Project: Mid-IR Amplifier based oN a Tm-Doped-fiber Ultrafast-pulse Source

The IR laser market (1.8-15 µm) is experiencing explosive growth according to the US think-tank Strategies Unlimited. The “Mid-Infrared Lasers Report” published in September 2010 predicts a yearly expansion by ~30% driven primarily by the emerging sensing and defense applications. The 5-9 µm spectral range, targeted by project MIRANDUS, is notoriously difficult to access with laser sources. Nevertheless, this is one of the most informative spectral regions for molecular makeup identification as it covers absorption fingerprints of the stretching and bending modes of amino, carbonyl groups, carbon-nitrogen groups, etc. The potential sensing applications span the whole range from the concentration measurement of green house gases, to the identification of explosive materials, to the chemically resolved imaging of biological tissue. The breakthrough in the development of suitable light sources occurred with the invention of the quantum cascade lasers which account for a predominant share of MIR sensing devices currently sold despite the inconvenience of the low-temperature operation. The alternative emerging techniques are based on nonlinear frequency conversion of near-IR pump laser sources in different parametric schemes. Synchronously pumped MID-IR OPOs are a promising way to implement straightforward Fourier Transform spectroscopy using a single photo-detector and without relying on an external moving delay line. However, both these techniques are incapable of reaching high pulse intensities that are required for the implementation of nonlinear optical detection techniques and for time-resolved spectroscopic analysis. The target of project MIRANDUS is to achieve tunable broadband femtosecond (~70 fs, 3-4 optical cycles) pulses with energies up to 1 µJ and repetition rate of up to 1 MHz, corresponding to a 1-W average output power. The proposed architecture is a seeded optical parametric amplifier (OPA) pumped by a Thulium-doped fiber laser amplifier that generates multi-µJ ultrashort pulses in the 1.9—2.1 µm range suitable for pumping ZnGeP2 (ZGP), a highly efficient mid-IR nonlinear optical crystal. Although Tm-doped fiber- and solid-state-based systems emitting femtosecond pulses have recently been demonstrated, they provide no straightforward solution to the problem of seeding and synchronization of a mid-IR OPA. As an alternative, we propose an elegant solution to this challenge based on an integration of a femtosecond Ytterbium-doped fiber amplifier (YDFA) system, developed in the ongoing Eurostars project YAFFLE, into a hybrid Tm-doped fiber and ZGP OPA system envisaged in project MIRANDUS. Starting with the white-light continuum generated by the YAFFLE frontend, we use difference frequency generation (DFG) to derive the corresponding seed pulses at the pump wavelength (1.9—2.1 µm) and the OPA signal wavelength (2.5—3.5 µm) using conventional tunable fan-out MgO-doped periodically poled LiNBO3 crystals (PPLN). The first seed wavelength is then seeded into a Tm-doped amplifier and the second one into the OPA, resulting in the generation of a 5—9 µm idler pulse. The notable advantages of the MIRANDUS scheme are the modular approach relying on well-developed front-end components and the straightforward scalability of the average output power and intensity achievable by upgrading the performance of the Tm-doped fiber amplifier. Added versatility comes from the opportunity to additionally boost the energy of the 2- µm wave in a stand-alone Holmium-doped solid stae amplifier, which opens the possibility to configure the system to generate lower-repetition-rate high energy mid-IR pulses suitable for strong field laser applications in basic research. A lightened-up version of the system that does not include the ZGP amplifier might also find a broad scope of applications given the booming interest in Tm-doped lasers. The advantage of MIRANDUS in this single-wave configuration is the built-in tunability across the entire usable gain bandwidth of the Tm-doped fiber amplifier which is determined by the DFG type seeding scheme. Another advantage of the DFG seeding scheme in the full OPA configuration is the automatic locking of the carrier phases of all three output pulses of the system, i.e. the 2-µm pump, ~2.5-µm and the MIR idler pulse, which also becomes carrier phase locked because of the DFG process in the parametric amplifier. Therefore, this scheme directly produces a passively stabilized frequency comb that covers a sizable part of the NIR-MIR spectral range, although the comb spacing is inconveniently narrow due to a (sub-)MHz fundamental repetition rate of the amplifier. An important implication of the phase stability between the three-color pulses is the possibility to use the output of this scheme for a coherent phase contrast detection imaging of plastic and semiconductor assemblies, time resolving the movement of electric charges and recording refractive index transitions.

Acronym MIRANDUS (Reference Number: 6698)
Duration 01/03/2012 - 30/06/2015
Project Topic We propose to develop and commercialize an up to 1 MHz-repetition-rate mid infrared (5-9 µm) hybrid laser + parametric amplifier system delivering femtosecond micro-Joule energy pulses for environmental sensing, biomedical imaging and materials characterization and processing applications.
Network Eurostars
Call Eurostars Cut-Off 6

Project partner

Number Name Role Country
2 Photonics Institute, Vienna University of Technology Partner Austria
2 Menlo Systems GmbH Coordinator Germany