The Stratakis Lab

The Stratakis Lab

Ultrafast Laser Micro and Nano Processing Laboratory

Ultrafast Laser Processing Modelling

Activities: Investigation of surface modification mechanisms in sub-ablation and sub-melting conditions in various types of materials (i.e. semiconductors, metals, dielectrics), exploration of carrier dynamics in multilayered materials, simulation of incubation effects, role of nonthermal electrons, strain propagation.

A desirable effect in the laser-mater processing applications is to control and influence the morphology of the material surface by regulating the way of energy delivery from the laser into the various degrees of freedom of the system. Femtosecond pulsed laser interaction with matter triggers a variety of timescale-dependent processes, influenced by the fluence and pulse duration. A multiscale theoretical investigation is pursued to describe the physical fundamentals and mechanisms that account for the associated experimental observations after single and multiple-pulse ultrashort pulse irradiation and provide a systematic and controllable way of linking the observed surface modification with the applied conditions.

Although surface patterning has been previously investigated upon irradiation with ultrashort pulses in ablation conditions, physics fundamentals of surface modification and a novel surface patterning mechanism for ultrashort pulses have never been addressed in conditions near evaporation (sub-ablation) [1-5]. More specifically, we suggested a new physical mechanism that governs surface patterning formation (i.e. ripples) based on a combination of interference effects (and development of surface plasmon waves) coupled with hydrodynamics capillary induced effects and the dynamics of a superheated liquid layer [2,3]. The ripple periodicity and morphological changes appear to agree satisfactorily with experimental observations (Fig.1). The model has been revised to allow the description of supra-wavelength structures (grooves) that result from the formation of hydrothermal convection rolls [1].

Figure 1: (a) SEM picture, (b). Simulation results.

An extension of the model has been performed to explore the role of laser polarisation. More specifically, radial and azimuthal polarisation was considered to elaborate on the effect on the ripple periodicity [3].
The significant influence of the contribution of the

dynamics of produced nonthermal electrons to electron thermalisation and electron-phonon interaction is thoroughly investigated within a range of values of the pulse duration. The consideration of the role of the nonthermal electrons in the thermalisation of the lattice leads to thermomechanical changes compared to the results the traditional Two Temperature Model (TTM) provides[6,7]

Figure 2: (a) Rippled profile with a radially polarized beam (b) Ripple periodicity for radially (RP) and linearly (LP) polarized beams

 

Figure 3: (a) Electronic and lattice temperature profile using the classical TTM and revised TTM, (b) Spatial strain profile simulated TTM and rTTM.

 

References

Tsibidis G.D., Skoulas E., A.Papadopoulos, and Stratakis E., (2016), Physical Review B (Rapid Communications) 94, 081305.
Tsibidis G.D., Fotakis C., and Stratakis E. (2015), Physical Review B (Rapid Communications), 92 ,041405.
Tsibidis G.D., Barberoglou M., Loukakos P.A., Stratakis E., and Fotakis C. (2012), Physical Review B, 86, 115316.
Tsibidis G.D., and Stratakis E., (2017), Journal of Applied Physics 121, 163106.
Tsibidis G.D., Skoulas E., and Stratakis E. (2015), Optics Letters, 40 (22), 5172.
Tsibidis G.D. (2014), Applied Physics Letters 104, 051603.
Tsibidis G.D. (2018), Journal of Applied Physics 123, 085903.
Tsibidis G.D. (2018), Applied Physics A, 124,311.

Representative publications
1. Tsibidis G.D. (2018), ‘The influence of dynamical change of optical properties on the thermomechanical response and damage threshold of noble metals under femtosecond laser irradiation’, Journal of Applied Physics 123, 085903.

2. Tsibidis G.D. (2018), ‘Ultrafast dynamics of non-equilibrium electrons and strain generation under femtosecond laser irradiation of Nickel’, Applied Physics A, 124,311.

3. Papadopoulos A., Skoulas E., Tsibidis G.D., and Emmanuel Stratakis E. (2018), ‘Formation of periodic surface structures on dielectrics after irradiation with laser beams of spatially variant polarisation: a comparative study’, Applied Physics A 124, 146.

4. Tsibidis G.D., Mimidis A, Skoulas E., Kirner S.V, Krüger J, Bonse J and Stratakis E. (2018), ‘Modelling periodic structure formation on 100Cr6 steel after irradiation with femtosecond-pulsed laser beams’, Applied Physics A 124, 27.

5. Zuhlke C., Tsibidis G.D., Anderson T., Stratakis E., Gogos G., and Alexander R.D. (2018), ‘Investigation of femtosecond laser induced ripple formation on copper for varying incident angle’, AIP Advances 8(1):015212.

6. Gaković B., Tsibidis G.D, Skoulas E., Petrović S.,Vasić B. and Stratakis E. (2017), ‘Selective ablation of Ti/Al nano-layer thin film by single femtosecond laser pulse’, Journal of Applied Physics 122, 223106.

7. Tsibidis G.D., and Stratakis E. (2017), ‘Ripple formation on silver after irradiation with radially polarized ultrashort-pulsed lasers’, Journal of Applied Physics 121, 163106.

8. Tsibidis G.D., Skoulas E., A.Papadopoulos, and Stratakis E. (2016), ‘Convection roll-driven generation of supra-wavelength periodic surface structures on dielectrics upon irradiation with femtosecond pulsed lasers’, Physical Review B (Rapid Communications) 94, 081305.

9. Tsibidis G.D., Skoulas E., and Stratakis E. (2015) “Ripple formation on Nickel irradiated with radially polarized femtosecond beams’, Optics Letters, 40 (22), 5172.

10. Tsibidis G.D., Fotakis C., and Stratakis E. (2015), ‘From ripples to spikes: a hydro-dynamical physical mechanism to interpret femtosecond laser induced self-assembled structures’, Physical Review B (Rapid Communications), 92 ,041405.

11. Tsibidis G.D., Stratakis E., Loukakos P.A., and Fotakis C. (2014), ‘Controlled ultrashort pulse laser induced ripple formation on semiconductors’, Applied Physics A (Invited Paper), 114:57–68.

12. Tsibidis G.D. (2014), ‘Thermal response of double-layered metal films after ultrashort-pulsed laser irradiations: the role of nonthermal electron dynamics’, Applied Physics Letters 104, 051603.

13. Barberoglou M., Tsibidis G.D., Grey D., Magoulakis M., Fotakis C., Stratakis E., and Loukakos P.A. (2013), ‘The influence of ultrafast temporal energy regulation on the morphology of Si surfaces through femtosecond double pulse laser irradiation’, Applied Physics A (Rapid Communications), 113, 273-283.

14. Tsibidis G.D., Barberoglou M., Loukakos P.A., Stratakis E., and Fotakis C. (2012) ‘Dynamics of ripple formation on silicon surfaces by ultrashort laser pulses in subablation conditions’, Physical Review B, 86, 115316.

15. Tsibidis G.D., Stratakis E., Aifantis K.E. (2012) ‘Thermoplastic deformation of silicon surfaces induced by ultrashort pulsed lasers in submelting conditions’, Journal of Applied Physics, 111, 053502.

Project Members

E.Stratakis and C.Fotakis (Experiment)

G.D.Tsibidis (Modelling of laser-matter Interactions)

Manolis N. Petrakakis (Modelling of laser-matter Interactions)

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