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IEEE Journal of Quantum Electronics

7C7 - Infrared quantum counter action in rare earth doped fluoride lattices

M. Brown, W. A. Shand

Published Aug 1, 1966• 7 citations
Publisher

Abstract

This paper reviews the results of a program of experimental work on infrared quantum counter action in trivalent rare earth doped CaF2, SrF2, BaF2, and LaF3lattices. The action has been found in eight of the nine possible ions that could give an output in the visible region. While the strengths of the various schemes at a 1 percent doping level are consistant with a low concentration theory, the strengths of the schemes at a 10 percent doping level indicate that there are ion-ion interactions influencing the systems. These ion-ion couplings are so effective that three photon addition schemes have been identified.

DOI
10.1109/jqe.1966.1074034

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The Journal of Chemical Physics•Oct 15, 1969•28 citations
This paper reviews the results of a program of experimental work on infrared quantum counter action in trivalent rare earth doped CaF2, SrF2, BaF2, and LaF3lattices. The action has been found in eight of the nine possible ions that could give an output in the visible region. While the strengths of the various schemes at a 1 percent doping level are consistant with a low concentration theory, the strengths of the schemes at a 10 percent doping level indicate that there are ion-ion interactions influencing the systems. These ion-ion couplings are so effective that three photon addition schemes have been identified.
Abstract : Quantum counter action has been observed in divalent rare earth doped ions lattices. The report presents the experimental work that has been done on Sm(2+) and Tm(2+) singly doped and Sm(2+) : Tm(2+) double doped systems in order to investigate the nature and efficiency of the schemes. The results show that while these systems are more efficient per ion than the trivalent rare earth doped systems the lower concentrations possible bring the overall efficiency back to the same level. (Author)
Abstract : Previous work on the infrared quantum counter action in Er3+ doped SrF2 showed that it was possible to increase the efficiency of the action by codoping with a second rare earth ion. This report covers the work done on the Er3+ doped LiYF4 and Er3+: Yb3+ doped LiYF4 system to evaluate the energy levels of the Er3+ in a site that does not require charge compensation and the increase of efficiency that comes with codoping with Yb3+. The results show that the positions of the energy levels are substantially unchanged in moving from one lattice to another and an increase in efficiency of the action, of the order, forty times can be achieved with a composition in the region of 2% Er3+: 18% Yb3+ doped LiYF4. (Author)
An analysis of an ideal five-level ir quantum counter (IRQC) is presented. The importance of the two additional levels is discussed and analyzed. The parameters for achieving optimum performance as an ir detector and/or an image converter are presented. In theory, the IRQC is the only quantum amplifier with photon gain that can approach a noise temperature of absolute zero. In practice, with the constriction of available materials and technology, the most feasible use for the IRQC in the near term would be in an active system. An ir laser would be used to scan the target while another laser would pump the excited state transition. The IRQC action has been observed in this laboratory in the tripositive rare earths of Pr, Nd, Eu, Tb, Dy, Er, and Tm. These ions were incorporated in single crystal lattices of CaF(2), BaF(2), SrF(2), CdF(2), LaF(3), CaWO(4), A1(2)O(3), YAG, LaCl(3), and in solutions of the various trichlorides (dissolved in D(2)O). A total of 165 schemes are reported. The rare earth impurity concentration varied from 0.05% to 20%. In our laboratory, the primary range of interest for detection and/or image conversion is between 1 micro and 2 micro. Therefore, almost all the systems studied involved the detection of an ir photon in this region.
This paper considers the mechanisms whereby the addition of Yb 3+ enhances the efficiency of quantum counter action in Er 3+ doped LiYF 4 . The particular scheme chosen for this investigation is the doubling scheme in which two photons of wavelength close to 9800 Å excite green fluorescence from the Er 3+ ion. The important factors which have been identified are that the influence of an increase of Yb 3+ concentration on the quantum efficiency of the 4 S 3/2 to 4 I 15/2 fluorescence is very much less than an equivalent increase in the Er 3+ concentration, the absorption coefficient of the Yb 3+ in the 9800 Å region is over an order of magnitude larger than that for Er 3+ and the efficiency of the transfer of energy from Yb 3+ to Er 3+ is sufficiently high to ensure the energy absorbed by the Yb 3+ is transferred to the Er 3+ . The optimum concentration has been found to be in the region of 2% Er 3+ : 18% Yb 3+ doped LiYF 4 .
The pumping intensity and concentration dependences of the fluorescence output from three infrared quantum-counter schemes that involve coupled ions in Er3+-doped SrF2 have been measured at 300 and 77°K. The pumping intensity depended linearly on the numbers of photons absorbed in the schemes. The power of the concentration dependence was found to be noninteger in the range 1%–10%. This has been interpreted as indicating the importance of energy migration between the Er3+ ions as mechanism for populating the energy levels of the coupled ions.