|1- Papazoglou, D. G., Abdollahpour, D., Tzortzakis, S., "Ultrafast electron and material dynamics following femtosecond filamentation induced excitation of transparent solids", Applied Physics A, 114, 161-168, (2014).|
We examine the spatiotemporal dynamics of filamentation and subsequent material changes in two transparent media, fused silica and poly(methyl methacrylate) (PMMA), using inline holographic microscopy. We are able to dynamically observe the nonlinear propagation of femtosecond laser pulses and the consequent evolution of the electronic excitatio n and trapping inside the bulk of both materials. In the case of fused silica we reveal the physical conditions for the formation of nanogratings, measuring excited electron densities well below the critical density while for PMMA we show that excited electrons with densities exceeding 1018 cm−3, exhibit complex trapping dynamics in a 200 fs time scale. The clear demonstration of ultrafast sub-ps photochemical processes that take place during the irradiation of PMMA with femtosecond pulses will have a strong impact on the laser microprocessing of polymers and nanosurgery applications of bio-related materials.
|2- Suntsov, S., Abdollahpour, D., Papazoglou, D. G., Panagiotopoulos, P., Couairon, A., Tzortzakis, S., "Tailoring femtosecond laser pulse filamentation using plasma photonic lattices", Applied Physics Letters, 103, 021106-1-021106-3, (2013).|
We demonstrate experimentally that by using transient plasma photonic lattices, the attributes of intense femtosecond laser filaments, such as peak intensity and length, can be dynamically controlled. The extended plasma lattice structure is generated using two co-propagating nondiffracting intense Bessel beams in water. The use of such transient lattice structures to control the competition between linear and nonlinear effects involved in filamentation opens the way for extensive control of the filamentation process.
|3- Panagiotopoulos, P., Abdollahpour, D., Lotti, A., Couairon, A., Faccio, D., Papazoglou , D. G., Tzortzakis, S., "Nonlinear propagation dynamics of finite-energy Airy beams", Physical Review, 86, 013842-1-013842-15, (2012).|
The nonlinear dynamics of intense truncated Airy beams inKerr ionizing media are investigated from numerical simulations and experiments. We show numerically that a competition between the linear and nonlinear effects takes place and may be modified by tuning the width of the main lobe of the Airy beam and the size of the truncating diaphragm. Our analysis shows that the acceleration of the Airy peak, an inherent feature of linear Airy beam propagation, is preserved only for powers in the main Airy lobe below a certain threshold. Nonlinear propagation of intense Airy beams with low power in the main lobe is sustained by a continuous energy flux from its neighbors, similarly to the mechanism sustaining nonlinear Bessel beam propagation. Airy beams with higher powers in the main lobe are reshaped into a multifilamentary pattern induced by Kerr and multiphoton nonlinearities. The nucleation of new filaments and their interaction affect the acceleration of the main Airy lobes. We finally show that the size of the truncation constitutes a control parameter for the energy flux that features the Airy beam acceleration. Experiments performed in water corroborate the existence of these two distinct nonlinear propagation regimes.
|4- Abdollahpour, D., Papazoglou , D. G., Tzortzakis, S., "Four-dimensional visualization of single and multiple laser filaments using in-line holographic microscopy", Physical Review, 84, 053809-1-053809-10, (2011).|
It is shown, both through simulations and experiments, that the in-line holographic microscopy technique can be used to retrieve very small refractive-index perturbations caused during the filamentation of ultrashort laser pulses. This technique provides the possibility of having spatially and temporally (four dimensions) resolved measurements of refractive-index changes, down to 10−4, from objects with diameters as small as 10 μm. Moreover, we demonstrate the power of the technique in discriminating multiple filaments in a precise quantitative
|5- Abdollahpour, D., Suntsov, S., Papazoglou, D. G., Tzortzakis, S., "Measuring easily electron plasma densities in gases produced by ultrashort lasers and filaments ", Optics Express, 19, 16866-16871, (2011).|
We present an easy way to calibrate the simple plasma conductivity (PCo) technique for measuring electron plasma densities in gases. We show that calibration can be achieved using a single absolute plasma density measurement through an independent analytical technique, in our case the in-line holographic microscopy (i-HOM). We show the validity and power of the method by comparing the calibrated PCo with results from i-HOM over an extended range of experimental parameters
|1- Aakhte, M., Abdollahpour, D., "Simulation of Linear Propagation of a Ring Airy Beam in Scattering Media
", OSA presents IONS-15, Turkey, Ankara, Bilkent University, 1-1, (2014).|
|2- Mohajerani, S., Aakhte, M., Mostafavi-Amjad, J., Abdollahpour , D., A. Akhlaghi, E., "Three Dimensional Surface Topography Measurement by Phase Modulated Mirau Interferometeric Microscope", 20th Iranian Conference on Optics and Photonics and 6th Iranian Conference on Engineering and Technology, 1-4, (2014).|
In this paper, a method for measuring 3D surface topography by using a phase modulated Mirau interferometric microscope is presented. Phase shifting is one of the methods to analyze interference patterns of the microscope. In this research an LCD is used as a phase modulator to apply the phase shifts. The advantages of this method compared to the conventional methods are the possibility of high-speed data acquisition and non-mechanical phase shifting.
|3- Couairon, A., Lotti, A., Panagiotopoulos, P., Abdollahpour, D., Faccio, D., Papazoglou, D. G., Tzortzakis, S., Courvoisier, F., Dudley , J. M., "Ultrashort laser pulse filamentation with Airy and Bessel Beams
", Proc. SPIE 8770, 17th International School on Quantum Electronics: Laser Physics and Applications, Nessebar, Bulgaria
, 8770, 87701E-1-87701E-14, (2012).|
We investigate the nonlinear propagation of intense Bessel and Airy beams forming _laments in transparent media. We identify two propagation regimes separated by the relative importance of multiphoton absorption and self-focusing of the main Bessel or Airy lobe, due to the Kerr e_ect. We show that intense Bessel or Airy beams are reshaped into stationary nonlinear beams whose propagation is sustained by a continuous energy ux to the main lobe from its neighbors. The stationary propagation regime is obtained for Bessel cone angles exceeding a certain threshold, by focusing a Gaussian beam of su_cient power with an axicon. With respect to linear Bessel beams, stationnary nonlinear Bessel beams exhibit ring compression and attenuation of contrast. For small cone angles, the nonlinear Bessel beams become unstable leading to an unsteady propagation regime. We demonstrate similar physics for intense Airy beam freely propagating in a Kerr medium: stationary nonlinear Airy beams are demonstrated in a planar geometry. These beams preserve the intensity pro_le and the transverse acceleration of the Airy peak. For powers in the main Airy lobe exceeding a certain threshold, this stationary propagation regime becomes unstable. In the 2-dimensional case, Airy beams with high powers in the main lobe reshape into a multi_lamentary pattern induced by Kerr and multiphoton nonlinearities. The nucleation of new _laments and their interaction, a_ects the acceleration of the main Airy lobes.
|4- Couairon, A., Lotti, A., Panagiotopoulos, P., Abdollahpour, D., Faccio, D., Papazoglou, D. G., Tzortzakis , S., "Nonlinear propagation and filamentation of intense Airy beams in transparent media
Proc. SPIE 8434, Nonlinear Optics and Applications VI, Brussels, Belgium
, 8434, 84340S-1-84340S-12, (2012).|
We investigate the nonlinear propagation of intense Airy beams forming filaments in transparent media. We demonstrate the existence of stationary nonlinear Airy beams in a planar geometry. These beams preserve the intensity profile and the transverse acceleration of the Airy peak. We show that stationary propagation is sustained by a continuous energy flux to the main Airy lobe from its neighbors. For powers in the main Airy lobe exceeding a certain threshold, this stationary propagation regime becomes unstable. We extend our results to the 2-dimensional case: Airy beams with high powers in the main lobe reshape into a multifilamentary pattern induced by Kerr and multiphoton nonlinearities. The nucleation of new filaments and their interaction, affects the acceleration of the main Airy lobes. Experiments performed in water corroborate the existence of these two regimes.
|5- Tzortzakis, S., Abdollahpour, D., Papazoglou, D. G., Georgiou , S., "Femtosecond Filamentation Induced Micro and Nano-Restructuring in the Bulk of Dielectrics and Polymer
", Proc. SPIE 7925, Frontiers in Ultrafast Optics: Biomedical, Scientific and Industrial Applications XI, San Francisco, California, USA , 7925, 79250O-1-79250O-6, (2011).|