Martin W¨olz, Agnieszka Pietrzak, Alex Kindsvater, Jens Meusel, Klaus Stolberg, Ralf H¨ulsewede, J¨urgen Sebastian, Valentin Loyo-Maldonado, "Laser diode stacks: pulsed light power for nuclear fusion," High Power Laser Sci. Eng. 4, 02000e14 (2016)
- High Power Laser Science and Engineering
- Vol. 4, Issue 2, 02000e14 (2016)
Fig. 1. Pump diode pulse energy levels of HEC-DPSSL installations, sorted by pump wavelength. Solid symbols: systems proven or under construction. Empty symbols: systems at design level.
Fig. 2. Illustration of Jenoptik’s 940 nm laser diode bar portfolio. For a given technology, the output power is linear with chip size. The New Generation (NG) QCW bars increase output power from 300 to 500 W at the fixed resonator length of 1.5 mm.
Fig. 3. 808 nm QCW laser diode: output power-versus-current characteristic and efficiency.
Fig. 4. Life testing of 808 nm 500 W QCW bar in constant current mode. The bars are mounted on microchannel heatsinks with $T_{c}=25\,^{\circ }\text{C}$ , ${\it\tau}=300~{\rm\mu}\text{s}$ , $f=100$ Hz.
Fig. 5. 880 nm QCW laser diode: light output power-versus-current characteristic and wall-plug efficiency.
Fig. 6. Reliability testing of the 880 nm QCW laser diode in constant current mode, mounted on microchannel heatsinks. $T_{c}=25\,^{\circ }\text{C}$ , ${\it\tau}=300~{\rm\mu}\text{s}$ , $f=100~\text{Hz}$ .
Fig. 7. Power–voltage–current characteristics of 940 nm laser bars with 75% filling factor and 1.5 mm resonator length. ${\it\tau}=1~\text{ms}$ , $f=60~\text{Hz}$ , 6% duty cycle, $T_{c}=25\,^{\circ }\text{C}$ .
Fig. 8. Comparison of epitaxial structures for kW-class laser bars. The NG structure used in the 500 W bars is compared to structure C. ${\it\tau}=1~\text{ms}$ , $f=10~\text{Hz}$ , $T_{c}=25\,^{\circ }\text{C}$ .
Fig. 9. Wall-plug efficiency of 940 nm laser bars based on the NG epitaxial structure optimized structure C.
Fig. 10. Photograph of JenLas®QCW Cool laser diode stack with 8 laser bars spaced at 1.7 mm pitch.
Fig. 11. Cross-section of actively cooled QCW stack on mount with illustration of the water passage.
Fig. 12. Transient thermal behaviour of the passively cooled QCW stack, showing the thermal impedance $Z_{\mathit{th}}(t)$ of one laser bar. The CW operating temperature is attained after 3 s.
Fig. 13. Temperature gradient in pulsed operation of the QCW stack with power dissipation of 1 W per bar during ${\it\tau}=300~{\rm\mu}\text{s}$ . The solid lines denote the exact temporal evolution. The dashed lines show the product of $R_{\mathit{th}}$ and the duty cycle.
Fig. 14. Pump power densities achieved with commercially available laser diodes. Squares: JENOPTIK, circles: NGCEO ARR179P6000HDS and Quantel QD-Q5912-B.
Fig. 15. Electro-optical data of a passively cooled QCW stack with eight laser bars emitting at 880 nm, ${\it\tau}=300~{\rm\mu}\text{s}$ , bar-to-bar pitch 1.7 mm, duty cycle (d.c.) varied between 1% and 10%. (The step in efficiency at 450 A is a measurement artefact.)
Fig. 16. Worldwide production capacities for GaAs LEDs and laser bars. InGaAlP (red) LED production capacity from Ref. [22]. LIFE and HiPER one-time demands from Table 1 , assuming 220 bars per $4^{\prime \prime }$ wafer.
Fig. 17. Functionalities of a diode laser pump.
Fig. 18. Utilization aspects of standardization at different levels.
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Table 1. Inertial fusion laser requirements on pump diodes.
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Table 2. Jenoptik QCW laser diode bar specifications. All devices possess 37 emitters with a fill factor of 75%.
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