CONTRACT 37 / 06.10.2011; PROGRAMUL 'IDEI', PN-II-ID-PCE-2011-3-0801


TITLE:                                 Ultraintense THz wave generated in air-plasma by short-pulse high-intensity laser beam

FINANTARE :                        Unitatea Executiva pentru Finantarea Invatamantului Superior, a Cercetarii, Dezvoltarii şi Inovarii (UEFISCDI), Ministerul Educatiei, Cercetarii, Tineretului si Sportului, Romania
FUNDED BY:                        
UEFISCDI, Ministry of Education, Research, Youth and Sport, Romania

DURATA PROIECTULUI:        Octombrie 2011 - Decembrie 2016
PROJECT DURATION:           October 2011 - December 2016

CONDUCATOR PROIECT:      Institutul National de Cercetare-Dezvoltare pentru Fizica Laserilor, Plasmei si Radiatiei, Magurele, Bucuresti, Romania
PROJECT LEADER:              National Institute for Laser, Plasma and Radiation Physics, Magurele, Bucharest, Romania

Contract value:                      1.500.000 lei

Valoare contract:                   1.500.000 lei

The research team:                DASCALU Traian, PhD

Echipa de cercetare:              PAVEL Nicolaie, PhD

                                            DINCA Mihai, PhD

                                            URSESCU Daniel, PhD

                                            GRIGORE Oana Valeria, PhD student

                                            SALAMU Gabriela, PhD student

                                            BANICI Romeo

                                            BRANDUS Catalina Alice, PhD student

                                            IONESCU Alina


The use of ultrashort THz pulses is facilitating terahertz spectroscopy of a wide range of physical, chemical, and biological samples, and enables time-resolved measuremets in which the terahertz is used to probe dynamical responses to an optical excitation pulse. Recently the development of intense ultrafast lasers have allowed table top sources of ultrafast THz pulses approaching the mJ level in energy opening a new way for ultrashort nonlinear THz spectroscopy and large protein conformational changes. This high energy THz pulses with large broad band have been obtained by laser filamentation in a gas. When a laser pulse is focused in a gas, due to balance among natural diffraction, plasma defocusing and Kerr self-focusing, laser pulses carries out periodic defocusing and self-focusing, and can propagate long distance. There are several models explaining THz generation in plasma filaments: dipole like current generated by the laser ponderomotive force, or four wave-mixing model in two-color ultrashort laser filments in air etc.

Stage 1. October - December 2011. Theoretical studies on intense ultrashort broadband THz pulse emission from gaseous media excited by focused single and 2-color femtoseconds laser pulses.
Stage 2. January - December 2012. Implementation of ultrashort intense THz sources by single color filament. Enhancement of THz high field strength by 2-color filamentation and multifilamentation.
Stage 3. January - December 2013. Development and optimization of intense ultrashort broadband THz pulse emission from gaseous media excited by focused single and 2-color femtoseconds laser pulses.
Stage 4. January - December 2014. Tailoring the shape and pulse duration of THz radiation through the multifilamentation characteristics.

Stage 5. January - September 2015. Development of the methods for producing high resolution single shot 2D THz imaging. The final research report.

The main objective of this project will be to carry on research about THz wave air plasma generated by high intensity laser beam, as a THz source yielding high strength electric field, over a large bandwidth, and perform preliminary experiments on single-shot THz imaging.
ADevelopment and optimization of intense ultrashort broadband THz pulse emission from gaseous media excited by focused single and 2-color femtoseconds laser pulses;
BTailoring the THz radiation (pulse shape, spectral content, polarization) produced by laser filamentation and multifilamentation;
Development of the methods for producing high resolution single shot 2D THz imaging.


Stage 1. October - December 2011
Value:   45.000 lei

- Theoretical studies on high energy THz pulses generation by laser filamentation were conducted.
Raportul stiintific pe anul 2011 este disponibil aici: | 2011

Stage 2. January - December 2012
Value:   800.000 lei

- The equipment for high energy THz setup was assembled.
- Filaments in air were studied in various environment conditions.

- Laser studies were performed for future development of high energy table top THz setup.
Raportul stiintific pe anul 2012 este disponibil aici: | 2012 |

Stage 3. January - December 2013
Value:   180.596,34 lei
- Enhancement of THz high field strength by two-color filamentation and multifilamentation.

- THz radiation with tailored shape and pulse duration was studied.

A 17 TW laser system delivering 25 fs laser pulses and with energy up to 300 mJ/pulse is used for filamentation experiments. The laser pulse is split in two parts used for THz generation and THz detection. The most intense one is focused in ambient air after being partially frequency doubled in a non linear BBO crystal to produce two color filament and following THz radiation. The polarizations, intensities, and the phases of the fundamental beam and its second harmonic should be controlled independently to further obtain an efficient conversion of THz energy. The weaker part of the optical pulse is used for probing the THz induced birefringence in a ZnTe crystal and by varying the optical path length the terahertz time domain can be sampled.
The project’s first stages results are:
        - Successful operation of the setup for single color and two color filamentation;
        - Calibration of the electro-optical sampling method for THz detection;
Novel design for a solid-state laser used as optical sources for THz generation.


 Raportul stiintific pe anul 2013 este disponibil aici: | 2013

Stage 4. January - December 2014
Value:   127.500 lei
- Multiple THz high energy pulses were obtained by using two methods: spectral clipping and thin film beam polariser.

- We proved that THz pulses trains (two to five) with controlable delay from 1 ps to 100 ps can be obtained by using few mJ, 50 fs optical pulses.
  Raportul stiintific pe anul 2014 este disponibil aici: | 2014 |

● Short resume of the results (2011-2014), in English:  | here|

Stage 5. January - December 2015
Value:   111.930 lei

- The THz wave forms that were obtained using the intrinsic physical properties of the THZ-REEF laser induced plasma in two colors were consistent with the waveforms measured by other methods, in our case EO sampling using a ZnTe crystal.
- The time dependence of THz-REEF was modified by changing the relative phase between the two pulses and polarization fields offering their unique approach to detect THz wave amplitude and phase.
  Raportul stiintific pe anul 2015 este disponibil aici: | 2015 |

Stage 6. January - December 2016
Value:   234.973,66 lei

The THz setup system used for studying the emission and detection of the high energy THz pulses was realized;
- Both, emission and detection, were theoretically studied and simulations controlling independently the polarization, intensities and the phase of the fundamental beam and its second harmonic as well as the probe beam were performed. Experimental measurements were in accordance with theoretically data;
A THz 2D imaging technique was developed in order to obtain the THz temporal waveform in a single-shot experiment.
  Raportul stiintific sintetic este disponibil aici: | 2016 |

 O. V. Grigore, G. Croitoru, T. Dascalu, N. Pavel, “Diode-laser edge-pumped Nd:YAG/YAG lens-shaped composite laser,” Opt. & Laser Techn. 94, 86-89 (2017).   [2015 Impact Factor: 1.879].
C.A. Brandus, L. Gheorghe, T. Dascalu, “Efficient laser operation at 1.06μm in co-doped Lu3+, Nd3+:GaCa4O(BO3)3 single crystal," Opt. Mat. 42, 376-380 (2015);   [2015 Impact factor: 2.183]. 
5. T. Dascalu, G. Salamu, O. Sandu, F. Voicu, and N. Pavel, “Novel laterally pumped by prism laser configuration for compact solid-state lasers,” Laser Physics Letters 10, 055804 (2013);   [2013 Impact factor: 2.964]. 
Note: This work was partially (30%) supported from this project.
4. M. Mernea, O. Calborean, O. Grigore, T. Dascalu, and D. F. Mihailescu, “
Validation of protein structural models using THz spectroscopy: a promising approach to solve three-dimensional structures,”
Opt. Quantum. Electron. 46 (4), 505-514 (2014); [2014 Impact factor: 0.987]. 
3. T. Dascalu, G. Salamu, O. Sandu, M. Dinca, and N. PavelScaling and passively Q-switch operation of a Nd:YAG laser pumped laterally through a YAG prism,” Opt. & Laser Techn. 67, 164-168 (2015).    [2013 Impact Factor: 1.649]
Note: This work was partially (30%) supported from this project.
O. Grigore, O. Calborean, G. Cojocaru, R. Ungureanu, M. Mernea, M.P. Dinca, S. Avram, D.F. Mihailescu, and T. Dascalu, “High-intensity THz pulses application to protein conformational changes,” Rom. Rep. Physics 67(4),1251-1260 (2015).   [2014 Impact factor: 1.517].
R. G. Ungureanu, O. V. Grigore, M. P. Dinca, G. V. Cojocaru, D. Ursescu and T. Dascalu, “Multiple THz pulse generation with variable energy ratio and delay,” Laser Phys. Lett. 12(4), 045301 (2015).   [2014 Impact factor: 2.458]. 

14.  C. Brandus, G. Stanciu, A. Achim, S. Hau, F. Voicu, L. Gheorghe, T. Dascalu, ”Efficient Laser Emission in Nd:GdLuCOB and Nd:GdCOB Single Crystals,” Siegman International School on Lasers 2016, 24-30 July 2016, Barcelona, Spain (poster presentation).
13. O. V. Grigore, G. Croitoru, T. Dascalu, M. Dinca, N. Pavel, “Edge-pumped Nd:YAG/YAG lens-shaped composite laser,” 7th EPS-QEOD EUROPHOTON CONFERENCE, Solid State, Fibre, and Waveguide Coherent Light Sources, 21-26 August, 2016, Vienna, Austria, PO-2.1 (poster presentation).
12. O. Grigore, R. Ungureanu, G. Cojocaru, R. Banici, M.P. Dinca, M. Mernea, S. Avram, D.F. Mihailescu, T. Dascalu, "Method for Generation Multiple High-Intensity THz Pulses within 1-100 ps Time Range," NATO Advanced Research Workshop on THz Diagnostics of CBRN effects and Detection of Explosives & CBRN, 3-6 November, 2015, Izmir, Turkey (invited presentation).
11. T. Dascalu, A. Popa, O. Grigore, M. P. Dinca, G. Cojocaru, R. Ungureanu, D. F. Mihailescu, “High-Intensity THz Pulses: Generation and Applications,” ROMOPTO 2015, 11th International Conference on Optics “Micro- to Nano-Photonics IV”, September 1-4, 2015, Bucharest, Romania; presentation I.I.4 (invited presentation)

10. T. Dascalu, A. Ionescu, G. Salamu, O. Grigore, M. Dinca, F. Voicu, C. Brandus, and N. Pavel, “Novel Thin Disk Lens Shaped Composite Nd:YAG/YAG Ceramic Laser,” CLEO Europe - EQEC 2015 Conference, 21-25 June 2015, Münich, Germany, presentation CA-10.4 (oral presentation).
C.A. Brandus, L. Gheorghe, A. Achim, G. Stanciu, and T. Dascalu, “Evaluation of co-doped Lu3+, Nd3+:GdCa4O(BO3)3 single crystal, a potential self-doubling material with emission in green spectral range,” CLEO Europe 9. EQEC 2015 Conference, 21-25 June 2015, Münich, Germany, presentation CA-P.32 (poster presentation).
T. Dascalu, ”Tailored High-Intensity Multiple THz Pulses for Pump-Probe Experiments,” 2014 Laser and Optoelectronics Conference (LOC 2014), 28-30 November, Beijing, China; presentation 20074 (oral presentation).
T. Dascalu, R. Ungureanu, G. Cojocaru, O. Grigore, R. Banici, and M. Dinca, "Multiple High-Intensity THz Generation by Consecutive Two-Color Filaments in Air," in Frontiers in Optics 2014, OSA Technical Digest (online) (Optical Society of America, 2014), paper LW1I.5 (oral presentation).
T. Dascalu, G. Cojocaru, R. Ungureanu, R. Banici, O. Grigore, and M. Dinca, “High intensity multiple THz sources and its applications,” 5th International Student Conference on Photonics, Orastie, Romania, 23-26 September 2014; presentation I.06 (invited presentation).
5. G. Salamu, F. Voicu, A. Achim, L. Gheorghe, N. Pavel, and T. Dascalu, “Efficient laser emission from a disordered Yb:CLNGG crystal,” 5th International Student Conference on Photonics, Orastie, Romania, 23-26 September 2014; presentation P.07 (poster presentation). Note: This work was partially (40%) supported from this project.
4. T. Dascalu, O. Grigore, M. Dinca, N. Pavel, C. Cojocaru, R. Ungureanu, and R. Banici, “Multiple THz Pulses Generated by Optical Filamentation,” The 14th International Balkan Workshop on Applied Physics, July 2-4, 2014, Constanta, Romania, presentation S2-OP3, Book of Abstracts p. 112 (oral presentation).
3.  N. Pavel, G. Salamu, and T. Dascalu, “Passively Q-switched, composite Nd:YAG/Cr4+:YAG laser pumped laterally through a prism,” The 2nd Laser Ignition Conference, 22 - 25 April 2014, Pacifico Yokohama, Yokohama, Japan, presentation LIC6-2 (oral presentation). Note: This work was partially (20%) supported from this project.
2. C. A. Brandus, L. Gheorghe, and T. Dascalu, “Infrared laser emission in a compact CW and quasi-CW diode pumped Nd3+:GdLuCOB laser,” 
Conference Proc. IEEE, Advanced Optoelectronics and Lasers (CAOL), 2013 International Conference on, 9 - 13 Sept. 2013, Sudak, Ukraine; pages 102 – 103, ISSN: 2160-1518, ISBN: 978-1-4799-0016-9, DOI: 10.1109/CAOL.2013.6657543.
1. O.  Grigore, M. Mernea, J. Pintea, D. Mihailescu, and T. Dascalu, ”Using of THz Radiation in Related Protein Solutions Discrimination,” NATO Advanced Research Workshop on Detection of Explosives and CBRN (Using Terahertz), Izmir, Turkey, 3-6 November 2012.

● T. Dascalu, N. Pavel, G. Salamu, O. Grigore, F. Voicu, M. Dinca, "Sistem laser monolitic, compozit si compact cu livrare simultana a doua fascicule laser / Compact, composite, monolithic laser system with simultaneous emission of two laser beams," Romanian patent, OSIM application number A-100417 / 03.05.2013.
Note: The patent was partially (20%) supported from this project.

Laboratory of Solid-State Quantum Electronics