Multifrequency room-temperature continuous diode and Ar laser-pumped Er3+ laser emission between 2.66 and 2.85 μm

cw pumped laser emission on six different wavelengths is obtained for the first time in a LiYF4:15% Er3+ crystal at room temperature under diode laser excitation for 2.66, 2.716, 2.81 μm emissions and under argon ion laser excitation for 2.77, 2.81, 2.84, 2.85 μm emissions. Threshold of 5 mW absorbed power at 0.795 μm (diode) is obtained for the 2.81 μm wavelength. Time and power evolution of the laser emissions are presented. The type of up-conversion taking place during 2.81 μm laser emission is shown to be of the addition of photons by energy transfer (APTE) type involving a two-photon summation which depopulates the 4I11/2 rather than the 4I13/2 state as up to now believed.