We report our investigations on measuring the energy transfer upconversion (ETU) parameter in various neodymiumdoped laser crystals (YAG, YVO4, GdVO4, KGW, and YLF) via the z-scan technique. Starting with a simple two-level macro-parameter spatially dependent rate equation model we obtain a good correlation for Nd:YAG at different concentrations and crystal temperatures, however the other crystals illustrate significant deviation between simulation and measurement. Currently we attribute this difference to additional ion-ion interactions in the respective samples, for which a more detailed model is currently being considered. Of the tested materials Nd:YAG appears to have the lowest ETU macro parameter, at around 0.35 x10-16 cm3/s for a 0.6 at.% doping concentration, compared with nominally thrice this for 0.5 at% Nd:YLF and almost an order of magnitude higher for the 0.5 at.% vanadates (YVO4 and GdVO4). These values are significant for determining additional heat load in the respective gain media, especially when trying to increase the output power/energy from lasers employing these crystals, typically achieved by increasing the pump and cavity mode size.
We present our measurements of the key spectroscopic properties over the temperature range of 77 K to 450 K for Nd3+ ions doped in Y3Al5O12 (YAG). From room to liquid nitrogen temperature (LNT), the peak absorption cross section
around 808 nm increased by almost 3 times, in conjunction the bandwidth of this absorption line reduced by the same
factor. At LNT the peak of the absorption line was blue shifted by 0.25 nm with respect to that at 300 K. The
fluorescence spectrum between 850 nm – 1450 nm was measured, from which the emission cross sections for the three
main transitions were calculated. One note of particular interest for the dominant emission wavelengths around 1064nm
and 1061nm (4F3/2 → 4I11/2) was the switch in their relative strength below 170K, and at LNT the 1061 nm line has
almost twice the cross section as at 1064nm.. The fluorescence and lifetime of the upper laser level (4F3/2) was measured
and the effective emission cross section determined by the Fuchtbauer-Ladenburg (F-L) method. The effective emission
cross section for 946 nm (R1 → Z5) increased by more than two times over the 300 K to 77 K range. A numerical fit for the temperature dependent emission cross section at 946 nm and 1064 nm and also calculated absorption coefficient at 808 nm pump diode laser have also obtained from the measured spectroscopic data.
We present the determination of the energy transfer upconversion (ETU) coefficient for Nd:YAG via the z-scan
technique, achieved by studying the irradiance dependence of the transmission of a pump laser tuned to the absorption
peak around 808 nm. A spatially dependent two-level rate equation model has been utilized to predict the transmission
dependence as a function of the sample’s position in the z-scan experiment, with the ETU coefficient the only free
parameter. Comparing experimental results with the model’s output, the ETU coefficient for 1 at.% Nd:YAG is
determined to be 5.1 ± 0.4 x 10-17 cm3/s.
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