 With the war over , Haber 's Kaiser Wilhelm Institute now returned to research , and Haber offered Franck a job . His new post came with more pay , but was not a tenured position . It did however allow Franck to pursue his research as he wished . Working with new , younger collaborators such as Walter Grotrian , Paul Knipping , Thea Krüger , Fritz Reiche and Hertha Sponer , his first papers at the Kaiser Wilhelm Institute examined atomic electrons in their excited state , results that would later prove important in the development of the laser . They coined the term " metastable " for atoms spending an extended time in a state other than that of least energy . When Niels Bohr visited Berlin in 1920 , Meitner and Franck arranged for him to come to the Kaiser Wilhelm Institute to talk with the younger staff without the presence of the bonzen ( " bigwigs " ) . 
