A.J. Silversmith

Avalanche upconversion in LaF3:Tm3+

Abstract Strong blue fluorescence corresponding to the 1 G 4 → 3 H 6 transition in LaF 3 :Tm 3+ is generated by excitation with a red laser at 635.2 nm. The upconversion mechanism is shown to be photon avalanche. The temporal behavior of the upconverted fluorescence and the dependence of the blue fluorescence intensity on excitation laser power are described by a four-level system of coupled rate equations. A unique set of parameters is found which describes the behavior at several different excitation levels, both below and above the avalanche threshold. Two cross-relaxation paths are shown to be important to the upconversion process.

Site selective excitation, upconversion and laser operation in Er3+:LiKYF5

Abstract The energy level structures of Er 3+ ions occupying two, almost identical, low symmetry Y 3+ sites in LiKYF 5 have been determined using site selective laser excitation and luminescence. The positions of the (2 J +1)/2 Stark levels of 10 of the lowest energy multiplets were obtained. Upconversion fluorescence in the green, blue and violet while exciting the 4 I 15/2 → 4 F 9/2 transition was observed and modelled via excited state absorption and energy transfer processes populating the energy levels of the 4 S 3/2 , 2 H 9/2 and 2 P 3/2 multiplets. Room temperature upconversion laser operation in the green at 550 nm has also been achieved by pumping the 1% Er 3+ :LiKYF 5 gain medium with laser diodes at 651 and 800 nm.

Red to blue upconversion in Tm-doped sol–gel silicate glasses

Abstract In thulium-doped glasses derived from the hydrolysis of orthosilicates we worked with different annealing conditions so as to enhance the fluorescence yield. In addition, we observed blue upconverted fluorescence from both the 1 G 4 and 1 D 2 levels of thulium when the glasses were excited with red laser light. Two-step absorption mechanisms with different intermediate levels are responsible for populating the two emitting levels.

Fluorescence line narrowing and decay dynamics in sol–gel glasses containing Eu3+

Abstract Fluorescence line narrowing and emission decay measurements on Eu3+ doped sol–gel glasses have been used to investigate and compare local Eu3+ environments in binary SiO2–TiO2 glasses, SiO2 glasses containing Al3+, and SiO2 glasses without co-dopant. In particular, clustering of rare-earth ions and the effects of annealing temperature on residual hydroxide concentration are studied. The Al and Ti co-doped samples show pronounced line-narrowing implying little energy migration among Eu3+ ions. The 5D0–7FJ fluorescence decays are faster in the Ti glasses.

Red to blue up-conversion in Y2SiO5:Tm3+

Abstract Avalanche up-conversion and two-step absorption are reported in Y 2 SiO 5 :Tm 3+ . Absorption of red laser light produces intense blue fluorescence. Steady-state and temporal measurements are used to investigate the up-conversion mechanisms.

Infrared to violet up-conversion in YLiF4 : Nd3+

Abstract We investigate ultraviolet and visible up-conversion in YLiF4 : Nd3+ (1%). The energy of the ultraviolet emission is more than twice the energy of the infrared pump light. The up-conversion is determined to be dominated by an energy transfer process. Our experimental results are compared with a rate equation analysis.

Upconversion excitation of green fluorescence in Er:YAG

Conversion of red and infrared laser light to green fluorescence is reported in the system YAG : Er3+. Cooperative energy transfer is not very efficient in YAG : Er3+ because of the short4I11/2 lifetime; however, a two-step resonant absorption process, with the second step corresponding to a4I13/2 →4F5/2 transition, uses the long lived4I13/2 state as an effective population reservoir.

Photon gated spectral hole burning in SrTiO3 : Cr3+

Abstract Persistent spectral holes were observed in the R-lines of SrTiO3:Cr3+ at 2 K. The hole burning mechanism was shown to be due to a two-photon or gated process, where a second optical excitation causes bleaching by photoionization of Cr3+. The trapping center responsible for the hole burning is postulated to be an oxygen vacancy in the lattice associated with a Cr3+ ion. A series of samples reduced at different temperatures was studied, and the hole burning efficiency was seen to be strongly dependent on reduction temperature.

Green infrared‐pumped erbium upconversion lasers

Upconversion pumping with near-infrared cw dye lasers was used to achieve laser action at 550 nm on the {sup 4}{ital S}{sub 3/2}{r arrow}{sup 4}{ital I}{sub 15/2} transition of Er{sup 3+}. In YAlO{sub 3}:Er{sup 3+}, upconversion excitation occurs via sequential two-photon absorption. In YLiF{sub 4}:Er{sup 3+}, energy transfer upconversion involving two Er{sup 3+} ions in the intermediate {sup 4}{ital I}{sub 11/2} state causes excitation of the upper laser level. These upconversion lasers operate at temperatures up to 90 K. With pump powers of several hundred milliwatt near 800 nm we have obtained 550-nm output powers in the miliwatt range.

Compact Blue And Green Lasers Based On Nonlinear Optical Processes

Nonlinear optical processes permit the design of miniaturized blue - green laser devices that are pumped by near-infrared sources such as GaAIAs diode lasers. Frequency upconversion of infrared pump light can be achieved by processes that use the nonlinear susceptibility of noncentrosymmetric materials for second harmonic generation or sum-frequency mixing. In addition, two-photon excitation mechanisms including sequential two-step absorption and energy-transfer upconversion can be used to pump visible solid-state lasers with infrared light. The operation of several nonlinear laser devices in the blue - green spectral region has been demonstrated. Intracavity frequency mixing of a 1064-nm Nd:YAG laser and its 809-nm pump source resulted in efficient generation of 459-nm radiation using KTi0PO4 as the nonlinear material. Intracavity frequency doubling of a diode-laser pumped 946-nm Nd:YAG laser was used to generate 473-nm radiation. Two-photon-pumped upconversion lasing at 550nm has been demonstrated in YA103:Er3+ and YLiF4:Er3+ at temperatures <90K using infrared cw dye lasers near 800nm as pump sources.