We report new laser channels for the rare earth praseodymium. Laser emissions at 1.6 and 5.2 /spl mu/m were studied using a 2.0 /spl mu/m Tm:YAG laser to pump the /sup 3/F/sub 2/ level in Pr/sup 3+/:LaCl/sub 3/. Efficient 5 /spl mu/m operation was demonstrated at 130 K. Temperature dependence of the 5 /spl mu/m laser threshold was determined in the range from 130 to 250 K. The complex dynamics and potential utility of these new rare earth lasers are discussed.>
We report new laser channels for the rare earth praseodymium. Laser emissions at 1.6 and 5.2 /spl mu/m were studied using a 2.0 /spl mu/m Tm:YAG laser to pump the /sup 3/F/sub 2/ level in Pr/sup 3+/:LaCl/sub 3/. Efficient 5 /spl mu/m operation was demonstrated at 130 K. Temperature dependence of the 5 /spl mu/m laser threshold was determined in the range from 130 to 250 K. The complex dynamics and potential utility of these new rare earth lasers are discussed.>
Short pulse laser-induced fluorescence experiments on the lowest-energy electronic states (υ<10−4 cm−1) of trivalent praseodymium ions are reported. Crystals of lanthanum trichloride with a range of Pr3+ concentrations were examined. We compute cross relaxation and upconversion coefficients for the metastable energy levels using a standard rate equation analysis. The limitations of the rate equation approach are examined with a focus on the underlying dynamics of this rare-earth system. The implications of these results for laser emission in the 1.3–7.2 μm spectral range are discussed.
We have made an unexpected discovery of highly nonlinear optical behavior in certain praseodymium-doped lanthanum halides. When a LaCl3 or LaBr3 crystal containing Pr3+ ions is exposed to green laser radiation slightly in excess of a certain critical intensity, Pr fluorescence increases by orders of magnitude. Infrared output near 4.5-μm wavelength is associated with the large visible output, and pump power is strongly absorbed. We call this new phenomenon a photon avalanche. Critical pump power density is in the 1–15 W/cm2 range. At higher pump rates, a population inversion and lasing action take place between the lowest infrared levels of the Pr ion. Experimental results are presented and compared to predictions of a photon avalanche model based on resonant energy transfer.
We propose that Dy/sup 3+/-doped chloride crystals be considered as candidates for amplification of the 1.3 /spl mu/m signal used by the telecommunications network. While several of these types of crystals can provide gain at the specified operating wavelength of 1.31 /spl mu/m, and furthermore offer adequate bandwidth, we have focused our attention on LaCl/sub 3/:Dy as an illustrative case to explore in greater depth. Spectroscopic measurements were made on un-oriented samples of this material; excited-state lifetimes and LaCl/sub 3/:Dy/sup 3+/ Judd-Ofelt parameters are reported. Wavelength-resolved absorption and emission cross sections are presented for the 1.3 /spl mu/m W/spl rlhar2/Z band. Pump-probe measurements (using 0.92 /spl mu/m and 1.32 /spl mu/m, respectively) prove that the observed gain properties of LaCl/sub 3/:Dy are consistent with those predicted on the basis of the spectroscopic cross sections. The Dy:chloride gain media appear to have fundamental optical characteristics amenable to superior 1.3 /spl mu/m telecom amplifier performance, although many fabrication issues would have to be addressed to produce a practical amplifier.
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.
Here we describe a class of cw upconversion lasers in which inversion is due exclusively to cooperative interactions of rare earth ions in highly doped solids, resulting in unique opportunities for output wavelength agility, large upconversion factors, and high quantum efficiencies through nonlinear dynamics. We have isolated capabilities of the cooperative mechanism by performing experiments in Er:CaF2 and Er:LiYF4 with infrared pumping of the first Er3+ resonance at 1.53 μm. At liquid helium temperatures, laser action at 544 nm was achieved in an astigmatically compensated, three-mirror cavity with 5% efficiency in LiYF4. The upconversion factor (ratio of pump to laser wavelength) was 2.81, to our knowledge the highest ever reported for cw upconversion lasers. At 77 K, laser action at 551 nm was observed. Surprisingly, output at both 544 and 551 nm was truly cw with cooperative pumping, unlike earlier green erbium lasers, which exhibited self-pulsing. Also at 77 K, near infrared laser action was obtained at 0.855 pm with exceptionally high efficiency in CaF2(28%) and LiYF4 (20%) on self-quenching transitions. Successful demonstration of cw laser action on such transitions also suggests a means whereby quantum efficiencies may exceed unity. The lower laser level in such cases is the origin of cooperative pumping to the upper laser level, but also receives population as the result of stimulated emission. Hence population can be recycled for enhanced quantum efficiency. Additionally, population pulsations can occur and sustained oscillations in laser output have been observed in a cooperative erbium upconversion laser at 2.8 μm.
Rare-earth ions in dielectric crystals play an important role in high-resolution laser spectroscopy and are interesting candidates for storing quantum states of photons. We characterize the praseodymium hyperfine interaction of the ground-state (3H4) and one excited-state (1D2) for two important compounds: praseodymium doped in yttrium aluminum perovskite and praseodymium doped in yttrium orthosilicate. The spin Hamiltonian parameters are determined by numerical analysis of Raman-heterodyne spectra, which were collected for a range of static external magnetic field strengths and orientations. For Pr3+:YAlO3, we present a full analysis without restrictions for the Zeeman and quadrupole tensors, and our new characterization for Pr3+:Y2SiO5 resolves a controversy in the literature.