The development of didoe-pumped self-frequency doubling (SFD) YCA4O(BO3)3 (YCOB) crystals doped with ND3+ or YB3+ ions offers an attractive alternative to traditional intra-cavity doubling techniques using a separate non-linear crystal. Here, we summarize the progress of scaling SFD lasers to higher powers. Moreover, we examine the potential and limitations of these devices. While SFD lasers are potentially more compact and less costly, scaling to higher powers in the visible region requires careful assessment of mode matching and cavity mode brightness. Combining optical gain and frequency conversion in the same material requires a compromise between the ideal cavity mode for mode matching and generating the largest available power density of the laser mode for optimum frequency doubling. The lack of adjustment of the cavity mode inherently limits scaling of SFD laser operation when using low brightness high power laser diodes. We have employed a new source developed by Polaroid Corp. using multiple high-brightness laser diodes to investigate the potential of increasing SFD laser output. We have then compared the efficiency of this novel pump technique to a single diode pumped system to determine the importance of brightness of the pump source to SFD operation.
This paper describes a novel, high-brightness, multi-laser- diode system that provides great flexibility for use in a wide array of applications. The system consists of eight individual, field-replaceable laser diodes, whose outputs are optically combined to provide a collimated beam. Field replaceability of the diodes and mechanical robustness of this system make it particularly suitable for highly demanding environments. CW optical power greater than 90 Watts at 915 nm was focused to a spot size of 140 X 130 micrometer and a numerical aperture of 0.22 NA. This high CW power density (approximately 5 X 105 W/cm2) was achieved by polarization coupling of two multi-laser-diode systems. Optical power in excess of 52 W was obtained from a single-end pumped, grating stabilized Yb:fiber laser at 1100 nm. This paper will also present results on digital printing, CD-RW disk initialization and solid-state laser pumping. A unique feature of this system is the ability for direct-diode coupling to fiber, eliminating any splicing or connector- related losses.
This paper deals with the opto-mechanical configuration of a newly developed high-speed initializing system for phase change recording media such as CD-RW, DVD-RAM, and DVD-RW. The mechanical layout of the system that ensured the mechanical alignment of each diode laser to be field replaceable. With the unique optical configuration implemented, up to six field- replaceable high-power diode lasers of wavelength 840 nm can be simultaneously installed onto this newly developed system. When all six diode lasers were installed, the internal anamorphic optical system can project the near-field intensity distribution of the high power diode lasers into a large 180 micrometer by 3 micrometer spot size while maintaining enough initialization laser power and providing large depth of focus. In this operational configuration, the system is capable of converting the standard outer diameter of 120 mm phase change optical disk from its originally sputtered amorphous state to initialized crystalline state in less than 20 seconds, which is approximate 2 to 3 times faster than today's commercially available system.
This paper discusses a high-brightness multi-laser source developed at Polaroid for such applications as coupling light to fibers, pumping fiber lasers, pumping solid state lasers, material processing, and medical procedures. The power and brightness are obtained by imaging the nearfields of up to eight separate multi-mode lasers side by side on a multi-faceted mirror that makes the beams parallel. The lasers are microlensed to equalize the divergences in the two principal meridians. Each laser is aligned in a field- replaceable illuminator module whose output beam, focused at infinity, is bore-sighted in a mechanical cylinder. The illuminators are arranged roughly radially and the nearfields are reimaged on the mirror, which is produced by diamond machining. The array of nearfields is linearly polarized. A customizable afocal relay forms a telecentric image of the juxtaposed nearfields, as required by the application. The lasers can be of differing powers and wavelengths, and they can be independently switched. Light from other sources can be combined. The output can be utilized in free space or it can be coupled into a fiber for transport or a fiber laser for pumping. A linearly polarized free space output can be obtained, which allows two units to be polarization combined to double the power and brightness.
High power laser diodes have been continuously gaining more practical applications. In the majority of these applications, device performance is a determining factor. However, device reliability determines whether a laser diode can be successfully introduced in a commercial product. We review some device reliability problems and their solutions found through customer experience while supplying packaged high power AlGaAs/GaAs quantum well laser diodes, utilized in medical, high resolution printers. The reliability problems were related to either photo-induced chemical reactions on the output facet leading to visible optical damage or the propensity of the material to rapidly develop dark line defects. To improve the reliability of high power laser diodes, we have performed numerous aging studies, followed by detailed failure mode analysis. Both hermetically packaged devices and devices exposed to air ambient were evaluated. The devices whose parameters deteriorated during aging were examined with optical microscopy, infrared microscopy, scanning electron microscopy, Auger spectroscopy, residual gas analysis and also electron beam induced current. We report the results of the failure mode analysis and suggest solutions to eliminate failures of high power laser diodes.
Packaged life testing of laser diodes revealed a dramatic degradation of product lifetime. Failure analysis revealed the presence of carbon based compounds deposited on the emission regime causing catastrophic failure. This phenomenon was limited to packaged product. Testing was begun to identify the source, understand the mechanism, and initiate corrective action. Analysis revealed that the epoxy used in assembly was the dominate source of carbon. Contaminated epoxy had been introduced into production by a material batch change at the vendor. It was also learned that deposition only occurred in the dry, oxygen free atmosphere of a hermetically sealed package. It was necessary to develop incoming test procedures and process monitoring to ensure that material of acceptable quality was used. This paper will discuss test methods and results obtained in controlling this failure mechanism.
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