Spectroscopic properties of Yb ions in La2(WO4)3 crystal

Yb³⁺-doped La₂(WO₄)₃ single crystals were grown by the Czochralski technique. Absorption and fluorescence spectra of the crystal were recorded at the room temperature. The stimulated emission cross-sections of Yb³⁺ ions were calculated using the reciprocity method and Fuchtbauer-Ladenburg formula, respectively. The fluorescence decay curves of ²F_5/2 manifold of Yb³⁺ ions were recorded at room temperature for both crystal and powder samples. The effect of radiation trapping on the spectroscopic properties is discussed. Comparison with other Yb³⁺-doped laser crystals is made. The results show that Yb³⁺:La₂(WO₄)₃ crystal is a promising laser material.     

Thermal effects investigation and cavity design in passively mode-locked Nd:YVO4 laser with a SESAM

A diode-pumped passively mode-locked Nd:YVO₄ laser with a five-mirror folded cavity is presented by using a semiconductor saturable absorber mirror (SESAM). The temperature distribution and thermal lensing in laser medium are numerically analyzed to design a special cavity which can keep the power density on SESAM under its damage threshold. Both the Q-switched and continuous-wave mode-locked operation are experimentally realized. The maximum average output power of 8.94 W with a 9.3 ps pulse width at a repetition rate of 111 MHz is obtained under a pump power of 24 W, correspondingly the optical slope efficiency is 39.2%.     

New green self-frequency-doubling diode-pumped Nd:Ca4GdO(BO3)3 laser

3+ :Ca₄GdO(BO₃)₃ (Nd:GdCOB). 21 mW of green cw laser emission for an absorbed pump power of 820 mW were achieved under laser diode-pumping. 64 mW of green cw laser output were obtained with 1 W of absorbed pump power under titanium-sapphire pumping. Its availability in large-size crystals with good optical quality makes Nd:GdCOB a true challenger to the best SFD laser crystal reported so far: Nd:YAl₃(BO₃)₄ (Nd:YAB or NYAB). Received: 2 March 1998/Revised version: 20 May 1998     

Comparison of Laser Performances of 5at.% Yb:Gd2xY2(1-x)SiO5 Crystals between Different Cutting Directions

We investigate the laser actions of 5at.% Yb:Gd_2xY_2(1-x)SiO₅ (Yb:GYSO; x=0.1) crystals with different cutting directions, parallel and vertical to the growth axis. Our results show that the cutting direction of the sample plays an astonished role in the laser operation. The sample cut vertically to the growth axis possesses the favourable lasing characteristics. Its output power reaches 3.13W at 1060nm with a slope efficiency of 44.68% when the absorbed pump power is 8.9,W. In contrast, the sample cut parallel reaches only 1.65W at 1044nm with a slope efficiency of 33.76% with absorbed pump power of 7.99W. The absorption and emission spectra of the two samples are examined and the merit factor M is calculated. Our analysis is in agreement well with the experimental results. The wavelength tuning range of the superior sample covers from 1013.68nm to 1084.82nm.     

Polarized spectroscopic properties of Nd-doped KGd(WO4)2 single crystal

The polarized absorption spectra, infrared fluorescence spectra, upconversion visible fluorescence spectra, and fluorescence decay curve of orientated Nd³⁺:KGd(WO₄)₂ crystal were measured at room-temperature. Some important spectroscopic parameters were investigated in detail in the framework of the Judd-Ofelt theory and the Fuchtbauer-Ladenburg formula. The effect of the crystal structure on the spectroscopic properties of the Nd³⁺ ions was analyzed. The relation among the spectroscopic parameters and the laser performances of the Nd³⁺:KGd(WO₄)₂ crystal was discussed.     

Characteristics of Nd：GdVO4 Laser with Different Nd-Doping Concentrations

We report the properties of a compact diode-pumped continuous-wave Nd：GdV04 laser with a linear cavity and different Nd-doped laser crystals. In a 0.2at.% Nd-doped Nd：GdVO4 laser, 1.54 W output laser power is achieved at 912nm wavelength with a slope efficiency of 24.8% at an absorbed pump power of 9.4W. With 0.3at.% Nd-doping concentration, we can obtain the either single-wavelength emission at 1064nm or 912nm or the dual-wavelength emission at 1064nm and 912nm by controlling the incident pump power. From an incident pump power of 11.6 W, the 1064nm emission between ^4Fa/2 and ^4I11/2 is suppressed completely by the 912nm emission between ^4Fa/2 and ^4I9/2. We obtain 670 mW output of the 912nm single-wavelength laser emission with a slope efficiency of 5.5% by taking an incident pump power of 18.4 W. Using a Nd：GdV04 laser with 0.4at.% Nd-doping concentration, we obtain either the single-wavelength emission at 1064nm or the dual-wavelength emission at both 1064nm and 912nm by increasing the incident pump power. We observe a strong competition process in the dualavelength laser.     

Spectral performance and intensive green upconversion luminescence in Er/Yb-codoped NaY(WO4)2 crystal

Using Czochralski (CZ) pulling method, an Er³⁺/Yb³⁺-codoped NaY(WO₄)₂ crystal was prepared. Absorption spectra, emission spectra and excitation spectra of this crystal were measured at room temperature. Some optical parameters, such as intensity parameters, spontaneous emission probabilities and lifetimes, were calculated from absorption spectra with Judd-Ofelt (J-O) theory. Upconversion luminescence excited by a 970 nm diode laser was studied. In this crystal, green upconversion luminescence is particularly intensive. Energy transfer mechanisms that play an important role in upconversion processes were analyzed. Two cross-relaxation processes: ⁴G_11/2 + ⁴I_9/2 → ²H_11/2 (or ⁴S_3/2) + ²H_11/2 (or ⁴S_3/2), and ⁴G_11/2 + ⁴I_15/2 → ²H_11/2 (or ⁴S_3/2) + ²I_13/2, which contribute to the intensive green luminescence under 378 nm excitation, were put forward. Background energy transfer ⁴G_11/2(Er³⁺) + ²F_7/2(Yb³⁺) → ⁴F_9/2(Er³⁺) + ²F_5/2(Yb³⁺) was also demonstrated.     

Laser operation of the new stoichiometric crystal KYb(WO4)2

We demonstrate for the first time laser operation with the monoclinic stoichiometric crystal KYb(WO₄)₂ (hereafter KYbW). Lasing on the ² F _5/2 ?² F _7/2 transition of Yb³⁺ at room temperature has been achieved near 1074 nm with >41% slope efficiency (>26% maximum conversion efficiency) using a 0.5-mm-thick plate of KYbW. This new laser material holds great promise for diode-pumped high-power lasers, thin-disk and waveguide designs as well as for ultrashort (ps/fs) pulse laser systems. Received: 10 October 2001 / Revised version: 19 November 2001 / Published online: 17 January 2002     

Diode-pumped passively Q-switched Nd:GdVO4 laser at 1342 nm with V:YAG saturable absorber

We have demonstrated an efficient diode-pumped passively Q-switched Nd:GdVO₄ laser working at 1342 nm by using an uncoated V³⁺:YAG crystal as the saturable absorber, in which both a-cut and c-cut Nd:GdVO₄ crystals are employed. At the maximum absorbed pump power of 9.45 W, the maximum average output power can reach 519 mW and 441 mW corresponding to the output coupler with different transmission of 3% and 10% by using an a-cut Nd:GdVO₄ crystal at 1342 nm, while the shortest pulse duration could be as low as 21.7 ns and 22.3 ns with the repetition rate of 48.41 kHz and 53.25 kHz by using a c-cut Nd:GdVO₄ crystal, corresponding to the output coupler with different transmission of 3% and 10% at 1342 nm, and the single Q-switched pulse energy are 6.67 uJ and 7.06 uJ, the pulse peak power are 307 W and 316 W, respectively. The experimental results show that c-cut Nd:GdVO₄ laser can generate shorter pulse with higher peak power in comparison with a-cut one.     

Spectroscopic properties of Tm -doped Ba3Gd2(BO3)4 crystal

crystal with the size up to Φ 13 mm×44 mm was grown successfully by the Czochralski technique and its optical properties were presented. The absorption cross-section and emission cross-section were presented. Also, the potential laser gain near 1.9 μm was investigated. In the framework of the Judd-Ofelt (J-O) theory, the intensity parameters were calculated to be: Ω₂=11.375×10⁻²⁰ cm², Ω₄=5.077×10⁻²⁰ cm² and Ω₆=6.524×10⁻²⁰ cm². The spectroscopic parameters of this crystal such as the oscillator strengths, radiative transition probabilities, radiative lifetime as well as the branching ratios were calculated, too. This crystal is promising as a tunable infrared laser crystal.     

Core level spectroscopy and RHEED analysis of KGd(WO4)2 surface

Structural and electronic characterisation of mechanically polished (010) KGd(WO₄)₂ (KGW) has been produced by reflection high-energy electron diffraction (RHEED) and X-ray photoelectron spectroscopy (XPS). With XPS analysis the original element binding energies, chemical composition and valence band structure of KGW have been determined.     

Efficient and highly photostable solid-state dye lasers based on modified dipyrromethene.BF2 complexes incorporated into solid matrices of poly(methyl methacrylate)

We report on the laser action of modified dipyrromethene.BF₂ complexes both dissolved in poly(methyl methacrylate) and copolymerized with methyl methacrylate. All recently synthesized dyes have the chromophore core of laser dye pyrromethene 567, differing in the substituent in position 8. The new dyes showed important and most significant increases in both lasing efficiency and photostability. When the laser samples were pumped transversely at 534 nm, laser emission was obtained with efficiencies of over 30% in most cases, to be compared with a lasing efficiency of 12% exhibited by reference dye pyrromethene 567 under the same experimental conditions. Some of the materials exhibited highly photostable laser action, with no sign of degradation in the laser output after 60000 pump pulses at the same position of the sample at a repetition rate of 10 Hz, whereas the laser emission of reference dye pyrromethene 567 dropped to zero after less than 40000 pump pulses. Received: 19 November 2002 / Revised version: 20 February 2003 / Published online: 9 April 2003 RID="*" ID="*"Corresponding author. Fax: +34-91/564-2431, E-mail: acostela@iqfr.csic.es     

Thermal lensing measurements and thermal conductivity of Yb:YAB

By using holographic shear interferometry, we have measured the thermal lens in a diode-pumped Yb:YAB crystal, under lasing and non-lasing conditions, as a function of absorbed power. From these purely optical measurements we estimate the fractional thermal loading and the thermal conductivity of Yb:YAB. Knowledge of these thermal parameters is essential for the optimisation of Yb:YAB laser cavity designs. Received: 5 February 2002 / Final version: 22 November 2002 / Published online: 26 February 2003 RID="*" ID="*"Corresponding author. Fax +61-2/9850-8915, E-mail: Judith@ics.mq.edu.au     

Linear and cross-linked polymeric solid-state dye lasers based on 8-substituted alkyl analogues of pyrromethene 567

The lasing properties of analogues of the commercial laser dye pyrromethene 567 (PM567) incorporated (dissolved or copolymerized) into polymeric matrices have been studied using both linear and cross-linked methyl methacrylate-based copolymers with different degrees of functionalization. All synthesized dyes have the chromophore core of PM567 but with an ω-acyloxypolymethylene chain at position 8. In general, the new materials exhibited laser emission with higher efficiencies and much higher photostabilities than those containing the commercial dye PM567 under the same experimental conditions. Lasing efficiencies of up to 40% were obtained under transversal pumping at 534 nm. The highest photostabilities, with the laser output remaining stable or dropping by less than 15% after 100 000 pump pulses at the same position of the sample, were reached in cross-linked materials with dyes covalently linked to the polymeric chains. When the polymeric samples were incorporated into a grazing-incidence grating oscillator, narrow-line-width operation with tuning ranges of up to 40 nm was obtained. These results show that efficient and photostable solid-state dye lasers competitive with their liquid counterparts can be developed by adequate chemical modifications in the dye molecules, as well as by the selection of appropriate polymeric formulations.     

Growth and spectral properties of Tm/Er:NaGd(MoO4)2 single crystal

The Tm³⁺/Er³⁺:NaGd(MoO₄)₂ crystal with dimensions of Φ22×30 mm³ was grown by Czochralski method. Polarized spectra and fluorescence lifetime for the ⁴I_13/2(Er³⁺)→⁴I_15/2(Er³⁺) transition at room temperature were investigated. Based on the Judd-Ofelt theory, the spontaneous transition probabilities, the fluorescent branching ratios and the radiative lifetimes were calculated. The fluorescence lifetime was measured to be 1.81 ms. The detailed excited-transition mechanism with 800 nm radiation is also discussed.     

Spectroscopic characteristic and energy levels of Cr in Cr:KAl(MoO4)2 crystal

This paper reports polarized spectral properties and energy levels of Cr³⁺ in KAl(MoO₄)₂ crystal. The absorption and emission cross sections are estimated as 3.72×10^-20 cm² at 669 nm and 2.74×10^-20 cm^-2 at 823 nm for σ-polarization, respectively. The energy levels of Cr³⁺ ion in KAl(MoO₄)₂ crystal were calculated based on the Tanabe-Sugano theory. It is suggested that Cr³⁺ ions occupy at an intermediate crystal field site in Cr³⁺:KAl(MoO₄)₂.     

Passive Q-switching at 1.54 μm of an Er–Yb: GdCa4O(BO3)3 laser with a Co2+: MgAl2O4 saturable absorber

We report, for the first time to our knowledge, efficient passive Q-switching of the 1.54-μm laser transition in an Er–Yb-doped crystalline medium. The laser configuration is a compact microchip design that is suitable for a range of practical applications such as range finding and lidar. The slope efficiency of 11.6%, pulse duration of 5–6 ns and average output power of 88 mW are all comparable with standard Er–Yb:glass lasers.     

Diode-pumped Nd:BaY2F8 picosecond laser

Picosecond pulse generation at 1050 nm by a diode-pumped Nd:BaY₂F₈ (Nd:BaYF) active crystal has been investigated under low-power pumping (440 mW absorbed). The sample was oriented along the optical axes and cut at Brewster angle for y-axis laser polarization to minimize birefringence effects. Stable passive mode-locking operation has been achieved by inverse saturable absorption with 80-mW output power and 3.7-ps pulses.     

Crystalline structure and optical spectroscopy of Er3+-doped KGd(WO4)2 single crystals

4 )₂ single crystals doped with Er³⁺ have been grown by the flux top-seeded-solution growth method. The crystallographic structure of the lattice has been refined, being the lattice constants a=10.652(4), b=10.374(6), c=7.582(2) Å, β=130.80(2)°. The refractive index dispersion of the host has been measured in the 350–1500 nm range. The optical absorption and photoluminescence properties of Er³⁺ have been characterised in the 5–300 K temperature range. At 5 K, the absorption and emission bands show the (2J+1)/2 multiplet splittings expected for the C₂ symmetry site of Er in the Gd site. The energy positions and halfwidths of the 72 sublevels observed have been tabulated as well as the cross sections of the different multiplets. Six emission band sets have been observed under excitation of the ⁴F_7/2 multiplet. The Judd–Ofelt (JO) parameters of Er³⁺ in KGW have been calculated: Ω₂=8.90×10^-20 cm², Ω₄=0.96×10^-20 cm², Ω₆=0.82×10^-20 cm². Lifetimes of the ⁴S_3/2, ⁴F_9/2, and ⁴I_11/2 multiplets have been measured in the 5–300 K range of temperature and compared with those calculated from the JO theory. A reduction of the ⁴S_3/2 and ⁴I_11/2 measured lifetimes with increasing erbium concentration has been observed, moreover the presence of multiphonon non-radiative processes is inferred from the temperature dependence of the lifetimes. Received: 15 December 1997/Revised version: 10 July 1998