Optical saturable absorption of conformal graphene directly synthesized on nonlinear device surfaces

•A transfer-free atomic carbon spraying provides large-area uniform surface coverage.•Strong nonlinearities owing to the high percentage of sp2 bonding (73.94 %)•Rapid saturation with the energy-efficient response of the absorber (32.14 MW cm−2).•Conformal graphene greatly outperforms conventional transfer-free spraying process.•Efficient saturable absorption comparable to that of CVD-grown graphene.