Laser action of Nd³⁺ doped GdLiF₄ (GLF) has been demonstrated for the first time for both pulsed and CW laser pumped operation. A slope efficiency of 60% was obtained in either manner of operation. Detailed comparison studies show that the spectroscopic properties and laser performance of Nd:GLF are very similar to those of Nd:YLF. GLF, on the other hand, can be doped with much higher Nd³⁺ concentration.

We report for the first time the growth of high quality single crystals of Nd doped GdLiF₄. We have revised the phase diagram of this system to search for optimum growth composition. The crystals were grown from a highly incongruent peritectic melt using the conventional weight-feed-back automatic diameter control Czoochralski puller. Higher Nd doping (up to 4%) was achieved and the lasing performance was encouraging. We believe that the crystal has the potential to be used for diode pumped miniature laser applications.

Polarized spectroscopic studies are reported of Nd³⁺ doped KLiYF₅ and Nd³⁺ doped KLiGdF₅--a new anisotropic mixed fluoride. Emission in the ⁴F_3/2 yields ⁴I_11/2 channel is strongly polarized. Explanations of the spectroscopic behavior are presented in terms of the local rare earth environment. Lifetime measurements of the ⁴F_3/2 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.

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.

The Cr:LiSAF (Cr-doped LiSrAlF₆) laser material is currently being studied and employed in many types of laser systems, such as flashlamp-pumped oscillators and amplifiers, femtosecond regenerative amplifiers, diode-pumped minilasers, alexandrite laser- pumped systems, and Ar-ion laser-pumped self-mode-locked oscillators. While researchers certainly require a basic knowledge of the parameters that characterize the Cr:LiSAF material operating under 'normal' conditions (e.g., the emission cross section, storage time, dn/dT, etc.), they now also need to better understand the natural limits encountered by the material in optimized or novel laser systems. In particular, three areas will be addressed including, firstly, the pump-induced Auger upconversion mechanism, which entails the annihilation of pairs of Cr³⁺-excited states. Secondly, the thermomechanical properties of Cr:LiSAF will be reported and compared to other materials. Lastly, the results of assessing the durability of Cr:LiSAF at various temperatures, and for water/ethylene glycol solutions, will be addressed and compared to values characterizing common crystals and glasses.

The growth of high quality, low scattering loss Cr doped LiSAF single crystals by Czochralski pulling technique is described. Scattering loss as low as 0.1%/cm has achieved. The loss depends on the Cr doping concentration. We found that maintaining flat interface growth is crucial to reduce scattering loss and minimize wavefront distortion. These low loss materials provide true prospect of all solid state diode pumped tunable laser as well as ultrashort pulse generation and amplification.

The Czochralski crystal growth of calcium fluorapatite Ca₅(PO₄)₃F and calcium- strontium fluorapatite (Ca_1-xSr_x)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.

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.

We report here the crystal growth and characterization of single domain KTiOAsO₄ crystals suitable for devices application. The presence of inversion domains were established by various techniques including piezoelectric resonances and electrostatic toning. Techniques for removing these domains from as grown crystals were discussed.

Single-domain crystals of MTiOAsO₄, where M equals K, Rb, & Cs were grown from various alkali arsenate self fluxes. Their refractive indices and Sellmeier coefficients were determined with critical angle of total reflection measurements. Type-II phase-matched SHG was used to check for crystal domains and to determine the accuracy of the Sellmeier coefficients. The d_ij coefficients for second harmonic generation were determined with Maker-fringe technique at 1.06 micrometers . Electro-optic coefficients r_ji were determined with interferometry. This paper reports the above measurement results and discusses the systematics of crystal structure, birefringence, and optical nonlinearities among the pure isomorphs and their solid-solutions. Calculated SHG cut-offs and tuning curves are also reported.

The new crystal KNB (KNbB₂O₆) has been discovered and the XYB₂O₆ family of isomorphs (where X equals Cs, Rb, K, Y equals Nb or Ta) has been identified as a potential structure for non-linear optical applications. KNB was grown using a resistance heated TSSG scheme in an excess of B₂O₃ and K₂O. It was found that KNB has orthorhombic symmetry with space group Pna2₁, unit cell parameters a equals 31.236(4), b equals 7.315(2), c equals 9.210(4) angstroms, and is isostructural with RNB (RbNbB₂O₆), which was also grown. The non-linear properties of both members were assessed and discussions are presented on the origin of the non-linearity in this family of compounds.

In order to achieve large-sized and high-quality BaTiO₃ crystals, a three-temperature-zone gradient transport technique has been developed. Samples of commercial BaTiO₃ photorefractive crystals are routinely grown with dimensions of approximately 30 X 30 X 25 mm. Polished and poled cubes as large as 12 X 10 X 10 mm can be fabricated.

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.

Cr⁴⁺:Mg₂SiO₄ crystals have been grown by a Czochralski method with a radio frequency generator of 150 KHz. The ambient gas is a mixture of N₂ + O₂ of total pressure 1.4 atm.. The oxidizing atmosphere is employed to promote the Cr⁴⁺ concentration in the crystal. A special growth procedure is adopted and the outer surface of the Ir crucible is coated with a ZrO₂ layer to reduce Ir consumption. The primary laser testing has been operated using Q-switch Nd:YAG laser as a pumping source. The maximum output energy is 11.5 mJ for 70 mJ incident energy. The laser wavelength can be tuned from 1167 nm to 1332 nm. The second harmonic generation with BBO crystal as a frequency doubler results in 584 nm to 666 nm laser beams.

Cr³⁺:LiCaAlF₆ single crystals were grown by vertical Bridgman method from stoichiometric composition melt on our growth apparatus which was simple and easily operated. Boules were grown unseedly firstly and then along [1010] at 1 mm/h in a following atmosphere of Ar. The micro-defects in Cr³⁺:LiCaAlF₆ have been studied in detail with the help of x-ray diffraction, optical microscope, SEM, EDS and WDS. Heterogeneous micro-crystallites, inclusions of impurity particles and bubbles are found the main defects in the crystal. Traces of OH^- are found in the boules by infrared spectroscopy. The absorption and emission spectra of Cr³⁺ in LiCaAlF₆ are also presented.

Spectroscopic and laser properties of Cr,Nd:GGG and Nd:YAG crystals in the 1.3 - 1.45 micrometers wavelength range have been compared. Flashpumped Cr,Ce,Nd:GGG laser operating at 1.331 micrometers with total efficiency up to 3% and average output power of 65 W has been developed. For the first time to our knowledge oscillation at 1.4237 micrometers wavelength in Cr,Nd:GGG crystal have been obtained. Output energy of 2.3 J at this eyesafe wavelength with total efficiency of 1.23% have been obtained for flashpumped Cr,Ce,Nd:GGG laser in free-running mode. Average output power of 21.6 W at 13 Hz repetition rate have been achieved. Cr,Nd:GGG crystals advantages for 1.4 micrometers lasing compared to Nd:YAG crystals are discussed.

We have examined the feasibility of applying laser heated pedastal growth (LHPG) to the preparation of crystal fibers of BaY₂F₈ doped with Yb and Tm in an investigation of the optimization of this system as a visible upconversion laser. Material of sufficient optical quality to perform laser experiments was produced. In preliminary experiments, we have been able to observe room temperature laser operation at 649 nm with chopped 960 nm pumping in a fiber of composition BaYYb_0.99Tm_0.01F₈.

Intense visible to uv up-conversion emission is observed in Er³⁺ doped crystals of CsMgCl₃, CsMgBr₃ and CsCdBr₃ when the ⁴S_3/2 (E), ²H_11/2 (F) and ⁴F_7/2 (G) states of Er³⁺ are pumped. The host crystals are of CsNiCl₃ type which exhibit a linear chain structure. These hosts incorporate trivalent rare earth ions such as Er³⁺ to form a M³⁺-vacancy-M³⁺ pair center. When both ions in an Er³⁺-vacancy-Er³⁺ center are simultaneously excited an efficient energy transfer occurs between Er³⁺ ions.

Detailed room temperature absorption and emission spectra and the dynamics of the upconversion energy transfer were investigated in Yb, Ho codoped KYF₄. It was found, in the concentration range studied, that the energy transfer rate from Yb³⁺ to Ho³⁺ ions is linearly dependent on Ho³⁺ concentration. The back transfer from Ho³⁺ to Yb³⁺ ions was demonstrated and the transfer rate was found to be superlinearly dependent on Yb³⁺ concentration. Discussions are presented on the optimization of Yb³⁺ and Ho³⁺ concentrations for the potential use of Yb, Ho codoped KYF₄ as an upconversion green laser.

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.

The spectroscopic properties of Er³⁺ in the fluoride hosts LiYF₄ and KYF₄ or YLF and KYF respectively, are presented as they relate to cascade lasing of the ⁴I_11/2 to ⁴I_13/2 and ⁴I_13/2 to ⁴I_15/2 transitions. In this manner simultaneous lasing at near 2800 and 1600 nm is obtained.

The polarized emission cross section and quantum efficiency for the 1.55 micrometers laser transition (⁴I_13/2 yields ⁴I_15/2) in Er:SBA single crystal have been investigated through a spectroscopic approach based on a Judd-Ofelt analysis and a polarized fluorescence measurement. The effect of crystal orientation on the emission cross section has been studied. It has been found that the (pi) -polarized orientation has a cross section of about 3 times larger than the (sigma) -polarized counterpart. The total emission cross section for the transition of interest is 1.1 X 10^-20 cm² at 77 K and 7.5 X 10^-21 cm² at room temperature, respectively. Fluorescence decay measurements suggest that a nearly 100% quantum efficiency is possible for this laser line in an Er:SBA system.

Solid state and dye lasers of a new ype are developed which permit to get a multicolor radiation in a superbroad spectral region. These lasers possess a number of peculiarities and d istinc­ tions from common ones: the resonator is used , which forms the correspondence of the active medium pointB and their image after each full pass of the radiation through the resonator; a new method of a lasing speci:,rum tuning is used ; the gain narrowing is violated. These pecularii:,ieB give the ability to form a desirable spectral distribu­ -c ion of the output energy in "the spec"tral region from violet to red. A simultaneous lasing at three or more independently "'t.unable lines is possible. Their relative intensities can be opera-Ced independently also. It is shown experimentaly , that it is poseible to change the linewidth and to get lasing at several tunable pa.rte of the continuum or to get continuous spect.rum with the width up to 0 . 6 - 0 . 8 of the luminescence spectrum of the active medium. The Theoretical model of the new lasers is developed. The spectral characteristics of the output radiation of lasing are calculated n different situations. The cavities of such a type lasers are investigated by the matrix optics method. The main properties of these lasers are investigated experimentally.

Clear and transparent MgO doped LiTaO₃ single crystals have been grown by the Czochralski method from a congruent melt. Their optical damage resistance has been characterized by measurement of the change of photoinduced birefringence. We compare the optical damage resistance of LiTaO₃ and LiNbO₃, each containing almost the same amount of Fe impurities (less than 1 ppm), and show that LiTaO₃ has about 4 times lower optical damage resistance, which is not consistent with the data previously reported in the literature. On the other hand, MgO doped yielded an improvement in the optical damage resistance, as reported for MgO doped LiNbO₃ crystals. The other important features of MgO doping are that: improved transparency spectra especially in a visible wavelength region, resulting in a change of color to clear and transparent from brown-yellow, and a shift in the absorption edge to shorter wavelengths of 270 nm. These are important advantages when considering shorter wavelength accessibility and high conversion efficiency in second harmonic generation devices.

We have initiated a program at West Virginia University to establish the properties of point defects that are relevant to the optical damage phenomena in KTP, BBO, and LBO crystals. Defects have been characterized using optical absorption, electron paramagnetic resonance (EPR), electron-nuclear double resonance (ENDOR), and luminescence techniques. Among the defects which have been observed are impurity ions (iron, platinum, hydrogen, etc.), trapped hole centers, and trapped electron centers.

High quality lithium triborate LiB₃O₅ (LBO) single crystals with dimension larger than (phi) 60 X 15 mm have been grown by the flux pulling method. It is found that higher rate of growth is available for LBO crystal grown by the flux pulling method as compared with the flux seeding method. The investigation of the viscosity of melt in the Li₂O-B₂O₃ system indicates that the phenomenon of 'Boron Abnormality' has much influence on the viscosity of melt. Therefore, some ordinary metal oxides, such as alkali metal oxide and alkaline-earth metal oxide, could hardly be used as the optimal flux for LBO crystal growth. Some suitable compounds were proposed as the flux for the improvement of the LBO crystal growth due to the high viscosity of melt in the Li₂O-B₂O₃ system. The habit of LBO crystal has been studied with different oriented seeds in different crystal growth conditions. Investigations of the defects in LBO crystal show that the defects have close relationship with the habit of the crystal. Some important crystallographic data are also linked.

Rapid development of new materials for nonlinear optics initiates research in the area of testing these materials and measuring their optical properties, such as refractive index, absorption, and nonlinear susceptibilities. As a rule, it is necessary to measure both the spectral dependence (dispersion) of these parameters and their spatial distribution. Speaking about the dispersion dependences, one should take into account the resonant behaviour of the optical properties in the vicinity of electron and lattice resonances; spatial distribution can be connected with inhomogeneities, growth layers, domains and so on. Studying of spectral and spatial distributions of optical properties is especially complicated in the IR region of spectrum, which is, however, very important for the materials used as parametric up- and down- converters and frequency doublers. Polariton spectroscopy is rather effective for these purposes. The spectra of light scattering by polaritons are in fact the up-converted to the visible range spectra of the infrared equilibrium fluctuations in the matter, and the scattering intensity is determined by the quadratic susceptibility. Therefore the spectra contain the information about the dispersion of complex dielectric function and complex quadratic susceptibility in IR. In case when these parameters are spatially modulated, the character of modulation can be studied. The spectra also allow to determine the dispersion of the cubic susceptibility imaginary part. The experimental setup for polariton spectroscopy - a "polariton scattering spectrograph" - consists of an Ar laser generating at 488 nm which is used as a pump, the nonlinear crystal, two Gian prizms, an optical system for analysing the angular spectum and a spectrograph for analysing the frequency spectrum. The resulting two­ dimensional frequency-angular spectra can be measured and processed at the exit of the spectrograph. It should be stressed that though the effect of light scattering by polaritons is possible only in non-centrosymmetric media, in order to investigate centrosymmetric materials one can use the effect of hyper-Raman scattering by po­ laritons. In the first part of the work we show how the dispersion of different-order complex susceptibilities can be measured using a polariton scattering spectrum, and also how such a spectrum can give information about the periodic modulation of the optical properties. The second part of the paper describes the experimental results demonstrating the abilities of the method which were obtained in o: -iodic acid, lithium niobate and barium-sodium niobate crystals.

Single crystals of three Nd³⁺-doped disordered oxides have been grown and characterized as candidates for improved diode-pumped solid state lasers. These hosts include one melilite, SrGdGa₃O₇ (SGGM), and two gallogermanates, La₃Ga₅GeO₁₄ (LGG) and its isomorph La₃Ga₅SiO₁₄ (LGS). Spectroscopic properties such as absorption and emission bandwidth, fluorescent lifetimes, and emission cross-sections are included. Laser properties of the ⁴F_3/2 - ⁴I_11/2 transition at 1.06 microns have been measured.