metal coating of crystals for thermal conduction is known in the art and is described, for example, in US Pat. No. 5,822,345, which is incorporated herein by reference in its entirety.

In addition, according to the present specification, debris plume and ionized gas plasma generated by thermal decomposition of the target section of the recording medium 102 in response to laser radiation block adjacent areas of the target section, making them unstable and non-conforming. This results in uniform image formation. In order to address the plasma and / or plume blocking or optical interference problems encountered during relatively fast image formation, the present invention provides a typical angle of incidence of the beam onto the printing member from 2 ° to 7.5 ° or more, preferably from 7.5 ° to 10 °. Increase. This is achieved directly by simply adjusting the angle of the mirror 136 relative to the surface of the recording medium 102.

The terms and phrases employed herein are used as the term describing, but not limiting, and are not intended to exclude any equivalent of the features or portions shown and described in the use of such terms and expressions, and various modifications are claimed. It is understood that this is possible within the scope of the present invention.

Claims (20)

An apparatus for forming an image on a laser responsive recording medium, A source that emits a radiation beam, An optical shielding element having an opening formed therethrough; Determining to receive radiation exiting the opening; An output coupler receiving a single mode light beam formed by the crystal and forming a resonator cavity with the crystal, The opening allows only a portion of the beam to pass through, and the transmitted portion exhibits a reduced divergence relative to the beam incident on the opening, Wherein the crystal forms a single mode radiation beam having an effective aperture based at least in part on the size of the aperture and the level of doping of the crystal. The method of claim 1, further comprising a second optical shielding element having a second opening formed therethrough, And the opening is disposed within the resonator cavity to reduce modal power disturbances and block unwanted modes. The device of claim 2, wherein the second opening exhibits a diameter in the range of about 0.02 to 0.05 in (0.508 to 1.27 mm). The apparatus of claim 1, wherein the radiation beam has a substantially ultraviolet wavelength. The device of claim 1, wherein the opening has a diameter in the range of about 5.0 to 6.5 mm. The apparatus of claim 1, wherein the crystal corresponds to at least one of an Nd: YVO ₄ crystal, an Nd: GdVO ₄ crystal, an Nd: YLF crystal, and an Nd: YAG crystal. The device of claim 1, wherein the crystal exhibits a dopant level in the range of about 0.2% to 0.5%. The apparatus of claim 1, wherein the crystal has a length of about 10 mm. The apparatus of claim 1, wherein the resonator cavity has a length in the range of about 50-53 mm. The apparatus of claim 1, wherein the single mode light beam exiting the output coupler is focused onto the recording medium at an angle of incidence in the range of about 7.5 to 10.0 °. A method of forming an image on a laser responsive recording medium, Forming a single mode light beam, Focusing the single mode light beam onto a recording medium at an angle of incidence in the range of about 7.5 to 10.0 °. Method of delivering laser radiation, Emitting a radiation beam, Guiding the beam through an optical shielding element having an opening formed therethrough; Guiding the transmitted portion of the beam to a crystal, Forming a resonator cavity utilizing the single mode light beam formed by the crystal to produce a laser output, The opening allows penetration of only a portion of the beam to reduce beam divergence, Wherein the crystal forms a single mode radiation beam having an effective aperture based at least in part on the size of the aperture and the level of doping of the crystal. 13. The method of claim 12, further comprising interposing a second optical shielding element with a second opening formed through the resonator cavity to reduce modal power disturbance and block unwanted modes. The method of claim 13, wherein the second opening has a diameter in the range of about 0.02 to 0.05 inches (0.508 to 1.27 mm). The method of claim 12, wherein the radiation beam has a substantially ultraviolet wavelength. The method of claim 12, wherein the opening has a diameter in the range of about 5.0 to 6.5 mm. The method of claim 12, wherein the crystal corresponds to at least one of an Nd: YVO ₄ crystal, an Nd: GdVO ₄ crystal, an Nd: YLF crystal, and an Nd: YAG crystal. The method of claim 12, wherein the crystals exhibit a dopant level in the range of about 0.2% to 0.5%. The method of claim 12, wherein the crystal has a length of about 10 mm. The method of claim 12, wherein the resonator cavity has a length in the range of about 50-53 mm.

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