Page 24 - 00. Complete Version - Progress Report IPEN 2014-2016

24 Lasers Technology | Progress Report

ments allowed determining the rate constant ser emission at 3930 nm was performed us-
of the non-radiative energy transfer that hap- ing two pump wavelength, one for the upper
pens due to multipolar interactions between laser level excitation (i.e. 5I8 → 5I5 = →P1) and
donor and acceptor ions in solids. Energy trans- the other for lower laser level de-excitation
fer mechanism involving two interacting erbi- (i.e. 5I6 → 5S2 = →P2). The pump wavelength
um (and holmium) ions in the first (and second) →P1 = 889 nm was chosen to match the funda-
excited state, energy-transfer up-conversion mental absorption of the 5I8 → 5I5 Ho3+ tran-
have (has) been observed and the rate con- sition and the pump wavelength →p2 = 962
stant determined. The aim of this study is the nm was determined based on the measure-
development of solid laser medium emitting ments of ESA and the application of the Mc-
in the mid-infrared (2700 - 3600 nm) and to Cumber method. Critically, the estimated ESA
improve the small signal gain laser emission cross-section at →p2 – 962 nm is approximate-
of Er3+ and Ho3+-doped materials. A detailed ly sixteen times larger than the ground state
investigation of the energy transfer process- (5I8) absorption process. Our calculation sug-
es involving one or two excited Ho3+ ions in gest(s) that even for high Ho3+ concentration
Ho3+-doped InF3 glass has been performed in which cross-relaxation has been shown in
to examine all the energy transfer rates rele- previously to quench the 5I6 level, ESA is nev-
vant to the 5I5 → 5I6 transition at 3930 nm as ertheless strong enough to allow a sufficient
a function of the Ho3+ concentration (2, 4 and population inversion required for practical
10 mol %). The decay times, branching ratios CW laser emission at 3930 nm. A Ho3+ -doped
and rate parameters for the energy transfer(,) InF3 glass with holmium concentration of 10
were measured and they were used as the in- mol% can be used as a practical laser medi-
put parameters for a rate equations analysis. um to generate continuous laser emission at
Excited state absorption (ESA) initiating from 3930 nm using two diode lasers pumping at
the lower laser level of Ho3+ was determined
in this study. Numerical simulation of CW la- 889 and 962 nm as shown by Fig. 6.
A B

Fig 6 - Calculated population inversion (in mol%) for the laser transition 5I5 → 5I6 (at 3925 nm) as a function of the pumping intensi-
ties for [Ho3+] = 10 mol% doped fluorindate glass under CW pumping at 889 nm (→p1) and CW pumping at 962 nm (→P2) (ESA) at 300 K.

Instituto de Pesquisas Energéticas e Nucleares