Achievements and Future Perspectives of the Trivalent Thulium-Ion-Doped Mixed-Sesquioxide Ceramics for Laser Applications

Kerr-lens mode-locked 49-fs Tm3+:YScO3 single-crystal laser at 2.1 µm

We report on a continuous wave (CW) and Kerr-lens mode-locked (KLM) Tm3+:YScO3 single-crystal laser centered at 2.1 µm. Efficient CW laser operation with a maximum slope efficiency of 51% was achieved under in-band pumping by an Er:Yb fiber master oscillator power amplifier (MOPA). In KLM operation, pulses as short as 49 fs corresponding to seven optical cycles were achieved at a repetition rate of 96.7 MHz with an average output power of 126 mW. Such short pulse durations are enabled by the inhomogeneously broadened emission spectrum of Tm3+:YScO3 extending to above 2200 nm.

Spectroscopy and 2.1 µm laser operation of Czochralski-grown Tm3+:YScO3 crystals

We report on growth, temperature-dependent spectroscopy, and laser experiments of Tm³⁺-doped YScO₃ mixed sesquioxide crystals. For the first time, cm³-scale laser quality Tm³⁺:YScO₃ crystals with 2.2 at.% and 3.1 at.% doping levels were grown by the Czochralski method from iridium crucibles. We reveal that the structural disorder in the mixed crystals allows for broad and smooth spectral features even at cryogenic temperatures. We obtained the first continuous wave laser operation in this material at wavelengths around 2100 nm using a laser diode emitting at 780 nm as a pump source. A maximum slope efficiency of 45% was achieved using a Tm^3 +(3.1 at.%):YScO₃ crystal. Our findings demonstrate the high potential of Tm³⁺-doped mixed sesquioxides for efficient ultrafast pulse generation in the 2.1 µm range.

Synthesis and Characterization of Li2MgGeO4:Ho3

In this work, the synthesis and characterization of Li2MgGeO4:Ho3+ ceramics were reported. The X-ray diffraction measurements revealed that the studied ceramics belong to the monoclinic Li2MgGeO4. Luminescence properties were analyzed in the visible spectral range. Green and red emission bands correspondent to the 5F4,5S2→5I8 and 5F5→5I8 transitions of Ho3+ were observed, and their intensities were significantly dependent on activator concentration. Luminescence spectra were also measured under direct excitation of holmium ions or ceramic matrix. Holmium ions were inserted in crystal lattice Li2MgGeO4, giving broad blue emission and characteristic 4f-4f luminescent transitions of rare earths under the selective excitation of the ceramic matrix. The presence of the energy transfer process between the host lattice and Ho3+ ions was suggested.

Watt-level femtosecond Tm-doped "mixed" sesquioxide ceramic laser in-band pumped by a Raman fiber laser at 1627 nm

We report on a semiconductor saturable absorber mirror mode-locked Tm:(Lu,Sc)₂O₃ ceramic laser in-band pumped by a Raman fiber laser at 1627 nm. The nonlinear refractive index (n₂) of the Tm:(Lu,Sc)₂O₃ ceramic has been measured to be 4.66 × 10^-20 m²/W at 2000 nm. An average output power up to 1.02 W at 2060 nm is achieved for transform-limited 280-fs pulses at a repetition rate of 86.5 MHz, giving an optical efficiency with respect to the absorbed pump power of 36.4%. Pulses as short as 66 fs at 2076 nm are produced at the expense of output power (0.3 W), corresponding to a spectral bandwidth of 69 nm. The present work reveals the potential of Tm³⁺-doped sesquioxide transparent ceramics for power scaling of femtosecond mode-locked bulk lasers emitting in the 2-µm spectral range.

Thermal Conductivity of Yttria-Gadolinia Solid Solution Optical Ceramics in the Temperature Range 50–300 K

This study looked at the thermal conductivity of translucent (Y1−xGdx)2O3 (where 0 ≤ x ≤ 1) solid solution ceramics in the temperature range from 50 K to 300 K. The samples were obtained by hot pressing from high-purity nanopowders at 1600 °C, no sintering additives were used. Compositions with cubic syngony (x ≤ 0.7) and a monoclinic one (x ≥ 0.9) were investigated. Furthermore, a dense sample of cubic Gd2O3 with a LiF sintering additive was obtained and its thermal conductivity was determined (k = 11.7 W/(m K) at 300 K). It was shown that in the range of solid solution ceramic compositions 0.2 ≤ x ≤ 0.7, the thermal conductivity was practically unchanged and close to the value k ≈ 5 W/(m K) at 300 K.