This article has two parts: the first part is investigated on Tesla’s claims about unified resonance of alternated current, he said that he could magnify the electromagnetic radiation to that extent to shake and swing Brooklyn bridge in 1898, I reached in this investigation that Einstein has an evident to confirm tesla’s demonstration, this evidence is his equation for stimulated emission. The second part of this paper is investigated on the idea that crossed my mind about finding a connection between Einstein’s stimulated emission and Einstein’s cosmological constant to support my former postulation that Dark Energy is just photon pressure on ordinary matter. In this investigation I found that Dark Energy density has direct relationship to Einstein’s stimulated emission coefficients. The argument of that is expressed like this: since photon is responsible for electron’s jump down onto lower orbital in atom, and I postulate before that Dark Energy is photon pressure, so there is a connection between this phenomenon and that through Einstein’s cosmological constant.