INFLPR - ECS, RESULTS

_________________________________________________________________________________________________________________________________

● An optical system, capable of producing cylindrical vector beams with adjustable characteristics in the focal plane, has been designed and analysed. Specifically, the focal spot can be changed from a typical doughnut spot with azimuthal polarization to an extended doughnut spot or a bi-lobed focal spot without circular symmetry, via simple rotation of certain optical elements around the optical axis. Moreover, if the focal spot is circularly non-symmetric, then it could be rotated around the optical axis by rotation of certain components. 

                                                                   

                                                          a) The set-up used to produce a beam with azimuthal or nearly azimuthal polarization in the focal plane.
                                                                        b) The layout designed to deliver an intensity profile that is nearly uniform in the focal plane.

                                         

               a) A radial polarized beam in the focal spot. b) An azimuthally polarized beam generated by first layout (Fig. 1a) in which PR does rotate the plane of polarization 45^o clockwise.
c) Beam distribution in the focal spot for a linearly-polarized beam incident on MC. d) Beam distribution for PR rotating the polarization plane 45^o clockwise followed with a  90^o rotation by QWP.
_________________________________________________________________________________________________________________________________

● A study was conducted on the interaction between a Gaussian beam and a multi-sectional diffractive optical element (spiral phase plate - SPP) made of glass deposited with a polymeric material. This optical element is a matrix of SPPs, each element with an aperture of 10 mm x 10 mm has a topological charge (TC) between 1 and 8. Negative values of TC were obtained by turning the plate 180^o around vertical axis. The advantage of using this plate is that it does not change the polarization of the incident beam; thus, the plate can be used independently, without being placed among two quarter-wave plates. SPP was designed for the wavelength of 633 nm; in experiments its illumination was done with a laser beam with a wavelength of 780 nm. For each TC, measurements of the beam distribution were made in order to establish that the laser beam generated by SPP illumination, at a different wavelength than the one for which it was made, remains of the vortex type.

                                                                   
                            The experimental set-up used to study the influence of the laser beam wavelength on the laser beam produced by the SPP designed for the wavelength of 633 nm.

                                         

                                        Laser beam distribution: a) experimental and b) theoretical, when the SPP was illuminated with the laser beam at 780 nm, for m from m= +/-1 to m= +/-8.
_________________________________________________________________________________________________________________________________

● An optical system comprising a c-cut uniaxial crystal positioned between two axicons and illuminated by a Gaussian or a Laguerre-Gauss beam was used to demonstrate the generation of various vector vortex beams.

                                                           
                     The experimental setup comprises four main parts: an SPP equivalent system (VPS) consisting of two quarter-wave plates (QWP) and a vortex half-wave plate; a polarization control system (PS)
                     composed of a quarter-wave plate (QWP) and a half-wave plate (HWP); a vector vortex beam generation system (AS) that contains two fused silica ultra-quality axicon lenses and an uniaxial crystal,
                                                                                  and a polarization analyser system (PAS) made up of a quarter-wave plate (QWP) and a cube polarizer.

                                                                                                                     
                      Theoretical modelling (column I) and experimental results (column II) obtained for a Sapphire crystal of 2.72 mm and an input beam generated by the laser oscillator. On the last two columns, III and IV,
                             theoretical and experimental results of the high-power laser system are presented. The polarization of the input beam is (i) right-handed circular, (ii) left-handed circular and (iii) linear.
_________________________________________________________________________________________________________________________________

INFLPR - CETAL, RESULTS

● In order to obtain helical laser beams with peak power of the order of hundreds of TW, an optical element in transmission has been configured to modulate the spatial phase of large laser beams. This optical element was used to obtain accelerated electron beams produced with high-power helical beams in jets of noble gases. Accelerated electron beams with maximum energies up to ~500 MeV were obtained by laser wakefield acceleration (LWFA) in the supersonic gas jet target. 

                                                         
                                                                                                         Experimental setup for CETAL-PW laser-gas jet interaction.

                                                 
                                                                                                                         a)  Electron spot centroids distribution on LANEX.
                                  b) Map of the pointing stability illustrated by an images matrix of the scintillating screen (LANEX) exposed to accelerated electrons during a 100-pulse irradiation campaign.
                                                                       
_________________________________________________________________________________________________________________________________

DISSEMINATION
ISI PAPERS
1. A. Craciun and T. Dascalu, “A method to generate vector beams with adjustable amplitude in the focal plane,” Appl. Sci. 10(7), 2313 (2020). https://doi.org/10.3390/app10072313
2 .C. Diplasu, G. Giubega, R. Ungureanu, G. Cojocaru, M. Serbanescu, A. Marcu, E. Stancu, A. Achim, M. Zamfirescu, “Commissioning experiment on laser-plasma electron acceleration in supersonic gas jet at CETAL-PW laser facility,” Rom. Rep. Phys. 73(1), 401 (2021).http://www.rrp.infim.ro/2021/AN73401.pdf
3. M. Serbanescu, R. Ungureanu, G. Cojocaru and P. Schiopu, ”A new method for the delays measurement of the complex optical pulses in a petawatt class laser systems,” Univ. Politeh. Buchar. Sci. Bull.-Ser. A-Appl. Math. Phys. 83(1), 247-258 (2021). https://www.scientificbulletin.upb.ro/rev_docs_arhiva/full8ac_957486.pdf
4. O.-V. Grigore, A. Craciun, “Method for exploring the topological charge of an optical vortex generated by a spiral phase plate,” Opt. Laser Technol. 141, 107098 (2021).  https://doi.org/10.1016/j.optlastec.2021.107098
5. A. Craciun, O.-V. Grigore, “Superposition of vortex beams generated by polarization conversion in uniaxial crystals,” Sci. Rep. 12, 8135 (2022). https://doi.org/10.1038/s41598-022-12223-3

CONFERENCES
1. A. Craciun and T. Dascalu, "Generation of cylindrical vector beams with adjustable diffraction pattern in the focal plane," in Conference on Lasers and Electro-Optics, OSA Technical Digest (Optical Society of America, 2020), paper JTu2F.10. https://www.osapublishing.org/abstract.cfm?uri=CLEO_AT-2020-JTu2F.10
2. O.-V. Grigore, A. Craciun, N. Pavel, T. Dascalu, “Exploring the topological charge and shape of an optical vortex generated with wavelength-detuned spiral phase plates,” 2021 Conference on Lasers and Electro-Optics/Europe - European Quantum Electronics Virtual Conferences (CLEO/Europe-EQEC 2021), 21-25 June 2021, presentation CA-P.15. https://www.osapublishing.org/abstract.cfm?uri=CLEO_Europe-2021-ca_p_15
3. A. Craciun, O. Grigore, T. Dascalu, “Theoretical and experimental study of the vector beams generated with an axicon pair and uniaxial crystals,” 2021 Conference on Lasers and Electro-Optics/Europe - European Quantum Electronics Virtual Conferences (CLEO/Europe-EQEC 2021), 21-25 June 2021, presentation CL-P.5. https://www.osapublishing.org/abstract.cfm?uri=CLEO_Europe-2021-cl_p_5
4. A. Craciun, T. Dascalu, “Accurate beam propagation methods assisted by ray-tracing,” 2021 Conference on Lasers and Electro-Optics/Europe - European Quantum Electronics Virtual Conferences (CLEO/Europe-EQEC 2021), 21-25 June 2021, presentation EJ-P.4. https://www.osapublishing.org/abstract.cfm?uri=EQEC-2021-ej_p_4
5. O. Grigore, A. Craciun, N. Pavel, T. Dascalu, ”Vector vortex beams generated by polarization conversion in uniaxial crystals,” International Conference on Laser, Plasma and Radiation - Science and Technology, June 7-10, 2022 Bucharest, Romania; poster presentation P1-06. Book of Abstracts, ISSN 2821-7128.
6. C. Diplasu, R. Ungureanu, G. Giubega, G. Cojocaru, M. Serbanescu, A. Mihalcea, A. Marcu, “Analysis of Ultrashort Laser-Driven Electromagnetic Pulses in Correlation with Electron Acceleration in Gas Target at CETAL PW- Laser System,” International Conference on Laser, Plasma and Radiation - Science and Technology, June 7-10, 2022 Bucharest, Romania; poster presentation P3-05. Book of Abstracts, ISSN 2821-7128.

PATENTS
1.  A. Craciun, T. Dascalu, ”Sistem Optic pentru Producerea de Fascicule Optice Elicolidal Vectoriale,” OSIM patent application, nr. A/00657, 17.10.2019; Derwent Primary Accession Number: 2020-C1184G.
2.  A. Craciun, T. Dascalu, “Optical System for Generation of Vortex Beams,” European patent application EP 3809188 A1; application  EP20020478.2 / 15.10.2020.