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fs-IONIGHT

Duration: 6 months, Start: November 2013

Academic project leader: Thomas Feurer, Institution: IAP Laser Physics, University of Bern. Industrial project partner: IONIGHT - Andreas Riedo, Davide Lasi, Mario Gruber, Jürg Jost, Manuel Ryser, Géraldine Brügger

The company IONIGHT is a Spin-Off of the Space Research and Planetary Sciences Division, University of Bern currently in the process of establishing itself. Its aim is in producing high performance Laser Ablation Ionization Mass Spectrometers (LIMS) [1] designed for laboratory and field applications, building on the unique and proven technology designed for in-situ measurements of the chemical (elemental and isotopic) composition of soils and regolith of solar system objects. The company will be situated in Bern, Switzerland and will officially begin operations towards the end of the year 2013 in form of a stock corporation. The products encompass one service and two product lines (Laboratory "Lab-LMS^TM" and Field Instruments "Field-LMS^TM") on the market between 3 and 24 months from incorporation. The product lines are in full accord with the company’s long term strategy.



In February 2015, scientists Valentine Grimaudo and Pavel Moreno-García were acknowledged in the high-ranked and world-known scientific journal “Analytical Chemistry” (http://pubs.acs.org/journal/ancham ) with a front cover for their science breaking through work with title “High-Resolution Chemical Depth Profiling of Solid Material Using a Miniature Laser Ablation/Ionization Mass Spectrometer” (http://pubs.acs.org/doi/abs/10.1021/ac504403j ).

Outcome
A follow-up CTI-project entitled “Laser micro-machining with sensitive and quantitative online mass-spectrometry feedback” was granted in January 2015.

In the course of this project the Optical Fibers and Fiber Laser group (Institute of Applied Physics, University of Bern) has successfully developed a self-optimizing and low noise femtosecond all-in fiber laser system delivering ultrashort laser pulses with micro-Joule pulse energy. The Ytterbium all normal dispersion fiber ring laser is compact, energy efficient and optimized to be used in conjunction with a miniature laser ablation/ionization mass spectrometer (LIMS) originally developed by the research project partner from the Space Research and Planetary Sciences Division at the University of Bern. The main implementation project partner is the startup company IONIGHT.

The aimed laser specifications were imposed by the requirements of the LIMS: (a) Ultra-short pulse duration of <500 fs with several µJ pulse energy needed for stoichiometric ion production during the ablation and ionization process of sample material, (b) low repetition rate of <50 kHz since recording of a full mass spectrum after laser ablation/ionization takes 20 µs, (c) and last but no least the key requirement to the laser system was, that it exhibits very low pulse-to-pulse energy fluctuations in the per mill range. Requirement (c) is crucial, since a full mass spectrum is recorded from each laser pulse and the ablation/ionization process is pulse energy dependent.

During the first part of the project, we have explored and evaluated three different fiber oscillator in terms of their operation characteristics: (i) self-optimizing additive-pulse mode-locking, (ii) frequency shifted feedback mode-locking, (iii) graphene saturable absorption mode-locking. Exploring these mode-locking schemes showed that the key requirement of high pulse-to-pulse stability was only achieved by system (i).

Hence, in the second part of the project we have successfully built a laboratory-prototype system based on the self-optimizing additive pulse mode-locked cavity. Compared to the standard configuration of similar fiber optic oscillators we have implemented the following two main innovations: (i) clever arrangement and choice of fiber-optic elements allowed us to reduce the number of fiber-optic elements needed to set up the cavity, (ii) three motorized polarization controllers allow for efficient optimization towards low-noise and strong mode-locking. Due to these measures our cavity finally delivered laser pulses of 7 nJ pulse energy, which is to the best of our knowledge the highest pulse energy ever reached with an all-fiber cavity employing 5 µm core sized single mode fibers. Thanks to the large pulse energy delivered by the cavity, only a single-stage large mode area Ytterbium fiber amplifier was needed to reach the desired micro-joule pulse energy. A pulse-picker and subsequent transmission grating compressor were further set up to allow for arbitrary generation of laser pulse bunches and for compression of the 40 ps long pulses delivered from the all-normal dispersion cavity to <500fs pulse duration.
In ongoing work the fiber laser system will be coupled to the LIMS at the space laboratories, in order to acquire mass spectra and optimize the overall system performance.

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