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Nonlinear optical coatings at high intensities

Periodic Reporting for period 1 - NICOS (Nonlinear optical coatings at high intensities)

Reporting period: 2015-10-01 to 2017-09-30

In the course of the project, the research fellow developed and characterized dielectric multilayers exhibiting nonlinear properties and satisfying at the same time all the technological requirements for laser applications such as wide transparency range, fast response, and high laser induced damage threshold. In order to use the potential of dielectric coatings as nonlinear optical devices, the researcher carefully explored the behaviour of dielectric multilayers at the intensities, which are, on the one hand, high enough to activate nonlinearities and lower, on other hand, than the laser induced damage threshold. For the first time, accurate characterization of nonlinear effects, in particular Kerr effect, in dielectric coatings was carried out. The research fellow developed a universal method for evaluation of intensity dependent reflectance and transmittance of dielectric multilayers. Due to this method, Kerr coefficients of thin-film dielectric materials typically used in multilayer coatings were reliably determined. It makes possible the incorporation of the nonlinear Kerr effect into multilayer design.
The achievement of the project goals was possible due to extensive scientific training, unique research facilities of the host institution as well as the professional toolkit of the researcher. The research fellow acquired new experimental skills and experience with lasers based on thin-disk technology, with two high-vacuum deposition systems and a large variety of measurement devices.
Work Package 1. Characterization of nonlinear properties of dielectric multilayer coatings
October 2015-March 2016: Characterization of nonlinear effects, pump-probe experiments, investigation of thermal effects; investigation of presence of the third-harmonic generation effect and self-focusing effect.
October 2015-December 2015: Scientific training with the laser setup; new skills with measurement devices.
March 2015: Training with the laser calorimetry (outside).
October 2015: Training “Manage your project successfully” (soft skill)
Summary: starting approximation of Kerr coefficients of some thin-film materials; decoupling nonlinear and thermal effects, absence of the third-harmonic generation and self-focusing effect.

Work Package 2. Modeling of interaction of high intensity laser pulses with dielectric multilayers
January 2016 – September 2016: Development of the method of evaluation of spectral characteristics of multilayer coatings in the nonlinear regime. Determination of the Kerr-coefficients of thin-film oxide materials.
February 2016-May 2016 – Preparation of Paper 1 for Optics Express.
March 2016 – May 2016 - Preparation of Paper 2 for Optics Express
September 2016: Training “Strategic planning of the research carrier” (soft skill)
April 2016: Girl’s day
Summary: Method for evaluation of nonlinear response of dielectric multilayers developed; Kerr coefficients of thin-film materials determined.

Work Package 3. Nonlinear optical coatings for laser applications
October 2016-July 2017: Production and characterization of new optical coatings. Study of the qualitative behaviour of nonlinear multilayers at different intensity ranges and stability with time. Exploiting nonlinear multilayers as intensity limiters. Study of nonlinear/thermal behaviour of nonlinear multilayers deposited on the substrates of different sizes. Subdivision the intensity range into five subranges with respect to the qualitative behaviour of dielectric coatings driven by different physical phenomena.
October 2016-December 2016: Scientific training with two high-vacuum deposition systems.
May 2017: Training with the electron-beam evaporation technique (advanced level).
November 2016: Proposal writing/reviewing skills at the seminar organised for women-scientists.
January 2017 – May 2017: Writing a proposal for getting further funding.
December 2016 – February 2017: Preparation of Paper 3 for Optics Express.
March 2017 - Preparation of Paper 4 for Optics Express.
Service for community as reviewer in some journals published by Optical Society of America, special recognition as Reviewer 2015-2016.
May 2017: Senior OSA Membership
Summary: qualitative behaviour of the nonlinear multilayers carefully studied, dynamic range for mode-locking applications determined.
August 2017 -September 2017: Secondment into an industrial company. Development of novel optical laser components.

Overview of the results: During the research period of two years, the researcher provided the scientific work aimed at development and characterization of novel nonlinear dielectric multilayers. The main results are published in peer-review Optics Express journal. The research fellow had a 2-months secondment to a company producing custom-oriented optical components. The research fellow presented the results in multiple conferences and seminars.

List of seminars, workshops and conferences:
June 2016, Optical Interference Coatings, USA
August 2016, 7th EPS-QEOD EUROPHOTON CONFERENCE, Solid State, Fibre, and Waveguide Coherent Light Sources, Austria
March 2017, 12. ThGOT: Thementage Grenz- und Oberflächentechnik and Optik-Kolloquium „Dünne Schichten in der Optik”, Germany
April 2017, Optical Coatings for Laser Applications Symposium, Switzerland
June 2017, CLEO®/Europe-EQEC 2017, Germany
September 2017, Laser-Induced Damage in Optical Materials 2017, USA
September 2016 and October 2017, Annual meetings of the Laboratory of Attosecond Physics, Czech Republic.
The majority of ultrafast lasers include multilayer optical components providing accurate group delay dispersion control as well as desired spectral characteristics. However, considerations of these multilayers are performed in the frame of the well-known linear theory. At the same time, under the illumination of optical coatings by high-intensity, generated by modern lasers, the nonlinear effects manifest themselves. Until NICOS project, the nonlinear interactions of ultrashort pulses with dielectric optical coatings were studied in the context of laser-induced damage, as an effect that should be minimized. It was demonstrated in the NICOS project that nonlinear effects in dielectric multilayers span a wide range of interesting physical phenomena, which are being now applied for development of a series of novel laser components. The method of calculation of nonlinear response of optical coatings developed by the researcher opens a new avenue in design of multilayers with predictable nonlinear properties.
The Kerr-effect-driven dielectric multilayers with intensity-dependent reflectance make them potentially useful for mode-locking applications. Experiments being carried out at the Host Institution will make possible to use nonlinear multilayers as amplitude modulators for initiating or assisting laser mode-locking. This result holds the prospect for devices purely based on dielectric materials and the optical Kerr effect allowing nearly-lossless operation for future laser systems. As the dielectric multilayers can be fabricated using standard coating techniques, they can become a substantial alternative for conventional nonlinear materials in laser applications. Nonlinear multilayers developed in the project can be integrated in laser oscillators as intensity limiters. The results of NICOS project is a valuable contribution to simultaneously three research fields: thin-film optics, nonlinear optics and laser physics.