G. B. Loutts

YTTERBIUM-DOPED APATITE-STRUCTURE CRYSTALS : A NEW CLASS OF LASER MATERIALS

A new class of Yb‐lasers is summarized in this article. The apatite family of crystals, based on the hexagonal structure of the mineral fluorapatite, has been found to impose favorable spectroscopic and laser properties on the Yb3+ activator ion. Crystals of Yb‐doped Ca5(PO4)3F, Sr5(PO4)3F, CaxSr5−x(PO4)3F, and Sr5(VO4)3F have been grown and investigated. Several useful laser crystals have been identified which offer a variety of fundamental laser parameters for designing diode‐pumped systems. In general, this class of materials is characterized by high emission cross sections (3.6–13.1×10−20 cm2), useful emission lifetimes (0.59–1.26 ms), a strong pump band (σabs=2.0–10.0×10−20 cm2), and pump and extraction wavelengths near 900 and 1045 nm, respectively. Efficient lasing has been demonstrated for several of the members of this class of materials, and high optical quality crystals have been grown by the Czochralski method. A summary of the laser parameters and a discussion of the Yb:apatite class of laser...

Efficient laser performance of Nd3+:Sr5(PO 4)3F at 1.059 and 1.328 μm

High efficiency, low threshold laser performance of Nd3+ doped Sr5(PO4)3F, or S‐FAP, crystals has been demonstrated. Its performance and properties compared with commercially available Nd:YVO4 indicate that Nd:S‐FAP is an outstanding medium for diode pumped laser applications at both 1.059 and 1.328 μm.

Growth of laser‐quality single crystals of Nd3+‐doped calcium fluorapatite and their efficient lasing performance

The Czochralski growth of laser‐quality Nd3+‐doped calcium fluorapatite single crystals and their lasing characterization are reported. Low threshold and high efficiency lasing performances were achieved in both continuous‐wave and long pulse laser‐pump‐laser operation. The effect of concentration quenching on laser performance is discussed.

Growth of high-quality single crystals of FAP (Ca5(PO4)3F) and its isomorphs

The Czochralski crystal growth of calcium fluorapatite Ca5(PO4)3F and calcium- strontium fluorapatite (Ca1-xSrx)5(PO4)3F is reported. The growth conditions for producing the rare earth and chromium doped crystals of high quality are presented. The influence of the replacement of some calcium for strontium in FAP on crystal quality and on spectroscopic properties is discussed.

Growth of high-quality single crystals of KYF4 by TSSG method

We report for the first time the growth of large size high quality single crystals of KYF4 (KYF) by TSSG method using the conventional weight-feed-back automatic diameter control Czochralski puller. We have made major revision of the KF-YF3 phase diagram and showed that KYF melts peritectically. The crystals can accommodate large size variations of the dopants. We were able to dope it with a large number of rare earth elements. The crystal has long fluorescence lifetime and weak phonon energy making it ideal as upconversion laser host.

Laser demonstration of neodymium-doped strontium chlorovanadate

Nd:Sr5(VO4)3Cl has been successfully lased using a Ti:sapphire pump laser operating at 810 nm. A slope efficiency of 52% for the 1.065 μm laser line and a lasing threshold of only a few tens of milliwatts have been measured. These favorable results are comparable to another Nd‐doped vanadate apatite, Sr5(VO4)3F. A brief survey of the spectroscopy of Nd3+ in Sr5(VO4)3Cl, Sr5(VO4)3F, and Ca5(VO4)3F reveals properties which suggest the vanadate‐based apatite crystals as a whole may represent a useful new class of Nd‐laser hosts.

Growth and characterization of pure Cr; Cr,Er and Cr,Ho codoped Y2SiO5

The Czochralski crystal growth of pure Cr, Er and Ho doped as well as Cr,Er and Cr,Ho codoped yttrium silicate Y2SiO5 (YSO) is reported. The growth conditions for producing the inclusion free single crystals of high optical quality are discussed. Spectroscopic properties of the singly doped and codoped material at room temperature are compared. Energy transfer processes from Cr4+ ions to Ho3+ and Er3+ ions in YSO host have been demonstrated for the first time.

Spectroscopy and lasing perfomance of Nd3+ doped Ca5(PO4)3F

Absorption and emission spectra and the fluorescence decay of Nd3+ doped Ca5(PO4)3F (FAP) are reported. A slope efficiency of 67% was obtained in pulse operation pumped by a long pulse Cr:LiSAF laser. Diode-laser-pumped lasing of Nd:FAP has been demonstrated for the first time. A slope efficiency of 25% was obtained without any optimization.

Growth of high-quality single crystal of KLiYF5 by TSSG method

We report for the first time the growth of large size single crystals of KLiYF5 (KLYF) by TSSG method using the conventional weight-feed-back automatic diameter control Czochralski puller. We also succeeded to grow for the first time single crystals of KLiGdF5 (KLGF). We constructed a new pseudo-binary phase diagram for the KF-LiF-YF3 system. Both KLYF and KLGF melt peritectically. They both showed high optical anisotropy as we expected. However, this anisotropy comes from the layer structure of the crystal which also gives a perfect set of (010) cleavage plane. At present, this is a problem preventing us to get crack-free single crystals.

Spectroscopy and lasing performance of Nd:KLiYF5 and KLiGdF5

Polarized spectroscopic studies are reported of Nd3+ doped KLiYF5 and Nd3+ doped KLiGdF5--a new anisotropic mixed fluoride. Emission in the 4F3/2 yields 4I11/2 channel is strongly polarized. Explanations of the spectroscopic behavior are presented in terms of the local rare earth environment. Lifetime measurements of the 4F3/2 state of Nd3+ ions in these monoclinic hosts and the dependence of fluorescence lifetime on dopant ion concentration are reported. Low threshold pulsed laser action was realized in both hosts with high efficiency, pumping with a long pulse Cr:LiSAF laser tuned to 797 nm.