Here laser studies of Ce3+:LiLuxMe1-x F4 (Me=Y3+,Yb3+) mixed crystals homologous to well-known Ce3+:LiYF4and Ce3+:LiLuF4 UV crystalline active media are reported. Optical spectroscopy and X-ray diffraction studies have
proved scheelite structure of the investigated mixture crystals. Advantages of LiLuYF4:Ce3++Yb3+ mixture crystals were
detected. Among them an opportunity to wider tuning range of laser oscillation in comparison to LiLuF4:Ce3++Yb3+
active medium by means of varying YF3/LuF3 content relation. As it was shown from laser experiments mutual shift of
5d-4f emitting transition of Ce3+ ions and color centers absorption band due to lattice parameter change gives an
optimum for YF3/LuF3 content relation corresponding to minimal overlap and maximal amplification band. EPR and
optical spectroscopy revealed the optimum ratio of Y3+ ions and Lu3+ in solid solutions of LiF-LuF3-YF3, where the
segregation coefficient Ce3+ of ions is increased 3-5 times compared with crystals LiYF4 and LiLuF4.
In present work the results of measurements of segregation coefficient of Nd3+ ions in LiLuxY1-xF4 (x=0- 1) crystals are
presented. Two methods for Nd3+ ions concentration measurements in the crystals are used. The first one - X-ray
fluorescence analysis (XRFA) - is used to establish the absolute concentration of impurity ions, and the second - optical
absorption spectroscopy (OAS) - allows to estimate not absolute, but relative impurity concentration. By comparison of
the results given by both methods the integral cross-sections of 4I9/2-2G7/2 transitions of Nd3+ ions doped in these crystals
were estimated. Thus, the standard samples, allowing to establish the absolute Nd3+ ions concentration in LiLuxY 1-x F4(x=0- 1) crystals by means of OAS-method, were created.
We have discovered that total intracavity losses, being dependent on color centers amount, go down for higher pump
energies for LiCaAlF6: Ce3+. This dependence is explained by the formation by the pump radiation and destruction of
color centers due to laser radiation. The more energy remains in the lasing cavity, the lower the color centers absorption.
Such dependencies were investigated for active medium crystals grown by different methods. Influence of growth
conditions on active media characteristics is discussed.
As a result we have shown for the first time that the crystal LiCaAlF6:Ce3+ internal losses depend on the pump energy.
Method has been worked out to determine the intracavity losses of the laser, which allows evaluation of prospects of its
practical use in the most correct way.
Here we report on pump-probe studies of KY3F10 and CaF2 doped with Ce3+ and Yb3+ ions. The crystals
Ce3+:KY3F10 and Ce3+:CaF2 show attractive spectral characteristics for tunable UV lasers application but have poor
photochemical stability. Their properties under intense UV pumping are affected by excited state absorption and color
centers formation.
This work was aimed at dynamic processes investigation induced by laser radiation of UV spectral range in
KY3F10 and CaF2 doped with Ce3+ and Yb3+ ions.
Optical gain was observed on CaF2:3++Yb3+ in the range 325-335 nm for the first time. It proves Yb3+ ions
coactivation antisolarant effect elaborated by us earlier. It is shown that in investigated crystals under a pump radiation,
resonant to 4f-5d Ce3+ ions transitions several types of color centers (CC) are formed. Set of these CC types are
determine the absorption at expected stimulated emission spectral range and magnitude of the induced loses is dependent
on many factors. As a result of competition between CC formation, free charges recombination and CC photodestruction
this balance can be shifted towards either rising or dropping losses at 5d-4f Ce3+ ions luminescence spectral range.
Here spectral-kinetic properties of Ce3+ ions and UV pumping induced color centers in KY3FI0 (KYF) crystals are reported and discussed. The efficiency of crystal-chemical approach of UV pumping induced solarization processes inhibition in these crystals was shown. Laser oscillation was achieved on the Ce:KYF crystals which were considered earlier as unpromising as active medium due to its photochemical instability.
We examine here the lasing conditions of a Ce :LiCAF laser crystal placed intracavity with a BBO nonlinear crystal and pumped longitudinally throughout an input dichroic mirror by the 532 nm radiation of a frequency-doubled diode-pumped Nd :YAG laser. The comparison with the results obtained with an off-axis configuration shows lower laser slope efficiencies but similar laser performance in terms of threshold absorbed pump fluences (around 200 mJ/cm2). A model based on revisited spectroscopic parameters is developed to account for these laser performance.
Laser-spectroscopic studies of polymeric laser-active media based on Rhodamaine 6G dye incorporated into modified Methylmethacrylate with Methacrylic Acid copolymer samples had been carried out. Absorption and luminescence spectra together with luminescence quantum yield were studied. The basic parameters of the laser oscillation and their stability were obtained. The new potential photostabilizator azotes- and sulphurs-containing organic compounds - Thiourea and Thiazol aromatic derivatives was specially synthesized and their role to dye and polymeric host photochemical stability were studied. In this paper it was shown that these synthesized compounds indeed are high effective photostabilizators. Also it was demonstrated that using of these additives leads to significant increasing of laser action efficiency, from one hand and to rising the working characteristics (operational lifetime) of solid-state laser-active media based on the new synthesized polymer composition materials, from other hand.
Opportunities of laser tests as a powerful and unique research tool of active medium fundamental properties directly in real laser operation conditions for variable intracavity losses are discussed. New technique of laser experimental data interpretation was developed and applied to the analysis of laser tests results for the series of Ce3+:LiYbxLu1-xF4 single crystals. Contribution coefficient into total pump-induced intracavity losses of ESA from upper laser level of Ce3+ ions and CC absorption at the laser wavelength was estimated. Basic parameters relevant to laser action performance were defined: Ce3+ ions ionization cross-section by pumping radiation and Ce3+ ion ESA at the laser wavelength, CC absorption (ionization) cross-section at the both pumping and laser radiation wavelength, life-times of transient and long-living color centers, stimulated emission cross-section and relative values of pump-induced free-charges trapping rate by host lattice defects and their corresponding recombination rate.
Here the photochemical properties of CaF2 crystal doped by Ce3+ and Yb3+ ions under pumping with ultraviolet (UV) irradiation resonant to the Ce3+ ion interconfigurational 5d-4f transitions were studied and significant codoping effect on the crystal solarization suppression was observed. The photodynamic processes model occurring in the active medium and which taking into account the color center formation and processes of enhanced free charges recombination via valence change of variety of impurity centers was proposed. This model allows to explain both electronic and hole types color centers suppression in Ce:CaF2 sampels codoped by Yb3+ ions. It was shown that Yb3+ ions in the crystal act as centers of electron and hole recombination with probability dependent on the extra charge compensation type. Therefore the proposed antisolarant mechanism of the coactivation effect satisfactorily describes photochemical properties of fluorite and other crystal hosts.
The spectral-kinetic characteristics of Ce3+ ions doped Na4Y6-xYbxF22 (x=0-0.05) single crystals were studied. Ce3+ ions 5d-4f interconfigurational fluorescence quantum yield versus Yb3+ ion codopant concentration was measured. Pump-induced color center absorption spectra were studied and the efficiency of Yb3+ ions codoping antisolarant crystal-chemical technique applied to Na4Y6F22:Ce3+ was demonstrated. The optimal Yb3+ ions content from the point of view of effective tunable laser action was estimated. The obtained results allow proposing Na4Y6-xYbxF22 as a new prospective photochemically stabilized material for UV/VUV application.
All known solid-state UV/VUV active media based on the interconfigurational 5d-4f transitions of trivalent rare earth ions in wide-band gap fluoride crystals are solarizable under intense UV/VUV pumping. Active media- specific pumping-induced color centers, on one hand, would absorb the laser radiation and reduce the laser efficiency. On the other hand they also get bleached by the pump laser radiation so that the current value of total intracavity losses is governed by dynamic equilibrium and depends on some active medium microparameters as well as the pump flux and is cavity specific. Presented here are the model of dynamic processes in a UV solarizable active medium under pumping conditions and the new technique of laser experimental data analysis for variable intracavity losses based on this model. It is shown that properly set laser experiment enables us to obtain the necessary active medium microparameters, including the pump excited state absorption and color center absorption of laser radiation cross- sections, photoelectron trapping rate by host lattice defects and their recombination rate. The results of this technique application to the laser experiment analysis for the series of Ce3+:LiYbxLu1-xF4 single crystals are presented.
Recently it was found that birefringence is induced in CaF2 crystals when they are illuminated with laser light at 157 nm. Taking into consideration that CaF2 is the only optical material used in 157 nm photolithography today, the possibility to use new wide band gap fluoride crystals as optical elements for 157 nm photolithography, even those of non-cubic symmetry, should be considered. Additionally fluoride dielectric crystals with wide band gaps doped with trivalent rare-earth (RE) ions can be used as passive or active optical elements int eh VUV. For doped crystals, applications depend on the structure of the energy level pattern of the 4fn-15d electronic configuration and RE ion concentration. In this work we are exploiting the use of wide band gap fluoride dielectric crystals doped with RE ions. The laser induced fluorescence spectrum at 157 nm, and the absorption spectra of the LiCaAlF6 crystals, pure and doped with RE ions, were investigated in the VUV region of the spectrum. A new m4tehod for monitoring RE concentration in wide band gap fluoride crystals, that is based on vibrating sample magnetometer measurement is presented as well.
The getting problems of UV and VUV laser action on the base of trivalent rare-earth ions activated crystals and the opportunities of upconversion pumping are discussed. The data of spectroscopical studies of stepwise multiphoton excitation of 4P'5d mixed configuration of Nd3, Pr3 and Ce3 ions in LiLuF4 and LiYF4 crystals are reported. The selection criterions of an intermediate 4f-state and a range of allowable pumping photon energies for the stepwise multiphoton excitation are proposed.
The laser induced fluorescence (LIF) spectrum of LiCaAlF:Nd3+ (LiCAF:Nd) single crystal, pumped by an F2 pulsed discharge molecular laser at 157.6 nm, was obtained in the vacuum ultraviolet (VUV) region of the spectrum. The fluorescence peaks were assigned to the 4f25dyields4f3 dipole allowed transitions of the Nd3+ ion. The LIF spectrum of the crystals, indicates that the 4f3yields4f25d dipole transitions, originate from the low Stark components of the 4K11/2 level of 4f25d configuration. The absorption spectrum of the crystal samples in the VUV was obtained as well. The electric crystal field splits all the levels of 4f25d mixed configuration. We observed seven dipole transitions, between the 4I9/2 ground level of 4f3 configuration and the Stark components of the levels of 4f25d configuration of the Nd3+ ion.
The excited state absorption (ESA) spectra in the UV active media LiCaAlF6:Ce3+ single crystal was studied by the amplified spontaneous emission technique. The nature of the ESA spectra is discussed.
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