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We report on the development of a high brightness laser diode module capable of coupling over 100W of optical power into a 105 µm 0.15 NA fiber at 976 nm. This module, based on nLIGHT's Pearl TM product architecture, utilizes hard soldered single emitters packaged into a compact and passively-cooled package. In this system each diode is individually collimated in the fast and slow axes and free-space coupled into a single fiber. The high brightness module has an optical excitation under 0.13 NA, is virtually free of cladding modes, and has an electrical to optical efficiency greater than 40%. Additionally, this module is compatible with high power 7:1 fused fiber combiners, and initial experiments demonstrated 500W coupled into a 220 µm, 0.22 NA fiber. These modules address the need in the market for higher brightness diode lasers for pumping fiber lasers and direct material processing.

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Rapidly maturing industrial laser applications are placing ever-tighter constraints on spectral width and wavelength emission stability over varying operating temperatures of high power diode laser pump sources. For example, improved power scaling and efficiency can be achieved by pumping the narrow upper laser level of Nd:YAG solid state lasers at 885 nm and the 1532-nm absorption band of Er:YAG solid state lasers, though taking full advantage of these configurations requires wavelength-locked pump sources. nLight offers a wide variety of wavelength-locked diode products based on external volume grating optics technology. It is often believed that the use of external gratings to wavelength lock diode lasers leads to an unavoidable loss in power and efficiency. nLight's design methodology is shown to eliminate the problem in our grating-locked diode laser products. These results are expected to enable improved performance in diode-pumped solid state and fiber laser systems. MOTIVATIONRapidly maturing industrial laser applications are placing ever-tighter constraints on spectral width and wavelengthtemperature control of high power diode laser pump sources. For example, improved power scaling and efficiency can be achieved by pumping the narrow upper laser level of Nd:YAG solid state lasers at 885 nm and the 1532-nm absorption band of Er:YAG solid state lasers, though taking full advantage of these configurations requires diode pump sources with narrowed spectral lines [1,2]. Figure 1 illustrates the absorption spectra of Nd:YAG and Er:YAG at these wavelengths. As shown, the absorption feature at 885 nm in Nd:YAG is < 2.5 nm FWHM and at 1532 nm in Er:YAG is < 1 nm FWHM. The typical unlocked 885-nm broad area diode laser spectral width is ~2.5 nm, with the peak wavelength shifting at ~0.25 nm/°C; at 1532-nm the spectral width of the diode increases to ~6 nm with the peak shifting at ~0.4 nm/°C. Efficient laser systems requiring uniform absorption of the pump light require the diode source be wellmatched (in terms of spectral width and spectral position) to the absorption feature. The drift of operating wavelength with temperature of conventional diode lasers also sets strict requirements on thermal control of the diode pump source. 875 880 885 890 895 Wavelength (nm) Absorption (arb. units) 0 0.5 1 1.5 2 2.5 3 3.5 4 1524 1528 1532 1536 1540 Absorption (arb. units) Wavelength (nm) 0.72nm FWHM Nd:YAG Er:YAG Fig. 1: The absorption spectra of (left) Nd:YAG around 885-nm [1] and (right) Er:YAG around 1532nm [2]. *paul.leisher@nlight.net; phone 360.713.5230; http://www.nlight.net Sponsorship by the High Energy Laser Joint Technology Office (HEL-JTO), Albuquerque, NM is acknowledged

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