Periodic Reporting for period 1 - MIDLIFT (Mid-infrared laser system for high-throughput bioprinting by laser-induced forward-transfer) Reporting period: 2019-10-01 to 2021-09-30 Summary of the context and overall objectives of the project The main goal of this project was the development of a novel nanosecond laser system, which operates in the wavelength range near the peak absorption wavelength of liquid water (2930nm). Laser radiation at these wavelengths has a penetration depth of few µm in water, enabling highly localised energy deposition and strong laser-material interactions in biological tissues. The development of high-power nanosecond laser sources at these wavelengths has the potential to enable the high precision processing, cutting, and printing of biological materials in a variety of medical applications and lead to significant advances European healthcare.The MIDLIFT laser system was developed to provide nanosecond pulses with sufficient pulse energies and peak powers to enable the precision processing of biological materials—specifically for applications in bioprinting by mid-infrared laser-induced forward-transfer (LIFT). To overcome the limitations of previously demonstrated laser sources in this wavelength range, we proposed a master-oscillator power-amplifier (MOPA) approach: to combine a compact, gain-modulated GaSb-diode laser with a single-mode Erbium-doped fluoride fibre amplifier. In the final part of the project, it was planned to demonstrate the application of the new laser system for mid-infrared LIFT bioprinting.At the end of the project a new nanosecond MOPA laser system operating at a wavelength of 2790nm was demonstrated. We achieved output pulse energies of 52.7µJ, pulse durations of 5.2ns and peak powers of more than 8kW at a repetition rate of 10kHz, from an Erbium-doped fluoride fibre amplifier with a nearly diffraction-limited output beam profile (M2 < 1.3). Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far We have developed a MOPA laser system consisting of a gain-modulated GaSb-based diode laser and a single-mode Erbium-doped fluoride fibre amplifier. The GaSb-diode laser was provided by an external academic partner. To develop the fluoride fibre amplifier, we cooperated with the European SME “Le Verre Fluore” (LVF), including a two-month secondment. The amplifier consisted of 2.2m of Er-doped, double-clad, single-mode fibre with a doping concentration of 7 mol%. The fibre was pumped with a multimode pump diode at 980nm. At a pump power 7.8W we obtained amplified output pulses with the following parameters: pulse energies of 3.9µJ, pulse duration of 100ns, repetition rate of 100kHz, and wavelength of 2760–2780nm. This corresponds to an amplifier gain of more than 27dB.To increase the output pulse energies of the MOPA system, we replaced the GaSb-diode laser with a bulk PPLN-OPO (optical parametric oscillator), pumped by a Nd:YAG laser with a repetition rate of 10kHz. While significantly less compact, the OPO-system provided higher seed pulse energies of 0.5µJ, shorter pulse durations of 5.2ns and enabled the optimisation of the laser wavelength. With this setup, we achieved the following laser parameters: pulse energies of 52.7µJ, pulse durations of 5.2ns repetition rate of 10kHz, and a laser wavelength of 2790nm. These laser parameters are suitable for biomaterial processing applications and LIFT-based bioprinting. The obtained results have been submitted to Optics Letters for publication. Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) To the best of our knowledge, this is the first time that the amplification of GaSb-diode lasers in an Erbium-doped fluoride fibre amplifier has been demonstrated. We intend to publish these results in a high impact peer-reviewed journal (manuscript is being prepared). The results obtained with the OPO-based seed laser are the first demonstration of nanosecond pulse amplification in single-mode Erbium-doped fluoride fibre amplifier (manuscript submitted to Optics Letters). We have shown for the first time that Erbium-fluoride fibre amplifiers can be used to provide nanosecond pulses with sub-10ns pulse durations and peak powers of more than 8kW, suitable for high precision material processing of biological tissues. Further progress and development of these laser can the potential to result in new processes and tools for advanced medicine and biological research. laser.jpeg
