How do W/cm2 relate to W/kg (used e.g. in https://www.biorxiv.org/content/biorxiv/early/2016/05/26/055699.full.pdf https://www.biorxiv.org/content/biorxiv/early

How do W/cm2 relate to W/kg (used e.g. in https://www.biorxiv.org/content/biorxiv/early/2016/05/26/055699.full.pdf https://www.biorxiv.org/content/biorxiv/early/2016/05/26/055...)? Furthermore, if I have a detector, that gives only the number of W, will it be equal to W/cm2?