Two color laser operation in Er-Ho:YLF

Simultaneous laser operation of two different ions, Ho(3+) and Er(3+), in LiYF4 is demonstrated at 77 K. The upper laser levels are shown to have reversible energy transfer. Measurement of the transfer rate is done spectroscopically. In addition, the upper level populations are shown to obey in a good approximation two simple coupled rate equations. It is noted that the transfer rates in the crystals investigated were lower than desired for efficient energy transfer. Finally, it is suggested that higher concentrations of the rare earth ions or a different host may lead to a more optimum transfer rate.