This paper reports two effective methods for improving the output of NaCl (OH-): color center laser. The first are eliminating the laser non – active color centers and enhancing the concentration of color center in laser crystal; The second is chosing the auxiliary light with suitable wavelength, such as 0. 475μm, during laser operation. The authors also discuss and interpretate the two methods in the paper.

High resolution spectroscopy of Nd3+ in Potassium Lithium Yttrium Fluoride (KLiYF5 ) at ≤80 K reveals two crystal-field sites which are equally populated independent of concentration. Site selective excitation of photoluminescence distinguishes each site's contribution to the spectra. The analysis of integrated line intensities reveals a bidirectional energy transfer between Nd3+ ions in different sites. A rapid increase in transfer rate with increasing Nd concentration is explained only if non-radiative transfer via exchange interaction contributes strongly to the effect. The observed relative decrease with increasing concentration of those emission lines which overlap strongly with opposite-site absorption lines implies that radiative transfer is also important. The energy transfer strongly depends on temperature (2 K – 80 K) which indicates the participation of phonons.

We have fabricated highly-orientated crystalline potassium titanyl phosphate (KTP) films on a variety of substrates by pulsed excimer laser ablation. The resulting films have been extensively characterized in terms of their compositional, crystalline, and optical properties. Nonlinear optical property of secondary harmonic generation of the films has been evaluated with a high d value comparable to that of KTP bulk crystals. The results are encouraging that the KTP films deposited are very promising for nonlinear optical waveguide device applications.

First order quasi-phase-matching in a proton exchanged LiTaO3 channel waveguide structure is reported, where the periodic domain inversion is created by the application of a periodic compressive stress near the Curie temperature. The processing conditions, driving force, and effects on resulting domain structure is reported, including the observation of domain structures with periods as small as 0.36 μm. A waveguide second-harmonic generation structure with a periodic 3.45 μm domain inversion structure is fabricated and evaluated to quasi-phase-match 420 nm blue light with 840 nm output available from standard laser diode sources.

Epitaxial PbTiO3 thin films have been grown on MgO substrate. The as grown PbTiO3 thin films were multi-domain with the existence of a-domain and c-domain. The amount of adomain can be reduced with the application SrTiO3 transitional layer, which also improve the crystalline quality and thus the nonlinear optical properties. Blue light generation in the PbTiO3/SrTiO3/MgO heterostructure was demonstrated based on waveguide mode dispersion.

The versatility of lanthanide-doped fluorozirconate glass fiber as a laser material is evident since over the past four years more than 30 laser transitions have been demonstrated in this medium, at wavelengths ranging from 480nm to 3.45μm. In this low phonon-energy glass metastable lanthanide energy levels are found wherever the gap to the next level exceeds ∼2000cm-1. The glass not only has extended transparency in the infrared but also appears resistant to photochromic damage by blue radiation, making it an attractive blue laser gain medium. In particular it has been shown that some blue and green laser transitions in these fibers can be operated efficiently with infrared pumping, offering the possibility of diodepumped operation. Various schemes are potentially of interest; for example 3mW of 493nm laser power has been generated from a praseodymium-doped fluoride fiber pumped at two wavelengths by the emission and unabsorbed 840nm pump radiation from an ytterbium-doped silica fiber laser.

Waveguide structures offer the possibility of making an upconversion laser operating at room temperature. By reducing the optical mode cross section can lead to a very high pump power density which allows modest pumping powers to overcome non-radiative decay processes. We have reported earlier on the observation of upconversion luminescence from both planar and channel waveguides of Erbium doped ZnF2 on MgF2(001) and Erbium doped PbF2 on GaAs(100). The epitaxial fluoride layers were all grown by Molecular Beam Epitaxy. Fluoride films preferentially grow on the (111) GaAs surface. In order to exploit this fact, we have grown Erbium doped PbF2 on GaAs(111)B with an intervening SrF2 cladding layer. The SrF2 and PbF2 growth conditions have been optimized on GaAs(111)B using X-ray rocking curve analysis. The crystalline quality of the films grown on GaAs(111)B are far superior to those grown on GaAs(100). Upconversion luminescence has been observed in the PbF2: Er/SrF2/GaAs(111)B planar waveguide structures. The guide ends were formed by cleaving the semiconductor wafer and the 800nm and 980nm pump light was introduced from a Ti-Sapphire laser by end pumping using a microscope objective.

CdS thin films with doping concentration as high as 1017 cm-3 for p-type or 1021 cm-3 for n-type were achieved by pulsed excimer laser deposition without any post-annealing process. These films were grown on InP or GaAs substrates with good crystalline quality. By using this technique, CdS thin film p-n junctions were produced successfully.

We report the 1.03 μm laser operation of a diode-pumped Yb doped YAG planar waveguide at room temperature. The fabrication of multilayer planar waveguides by Liquid Phase Epitaxy and their characterization are also described.

Laser results (40 mW threshold, 80 % slope efficiency) obtained with a 2.9 % output coupler compares favourably with bulk results reported elsewhere.

This work assesses the incorporation of dopant ions such as Al3+, Ga3+, Zr4+, Nb5+, Ta5+ and Er3+ into the core of germanosilicate optical fibres via modified-chemical-vapour-deposition plus solution doping fabrication techniques. We find that highly-charged smaller ions, like Al3+ and Ta5+, behave similarly. These ions are more efficiently incorporated, assist in the incorporation of Er3+, and have the same influence on the fluorescence spectra of Er3+. The structural role of these ions appear to be their ability to provide nonbridging oxygens around Er3+. The waveguide and lasing characteristics of Er3+ codoped with Ta5+ are presented.

Diode pumped thulium and holmium lasers have long been thought to be the ideal solution to be problem of producing a high energy, efficient, diode-pumped, laser source due to the long upper state lifetimes. However the fundamental energy transfer process of upconversion can limit the storage of energy in the system and increase the thermal loading on the crystal. A numerical solution to the rate equations is used to model the laser performance of both 785 nm pumped Tm: YAG and 1.9 μm pumped Ho: YAG, including the effects of ground state depletion and upconversion. The benefits and problems of both systems will be discussed in detail.

Expanding the crystal field in terms of operators that transform as the irreducible representations of the Td group leads to an intuitive interpretation of the crystal-field parameters. We apply this method to the crystal field experienced by Nd3+ dopants in the laser crystals YLiF4, YVO4, and KLiYF5.

The material and spectroscopic properties of Cr-doped Ca5(PO4)3F (FAP) were investigated using several different chemical and physical means. From analytical titration measurements the chromium in Cr:FAP was found to be tetravalent. ESR measurements detected a trace (0.5 - 10 ppm) of Cr5+ (3d1) and no evidence for Cr3+ (3d3). The absorption and emission spectra of Cr: FAP can be interpreted on the basis of Cr4+ (3d2) ions substituting for P within a distorted tetrahedron of oxygen ions. Calculated electronic (Stark) levels for Cr4+ based on an approximate site symmetry of C4 agree well with levels deduced from an analysis of the experimental optical data. The model Hamiltonian includes Coulombic parameters B and C, interconfiguration interaction terms and the spin-orbit coupling for the 3d2 atomic configuration of Cr4+ and crystal-field terms in C4 symmetry. The parametrized Hamiltonian was diagonalized within the complete d2 configuration. Both free ion and crystal field parameters are presented.

In this paper the relationships between the crystal structure, chemical composition and electronic structure of laser materials, and their optical properties are discussed. A brief description is given of the different laser activators and of the influence of the matrix on laser characteristics in terms of crystal field strength, symmetry, covalency and phonon frequencies. The last part of the paper lays emphasis on the means to optimize the matrix-activator properties such as control of the oxidation state and site occupancy of the activator and influence of its concentration.

Oxygen and moisture present in the growth atmosphere, may react with fluoride melts, compromising the optical quality of the grown crystals. Low level oxygen contamination can appear as an oxyfluoride coating over YLF boules without affecting their quality or as haze or milkiness in BaY2F8 and in LISAF and its analogs. Vacuum furnaces used to lower the level of these contaminants introduce hydrocarbon residues that might reduce the valence state of dopant ions such as Cr and Yb in some fluoride systems. Cr-doped LICAF and LISAF have similar behavior in contaminated atmospheres, whereas Cr-doped LISGAF displays very different behavior.

An X-cut LiNbO3 substrate has been doped with Yb3+ ions by thermal diffusion from an Yb metal film of thickness 7nm. Polarised absorption and fluorescence spectra of the dopant ion have been measured using Ti-diffused y-propagating channel waveguides prepared in the doped region. Yb is a diode pumpable laser ion with characteristics that can be compared favourably with those of Nd in some respects; for example the small energy difference between pump and laser photons reduces thermal load facilitating high power operation. A waveguide laser geometry is particularly advantageous for Yb due to the quasi-3-level nature of the laser transition. The simple fabrication technique described here has been used to produce a system which may have the potential to operate as an Yb waveguide laser in an electro-optic host crystal.

Mn5+:Sr5(VO4)3F is a new laser material with spectroscopic and laser properties similar to those of other recently reported Mn doped vanadates, but with the advantage of easier crystal growth. It has strong, broad absorption bands from 600–1000 nm and a sharp emission peak at 1164 nm. The splittings and polarization dependence of the spectra are consistent with the approximate C3v site symmetry reported for other apatites. Despite relatively large distortion from tetrahedral symmetry, the 1E and 3T2 states remain sufficiently separate that the emission is almost purely from the 1E state. As a result, laser operation is of the three-level type. Single pass gain/loss measurements indicate that any excited state absorption at the laser wavelength must be significantly smaller than the stimulated emission.

During crystal growth of yttrium orthovanadate (YVO4) from the Y-V-O melt system, strong incongruent vanadium oxide vaporization occurs, causing changes in both oxygen and Y/V stoichiometry and resulting in significant color centers and inclusion problems in the crystal. Oxygen deficiency is an inherent problem in melt grown YVO4 crystals, and this work seeks to clarify this phenomenon. Lattice parameter decrease was observed in oxygen deficient YVO4-x fibers grown by the laser heated pedestal growth (LHPG) technique. Although post-growth annealing in O2 atmosphere can eliminate the black color centers in the fibers, it causes anisotropic lattice distortions within the crystal. Consequently, preventing the formation of oxygen deficient YVO4-x holds the most promise for production of scattering free YVO4 crystals. Since the complete suppression of incongruent vaporization is very difficult during high temperature growth procedure, utilization of a proper flux system having a low melting temperature “compensating phase” for collecting non-pentavalent vanadium oxides is recommended to achieve directly-grown oxygen deficiency free yttrium orthovanadate crystals.

This paper reports the main spectroscopic characterizations and laser experiments carried out on two new crystal hosts: the! yttrium orthosilicate Y2SiO5 and the silicate oxyapatite Sr2Y8(SiO4)6O2 (hereafter noted SYS), doped with Ytterbium and Erbium for a 1,55 μm laser emission and with Thulium for a 2 μm emission. Four new lasers have been demonstrated at 1,554 μm, 1,576 μm, 1,99 μm and 2,05 μm for respectively Yb,Er:SYS; Yb,Er:Y2SiO5; Tm:SYS and Tm:Y2SiO5. If for the Yb,Er codoped materials laser performances are still poor compared with the Yb,Er phosphate glass, the Tm doped materials exhibit laser performances similar to the Tm:YAG and look very promising.

We have investigated new solid-state passive Q-switch materials for the Er:glass laser at 1.53 μm. Saturable absorber Q-switching has been obtained using Er3+:Ca5(PO4)3F, Er3 +:CaF2, and U4+:SrF2.