Elena Vilejshikova

Crystal growth, optical spectroscopy and laser action of Tm^3+-doped monoclinic magnesium tungstate

We report on the crystal growth, spectroscopic investigation and laser performance of Tm3+-doped monoclinic magnesium tungstate (Tm:MgWO4), for the first time, to the best of our knowledge. A high-quality crystal has been grown by the top seeded solution growth method. The relevant spectroscopic properties are characterized in terms of absorption, luminescence and Raman spectroscopy. Judd-Ofelt (J-O) analysis is performed to evaluate the spontaneous emission probabilities and the radiative lifetimes. The absorption, stimulated-emission and gain cross-section spectra are determined for the principal light polarizations. The first laser action in the 2 μm spectral range is demonstrated in the regime of continuous-wave operation with a maximum output power of 775 mW and a slope efficiency of 39%.

Disordered Tm:Ca 9 La(VO 4 ) 7 : a novel crystal with potential for broadband tunable lasing

We report on the crystal growth, structural and spectroscopic investigation of a novel trigonal calcium vanadate crystal, Tm3+:Ca9La(VO4)7. Polarized absorption, stimulated-emission and gain cross-section spectra are determined for this material. The maximum σSE corresponding to the 3F4 → 3H6 transition amounts to 1.28 × 10−20 cm2 at 1854 nm for σ-polarization. The measured lifetime of the Tm3+ ions in the 3F4 state is 1.19 ms. The Judd-Ofelt analysis performed yielded intensity parameters of Ω2 = 4.682, Ω4 = 0.659 and Ω6 = 0.475 [10−20 cm2]. The polarized Raman spectra indicate a strong and broad band centered at 867 cm−1. Owing to the disordered nature of Ca9La(VO4)7, the Tm3+ ions exhibit a broad and smooth gain profile at ~2 μm. The spectroscopic properties of Tm3+:Ca9La(VO4)7 are very promising for broadly tunable and ultrashort pulse lasers near 2 µm.

Highly-efficient laser operation of a novel trigonal silicate crystal Yb^3+:Ca_3NbGa_3Si_2O_14

A novel trigonal ordered langasite-type silicate crystal, Yb3+:Ca3NbGa3Si2O14 (Yb:CNGS), is characterized with respect to absorption and stimulated-emission cross-sections as well as Raman spectra using polarized light. Thanks to its excellent thermo-mechanical properties, highly-efficient multi-watt lasing is demonstrated. A compact a-cut 5 at .% Yb:CNGS crystal diode-pumped at 978 nm generated a maximum output power of 7.27 W at 1062-1068 nm with a slope efficiency of 78%. These values represent record parameters for ~1 μm lasers based on langasite-type crystals. The very broad and smooth gain cross sections of Yb:CNGS are attractive for ultrashort pulse and broadly tunable lasers at ~1 μm.

Crystal growth and properties of the disordered crystal Yb:SrLaAlO4: a promising candidate for high-power ultrashort pulse lasers

A high quality Yb3+-doped strontium lanthanum aluminate crystal, Yb:SrLaAlO4 (Yb:SLA) is grown by the Czochralski method. It is tetragonal (sp. gr. I4/mmm, a = b = 3.7536 A, c = 12.6253 A). Room- and low-temperature spectroscopy of Yb3+ ions in this crystal are studied. The Stark splitting is resolved. Absorption, stimulated-emission (SE) and gain cross-sections are determined with polarized light. In the spectral range of laser emission, the maximum σSE is 0.57 × 10−20 cm2 at 1047 nm for σ polarization. The polarized Raman spectra of Yb:SLA are presented. Thermal properties of Yb:SLA are characterized in terms of the linear thermal expansion, specific heat and thermal conductivity. The latter is as high as 6.06 and 4.30 W m−1 K−1 along the a- and c-axes, respectively (at room temperature). Broadband tuning of a continuous-wave (CW) Yb:SLA laser, from 1011 to 1082 nm has been achieved. Due to its good thermal properties, broad and smooth gain spectra, Yb:LSA is a promising material for power-scalable, broadly tunable CW and sub-100 fs mode-locked lasers at ∼1 μm.

Growth and spectroscopy of novel Raman-active molybdate laser crystals: Yb:Li 2 M 2 (MoO 4 ) 3 where M = Mg or Zn

Complex tungstate and molybdate crystals are known as excellent host materials for doping with trivalent rare-earth ions RE³+, e.g. Yb³+ or Tm³+, [1] and they are Raman-active. Due to the structure features, they offer high RE³+ doping levels, low non-radiative relaxation rates, weak concentration quenching, and broad and intense spectral bands of the RE³⁺ ions in polarized light. Lithium metal molybdate crystals with the lyonsite structure, Li<inf>2</inf>M<inf>2</inf>(MoO<inf>4</inf>)<inf>3</inf> where M²+ = Mg, Zn, Mn, Ni, etc. (shortly LiMMo) [2] have been poorly studied as laser host matrices. In the present paper, we report on the growth, structure, vibronic, thermal and spectroscopic properties of Yb:LiMgMo and Yb:LiZnMo single-crystals showing high potential for broadly tunable and sub-100 fs mode-locked lasers at ∼1 μm.

Synthesis, spectroscopy, and efficient laser operation of “mixed” sesquioxide Tm:(Lu,Sc) 2 O 3 transparent ceramics

A novel transparent 4.76 at.% Tm:(Lu2/3Sc1/3)2O3 “mixed” sequioxide ceramic is synthesized by hot isostatic pressing (HIP) at 1800 °C / 195 MPa in an Ar atmosphere. Its structure is studied by scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. The spectroscopic properties of the Tm3+ ion are described within the Judd-Ofelt theory, which resulted in intensity parameters of Ω2 = 2.429, Ω4 = 1.078 and Ω6 = 0.653 [10−20 cm2]. For the 3F4 → 3H6 transition, the maximum stimulated-emission cross-section σSE is 7.15 × 10−21 cm2 at 1951 nm. The radiative lifetime of the 3F4 state is 4.01 ms. Under diode-pumping at 802 nm, a microchip Tm:(Lu,Sc)2O3 ceramic laser generated ~1 W at 2100 nm with a slope efficiency of 24%. The spectroscopic and laser properties of the Tm:(Lu,Sc)2O3 ceramic are compared with those of a Tm:LuScO3 single crystal. The ceramic exhibits very broad and flat gain cross sections, which is promising for ultrashort pulse generation.

Glass-ceramics with Yb, Tm:YNbO 4 nanocrystals: Novel NIR-to-NIR upconversion phosphor

Transparent lithium alumosilicate glass-ceramics containing nanosized (8-15 nm) crystals of rare-earth orthoniobates, Yb, Tm:YNbO₄, and β-quartz solid solutions are synthesized. Under the near-IR excitation by an InGaAs diode, they demonstrate intense near-IR upconversion luminescence at ~800 nm. The efficiency of Yb³⁺ →Tm³⁺ energy transfer is ~90%.