The market for piezoelectric-operated actuators and motors shows an average annual growth rate of 13.2% (optics, photonics, nanometrology equipment, medical technology…). Piezoelectric materials that can operate under very high temperature without degradation are sought for the control of structure materials and control system in turbines, engines, nuclear reactors, etc ...The huge industrial need of these materials in piezoelectric-operated devices (sensors and actuators) have led the industry and the scientific community to expose the need for new generations of reliable piezoelectric lead-free materials which can operate in a wide temperature range and allow the miniaturization of the devices. However, the application of a piezoelectric material at elevated temperature presents many challenges such as possible phase transition which can cancel or lead to instability of the piezoelectric properties. GeO2, with the alpha-quartz structure (alpha-GeO2), has a wide operation temperature range (until its melting at 1115°C); its strong structural distortion prevents the transition to centrosymmetric phase which is close to 573°C for alpha-SiO2. In addition, a DFT ABINIT prediction of the elastic and piezoelectric properties of alpha-GeO2 confirms that materials of the quartz family with a highly distorted crystal structure should have an electromechanical coupling coefficient kt of about 20% compared to 8% of quartz . The PIEMON project is the result of a process of theoretical and experimental researches for industrial applications. This project plans to follow all the process, from the growth of GeO2 single crystal to its use in piezoelectric systems in a large temperature range, targeted in this project to high added value components as accurate inertial sensors (accelerometer & gyro) and resonators for time & frequency applications. All the results obtained from this project will allow us to measure the contribution that alpha-GeO2 material could have in piezoelectric devices dedicated to specific applications at very high temperature, 600-1000°C, inaccessible to most piezoelectric materials such as single crystals or ceramics. The PIEMON project will be based on a multi-disciplinary partnership of four entities (3 academics and 1 industrial) whose areas of expertise in scientific and technological fields will be focused in the three main aims developed during the scientific program: 1) Development of the experimental conditions to control the seeded growth of high crystalline quality alpha-GeO2 by the high temperature flux method. Numerical simulation will be used as a tool for studying the growth medium and X-ray topography as a tool for characterizing (extended defects) and improving the crystal quality (selection of seeds). Then, the work will be addressed to optimize the scale factor in order to produce large crystals of GeO2 (V>10 cm3) suitable for industrial piezoelectric devices. 2) Experimental characterizations of the alpha-GeO2 material in terms of thermal and physical properties. The behavior of the thermophysic, linear expansion coefficient, piezoelectric and dielectric properties with temperatures will be analyzed using several crystal orientations. Their temperature dependence will lead to the determination of of 1st and 2nd order temperature coefficients needed to obtain the orientation of GeO2 compensated cuts and its associated electromechanical coupling coefficients. The refractive indices and the elastic properties will also be accurately measured. 3) Enhance from the technological point of view the alpha-GeO2 material by estimating its performances in piezoelectric systems (inertial sensors, resonators…) and by comparing them with those of alpha-quartz-like structure materials already used in industrial applications such as SiO2 and GaPO4. It will be also necessary to optimize the design of resonators in bending and expansion modes and to make their assembly in order to measure their performances.

Cristal Laser has always had a strong philosophy of continuous improvement of its growth processes and products manufacturing. Today, Cristal Laser is especially focusing on strengthening the quality of its nonlinear crystals to offer both robust and reliable solutions over time for high-power ultraviolet lasers. Indeed, the high-power UV lasers market is currently booming with applications range from semiconductors to space. And we witness a real technological race for higher power that always demands components of higher performance. Therefore, it is important for Cristal Laser to offer a technically suitable product for UV lasers that would give the company a significant competitive advantage on the world stage in the years to come. Here’s one example of higher requirements in UV laser field : the European Space Agency (ESA) is starting a new Aeolus follow-on program whose goal is to multiply by 3 the power of the UV laser and by 7 the lifetime of the 355nm laser within 5 years. Such a technological breakthrough will inevitably require the development of technical solutions for UV-generating crystals. Cristal Laser also notices these higher technical requirements in its industrial partners : Airbus, Amplitude, Thales, Trumpf, or Nikon As for the CEA, it offers a unique platform with a wide range of lasers, from the ultra-short pulses (20fs) to the continuous regime, from the near infrared (1µm) to the medium ultraviolet (200nm). The CEA will therefore be able to provide its industrial partner with extensive opportunities for trials and tests that will enable to determine which are the components key parameters depending on the laser type, and especially in the UV. On the other hand, CEA researchers will also provide Cristal Laser with a deep theoretical scientific support in laser-matter interaction so that it can orient its developments, improve its crystal growth processes, and refine the important parameters of the components that would be integrated into its customers' lasers. The instrumentation implemented at the CEA will also serve as a reference for the jointly developed benches that will later be installed at the industrial partner’ site for production monitoring or R&D. At the same time, the CEA will also renew part of its instrumentation and develop new benches that will allow an in-depth study of the processes of creation and relaxation of defects induced by ultraviolet laser at different time scales in dielectrics, a very rich scientific theme that is now booming.

The UV-CHALLENGE project (duration of 36 months) is proposed by an academic-industrial consortium. The latter includes three academic French laboratories [Laboratoire de Chimie de la Matière Condensée (LCMCP) at Ecole Nationale Supérieure de Chimie de Paris (ENSCP), Laboratoire Charles Fabry (LCF) at Palaiseau and Laboratoire de Matériaux Optique, Photonique et Système (LMOPS) at Metz (University de Lorraine)], two French industrial partners [EOLITE Systems in Bordeaux and Cristal Laser (CLASER) in Nancy] and one German industrial partner [Forschungsinstitut für Edelsteine/Edelmetalle GmbH (FEE)] which is member of the consortium without any requested financial support from ANR. The main purpose of this project is to demonstrate the capabilities of new non linear optical (NLO) crystals for practical UV laser light generation. The generation of UV light by means of non linear optical (NLO) processes from an infrared fundamental beam is indeed a promising path to design all solid-state UV lasers. For this purpose, several non linear optical crystals have to be used, but there are only very few NLO crystals that can achieve the last stage of frequency conversion towards UV, especially when wavelengths below 270 nm are targeted. In this framework, the consortium involved in this project has already identified two families of crystals with real potentialities. They are based on YAl3(BO3)4 (YAB) and Ca5(BO3)3F (CBF). These crystals were identified in a previous project, called “UV-Borates” (2006-2010), and they have been developing to compete with the commercial crystals which are practically used today for UV conversion: LiB3O5 (LBO) for third harmonic generation (THG: 343 – 355 nm) and ß – BaB2O4 (ß – BBO) or CsLiB6O10 (CLBO) for fourth harmonic generation (FHG: 237 – 266 nm) by frequency doubling of green light. These commercial crystals have some severe drawbacks: they are hygroscopic (very critical for CLBO) and their lifetime in UV laser systems is unsatisfactory. YAB, CBF and some of their related compounds are proposed to solve these limitations and to increase the reliability and/or the efficiency of the THG and FHG processes. For deeper understanding of aging effect, this study will extend to the analysis of the behavior of commercial crystals like LBO and BBO. UV-CHALLENGE is a multidisciplinary project involving materials science, crystal growth and machining, linear and non linear optics, conversion efficiency and material aging studies. The consortium of the present project consists of 6 partners having more than 4 years of collaboration in the field of nonlinear optical materials. The first objective is first to optimize the crystal growth conditions leading to enhanced optical quality crystals for fabrication of NLO crystals oriented and polished for specific configurations. Second, the precise determination of the physical properties as well as the relationships between optical and structural properties (impurities, twinning, absorption spectroscopy, EPR and Raman spectroscopy, surface characterization) of the new NLO crystals proposed in this project will be emphasized. Finally, the nonlinear optical properties and the aging behavior of the crystals will be tested in practice and compared to commercial NLO crystals. Aging in particular is a key issue to any practical application of UV sources. The achievement of these objectives will require a large panel of basic optical measurements, the accurate machining of many crystals, and the direct evaluation of UV conversion performances. All these studies will be analyzed and provided as feedback to the crystal growth process.

The NUTS project (New UltravioleT laser System) aims to develop a high power diode-pumped solid state laser in the deep UV (236,5 nm). Deep UV lasers have numerous applications in detection and sensing and in material processing. A laser at 236,5 nm can be used in detection of NO molecules (component of explosive like TNT) by fluorescence or by Raman spectroscopy. Below 250 nm, gas laser are widely used despite their well known drawbacks (size, toxicity for excimer lasers, low efficiency, price). Standard 1 µm diode-pumped solid state lasers have difficulties to adress this wavelenth range because they require at least three non linear conversion stages. The NUTS project proposes the development of a diode-pumped solide state laser emitting at 236,5 nm with only two non linear conversion stages. The fundamental laser is a single crystal fiber emitting at 946 nm. The targeted power is 1 W in the UV, 50 times higher than the previous state of the art. To take this challenge up, the Laboratoire Charles Fabry (LCF) de l'Institut d'Optique and its industrial partners, Fibercryst and Cristal Laser propose to work on two keys : - The first one concerns the laser at 946 nm with the single crystal fiber (SCF) technology. SCFs are long and thin rods (typ. 1mm in diameter and 50 mm long). Their designs allows excellent thermal management and pumping confinement. This is particularly important for 946 nm emission as the lower level of the laser transition is close to the fundamental level. First demonstrations of SCF emitting at 946 nm give results higher than the state of the art. However, to adress the challenge of the NUTS project, SCF have to go further in terms of power scaling and beam quality. The NUTS project proposes to pump the SCF at 885 nm instead of 808 nm in order to reduce the quantum defect and consequently the heating of the SCF induced by the pump by a factor higher than two. We plan to develop a Q-switched SCF laser emitting an average power of 20 W at 946 nm at a repetition rate between 20 kHz and 100 kHz with an excellent beam quality (including spatial profile and polarisation). This quality is very important for efficient non linear conversions. - The second key is related to the non linear conversion stages. Two cascaded second harmonic generations are considered : the first one producing 473 nm emission, and the second one 236,5 nm photons. Previous works on 236,5 nm lasers reported low conversion efficiency (less than 2 %) from 946 nm to 236,5 nm. The NUTS project aims to reach an efficiency of 5%. This will be possible thanks to the quality and to the peak power of the 946 nm SCF laser. The NUTS project proposes innovative ways to use non linear crystals that can benefit to the conversion efficiency. Both civilian and defence applications are concerned by this works : - Remote detection of explosive or dangerous chemical agents by UV spectroscopy are clearly in the scope of the ASTRID call for proposals - The blue and UV performance targeted in the NUTS project can adress medical applications, sub marine sensing, or material processing. - For Fibercryst, the NUTS project is the opportunity to push the SCF technology at its limits and to offer an power scaled version of SCF modules for its customer (improvement of 2-3 in terms of output power at 1064 nm for example). - For Cristal Laser, the NUTS project innovations may give new opportunities of markets of its crystals (LBO, RTP, KTP).