The project focused on the research of laser systems with ultra-short pulses (ps/fs range), which enable synchronization with high-speed scanning systems at a time resolution of 5 ns for precise positioning of the laser pulse on the sample. This addressed the industry's need for machining systems for laser micro-processing where precision and high processing speed are desired.

A new concept of an on-demand ultrashort pulse laser based on a directly controllable seed source has been successfully investigated. Unlike existing laser sources, which are based on mode-locked oscillators (operating at a constant frequency), we used DFB laser diodes, which enable advanced control and, consequently, completely arbitrary generation of pulses on demand.

In order to realize a laser with ultrashort pulses on demand, it was necessary to solve the challenge of modifying laser pulses of low peak powers and a duration of slightly more than 50 ps from a DFB seed laser diode into laser pulses of high peak powers with a duration of the order of picoseconds with an arbitrary pulse sequence.

Thus, with the help of non-linear optical phenomena (self phase modulation - SPM), the spectrally inadequate laser pulses from the laser diode were suitably spectrally transformed in such a way that they would be suitable for amplification in the MOPA system according to the CPA principle (so-called linear chirp) in active optical fibers. The appropriate spectral expansion of the seed diode was realized in a way that enables the compactness of the laser source and avoids the use of PCF fibers (more complex design). We studied and included solutions such as the use of tapered fibers with a very small diameter (tapered fibers), as well as spreading the spectrum in a circular amplifier using classic optical fibers.

Finally, in order to optimize the spectral transformation and thus the entire laser system, we researched and developed an innovative and original, highly sensitive system for the analysis of ultrashort laser pulses based on the FROG method. Research in this area was carried out in close cooperation with the group led by prof. dr. Rick Trebino. Prof. Trebino (Georgia Institute of Technology). The pulse characterization system is also one of the key results of the project. With its help, we were able to analyse the transformed and broadened spectrum, which helped to compensate for the nonlinear phase obtained during the transformation of the spectrum from the excitation diode and the amplification process in fiber/hybrid amplifiers.

With the researched laser source, it is possible to fully exploit the potential of fast scanning systems of the new generation - that is, complete and arbitrary synchronization between the pulsed laser source and the scanning system is enabled. We expect that such a system will in the future help to open completely new areas of potential applications of high-precision and ultra-fast laser micro-processing and related new research directions.

All the project phases were realized in full:

Research and upgrade of the FROG measurement method  / realized

Seed source based on DFB laser diode  / realized

Tapered fiber development  / realized

Preparation of the excitation pulse for amplification to high energies  / realized

Amplification and compression of broadened laser pulses  / realized

Bibliographic references resulting directly from the project implementation

[1]   P. Šušnjar, T. Jones, R. Trebino, R. Petkovšek, ‘Crystal-Configuration Considerations for Higher-Sensitivity Picosecond-Pulse SHG FROG’, IEEE J. Quantum Electron., vol. 56, no. 2, pp. 1–8, Apr. 2020, [COBISS.SI-ID 17035547]

[2] T. Jones, P. Šušnjar, P. Petkovšek, and R. Trebino. High-sensitivity, simple frequency-resolved-optical-gating device. IEEE journal of quantum electronics. 2020, vol. 56, iss. 3, str. 1-6 [COBISS.SI-ID 16641283]

[3]     R. Podlipec, J. Mur, J. Petelin, J. Štrancar, R. Petkovšek. Two-photon retinal theranostics by adaptive compact laser source. Applied physics. A, Materials science & processing. 2020, vol. 126, iss. 6, str. 1-9,[COBISS.SI-ID 14993923]

 [4]   V. Agrež, T. Požar, R. Petkovšek, ‘High-speed photography of shock waves with an adaptive illumination’, Opt. Lett., vol. 45, no. 6, pp. 1547–1550, Mar. 2020 [COBISS.SI-ID 17080347]

 [5]   L. Černe, J. Novak, V. Agrež, R. Petkovšek, ‘Optimization of a supercontinuum source based on tapered ordinary fibers’, Laser Phys., vol. 29, no. 2, p. 025103, 2019, [COBISS.SI-ID 16453659]

 [6]  L. Černe, J. Petelin, R. Petkovšek. Adaptive nonlinear phase compensation in a femtosecond hybrid laser with varying pulse repetition rate. Photonics. Sep. 2021, vol. 8, iss. 9, f. 1-10, [COBISS.SI-ID 76393731]

 [7]   L. Černe, J. Petelin, R. Petkovšek, ‘Femtosecond CPA hybrid laser system with pulse-on-demand operation’, Opt. Express, vol. 28, no. 6, pp. 7875–7888, Mar. 2020, [COBISS.SI-ID 17063707]

 [8]   V. Agrež and R. Petkovšek, ‘Highly adaptable gain-switched fiber laser with improved efficiency’, Opt. Express, vol. 27, no. 9, pp. 12100–12109, Apr. 2019, [COBISS.SI-ID 16599835]

[9] M. Marš, R. Petkovšek,  V. Agrež,  'Pump control based pulse on demand operation of frequency doubled Nd:YVO4. Optics and laser technology, Aug. 2022, vol. 152, str. 1-6, [COBISS.SI-ID 106326531]

[10] L. Černe, P. Šušnjar,R. Petkovšek. Compensation of optical nonlinearities in a femtosecond laser system in a broad operation regime. Optics and laser technology, Mar. 2021, vol. 135, str. 1-9, [COBISS.SI-ID 36354563]

[11] R. Petkovšek, V. Agrež, J. Petelin, L. Černe, U. Bünting, B. Podobnik. 'Pulses on demand in fibre and hybrid lasers'. Strojniški vestnik. Nov.-Dec. 2019, vol. 65, no. 11/12, str. 680-689, si 87, [COBISS.SI-ID 16944411]

[12]  J. Petelin, L. Černe, J. Mur, V. Agrež, J.J. Kočica, J. Schille, U. Loeschner, R. Petkovšek, Pulse-on-demand laser operation from nanosecond to femtosecond pulses and its application for high-speed processing. Advanced optical technologies. 2021, vol. 10, iss. 4/5, str. 305-314,  [COBISS.SI-ID 74192131]

[13]  J.Mur, A. Mikelj, B. Podobnik, R. Petkovšek. Precision fabrication of flexible microfluidic circuits using direct laser rapid prototyping solution. Journal of micromechanics and microengineering.,Nov. 2020, vol. 30, no. 11, str. 1-8, [COBISS.SI-ID 24398851],

[14]  J.J. Kočica, J. Mur, J. Petelin, R. Petkovšek. Laser-based material interactions and ablation processes by bursts of 70 ps pulses. Optics express. Jul. 2021, vol. 29, no. 15, str. 22868-22882, [COBISS.SI-ID 69644547]

[15]  R. Podlipec, J. Mur, J. Petelin, J. Štrancar,R.  Petkovšek. Method for controlled tissue theranostics using a single tunable laser source. Biomedical optics express. 2021, vol. 12, no. 9, str. 5881-5893. [COBISS.SI-ID 75069699]