Thulium doped sesquoxide transparent ceramics for high energy class laser in nano second regime at cryogenic temperature

Project leaders

Valentina Biasini, Antonio Lucianetti

Agreement

REPUBBLICA CECA - CAS (ex AVCR) - Czech Academy of Sciences

Call

CNR/CAS triennio 2019-2021 2019-2021

Department

Chemical sciences and materials technology

Thematic area

Chemical sciences and materials technology

Status of the project

New

Research proposal

High quality transparent laser ceramics based on Thulium (Tm) doped Y2O3 with different dopant concentrations will be fabricated starting from commercial raw materials. The fabrication of optically transparent ceramics is one of the major challenges of the ceramic technology, since to achieve transparency these materials need to be free of pores and defects. . Finally, laser experiments at cryogenic temperatures will assess the suitability of this material for development of diode-pumped high-energy lasers.
Solid state laser sources operating around 2 ¼m have numerous applications that include lidar, gas sensing, medical treatments and as pump source of optical parametric oscillators (OPOs) [1]. These potentialities have prompted intense research in the development of new laser gain media for the 2 ¼m wavelength range. Different hosts such as YAG, LuAG, YLF and YAP doped with Tm3+ have been demonstrated by direct pumping and achieved high efficiency. Sesquioxides doped with Tm3+, such as Tm:Lu2O3, Tm:Y2O3, and Tm:Sc2O3, are also emerging materials: their better thermo-optical properties make them promising for power scaling applications [2]. However, the growth of sesquioxide single crystals is very complicated, while it is possible to produce them in transparent ceramic form thanks to their cubic crystalline structure and optical isotropy. Up to now very few publications reported on Tm:Y2O3 transparent ceramics [3, 12]. Moreover, continuous-wave high-power, Q-switched, and mode-locked operations of this class of solid-state lasers with the use of sesquioxides have been so far realized only at room temperatures [4 -12]. For the generation of high energy the material has to be cooled to cryogenic temperatures in order to reduce thermal load in the laser gain media. The cryogenic cooling not only improves the thermo-optic properties to tenfold, but it also enhances the spectroscopic properties, leading to overall improved laser performance [13].
The process is based on the use of commercial Y2O3 and Tm2O3 powders mixed in stoichiometric ratio. Raw powders from different producers will be tested. A small amount of a sintering aid will be added during the mixing process. Specific powder treatment methods will be tested to avoid the formation of large agglomerates (e.g. spray drying). Powders and powder mixtures will be characterized by scanning electron microscopy and x-ray diffraction. The obtained mixture will be uniaxially pressed into disks. The disks will be calcined to remove organics, cold isostatically pressed (CIP) and vacuum sintered to achieve full density. The produced samples will be polished and characterized at ISTEC to optimize the fabrication process (microstructure, optical transmittance); in addition, the best samples will be sent to IoP for laser experiments.
Laser experiments at cryogenic temperatures (80 K - 300 K) will be performed using two different cavity setups. The first one will be used for continuous-wave (CW) and passive Q-switching laser experiments with variable output coupler transmission and Cr:ZnS/ZnSe as passive Q-switching element.. The other setup will be used for active Q-switching experiments for the generation of nanosecond pulses, where thin film polarizer and quarter wave plate will act as variable output coupler and RTP crystal will be used as Pockels cell. In both cases, the laser gain material will be cooled using a helium gas cryostat. As pump sources, commercially available fiber coupled laser diodes lasers emitting at 796 nm will be used.

ISTEC CNR, Italy, has the required infrastructure for the fabrication of transparent ceramics: nanopowders treatment laboratory, spray dryer for the atomization of selected compositions, furnace for the sintering in high vacuum in clean atmosphere, instrumentation for microstructural and mechanical characterization. Moreover, it has a team of scientists with more than 5 years of experience in transparent ceramic fabrication. The required infrastructures for laser experiments for two micron lasers are available at HiLASE Centre, Institute of Physics, CAS. It has a dedicated team of scientists with more than 5 years of experience working in this field of cryogenic lasers and is actively involved in building cryogenic oscillators and amplifiers based on various Yb doped laser materials. This team has previous experience in two micron lasers at room temperature and presently cryogenic temperature. We believe that the world-class infrastructure at HiLASE Centre, Institute of Physics, CAS and the expertise from the team of scientists will enable us for smooth running of the project and to achieve the proposed results.
It is worth mentioning that HiLASE Centre and ISTEC CNR have already started cooperation on the level of Memorandum of Understanding from January 2018.

[1] K. Scholle et al., Frontiers in Guided Wave Optics and Optoelectronics, B. Pal, Ed. London, U.K. InTech, 2010
[2] C. Krankel, IEEE J. Sel. Topics Quantum Electro 21, Art. no. 1602013 (2015)
[3] P. A. Ryabochkina et al., Quantum Electron.46 597 (2016)
[4] L. Fornasieroet al., in Advanced Solid State Lasers, Optical Society of America, 1999, paper WD5
[5] P. Koopmann et al., Appl. Phys. B 102, 19 (2011)
[6] P. Koopmann et al., Opt. Lett. 36, 948 (2011)
[7] O. L. Antipov et al., Quantum Electron 41, 863 (2011)
[8] A. A. Lagatskyet al., Opt. Express 20,19349 (2012)
[9] A. Schmidt et al., Opt. Express 20, 5313 (2012)
[10] P. Koopmann et al., in Proc. CLEO, San Jose, CA, USA, 2010, Paper CMDD1
[11] O. L. Antipovet al., Phys. Status Solidi C 10,969 (2013)
[12] H. Wanget al., Opt. Mater. Express 7, 296 (2017)
[13] D. C. Brown, IEEE J. Sel. Top. Quantum Electron 11, 587 (2005)

Research goals

The goal of the proposed project is to develop thulium doped sesquioxide transparent ceramics with different dopant concentrations for high-energy class lasers working in nanosecond regime at cryogenic temperature as an alternative to single crystals.
The proponents aim to overcome the commercial monopoly of the only ceramic Tm:Y2O3 producer (a Japanese company) by developing a method for the production of high quality Tm:Y2O3 transparent ceramics with various doping levels using commercially available oxide powders as raw materials and testing different sintering additives.
This objective will be pursued by the thorough design of the Tm:Y2O3 fabrication process conditions: starting powders characteristics, powder treatment methods, sintering aids and heat treatments will be carefully studied and optimized.
The suitability of the produced transparent ceramics for the use in diode-pumped high-energy class lasers will also be assessed in continuous-wave regime and pulsed regime (active and passive Q-switching) at cryogenic temperatures.

Last update: 23/04/2024