The microstructure evolution and optical properties of vacuum combined with hot isostatic pressing(HIP) sintered Tm,Ho:(Lu2/3Sc1/3)2O3 transparent ceramics were studied. The ceramics were sintered in vacuum followed by HIP to obtain Tm,Ho:(Lu2/3Sc1/3)2O3 with high transparency. Changes of microstructure and densification rate due to the vacuum sintering temperature increasing were studied from 1100°C to 1780°C. With the increase of the operating temperature, the densification rate of the ceramics presented nonlinear characteristics. The growth of the grains was remarkably accelerated at higher temperatures (above 1500°C). The in-line transmittance of Tm,Ho:(Lu2/3Sc1/3)2O3 ceramics vacuum sintered at 1780°C followed by HIP at 1700°C exceeded 81.68% at 2090 nm.
Mode-locked lasers emitting ultrashort pulses in the 2-μm spectral range at high (100-MHz) repetition rates offer unique opportunities for time-resolved molecular spectroscopy and are interesting as pump/seed sources for parametric frequency down-conversion and as seeders of ultrafast regenerative laser amplifiers. Passively mode-locked lasers based on Tm3+- and Ho3+-doped bulk solid-state materials have been under development for about a decade. In 2009 we demonstrated the first steady-state operation of such a Tm:KLu(WO4)2 laser using a single-walled carbon nanotube (SWCNT) saturable absorber (SA), generating 10-ps pulses at 1.95 μm. In 2012 this laser produced 141-fs pulses at 2.037 μm. More recently, the study of numerous active media with different SAs resulted in the generation of sub-100-fs (sub-10-optical-cycle) pulses. Materials with broad and smooth spectral gain profile were selected, naturally emitting above 2 μm to avoid water vapor absorption/dispersion effects, including anisotropic materials, strong crystal-field distortion in hosts that do not contain rare-earths, crystals with structural or compositional (i.e. mixed compounds) disorder that exhibit inhomogeneous line broadening, mixed laser ceramics, and Tm,Ho-codoping of ordered and disordered crystals and ceramics. A broad absorption band in semiconducting SWCNTs spans from 1.6 to 2.1-μm whereas the absorption of graphene extends into the mid-IR and scales for multilayers, increasing the modulation depth. Compared to GaSb-based semiconductor SA mirrors (SESAMs), the carbon nanostructures exhibit broader spectral response and can be fabricated by simpler and inexpensive techniques. Chirped mirrors were implemented for groupvelocity dispersion compensation, to generate the shortest pulses, down to 52 fs at 2.015 μm.
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