New mixed sesquioxide transparent ceramics for advanced laser applications: fabrication, spectroscopy, and laser emission performances

Joint research project

Project leaders: Guido Toci, Roman Maksimov
Agreement: RUSSIA - RFBR-suspended - Russian Foundation for Basic Research
Call: CNR/RFBR triennio 2018-2020 2018-2020
Department: Physical sciences and technologies of matter
Thematic area: Physical sciences and technologies of matter
Status of the project: New

Research proposal

The project aims to the development and characterization of new transparent polycrystalline ceramics doped with several rare earths ions, to be used as laser media with expected improved laser performances. The project partners will be the National Institute of Optics (INO), the Institute of Applied Physics (IFAC) of CNR and the Institute of Electrophysics of the Ural Branch of the Russian Academy of Sciences (IEP UrB RAS). This cooperation is synergic with CNR ongoing activities and European projects (e.g. EuPRAXIA, www.eupraxia-project.eu, and the European network Extreme Laser Infrastructure, ELI) on laser materials and on the design of laser devices.
Transparent ceramics are acquiring increasing importance as laser hosts, for several reasons: their fabrication usually require lower processing temperatures than conventional crystal growth techniques; this is convenient for the fabrication of materials with high melting point such as sesquioxides and some garnets. Also, ceramics are better suited than single crystals for the fabrication and structuring of large gain elements tailored for high power laser applications, and at least in some cases, they exhibit a higher mechanical resistance.
The proposed host compositions are solid solutions of sesquioxides (i.e. Y2O3, Sc2O3, Lu2O3), doped with several Rare Earth ions with emission in the near infrared (i.e. Yb, Tm) and in the visible (i.e. Dy).
The solid solution compositions result in a disordered lattice structure at the nanoscale level, broadening the emission spectra of the lasing ions with respect to the ordered lattices. This effect, already demonstrated for instance for some Yb doped garnets [1] and sesquioxides [2], is advantageous for the generation of ultrashort laser pulses [2] and for the extension of the laser tuning range. These developments will have significant impact on applications of laser sources based on these ions.
Also, composite ceramic structures (e.g. multilayer), featuring non-uniform doping distribution and chemical composition will be designed and tested. These composite structures, if properly designed, can be advantageous for the mitigation of detrimental effects (e.g. thermomechanical and parasitic lasing) in high power laser systems [3]. Moreover, the superimposition of hosts with different emission bands, can be exploited to extend the emission range of the resulting gain element.
Yb3+ is a well assessed laser dopant for hosts as crystals, fibers and ceramics. Due to its favorable features, Yb lasers are widely used for industrial applications. The available Yb doped materials can produce ultrashort laser pulses with duration down to about 100 fs. The development of new Yb doped laser media with broader emission band will allow the generation of even shorter pulse durations. As for the applications, this will enable for instance new, high precision laser processing techniques (based on ultrashort pulses) addressing heat-sensitive materials that are difficult to process with conventional techniques.
Laser emission wavelength of Tm3+ (~ 2 microns) falls in the eye-safe region of the IR. This allows the development of eye-safe free space propagation applications (e.g. LIDAR, range finders, environmental monitoring, optical data links). The use of eye-safe wavelengths in laser industrial applications would improve the safety of the work environment. Finally, Tm lasers are widely used for medical applications. The development of improved Tm laser materials will benefit further developments of these applications.
Dy3+ in fluoride and oxide hosts is emerging as a lasing ion in the yellow-red region of the spectrum [4]. The recent availability of blue-violet (~450nm) powerful diode lasers for pumping can stimulate the development of applications for display technology, medicine, material processing and microscopy.

During the project the following topics will be investigated:
- fabrication of mixed sesquioxide ceramics starting from the formulations Lu2O3, Sc2O3, Y2O3. The chemistry of these systems allows for a wide range of Lu/Sc/Y balances;
- structured (multilayer) ceramic elements realized by co-sintering of layers with different composition and doping.
These hosts will be doped with Yb, Tm, and Dy lasing ions.
The project will carry out a systematic study of the proposed compositions as laser media. Samples of mixed sesquioxide ceramics with different cation balances and doping levels will be prepared by means of various sintering techniques. The impact of the fabrication process and of the compositions on the microcrystals structure, spectroscopic and thermomechanical properties will be assessed.
The laser performances of the samples will be verified by means of laser emission measurements.
The capabilities of IEP and CNR are strongly complementary: IEP will be in charge of the ceramics fabrication and microstructural characterizations (where the partner has already achieved a significant experience, see for instance [5,6]). The spectroscopic characterization and the assessment of laser performances will be carried out at CNR INO (Tm, and Yb doped samples) and IFAC (Dy doped samples) in the framework of a well established activity on laser ceramics characterization [7,8]. INO-CNR will also define the design of the multilayer structures with different compositions to optimize thermomechanical properties [3] and laser emission performances.

References
1) G.Toci et al. Opt. Mater. Express, 7 170-178, 2017
2) K. Beil et al. Appl. Phys. B 113 13-18, 2013
3) P. Ferrara et al. Opt. Express 22, 5375-5386 (2014)
4) Kränkel et al., Laser & Photonics Reviews 10, 548-568 (2016)
5) V. V. Osipov et al. Ceram. Int. 41, 13277-13280 (2015)
6) V. V. Osipov et al. Opt. Mater. 50, 65-70 (2015)
7) A. Pirri et al. Opt. Lett. 2011
8) G. Toci et al., Opt Mater. 41, 12-16, 2015

Research goals

The activity aims to develop disordered sesquioxide ceramics for laser applications, i.e. mixed. RE3+:(AxB(1-x))2O3 (with A, B= Lu, Y, Sc and RE=Yb, Tm, Dy), and to assess their spectroscopic and laser properties. More in details:
1. Systematic study of the impact of the different compositions and doping levels on the crystalline structure and on the spectroscopic properties of the lasing ions;
2. Identification of the most suitable compositions, multilayer structuring and doping levels for the different dopants, for different laser applications, in terms of spectroscopic and thermomechanical parameters;
3. Experimental evaluation and comparison of the laser performances (output power, efficiency, tunability, impact of thermal load) in a test laser set-up; the laser emission will be tested at around 1 micron (Yb) and 2 microns (Tm), under high power semiconductor lasers pumping.
4. Demonstration and characterization of laser emission of Dy in sesquioxides on various transitions between ~580 and ~720 nm (depending on the host), under blue laser pumping (at ~ 450 nm).
5. Evaluation of the potential for ultrashort pulses generation for Yb doped mixed sesquioxides, under mode-locked laser oscillation.
6. Publication of the results on high level, peer reviewed journals on laser physics and material sciences. At least six research papers are expected.

Last update: 19/04/2024