S.L. Baldochi

Crystal growth of Ce-doped and undoped LiCaAlF6 by the Czochralski technique under CF4 atmosphere

Ce-doped and undoped LiCaAlF6 (LiCAF) single crystals 50 mm in diameter were grown by the Czochralski technique. The formation of inclusions and cracks accompanying the crystal growth was investigated. The dependence of lattice parameters on the temperature was measured for LiCAFand LiSrAlF 6 single crystals. Linear thermal expansion coefficients for both these crystals were evaluated. Higher transmission properties for LiCAFsingle crystals were achieved in the UV and VUV wavelength regions. # 2001 Elsevier Science B.V. All rights reserved.

Ce-doped LiYF4 growth under CF4 atmosphere

Abstract Single crystals of Ce-doped LiYF 4 have been grown by the Czochralski technique directly from raw materials under CF 4 atmosphere. Optically clear single crystals were obtained without the previous conventional hydrofluorination of the starting charge or the direct use of HF during the growth process. Optical characteristics were examined and compared with those of other rare-earth LiYF 4 -doped crystals.

Laser development of rare-earth doped crystals

Rare earth doped laser crystals present good optical properties providing most of the solid state lasers available today. In particular, some fluoride crystals are capable of forming solid solution with several rare earth fluorides, allowing one to take full advantage of the energy transfer mechanisms that might occur among them. LiREF4 (RE=rare earth) crystals, for example, are so flexible that in some cases the doping concentration can go up to 100%. The Nd:LiLuF4 (Nd:LuLF) system has a 1047-nm emission bandwidth 25% larger than Nd:YLF, which makes it very promising for laser mode-locked operation. Nevertheless, lutetium compounds are very difficult to obtain, therefore Nd-doped mixed crystals grown from LiF-Y1−xLuxF3 (0<x<1) solid solutions were studied. A new laser medium was obtained for the Nd:LiLu0.5Y0.5F4 crystal, which presents a Nd emission bandwidth close to the Nd:LuLF (1.82 nm). The mode-locked operation in a diode pumped laser system using the KLM technique was performed and pulses of 4.5 ps were readily obtained. It is also shown that the LiGdF4 (GLF) is a promising host for diode pumped high power Nd lasers which require crystals with higher dopant concentrations. Another example is the Ho:LiYF4 (Ho:YLF) laser operating at 2065 nm obtained as a result of concentration optimization of the sensitizers Er and Tm. The optimization was based on a model comprising the various energy transfer mechanisms that take place in these long lived metastable states, heavily dependent on the dopants concentration. As a quasi-four-level system, the Ho concentration must be kept very small (≤0.005 mol%). The laser operation was optimized by the dynamical coupling of pump and laser modes, and by the dopants optical cycle. These optimizations resulted in a CW Ho laser with 2 W output, in a diode pumped system operation.

High-Pulse-Energy, All-Solid-State, Ultraviolet Laser Oscillator Using Large Czochralski-Grown Ce:LiCAF Crystal

A large Ce3+:LiCaAlF6 (Ce:LiCAF) crystal of 15 mm diameter was grown successfully by the Czochralski method. Owing to its large size, the Ce:LiCAF crystal demonstrated a maximum output pulse energy from the Ce:LiCAF laser of 21 mJ at a wavelength of 290 nm with an absorbed pump energy of 54 mJ from the fourth harmonic of a Q-switched Nd:YAG laser operated at a 10-Hz repetition rate. Furthermore, the lasing threshold was a low 12 mJ, and the slope efficiency was 39%.

Insights into the Local Structure of Tb-Doped KY3F10 Nanoparticles from Synchrotron X-ray Diffraction

Pure and Tb-doped nanocrystalline KY3F10 specimens were synthesized by coprecipitation, and portions of the samples underwent further heat treatment at 600 °C in a fluorinated atmosphere. Synchrotron X-ray diffraction patterns acquired at 30 keV allowed to determine both long- and short-range ordered structures by Rietveld and pair distribution function (PDF) analyses, respectively. PDF examination of the as-synthesized sample allowed to discern a slight deviation from the basic cubic building unit because the Y–F bond lengths could be explained in S.G. I4/mmm with cell parameters a = 8.1520(9) Å and c = 11.5876(29) Å, whereas Rietveld analysis could equally well fit both the cubic and tetragonal descriptions for the heat-treated specimens. Also, PDF revealed that the as-synthesized sample exhibited less structural coherence than the heat-treated one.

LiCAF crystal as a new vacuum ultraviolet optical material with transmission down to 112 nm

We report the superior transmission characteristics of LiCaAlF/sub 6/ (LiCAF) down to 112 nm. From the transparent wavelength shorter than that of conventional LiF, the non-hydroscopic nature of LiCAF, and the better mechanical properties compared with LiF, LiCAF is shown to be an ideal optical material for the vacuum ultraviolet region.

Growth and characterization of new oxide and fluoride crystals for optical applications

High quality oxide and fluoride single crystals for optical applications have been grown by the Czochralski technique. Lattice parameter investigation of grown Gd3YbxGa5−xO12 suggested that this crystal will be a superior material as substrate for optical isolators with large Faraday effect. Growth conditions of (La,Sr)(Al,Ta)O3 single crystals are discussed. These crystals have excellent lattice matching with GaN, a promising material for optoelectronic devices. Ce-doped fluoride single crystals—LiCaAIF6, LiYF4 and BaLiF3—have been grown for solid state UV laser applications. Growth results and optical characterization are discussed.

HIGH POWER SOLID STATE LASERS IN THE NEAR INFRARED

Since the early discovery of the laser, Nd:YAG crystals became one of the most used laser medium, in spite of the difficulty of processing the host material and the associated thermal problems during laser operation. As an alternative for the host material we have been developing lasers based on an alphabethic material, LiYf4, where the Nd is one of the possible dopants. Along with the crystal growing developments we have been developing the associated laser technology, including rod preparation, pumping cavities, power supplies, cooling systems, resonator configurations and contolling of the temporal behavior of the laser regime. So far we have developed three prototypes in the pulsed regime and three in the C.W. .

Spectroscopy and Modelling of a High Power Diode-pumped 2.3 μm Yb:Tm:YLF Laser

Energy transfer processes in Yb:Tm:YLF under 960 nm pumping have been quantitatively studied and a computer simulation considering the full rate-equation scheme has been performed. The 2.3 µm laser achieved 620 mW of output power.

Laser operation of Nd/sub x/:Y/sub y/Gd/sub 1-x-y/LiF/sub 4/ mixed crystals

In this paper laser operation in mixed Nd:YGLF crystals with different gadolinium concentration is presented. The results of Nd:GLF are compared with the advantages of the mixed crystals. Nd:YLF continues to be an excellent laser medium for near infrared high power lasers, especially for Q-switched and amplifier applications where its long storage lifetime is of advantage. The material Nd:YLF when considering its use for high power laser action under diode pumping.