Domestic research projects

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Research projects (co)funded by the Slovenian Research Agency.

 

  • Member of University of Ljubljana: UL Faculty of Mechanical Engineering
  • Project code: L2-9240
  • Project title: Ultrashort pulses on demand
  • Period: 01.07.2018 - 30.06.2021
  • Range on year: 0,67
  • Head: izr. prof. dr. Rok Petkovšek
  • Research activity: Engineering sciences and technologies 
  • Research Organisation: Link
  • Researchers: Link
  • Citations for bibliographic records: Link
Abstract:

Today’s industry is increasing its investment in to the research of laser micro-processing, where precision and high speed of processing are required. These requirements are directly correlated to two key components of laser processing systems: the laser source and the scanning system. Above all the scanning system must provide high speed. In addition to high precision, the laser source must also meet the requirement for high speed and thus flexibility in terms of efficient synchronization with the scanning system.

The latest and more importantly the now emerging generations of polygon and resonance scanners already provide exceptional scanning speeds. For example in the case of polygon scanners, the beam scanning speed along the sample can reach several km/s. The problem arises because they operate at a constant speed, so that with standard laser pulse sources operating at a constant repetition rate, we can only construct structures with equal spacing on the sample. Similar problem arises in the case of resonant scanners which are demanding for synchronization because of nonlinear response (resonant response - sinusoidal oscillation) of the scanner. The solution in both cases is the use of laser source capable of producing pulses on demand with pulse duration in the ps/fs range.

The need for high scanning speed and high precision of the laser beam on the subtract define the needed time resolution of the pulse position on demand; at scanner speed of 2 km/s and required precision of 5-10 µm a laser pulse with time resolution of under 5 ns is required which is not achievable with the modern laser systems

The goal of the project are R&D of the laser systems with ultra-short laser pulses (ps/fs range) which adhere to requirements stated above. The proposed concept is based on direct driving of seed source. In contrast to the established mode locked sources we will use the DFB type laser diodes, which allow for such driving operation and thus totally arbitrary generation of pulses on demand.

For achieving this, three key innovative and breakthrough solutions will be introduced:

First a spectral broadening of the seed pulses from the laser diode by means of the otherwise undesired effect of self-induced phase modulation (SPM). With the use of SLM the pulse will be transformed in such a way that it will be suitable for amplification in the CPA MOPA system based on active optical fibers.

Second innovative approach to realization of the project goals will be the use of tapered fibers with which an alternative to usually used complex photonic crystal fibers PCF will be achieved. The tapered fibers applied to the CPA systems will served for adequate spectral broadening of the seed diode, which is the key for working of CPA amplifiers.

Thirdly: to optimize the spectral transformation and thus the entire proposed laser system, we will research and develop an innovative and original, highly sensitive system for the analysis of ultra-short laser pulses based on the FROG method. Research on this work package will be carried out in close cooperation with the group led by prof. dr. Rick Trebino. Prof. Trebino is a worldwide authority in this field since he is the inventor of several methods for the characterization of ultra-fast laser pulses. The system for characterization of pulses is also one of the key results of the project. With his help we will be able to analyze the transformed and broadened spectrum obtained from different types of narrowed fibers, which will help to compensate the non-linear phase using the SLM modulator.

With the proposed laser system, it will be possible to take full advantage of the potential of fast new-generation scanning systems - full and arbitrary synchronization between the pulsed laser source and the scanning system will be possible. In the future, such systems will open up completely new areas of potential applications of high-precision and ultra-fast laser micro-processing and related new research directions.

The phases of the project and their realization:
  1.  Research and upgrade of the FROG measurement method
  2. Seed source based on DFB laser diode
  3. Tapered fiber development
  4. Preparation of the excitation pulse for amplification to high energies
  5. Amplification and compression of broadened laser pulses

The project is being implemented according to the plan.