Thermo-optic properties of Yb:Lu2O3 single crystals

Abstract

Lu 2 O 3 ). Initial growth attempts of sesquioxides utilized the Verneuil method [2,3] or the floating zone technique [4]. The resulting mm-size crystals of low quality were utilized for the initial determination of the optical and thermomechanical properties of these materials and even allowed for first flash-lamp-pumped laser experiments [5]. Afterward, different growth methods such as the laser-heated pedestal growth (LHPG) [6], the micro-pulling down technique [7] and the Czochralski technique [8] were applied, but still the crystals were limited in size and quality. It was not before 2008 that by the optimization of the heat exchanger method [9] the growth of cm-scale single-crystalline sesquioxides with excellent optical quality became possible [10]. In the following years, in particular cubic sesquioxide host material lutetia (Lu 2 O 3 ) has been shown to be an excellent host material for various rare earth ions [11]. Efficient and high-power laser operation has been demonstrated utilizing various laser ions such as Yb 3+ [12,13] at 1 µm, Tm 3+ [14] and Ho 3+ [15] at 2 µm as well as Er 3+ at 3 µm [16].These outstanding laser results obtained in the past motivate a reexamination of the thermo-optic properties of Lu 2 O 3 that affect the parameters of the thermal lens. The lens-like behavior is related with three main effects, namely temperature dependence of the refractive index (expressed by the thermo-optic coefficient, dn/dT), end-bulging related to the thermal expansion coefficient α, as well as photoelastic effect that is responsible for the lens astigmatism and birefringence losses. Under the plane stress approximation (that refers to the diode pumping case), first two terms are dominant [17]. Thus, the knowledge of dn/dT and α values as well as their combination, called thermal coefficient of the optical path (TCOP) [18], is crucial for the determination of the thermal lens parameters and, hence, the cavity design. Indeed, non-compensated thermal lens can lead to Abstract A detailed study of thermo-optic properties of 1.5 at.% Yb:Lu 2 O 3 single crystal is performed. Thermooptic dispersion formulas are derived for dn/dT coefficient and thermal coefficient of the optical path. At the wavelength of 1.03 μm, dn/dT = 5.8 × 10 −6 K −1 . High-precision temperature-dependent measurements of the thermal expansion coefficient α are performed. At the room temperature (RT), α = 5.880 ± 0.014 × 10 −6 K −1 . Temperature dependence of the bandgap is analyzed, yielding RT value of E g = 5.15 eV and dE g /dT = -3.7 × 10 −4 eV/K. Sensitivity factor of the thermal lens is calculated for a diodepumped Yb:Lu 2 O 3 crystal versus the pump spot radius and crystal temperature.

Oxygen Vacancy, Oxygen Vacancy–Vacancy Pairs, and Frenkel Defects in Cubic Lutetium Oxide

“…Yet another phenomenon observed in Lu 2 O 3 -based materials and related to oxygen vacancies is coloration. Lu 2 O 3 monocrystals may appear colored, dark, or black , (which is reflected by a broadband absorption in the visible range, 300–600 nm). The coloration can be healed via annealing in air and is thus attributed to oxygen vacancies .…”

On the use of photoelastic effect and plane strain or plane stress approximations for the description of thermal lensing

“…This feature allows obtaining pulses with duration down to 50 fs at the oscillator output in the mode-locking regime. Thermally induced depolarization and thermooptic properties of sesquioxide class m3 single crystals and ceramics are studied in recent papers [36][37][38]. Therefore, finding relations between β σ and β e is very relevant for such sesquioxide class m3 single crystals.…”

Spectroscopy and efficient laser operation around 2.8 μm of Er:(Lu,Sc)2O3 sesquioxide ceramics

“…So far, cubic sesquioxides A 2 O 3 (where A stands for Y, Sc, Lu or their combination) were found to be very suitable for Er 3+ doping with the aim of ~2.8 µm laser operation [8]. These crystals provide good thermal properties such as high thermal conductivity with weak concentration-dependence (κ ~10.7 Wm -1 K -1 for ~7 at.% Er:Lu 2 O 3 [9]) and positive thermooptic coefficients [10], low phonon energies (the most intense phonon mode of Lu 2 O 3 is 393 cm -1 [11]) and easy doping with Er 3+ ions in high concentrations. In addition, sesquioxides provide high crystal-field strength resulting in large total Stark splitting of the 4 I 13/2 multiplet leading to broadband emission properties [12].…”