 Samarium @-@ doped calcium fluoride crystals were used as an active medium in one of the first solid @-@ state lasers designed and constructed by Peter Sorokin ( co @-@ inventor of the dye laser ) and Mirek Stevenson at IBM research labs in early 1961 . This samarium laser emitted pulses of red light at 708 @.@ 5 nm . It had to be cooled by liquid helium and thus did not find practical applications . 
