Donald E. Wortman

Analysis of the optical spectrum of Ho3+ in LiYF4

Abstract The energy levels for Ho3+ in single crystal LiYF4 from 0–21,300 cm−1 have been determined from polarized absorption and fluorescence spectra using crystals at temperatures between 4 and 300°K. Energy level assignments were made initially by comparing the crystal spectra with energy levels calculated by using crystal field parameters interpolated from previously reported analyses of Nd3+, Er3+ and Tm3+ in LiYF4. The energy level scheme identifies energy levels in the 10 lowest J-multiplets and gives calculated energies for the next six higher J-multiplets. The crystal field parameters were varied to obtain a best fit between experimental and theoretical energies, and the final values B20 = 410, B40 = − 615, B44 = 819, B60 = − 27.9 and B64 = 677 ± i32.8 cm−1 give an r.m.s. fit of 2.78 cm−1. The calculations were made by diagonalizing the crystal field Hamiltonian, Hx = ΣkmBkmCkm, in the space of ten lowest J-multiplets spanned by intermediate coupled free-ion wavefunctions calculated using the free-ion parameters of Carnall et al. for Ho in aqueous solution. The calculated g∥ for the Γ3.4 ground state of 13.63 compares favorably with a previously reported value of 13.3 ± 0.1.

Power, efficiency, and thermal characteristics of type-II interband cascade lasers

High-performance mid-infrared type-II interband cascade lasers have been demonstrated under continuous-wave (CW) conditions with record-high wall-plug efficiencies (>14%) and output powers (>100 mW/facet) above 77 K. Device characteristics of these type-II interband cascade lasers are investigated systematically in terms of their output powers and efficiencies. Also, by comparing the temperature dependence of the threshold currents under pulsed and CW conditions, the thermal resistance and maximum heat sink temperature for CW operation are estimated for several mesa sizes. The limiting factors due to device heating for high-power/high-efficiency operation are identified and discussed in connection with device dimensions and packaging for the purpose of assessing further improvements.

Optical spectra, energy levels and branching ratios of trivalent dysprosium-doped yttrium scandium gallium garnet

Abstract Absorption spectra of trivalent dysprosium ions in yttrium scandium gallium garnet are reported between 2.9 and 0.4 μn at 4K. Laser-excited fluorescence was observed at 4 K for transitions between the 4 F 9 2 manifold and several of the lower-lying 6HJ and 6FJ manifolds. A crystal-field splitting calculation was carried out in which a parametrized Hamiltonian (including Coulombic, spin-orbit, and crystal field terms in D2 symmetry) was diagonalized for selected manifolds of the Dy3+ (4f9) configuration. The RMS deviation between 69 experimental and calculated Stark levels was 8 cm−1. Calculations were carried out to predict branching ratios for emission from the 4 F 9 2 manifold.

Optical spectra and analysis for Pr3+ in SrAl12O19

Energy levels of the 4f2 electronic configuration of Pr3+ in SrAl12O19 (SAM) have been determined from polarized absorption and fluorescence spectra using crystals, charge-compensated with Mg2+, at temperatures between about 20 and 300 K. Energy level assignments were made initially by comparing the crystal spectra with energy levels calculated by using crystal-field parameters, Bkm, compatible with those previously reported for Nd3+ in SAM. The Bkm were varied to obtain a best fit between experimental and theoretical energies, and the final values: B20=−94, B40=1047, B60=−1397, and B66=−1245 cm−1 give an rms fit of 14.5 cm−1. The Bkm for Pr3+ in SAM were also used along with a result relating the Bkm to crystal-field components, Anm, derived in a lattice sum calculation to obtain Bkm values for all the triply ionized rare-earth ions in SAM. Odd-fold Akm are also given that are required in the intensity and lifetime calculations and yield results in good agreement with the measurements. In addition, the r...

Enhanced CW performance of the interband cascade laser using improved device fabrication

Continuous-wave (CW) operation of a mid-infrared type-II interband cascade (IC) laser has been demonstrated at temperatures up to 142 K by improving device processing and fabrication. Also, the IC laser exhibited record-high wall-plug efficiencies (/spl sim/18% at 60 K) with considerable CW output powers. An analysis of the thermal resistance partially explains the still low maximum CW operating temperature and suggests further potential for improvement with continued development of fabrication/packaging techniques.

OPTICAL SPECTRA AND ANALYSIS OF ER3+ IN SILICON WITH C, O, AND N IMPURITIES

Photoluminescence (PL) spectra of Er3+ in an Er-doped silicon film were recorded at 2 and 77 K over the wavelength range from 1.52 to 1.68 μm, which includes optical transitions between the Er3+ 4I13/2 and 4I15/2 manifolds. These spectra were then analyzed to determine the nature of the electrostatic field at the site of the Er ion that governs the ion’s optical behavior. The PL spectra were analyzed three different ways: by considering the Er3+ ions to be occupying sites of Td, C3, or D2d point group symmetry. Transition energies and magnetic dipole transition probabilities were calculated for each case by diagonalizing a Hamiltonian representing the free-ion and crystal-field interactions in a Russell–Saunders basis of states spanning the lowest 15 J multiplets of the 4f11 electronic configuration of Er3+. Crystal-field parameters were varied in each case to find the best agreement with the experiment. Our results showed that the site symmetry of the Er3+ ions most consistent with the data is D2d. For t...

Optical properties of Nd3+ in single crystal SrAl12O19

Abstract The spectroscopic characteristics of triply ionized neodymium in Sr1−xNdxAl12−xMgxO19 for x = 0.03 and 0.15 are presented; one Mg2+ ion per Nd3+ is required for charge compensation. Crystals of this composition are optically uniaxial, with absorption and emission depending strongly on polarization. The room-temperature fluorescence lifetime is 430 μs for x = 0.03 and 280 μs for x = 0.15. The main absorption and emission peaks can be fit by assuming the Nd3+ ion substitutes for Sr2+ in a site of D3h point-group symmetry. A crystal-field Hamiltonian of D3h symmetry is used to fit the data. A best-fit rms deviation of 4.2 cm−1 is obtained between 32 experimental and theoretical energy levels for the 13 lowest J-multiplets of the 4f3 electronic configuration of Nd3+ with the following crystal field parameters: B20 = −202.8 cm−1, B40 = 632.7 cm−1, B60 = −1752 cm−1, and B66 = −1180 cm−1. The stimulated emission in the 4 F 3 2 → 4 I 9 2 , 4 F 3 2 → 4 I 11 2 , and 4 F 3 2 → 4 I 13 2 channels peaks at 902, 1049.7, and 1306.5 nm, respectively, and in all cases it is σ-polarized. The respective spectroscopically determined stimulated emission cross sections for these wavelengths are 3.7 × 10−20, 1.1 × 10−19, and 2.6 × 10−20 cm2. The best absorption band for diode-laser pumping is centered at 798 nm, with an absorption coefficient of 14 cm−1 for x = 0.15 and a full-width at half-maximum of 2.5 nm.

Analysis of the energy levels of Mn2+ in halo apatite structures

Abstract Reported optical spectra of Mn2+-doped halo apatites are analyzed in octahedral, cubic, and C3 symmetries. Specifically the apatites doped with Mn2+ are Ca10F2(PO4)6, Cd10Cl2(PO4)6, Ca10F1.8Cl0.2(PO4)6, and Sr10F1.8Cl0.2(PO4)6. The cubic approximation was assisted by the use of Tanabe-Sugano-like plots, and the experimental data were averaged for a best analysis where the Slater parameters F(2) and F(4) and the crystal-field parameter B40 were varied. A point charge calculation of the crystal-field parameters for the C3 sites in each of the apatites and the resulting crystal-field parameters, B20, B40, and B43, weer used as starting values in fitting the reported energy levels in C3 symmetry. The parameters that best fit both the cubic approximation and the C3 symmetry are given for each of the apatite host crystals.

High-power mid-IR type-II interband cascade lasers

Type-II interband cascade (IC) lasers take advantage of the broken-gap alignment in type-II quantum wells to reuse electrons for sequential photon emissions for serially connected active regions. Here, we describe recent advances in InAs/GaInSb type-II IC lasers at emission wavelengths of 3.6 - 4 micrometers ; these semiconductor lasers have exhibited significantly higher differential quantum efficiencies and peak powers than previously reported. Low threshold current densities (e.g., approximately 56 /A/cm2 at 80 K) and power efficiency exceeding 9% were observed from a mesa- stripe laser in cw operation. Also, these lasers were able to operate at temperatures up to 250 K in pulsed mode and 127 K in cw mode. We observed from several devices at temperatures above 80 K, slope efficiencies exceeding 1 W/A/facet, corresponding to a differential external quantum efficiency exceeding 600%. A peak optical output power of approximately 6 W/facet was observed from a type-II IC laser at 80 K.

Mid-IR type-II InAs/GaInSb interband cascade lasers

We report our progress to date in the development of type-II interband cascade lasers emitting in the mid-IR (3.8-to-4.0 micrometers ) spectral region. We have demonstrated significant improvements over previously reported results in terms of differential external quantum efficiency (approximately 500%), peak power (>4 W/facet), peak power conversion efficiency (approximately 7%), maximum operating temperature (217 K), and continuous-wave (cw) operation. We briefly review some results for pulsed excitation and then present more detailed operating characteristics for the cw performance of our lasers, including the output power characteristics and the dependence of the output spectrum on current.