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High-power dense wavelength division multiplexing (HP-DWDM) of frequency stabilized 9xx diode laser bars with a channel spacing of 1.5 nm

: Hengesbach, S.; Holly, C.; Krauch, N.; Witte, U.; Westphalen, T.; Traub, M.; Hoffmann, D.


Zediker, M.S. ; Society of Photo-Optical Instrumentation Engineers -SPIE-, Bellingham/Wash.:
High-power diode laser technology and applications XII : 2 - 4 February 2014, San Francisco, California, United States
Bellingham, WA: SPIE, 2014 (Proceedings of SPIE 8965)
ISBN: 978-0-8194-9878-6
Paper 89650C, 9 S.
Conference "High-Power Diode Laser Technology and Applications" <12, 2014, San Francisco/Calif.>
Fraunhofer ILT ()

We present a compact High-Power DenseWavelength Division Multiplexer (HP-DWDM) based on Volume Bragg Gratings (VBGs) for spectrally stabilized diode lasers with a low average beam quality M2 50. The center wavelengths of the five input channels with a spectral spacing of 1.5 nm are 973 nm, 974.5 nm, 976 nm, 977.5 nm and 979 nm. Multiplexing efficiencies of 97%±2% have been demonstrated with single mode, frequency stabilized laser radiation. Since the diffraction efficiency strongly depends on the beam quality, the multiplexing efficiency decreases to 94% (M2 = 25) and 85%±3% (M2 = 45) if multimode radiation is overlaid. Besides, the calculated multiplexing efficiency of the radiation with M2 = 45 amounts to 87:5 %. Thus, calculations and measurements are in good agreement. In addition, we developed a dynamic temperature control for the multiplexing VBGs which adapts the Bragg wavelengths to the diode laser center wavelengths. In short, the prototype with a radiance of 7 0GWm-2 sr-1 consists of five spectrally stabilized and passively cooled diode laser bars with 40Woutput after beam transformation. To achieve a good stabilization performance ELOD (Extreme LOw Divergence) diode laser bars have been chosen in combination with an external resonator based on VBGs. As a result, the spectral width defined by 95% power inclusion is < 120pm for each beam source across the entire operating range from 30 A to 120 A. Due to the spectral stabilization, the output power of each bar decreases in the range of < 5 %.