1240 nm diamond Raman laser operating near the quantum limit

Abstract

An external-cavity diamond Raman laser generating up to 2.0 W at 1240 nm from 3.3 W of 1064 nm pump power is investigated as a function of pump polarization direction. The maximum conversion efficiency was 61%, and the slope efficiency of 84% closely approaches the quantum limit of 85.8%. The lowest threshold for Raman lasing is achieved for pump polarization parallel to the <111> axis, which we show is consistent with theory.

Characterization of Single-Crystal Synthetic Diamond for Multi-Watt Continuous-Wave Raman Lasers

“…In this case, the maximum and minimum Raman scattering efficiencies predicted by (2) do depend on the pump polarisation angle, and the minimum Raman scattering efficiency is in general non-zero. The absolute maximum value of the Raman scattering efficiency is 33% higher than that of the <100>-cut diamond, in accordance with [17] and the experimental data presented above (Fig. 5 (b)).…”

“…In line with the theory presented below, and as observed by Sabella et al [17] in measurements of Raman laser threshold, the gain in <110>-cut diamond, when the pump and probe are co-polarised along a <111> direction (i.e. at 54.7º to a <100> direction), should be 33% higher than if the pump and probe polarisations are perpendicular and the pump polarisation is along <100> direction.…”

“…There was also a wedge of 0.9º between the end faces, further reducing the likelihood of resonance. Both theory [35,36] and recent experimental results [17] indicate that Raman gain in diamond is dependent on both the propagation direction and the polarisation of the pump and probe with respect to the crystallographic axes. Therefore, the relative Raman gain in diamond for propagation along both <100> and <110> directions was measured as a function of crystal orientation with respect to the pump and probe beam polarisation.…”

“…Recent developments in chemical vapour deposition growth have led to material with low birefringence and low absorption through the minimisation of the dislocation density and nitrogen impurities respectively [20,21]. This has made the intracavity use of diamond in solid-state lasers more practical -as a heat spreader [28,29] and in Raman lasers [11,[15][16][17][18].…”

“…This is compounded by the low thermal conductivity of common Raman laser crystals. As a result there is considerable interest in the use of diamond as a Raman laser material, both in pulsed [15][16][17] [11,18]. This work is motivated by the exceptional thermal properties of diamond [19] and enabled by the recent development of high optical quality synthetic diamond grown by chemical vapour deposition [11,20,21].…”