Abstract

High power diode lasers are the most efficient devices for converting electrical input power into optical output power. Further increased power conversion efficiency, η_E, is crucial to reduce energy use in large laser systems. Operation at heat sink temperatures, T_HS < 0°C leads immediately to higher η_E, and is of particular interest for extremely high energy systems where cryogenic cooling of the pumped laser medium is often required [1]. Lower T_HS increases the optical gain in the diode laser and reduces non-radiative recombination, lowering threshold and increasing slope, with external quantum efficiency, η_D →1 as T_HS→0 K [2]. A peak value of η_E = 85% has been reported at T_HS = −50°C for short-cavity (L = 1 mm) single emitters with low output power P_out < 5 W at an emission wavelength of λ = 975 nm and stripe width W = 200 µm [2]. For reference, long cavity (L = 4 mm) high power devices with W = 100 µm deliver 15 W with η_E = 65% at T_HS = 25°C [3].

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