Richard S. Quimby

General procedure for the analysis of Er 3+ cross sections

We have applied the theory of McCumber to the (4)4I(13/2) ? (4)I(15/2) transition of Er(3+) -doped glasses and confirmed its ability to provide both spectra and accurate values of cross sections. For an Al/P-silica fiber, the exact McCumber treatment is within 3% of the measured emission cross section, whereas an Einstein analysis is off by >50%. An approximate treatment that eliminates the McCumber theorys requirement of detailed electronic structure has been developed and found to usually provide more accurate values than an Einstein analysis.

Clustering in erbium‐doped silica glass fibers analyzed using 980 nm excited‐state absorption

A nonsaturable component to the 980 nm excited state absorption (ESA) is found in Er3+‐doped silica glass fibers. This anomalous behavior of the ESA provides a way of quantitatively characterizing the degree of clustering in these glasses. It is found that the degree of clustering is greater for higher Er3+ concentrations, and is significantly reduced with the addition of aluminum to the glass. With this method it is also found to be possible to distinguish between true clustering and the occurrence of closely spaced Er3+ pairs in a random distribution.

Modified Judd-Ofelt technique and application to optical transitions in Pr3+-doped glass

An extension of the Judd–Ofelt technique [B. R. Judd, Phys. Rev. 127, 750 (1962)] is introduced in which measured fluorescence branching ratios are incorporated into the calculation of the Judd–Ofelt parameters. It is found that including branching ratio measurements into the analysis allows the Judd–Ofelt parameters to be reliably calculated with fewer ground‐state absorption measurements than would otherwise be necessary. The method is applied to Pr3+:ZBLAN glass, an important material for 1.3 μm optical amplifiers. A closed‐form expression is also derived for determining the Judd–Ofelt parameters from ground‐state absorption data.

Quantum efficiency of Pr3+ doped transparent glass ceramics

The quantum efficiency of the 1.3 μm transition in Pr3+ doped oxyfluoride transparent glass ceramics is measured using a self-calibrating fluorescence ratio technique. The measured value of 8%±1% is much higher than expected for Pr3+ in an oxide glass, and is consistent with the incorporation of the Pr3+ ions into the fluoride nanocrystals of the glass ceramic. Measured quantum efficiencies are compared with values calculated using the Judd–Ofelt theory, and it is found that the best agreement is obtained when fractional differences between calculated and measured oscillator strengths are minimized, rather than absolute differences. The Judd–Ofelt analysis is used along with a spectral analysis to show that excited-state absorption should not significantly reduce the gain around 1.3 μm in these materials. The fluorescence ratio technique used to measure the quantum efficiency also provides information about ion–ion interactions at higher concentrations. It is found that the addition of the monovalent dopa...

Continuous-wave lasing on a self-terminating transition.

The condition for cw lasing in a four-level system is generalized to include situations where the upper laser level relaxes to the ground state as well as to the lower laser level. It is found that cw lasing is possible in certain cases even when the fluorescence lifetime of the upper level is shorter than that of the lower laser level.(AIP)

New excited‐state absorption measurement technique and application to Pr3+ doped fluorozirconate glass

A new technique for analyzing excited state absorption (ESA) is introduced, in which the relative ESA spectrum is determined directly from fluorescence measurements. This represents, to our knowledge, the first application of the McCumber theory [D. E. McCumber, Phys. Rev. 136, A954 (1964)] to the calculation of excited state absorption spectra. The new technique is used to study ESA transitions from the 1G4 level in Pr3+ doped fluoride glass (ZBLAN). An ESA transition around 1380 nm is found, which shifts the peak of the gain curve for a 1.3 μm Pr3+ fiber amplifier about 10 nm to shorter wavelengths, and gives rise to negative gain for wavelengths longer than 1380 nm. Another ESA transition around 840 nm is found, which is an order of magnitude stronger than the 1 μm ground state absorption.

Optical cooling in Er3+:KPb2Cl5.

For the first time, optical cooling has been observed in the (4)I(13/2) excited state of erbium(III), using the low phonon energy host materal, potassium lead chloride (KPb(2)Cl(2)). Cooling was observed when samples were pumped at wavelengths longer than 1557 nm, 17 nm longer than the mean fluorescence wavelength of 1540 nm, which implies a nonradiative heat load of 1.1% for the (4)I(13/2)-->(4)I(15/2) transition. When pumped at 1568 nm, the total cooling efficiency was 0.38% of the absorbed power. These results highlight the potential of Er(3+):KPb(2)Cl(5) as a material for lasers operating in an eye safe spectral region.

Excited-state absorption at 980 nm in erbium-doped glass

Excited state absorption (ESA) spectra were measured for the 4I11/2? 4F7/2 transition at 980 nm in Er-doped fluoride and fluorophosphate glass, by varying the pump wavelength from a tunable Ti:sapphire laser and monitoring the relative strength of the green upconverted fluorescence. The ESA cross section spectra are the same order of magnitude in strength as the 980 nm ground state absorption, but shifted to shorter wavelength by 4-6 nm. The 980 nm ESA may limit the efficiency of high power erbium-doped fiber amplifiers, and provides a possible pump mechanism for IR upconversion pumped fiber lasers operating in the visible.

Self-calibrating quantum efficiency measurement technique and application to Pr 3+ -doped sulfide glass

A measurement technique is described in which the radiative quantum efficiency of certain transitions in rare-earth-doped glasses can be determined based only on relative fluorescence measurements. We calibrate the emission from the level of interest by measuring emission into that level from a higher excited level. Application of the technique to Pr(3+)-doped sulfide glasses yields quantum efficiencies for the (1)G(4) ? (3)H(5) transition as high as 60%, in good agreement with measurements using the integrating sphere technique. Calculated efficiency values based on the Judd-Ofelt technique are shown to be subject to inherent uncertainties.

Output saturation in a 980-nm pumped erbium-doped fiber amplifier

A fiber amplifier model is developed which includes a finite lifetime for the pumped level. Pump excited state absorption (ESA) from the pumped level is also included. The model is solved numerically for a erbiumdoped fiber amplifier pumped at 980 nm. The signal output power at 1.5 microm is found to be limited by the finite lifetime of the (4)I(11/2); ESA of the pump from the (4)I(11/2) further limits the signal output. Lifetimes of the (4)I(11/2) were measured for Er(3+) in a series of oxide and fluoride glasses. Output saturation is most important in the fluoride based glasses, where the (4)I(11/2) lifetime is longest.