Nigel J. Cockroft

Uniform upconversion in high-concentration Er 3+ -doped soda lime silicate and aluminosilicate glasses

Uniform upconversion in erbium-doped silicate glasses is investigated as a function of glass composition, concentration, and fabrication method. Comparisons of upconversion coefficients are made among soda lime silicate and aluminosilicate bulk glasses and soda lime silicate waveguides. Comparisons are also made with studies performed by other researchers. The results indicate that both the composition and the preparation method of the glass affect the value of the upconversion coefficient, with as much as a factor-of-4 variation observed at fixed Er(3+) concentration. Values of the upconversion coefficient are found to be consistent with the Förster-Dexter microscopic model.

Spectroscopy and dynamics of upconversion in Tm3+: YLiF4

Abstract Spectroscopic and dynamic properties of Tm3+: YLiF4 as an upconversion material with blue emission are presented. Absorption, fluorescence and excitation spectra at low temperatures were used to determine the crystal field levels of all manifolds except 1S0 of Tm3+. The observed energy levels were fitted in a least-square analysis to determine crystal-field parameters of the S4 site of Tm3+ in YLiF4 with a standard deviation of 16 cm−1 between the calculated and measured energy levels. Judd-Ofelt calculations usuing measured integrated absorption yield the intensity parameters μ2,4,6 for Tm3+ in YLiF4. From these parameters, the calculated stimulated emission cross section of the 1D2→3F4 transition is 2.4 × 10−19 cm2, in good agreement with the measured value of 3 × 10−19 cm2. An estimate of the dipole-dipole interaction which gives rise to quenching of the excited state was derived from the fluorescence decay curves at different concentrations.

Optical Characterization and Electronic Energy-Level Structure of Er3+-Doped Cscdbr3

Information obtained from optical absorption, excitation, and emission experiments on erbium doped crystalline CsCdBr3 is analyzed, using a semiempirical Hamiltonian, to calculate atomic and crystal‐field interaction parameters and electronic state wave functions. A majority of the Er3+ ions substitute at a Cd2+ site giving C3v point group symmetry and forming an Er3+ ion dimer center. This dimerization, together with the material’s low phonon energies, and the specific positioning of states in the Er3+ (4f11) configuration, produce the interesting and useful emission properties of the material. Comparisons are made with other erbium halide crystals, and interaction parameter and energy‐level results for Nd3+:CsCdBr3 are also presented. The inclusion of second order correlation crystal‐field interaction parameters is shown to be essential for accurately characterizing splittings of several J multiplets important in visible emission pathways.

Application of energy upconversion spectroscopy to novel laser and phosphor design

Abstract Energy-transfer and sequential-absorption upconversion processes, normally considered detrimental to conventional laser operation, are rapidly emerging as the key to an exciting new class of optical device. Energy-upconversion processes may be designed to take advantage of strong rare earth ion emission transitions in the visible region and of valuable co-incidences with diode-laser outputs in the near-infrared to produce compact visible lasers. This paper reviews the use of sequential-absorption and energy-transfer spectroscopy to derive information that is essential to the optimization of novel device designs as well as ‘conventional’ laser or phosphor designs. Transfer-rate extraction using upconverted temporal transients, determination of high-lying energy levels using sequential-absorption laser spectroscopy, ion dimer identification by line-narrowing experiments and direct identification of energy storage states using dual-laser techniques are presented. The use of dimer-dominated host crystals, such as CsCdBr3, that can be used to isolate individual energy-transfer rates relevant to the optimization of many different laser types, is emphasized.

Comparison of the spectra and dynamics of Er3+:Y2−xScxO3 (x = 0, 1, 2)

We have studied the spectra and lifetimes of Er3+ in the isostructural series, Y2O3, YScO3. Addition of Sc3+ to Er3+:Y2O3 shifted the energy level positions, changed the inhomogeneous broadening and shortened the fluorescence lifetimes for Er3+ in the C2 site. Going from Er3+:Y2O3 to Er3+: Sc2O3 increased the barycenter of the four lowest J-multiples, decreased the barycenter of the 4F92 and higher multiplets, and increased the crystal-field splitting within each J-multiplet. The inhomogenous line widths in the Er3+:YScO3 spectra were much larger than in Er3+:Y2O3 or Er3+: Sc2O3 due to random substitutional disorder in the mixed system. The random disorder in Er3+:YScO3 removed the inversion symmetry of the C31 lattice site and allowed observation of transitions from Er3+ ions in this site. All fluorescence lifetimes decreased with addition of Sc3+ indicating an increase in the nonradiative relaxation.

Materials characterization, optical spectroscopy, and laser damage studies of electrochromically and photochromically damaged KTiOPO4 (KTP)

The techniques utilized to study the surface and bulk properties of KTiOPO4 (KTP) were Rutherford backscattering (RBS), particle induced x-ray emission (PIXE), secondary ion mass spectrometry (SIMS), optical absorption and emission spectroscopy, and controlled laser damage. RBS and SIMS results provide strong evidence for potassium ion and titanium ion migration from the bulk to the electrode surface under an applied DC voltage. Optical measurements suggest the presence of Ti3+ ions in pristine, EC and PC damages KTP. Catastrophic damage was induced models will be presented to rationalize the RBS, PIXE and SIMS data for the impurities, and a damage mechanism consistent with the findings of the laser damage and optical absorption and emission experiments will be discussed.

HIGH ENERGY DIODE SIDE-PUMPED Cr:LiSAF LASER

A diode side-pumped Cr:LiSAF laser has been demonstrated with a 30 mJ normal mode output energy, and an optical to optical eficiency of 17%. Improved optical quality laser material has been grown with several Cr concentrations. Optimum Cr concentration has been calculated and experimentally confirmed.

Dual-rod Cr: LiSAF oscillator/amplifier for remote sensing applications

A dual rod configuration is used to achieve 16W average power operation from a flashlamp-pumped Cr:LiSAF laser oscillator. A double-pass dual-rod amplifier configuration was used to amplify 141{mu}J pulses from a Q-switched diode-pumped LiSAF oscillator by a factor of {approximately}120. This experiment established a small signal gain of 13.4% per cm at 820 nm. Improved slope efficiency (7.4% electrical-to-light) and pulse repetition frequency (40Hz) were achieved with a single-rod oscillator using improved Cr:LiSAF material.

Energy transfer between thulium and praseodymium ions in solids

Abstract New thulium-to-praseodymium up-conversion and cross-relaxation energy transfer mechanisms are observed. YLiF 4 has several subsets of dopant ions, which exhibit a variety of transfer efficiencies. Dual-pulse laser excitation of dimers in CsCdBr 3 is used to demonstrate a probable up-conversion pathway.

Preliminary analysis of lidar techniques for regional meteorological studies

Preliminary scoping exercises indicate that remote-sensing lidar can play a useful role in missions that involve determining regional weather patterns and atmospheric transport conditions. Both meteorological modeling and local atmospheric sensing should be employed. Satellite-based remote sensing systems, using an incoherent Doppler wind-sensor, seem feasible.