Actively mode-locked Tm-Ho:LiYF<Subscript>4</Subscript> and Tm-Ho:BaY<Subscript>2</Subscript>F<Subscript>8</Subscript> lasers

We report on the generation of mode-locking pulse trains with high average output powers from diode-pumped Tm-Ho:LiYF₄ and Tm-Ho:BaY₂F₈ lasers emitting at around 2 μm. The highest output power of 365 mW was obtained with the Tm-Ho:YLF₄ laser, whereas the shortest pulse duration of 120 ps and the widest tunability range of 59 nm was achieved with the Tm-Ho:BaY₂F₈ laser. PACS 42.55.Xi; 42.60.Fc; 42.72.Ai; 42.55.Rz; 42.70.Hj     

VUV luminescence of Er<Superscript>3+</Superscript> ions in LiYF<Subscript>4</Subscript> and BaY<Subscript>2</Subscript>F<Subscript>8</Subscript> crystals

Vacuum ultraviolet luminescence of Er³⁺ ions in LiYF4 and BaY₂F₈ crystals has been investigated. It is revealed that under excitation by 193 nm radiation from an ArF excimer laser the interconfigurational 5d–4f radiative transitions in Er³⁺ ions are observed. It is shown that from the LiYF₄:Er crystal only the spin-forbidden luminescence (λ = 165 nm) is detected, whereas both the spin-forbidden (λ = 169 nm) and spin-allowed (λ = 160.5 nm) components are observed from the BaY₂F₈:Er crystal.     

Upconversion excitations in Pr<Superscript>3+</Superscript>-doped BaY<Subscript>2</Subscript>F<Subscript>8</Subscript> crystal

We report the orange-to-blue and infrared-(IR)-to-blue wavelengths upconversion luminescence in Pr³⁺:BaY₂F₈ crystals. Mechanism of the orange light upconversion into blue ³P₀ state emission was confirmed to be energy transfer between two Pr³⁺ ions in the ¹D₂ state. IR-to-blue upconversion has only been observed under two different color IR pumping. The first resonant step was the ³H₄→¹G₄ ground state absorption transition, and the second resonant transition was the excited state absorption from the ¹G₄ to ¹I₆ and ³P_J levels. A comparison of the efficiency of the IR-to-blue upconversion in several praseodymium activated host is presented and discussed. A model of the IR pumped upconversion praseodymium blue laser is presented and the population inversion conditions are calculated.     

Thermal quenching of luminescence of BaY<Subscript>2</Subscript>F<Subscript>8</Subscript> crystals activated with Er<Superscript>3+</Superscript> and Tm<Superscript>3+</Superscript> ions

Thermal quenching of interconfigurational 5d-4f luminescence of Er³⁺ and Tm³⁺ ions in BaY₂F₈ crystals is studied in the temperature range of 330–790 K. The quenching temperatures are ~575 and ~550 K for Er³⁺ and Tm³⁺, respectively. It is shown that quenching of 5d-4f luminescence of Tm³⁺ ions is caused by thermally stimulated ionization of 5d electrons to the conduction band.     

Luminescence and electronic excitations in KBe<Subscript>2</Subscript>BO<Subscript>3</Subscript>F<Subscript>2</Subscript> crystals

This paper reports on a study of the dynamics of electronic excitations in KBe₂BO₃F₂ (KBBF) crystals by low-temperature luminescent vacuum ultraviolet spectroscopy with nanosecond time resolution under photoexcitation by synchrotron radiation. The first data have been obtained on the kinetics of photoluminescence (PL) decay, time-resolved PL spectra, time-resolved PL excitation spectra, and reflection spectra at 7 K; the estimation has been performed for the band gap E _g = 10.6−11.0 eV; the predominantly excitonic mechanism for PL excitation at 3.88 eV has been identified; and defect luminescence bands at 3.03 and 4.30 eV have been revealed. The channels of generation and decay of electronic excitations in KBBF crystals have been discussed.     

VUV F<Subscript>2</Subscript> laser ablation of sodium chloride

We report an investigation of the ablation of NaCl crystals at the 157-nm wavelength of the F₂ laser where there is very strong excitonic absorption. Probe-beam deflection and etch-rate measurements show that the interaction is characterised by a low ablation threshold (∼80 mJ cm^-2) and a capability for controllable material removal at the nanometer level. Scanning electron microscopy of the exposed surfaces show this to be microscopically smooth but with fine cracks present. It is demonstrated that micron-scale features can be formed in NaCl using 157-nm laser ablation, a result attributed to the strongly localised optical and thermal nature of the interaction. The results are discussed within the framework of a thermal vaporisation model. Received: 29 May 2002 / Accepted: 17 July 2002 / Published online: 4 November 2002 RID="*" ID="*"Corresponding author. Fax: +44-1482/465606, E-mail: p.e.dyer@hull.ac.uk     

Quasi-three-level Nd:YVO<Subscript>4</Subscript> laser by diode pumping at 888 nm

We report efficient laser emission on the 914 nm ⁴ F _3/2 to ⁴ I _9/2 transition in Nd:YVO₄ under the pump with diode lasers at 888 nm for the first time. Continuous wave 6.57 W output power at 914 nm is obtained from a V-type resonator under 18.3 W of absorbed pump power; the slope efficiency with respect to the absorbed pump power was 60.6%. Moreover, intracavity frequency doubling with BiB₃O₆ (BiBO) nonlinear crystal yielded 1.77 W of deep-blue light at 457 nm with beam quality characterized by an M₂ factor of 1.25.     

All-solid-state Nd:YVO<Subscript>4</Subscript> laser at 1342 nm under 914 nm diode laser pumping

A Nd:YVO₄ crystal was pumped directly into the emitting level by a laser diode at 914 nm. We achieved an output power of 1.46 W at 1342 nm for an incident pump power of 18.3 W, corresponding to an optical-to-optical conversion efficiency of 8.0%. The fluctuation of the output power was better than 2.3% in the given 30 min. The beam quality M₂ factor value was equal to 1.15 at the maximum output power.     

Charge carrier mobility in crystals of the Pb<Subscript>0.67</Subscript>Cd<Subscript>0.33</Subscript>F<Subscript>2</Subscript> superionic conductor

The frequency (ν = 10^?1–10⁷ Hz) dependences σ(ν) of the conductivity of single crystals of the Pb_0.67Cd_0.33F₂ superionic conductor with the fluorite-type structure (CaF₂) in the temperature range of 132–395 K have been studied. The dependences σ(ν) have been discussed in the framework of the hopping relaxation of ionic carriers, which are mobile anions F^?. From experimental curves σ(ν), the direct-current (dc) conductivity σ_dc and the average charge carrier hopping frequency ν_h have been determined. This has made it possible to calculate the charge carrier mobility μ_mob and charge carrier concentration n _mob in these crystals. At room temperature (293 K), the electrical parameters are σ_dc = 1.6 × 10^?4 S/cm, ν_h = 2.7 × 10⁷ Hz, μ_mob = 2.0 × 10^?7 cm²/(s V), and n _mob = 5.1 × 10²¹ cm^?3.     

Thermodynamic properties and structure of oxyfluorides Rb<Subscript>2</Subscript>KMoO<Subscript>3</Subscript>F<Subscript>3</Subscript> and K<Subscript>2</Subscript>NaMoO<Subscript>3</Subscript>F<Subscript>3</Subscript>

According to the results of calorimetric and structural studies, the Fm{ie1202-1}m phase in K₂NaMoO₃F₃ remains stable at least to 100 K. No ferroelectric transformation assumed earlier has been revealed in a series of Rb₂KMoO₃F₃ samples prepared using various technologies. Only a phase transition of nonferroelectric origin has been observed near 195 K, and its thermodynamic characteristics have been determined. An analysis of the stability of the cubic structure of molybdenum fluorine-oxygen elpasolites-cryolites has been performed in the framework of the hypothesis on strengths of interatomic bonds. The barocaloric effect in Rb₂KMoO₃F₃ has been estimated.     

Spectral dynamics of narrow-band F<Subscript>2</Subscript> laser for optical lithography

We describe the spectral dynamics of a line-narrowed F ₂ laser, based on numerical simulation by a newly developed simulation code. The results were compared with the experimental results and it was found that the code could predict well the performance of a line-narrowed operation of the F ₂ laser. The code was also used to obtain a guideline for the optimized operation of an injection-seeded F ₂ laser system. In addition, a new spectral narrowing technique for the F ₂ laser has been proposed and its effectiveness was evaluated by the simulation code.     

Raman scattering by Hg<Subscript>2</Subscript>F<Subscript>2</Subscript> polycrystals

The Raman spectra of Hg₂F₂ polycrystals are experimentally measured for the first time. The spectra of Hg₂F₂ are interpreted using X-ray diffraction analysis and group-theoretical treatment. The results obtained are discussed in comparison with the spectra of Hg₂Hal₂ crystals.     

Quasi-three-level Nd:YVO<Subscript>4</Subscript> laser operation at 914 nm under 879 nm diode laser pumping

We present experimental investigation on quasi-three-level Nd:YVO₄ laser operation at 914 nm under 879 nm diode pumping directly into emitting level. A maximal output power of 3.0 W under an absorbed pump power of 13.4 W was got, corresponding to an optical conversion efficiency of 22.4% and a slope efficiency of 40.3%. To the best of our knowledge, this is the first report on a Nd:YVO₄ laser at 914 nm using rod-type single crystal as the gain medium and end pumped by diode directly into the emitting level.     

Continuous wave Nd:LuVO<Subscript>4</Subscript>-LBO blue laser under direct 888 nm diode laser pumping

We report the efficient blue laser at 458 nm generation by intracavity frequency doubling of a continuous wave (CW) laser operation of a diode pumped Nd:LuVO₄ laser on the ⁴ F _3/2 → ⁴ I _9/2 transition at 916 nm. An LiB₃O₅ (LBO) crystal, cut for critical type I phase matching at room temperature is used for second harmonic generation of the laser. At an incident pump power of 18.2 W, as high as 1.73 W of continuous wave (CW) output power at 458 nm is achieved. The optical-to-optical conversion efficiency is up to 9.5%, and the fluctuation of the red output power was better than 3.5% in the given 30 min.     

Lasing from a solid-state Ca<Subscript>3</Subscript>Ga<Subscript>2</Subscript>Ge<Subscript>3</Subscript>O<Subscript>12</Subscript>:Nd<Superscript>3+</Superscript> laser at a high power of diode pumping

Experimental data for cw lasing from a compact solid-state laser based on a neodymium-doped calcium-gallium-germanium-garnet crystal (Ca₃Ga₂Ge₃O₁₂:Nd³⁺) at a wavelength of 1.06 μm in the case of intense diode pumping are reported. The laser output reaches 0.7 W for a cavity 15 mm long and an active element 1 mm thick. It is shown that the output power is limited by a thermal lens placed in the active element.     

Efficient intracavity frequency-doubled Nd:YLiF<Subscript>4</Subscript>-LiB<Subscript>3</Subscript>O<Subscript>6</Subscript> red laser emission under diode pumping into the emitting level

We report for the first time (to our knowledge) an efficient compact red laser at 660.5 nm generation by intracavity frequency doubling of a continuous wave laser operation of a diode direct pumped Nd:YLiF₄ (Nd:YLF) laser on the ⁴ F _3/2 → ⁴ I _13/2 transition at 1321 nm. A LiB₃O₆ (LBO) crystal, cut for critical type I phase matching at room temperature is used for second harmonic generation of the laser. At an absorbed pump power of 16.2 W, as high as 1.5 W of continuous wave output power at 660.5 nm is achieved with 10-mm-long LBO. The optical-to-optical conversion efficiency is up to 9.3%. Comparative results obtained for the pump with diode laser at 806 nm, into the highly-absorbing ⁴ F _5/2 level, are given in order to prove the advantages of the 880 nm wavelength pumping.     

Excitons and energy transfer in KPb<Subscript>2</Subscript>Cl<Subscript>5</Subscript> and RbPb<Subscript>2</Subscript>Br<Subscript>5</Subscript> laser crystals

Excitonic states, radiative relaxation of electronic excitations, and energy transfer to luminescence centers in both undoped and rare-earth activated (Pr, Er, Nd, Ho, Tb, Tm) KPb₂Cl₅ and RbPb₂Br₅ crystals were studied using low-temperature (8 K) time-resolved VUV spectroscopy under selective photoexcitation by synchrotron radiation.