Temperature-dependent absorption and emission of potassium double tungstates with high ytterbium content

Abstract

We study the spectroscopic properties of thin films of potassium ytterbium gadolinium double tungstates, KYb_0.57Gd_0.43(WO₄)₂, and potassium ytterbium lutetium double tungstates, KYb_0.76Lu_0.24(WO₄)₂, specifically at the central absorption line near 981 nm wavelength, which is important for amplifiers and lasers. The absorption cross-section of both thin films is found to be similar to those of bulk potassium rare-earth double tungstates, suggesting that the crystalline layers retain their spectroscopic properties albeit having >50 at.% Yb³⁺ concentration. The influence of sample temperature is investigated and found to substantially affect the measured absorption cross-section. Since amplifiers and lasers typically operate above room temperature due to pump-induced heating, the temperature dependence of the peak-absorption cross-section of the KYb_0.57Gd_0.43(WO₄)₂ is evaluated for the sample being heated from 20 °C to 170 °C, resulting in a measured reduction of peak-absorption cross-section at the transitions near 933 nm and 981 nm by ~40% and ~52%, respectively. It is shown that two effects, the change of Stark-level population and linewidth broadening due to intra-manifold relaxation induced by temperature-dependent electron-phonon interaction, contribute to the observed behavior. The effective emission cross-sections versus temperature have been calculated. Luminescence-decay measurements show no significant dependence of the luminescence lifetime on temperature.

Ion Beam Modification of ZnO Epilayers: Sequential Processing

“…It corresponds to the main radiative transition from the excited 2 F 5/2 energy state to the 2 F 7/2 ground state of Yb 3+ . Broad peaks located between 1000 and 1150 nm correspond to the Yb 3+ ion emission vibronic band ( 2 F 5/2 → 2 F 7/2( n ) ; n = 1–4) . As can be seen, the intensity of the broad emission band centered around 1046 nm is highest for samples subjected to sequential processing.…”

Gain dynamics in a highly ytterbium-doped potassium double tungstate thin-film amplifier

“…A KGd0.43Yb0.57(WO4)2 layer was grown onto a KY(WO4)2 substrate by liquid-phase epitaxy [6,10], resulting in a layer thickness of ~ 32 µm after polishing. The sample was mounted on a small holder made of thin copper plates with a clear aperture of ~ 8.6 mm × 8.6 mm.…”

“…The experimental setup for signalenhancement measurement included a CW Ti:Sapphire laser at 932 nm for pumping at the local absorption peak of KGd0.43Yb0.57(WO4)2 at ~ 932 nm. The signal beam at ~ 981 nm, exploiting the high emission cross-section [6], with a bandwidth ≤ 1 nm from a supercontinuum light source passed through a monochromator was mechanically chopped at 233 Hz for lock-in detection to discriminate the detected 981 nm wavelength signal from spontaneous emission produced by the sample and from different background noise sources. A small launched signal power (< 100 nW) was used to ensure signal amplification within the small-signal-gain regime.…”

“…Potassium rare-earth double tungstate crystals doped with ytterbium, KRE(WO4)2:Yb 3+ , have been widely used for microchip [1,2], mode-locked [3], and high-power lasers [4,5]. The KRE(WO4)2:Yb 3+ gain medium exhibits transition cross-sections significantly higher than those of many other Yb 3+ -doped materials, such as YAG:Yb 3+ [6,7]. By use of a lattice-engineering approach [8,9,10], a crystalline waveguiding epitaxial layer with high amounts of Yb 3+ ions can be grown onto an undoped KY(WO4)2 substrate, enabling efficient continuous-wave (CW) [11] and Q-switched [12,13,14] KRE(WO4)2:Yb 3+ planar waveguide lasers.…”

Energy-transfer upconversion and excited-state absorption in KGdxLuyEr1-x-y(WO4)2 waveguide amplifiers

“…(b) Simulated internal gain assuming a high propagation loss (α loss = 4 dB/cm), including ESA and ETU (black continuous line), excluding ESA and including ETU (red dashed line), and including ESA and excluding ETU (blue dotted line). performance of Yb 3+ -doped waveguide amplifiers [48,49], which typically generate less heat, temperature increase, and a consequent reduction of transition cross sections than comparable Er 3+ -doped devices. Nevertheless, the optimum dopant concentration is rather well predicted.…”