Johnson noise thermometry of optically excited hot electrons in hBN encapsulated graphene

Hot electrons in graphene have unique thermal properties. Owed to graphene's unique combination of an exceedingly low electronic heat capacity and a strongly suppressed electron-phonon thermal conductivity G$_{\mathrm{th}}$, the electronic and phononic temperatures can be highly decoupled. Through space and time resolved laser excitation and a Johnson noise read out we can directly measure the spatial and time dependence of G$_{\mathrm{th\thinspace }}$and estimate the electronic heat capacity of graphene C$_{\mathrm{e}}=\tau $G$_{\mathrm{th}}$. We use these insights to design a photonic crystal integrated graphene bolometer with a NEP \textasciitilde 1pW/Hz$^{\mathrm{1/2}}$, a response time of \textasciitilde 1ps and a high operation temperature of 20K.