An optical system comprising a c-cut uniaxial crystal positioned between two axicons and illumina... more An optical system comprising a c-cut uniaxial crystal positioned between two axicons and illuminated by a Gaussian or a Laguerre–Gauss mode was used to demonstrate the generation of various vector vortex beams. We focused the generated beams using a 1 m focal length lens and we investigated their intensity profile and the polarization state in the focal plane of the focusing element. We showed that the achieved intensity profile can be controlled by changing the polarization state of the beam incident on the crystal. We observed that, for a particular configuration of the system, the initial circular symmetry of the beam is no longer preserved. The experiments were performed with Ti:Sapphire lasers that were operated in continuous wave mode, as well as in pulsed regime. The optical system presented here ensures a convenient way to generate a great variety of vector vortex beams and it is expected to be of interest for applications that use low and high-power laser sources, such as S...
The Solderjet Bumping technique has been used to assemble by soldering means the optical componen... more The Solderjet Bumping technique has been used to assemble by soldering means the optical components of a laser spark-plug ignition device, hence guaranteeing high robustness and space compatibility devices. The laser could deliver pulses with adjustable energy between 4.70 mJ and 2.40 mJ and duration around 0.8 ns, thus being suitable for inducing air breakdown phenomenon.
We report on the design and output performances of a diode pumped, high-peak power Nd:YAG/Cr 4+ :... more We report on the design and output performances of a diode pumped, high-peak power Nd:YAG/Cr 4+ :YAG laser with four-beam output. The system posses the ability to chose independently the focus of each laser beam, being seen as a solution for a laser spark with multiple-point ignition. The laser ignition of a gasoline direct injected engine has several advantages in comparison with ignition by electrical spark plugs, like absence of quenching effect during the developing flame kernel, ability in positioning the ignition point inside the engine cylinder or the possibility to ignite leaner air-fuel mixtures [1]. Based on extensive research, the first report on an automobile that was fully ignited by laser sparks was presented in 2013 [2]. Recently, a Renault automobile engine was also run only by laser sparks [3]. Several key parameters were measured at various engine speeds and loads, proving the advantages of laser ignition in comparison with classical ignition, such as better engine...
We developed a combination of technology for deposition contacts/wires upon nanoporous InP thin f... more We developed a combination of technology for deposition contacts/wires upon nanoporous InP thin film structures and RF sputtering InP films. Indium phosphide (InP) films were deposited onto glass substrate using RF magnetron sputtering by varying the substrate temperature (50–100 o C), under constant argon pressure (6.3•10 -3 Bar) and RF power (100 W). Index Terms —InP film, RF sputtering, porous InP, THz antenna, THz-TDS. 2 International Conference on Nanotechnologies and Biomedical Engineering, Chisinau, Republic of Moldova, April 18-20, 2013 162 The porous structure have been made using the [111]oriented substrates of n-InP single crystals with 500 μm thickness and free electron concentration of 1.3x10 18 cm −3 . The electrochemical etching was carried out in 5% HC1 aqueous solution in potentiostatic regime as described elsewhere [2]. Indium phosphide (InP) films were deposited onto glass substrate with the thickness of film around 100nm, using RF magnetron sputtering by varying ...
A new method for conformational changes of enzymes under very intense and short electric field is... more A new method for conformational changes of enzymes under very intense and short electric field is proposed. The molecular dynamics of linoleate 9/13-lipoxygenase from Pseudomonas aeruginosa was simulated for frequencies ranging from 1 to 15 THz under electric field of 10 V/m with pulse length of 2 ps. Multiple intense THz field is generated by combining two-color plasma filamentation with a method for splitting and delaying short laser pulses. Large conformational changes of protein structure are predicted by using μJ THz pulse energy with 15 THz bandwidth.
The authors outline progress made over the last years in laser ignition (LI) research, in particu... more The authors outline progress made over the last years in laser ignition (LI) research, in particular that targeting laser sources (or laser spark plugs) with dimensions and properties suitable for operating directly on engines. Some of the envisaged solutions for design and implementation are introduced. The path taken, from the first approach to build a compact laser suitable for engine ignition, to the practical realization of a laser spark plug, is described. Some results obtained from LI of test engines with devices resembling classical engine spark plugs are discussed, emphasizing the technological advances which have brought LI close to application in automobile gasoline engines. Scientific and technical advances have led to the realization of laser devices with multiple beam outputs, but many other important aspects such as integration, thermal endurance and vibration resilience are still to be solved. Recent results of multi-beam LI of a single-cylinder test engine are encou...
A diode-pumped, passively Q-switched, compact and monolithic Nd:YAG/Cr 4+ :YAG ceramic laser with... more A diode-pumped, passively Q-switched, compact and monolithic Nd:YAG/Cr 4+ :YAG ceramic laser with four-beam output is presented. The energy of each laser pulse could be increased up to 5.9 mJ at pulse duration around 1 ns. The system is seen as a solution for a laser spark with multiple-point ignition. In comparison with ignition by electrical spark plugs, the laser ignition of a gasoline direct injected engine offers several potential benefits; often discussed are the no quenching of the combustion flame kernel, the ability to focus a laser beam at any location of interest in the combustion chamber, or the possibility to deliver beams in different positions, simultaneously or with temporal control. The first report on an automobile that was fully ignited by laser sparks was presented in 2013 [1]; also, a Renault vehicle was run only by laser sparks recently, in 2015 [2]. Better engine stability and reduced CO and HC emissions were measured for the engine ignited by laser sparks. A ...
2021 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 2021
An optical vortex (OV) has a number of intrinsic properties, such as spiral phase structure, holl... more An optical vortex (OV) has a number of intrinsic properties, such as spiral phase structure, hollow-core intensity distribution or orbital angular momentum, which leads to many interesting applications in the field of frontier research, like cold atom trapping [1] , [2] , laser-plasma interaction [3] , or communications and quantum-information coding [4] , [5] . The determination of topological charge (TC) is an important aspect for OV’s characterization. In this work, we present a procedure to determine TC of an OV by probing the spiral phase plate (SPP) element with a laser beam of a different wavelength than the one for which SPP was designed.
2021 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 2021
Vector beams (VB) are optical beams with a variable polarization state on the transversal section... more Vector beams (VB) are optical beams with a variable polarization state on the transversal section of the beam. The more standard VB are composed of two complex conjugated modes with orthogonal polarization states. Specific applications of VB are beginning to emerge, for instance in StED Microscopy [1] or laser material processing [2] . It has been demonstrated that a particular category of VB that are composed of modes that are not complex conjugated, exhibit a rotation of the transversal profile with the propagation to the focal plane [3] . This effect is caused by the accumulation of a different amount of Gouy phase between the composing modes. This kind of beams will be further called hybrid vector beams (HVB). A recent study on the propagation of HVB demonstrated that far-field diffraction pattern may considerably change depending on the mode composition and/or polarization state [4] . We showed in [5] that a change in the mode composition of the HVB can be realized by an adjustment of the incoming polarization state on a system consisting from a spiral phase plate (SPP) and a uniaxial crystal that acts as a radially symmetric quarter waveplate.
Abstract A spiral phase plate (SPP) represents one of the most efficient and cost-effective optic... more Abstract A spiral phase plate (SPP) represents one of the most efficient and cost-effective optical devices used for vortex beam generation. In this work, we studied, both experimentally and theoretically, the effect of illumination of an SPP with a laser beam of a different wavelength than the one for which it was designed. We visualized the transversal intensity profile without any additional focusing element and the spatial phase of the beam was investigated using a Sagnac interferometer. SPPs with topological charges from 1 to 8 were used in these investigations. The results of the study revealed that the characteristic diffraction patterns which show rotational symmetry of order m, but no inversion symmetry, can be used to determine the absolute value m and the sign of the topological charge of the SPP. In addition, the same technique has the potential to be used for singularity manipulation and shaping the intensity distribution of vortex beams.
We report on the design, realization, and output performance of a diode-pumped high-peak-power pa... more We report on the design, realization, and output performance of a diode-pumped high-peak-power passively Q-switched Nd:YAG∕Cr 4 :YAG composite medium monolithic laser with four-beam output. The energy of a laser pulse was higher than 3 mJ with duration of 0.9 ns. The proposed system has the ability to choose independently the focus of each beam. Such a laser device can be used for multipoint ignition of an automobile gasoline engine, but could also be of interest for ignition in space propulsion or in turbulent conditions specific to aeronautics.
A laser configuration made of a thin-disk Nd:YAG/YAG composite medium that consists of a circular... more A laser configuration made of a thin-disk Nd:YAG/YAG composite medium that consists of a circular Nd: YAG core bonded by diffusion to a circular undoped YAG and that has the shape of a plane-concave lens is presented. The pump is done through the undoped YAG edge, in a threefold scheme, directly from the diode-laser optical fibers. Such a laser was built employing a Nd:YAG/YAG ceramics made of a 1.0-at.% Nd:YAG core of 2.0-mm diameter surrounded by a 10 mm in diameter YAG. The thickness was 180 lm at the center of Nd:YAG and 500 lm at the YAG edge. The Nd:YAG/YAG medium was attached to a water-cooled copper finger. At 2 Hz repetition rate the laser yielded pulses at 1.06 lm with energy E p = 31.8 mJ under the pump at 807 nm with total energy E pump = 114.6 mJ; the slope efficiency was 0.31. A decrease of laser pulse energy with the repetition rate was observed. This indicates that a better thermal management, which could be made through metallic bonding of Nd:YAG/YAG to the cooling system, is necessary.
ABSTRACT Two methods for multiple high energetic THz pulse generation by two-color filamentation ... more ABSTRACT Two methods for multiple high energetic THz pulse generation by two-color filamentation in air with controllable energy ratio and delay ranging from one to hundreds of ps were investigated. In the first method the laser pulse is split into two inside the optical stretcher of a CPA laser system, the resulting consecutive filaments occur in the same region and allows the study of the influence of the first plasma filament on the THz emission of the delayed filament. Based on a polarization sensitive thin film beam splitter placed in front of a 45° mirror, the second method produces multiple parallel consecutive filaments. Above a certain total pump level the THz energy delivered by multiple pulses exceeds the value given by a single filament for the same pump energy, thereby overcoming the THz emission saturation of the single filament.
An optical system comprising a c-cut uniaxial crystal positioned between two axicons and illumina... more An optical system comprising a c-cut uniaxial crystal positioned between two axicons and illuminated by a Gaussian or a Laguerre–Gauss mode was used to demonstrate the generation of various vector vortex beams. We focused the generated beams using a 1 m focal length lens and we investigated their intensity profile and the polarization state in the focal plane of the focusing element. We showed that the achieved intensity profile can be controlled by changing the polarization state of the beam incident on the crystal. We observed that, for a particular configuration of the system, the initial circular symmetry of the beam is no longer preserved. The experiments were performed with Ti:Sapphire lasers that were operated in continuous wave mode, as well as in pulsed regime. The optical system presented here ensures a convenient way to generate a great variety of vector vortex beams and it is expected to be of interest for applications that use low and high-power laser sources, such as S...
The Solderjet Bumping technique has been used to assemble by soldering means the optical componen... more The Solderjet Bumping technique has been used to assemble by soldering means the optical components of a laser spark-plug ignition device, hence guaranteeing high robustness and space compatibility devices. The laser could deliver pulses with adjustable energy between 4.70 mJ and 2.40 mJ and duration around 0.8 ns, thus being suitable for inducing air breakdown phenomenon.
We report on the design and output performances of a diode pumped, high-peak power Nd:YAG/Cr 4+ :... more We report on the design and output performances of a diode pumped, high-peak power Nd:YAG/Cr 4+ :YAG laser with four-beam output. The system posses the ability to chose independently the focus of each laser beam, being seen as a solution for a laser spark with multiple-point ignition. The laser ignition of a gasoline direct injected engine has several advantages in comparison with ignition by electrical spark plugs, like absence of quenching effect during the developing flame kernel, ability in positioning the ignition point inside the engine cylinder or the possibility to ignite leaner air-fuel mixtures [1]. Based on extensive research, the first report on an automobile that was fully ignited by laser sparks was presented in 2013 [2]. Recently, a Renault automobile engine was also run only by laser sparks [3]. Several key parameters were measured at various engine speeds and loads, proving the advantages of laser ignition in comparison with classical ignition, such as better engine...
We developed a combination of technology for deposition contacts/wires upon nanoporous InP thin f... more We developed a combination of technology for deposition contacts/wires upon nanoporous InP thin film structures and RF sputtering InP films. Indium phosphide (InP) films were deposited onto glass substrate using RF magnetron sputtering by varying the substrate temperature (50–100 o C), under constant argon pressure (6.3•10 -3 Bar) and RF power (100 W). Index Terms —InP film, RF sputtering, porous InP, THz antenna, THz-TDS. 2 International Conference on Nanotechnologies and Biomedical Engineering, Chisinau, Republic of Moldova, April 18-20, 2013 162 The porous structure have been made using the [111]oriented substrates of n-InP single crystals with 500 μm thickness and free electron concentration of 1.3x10 18 cm −3 . The electrochemical etching was carried out in 5% HC1 aqueous solution in potentiostatic regime as described elsewhere [2]. Indium phosphide (InP) films were deposited onto glass substrate with the thickness of film around 100nm, using RF magnetron sputtering by varying ...
A new method for conformational changes of enzymes under very intense and short electric field is... more A new method for conformational changes of enzymes under very intense and short electric field is proposed. The molecular dynamics of linoleate 9/13-lipoxygenase from Pseudomonas aeruginosa was simulated for frequencies ranging from 1 to 15 THz under electric field of 10 V/m with pulse length of 2 ps. Multiple intense THz field is generated by combining two-color plasma filamentation with a method for splitting and delaying short laser pulses. Large conformational changes of protein structure are predicted by using μJ THz pulse energy with 15 THz bandwidth.
The authors outline progress made over the last years in laser ignition (LI) research, in particu... more The authors outline progress made over the last years in laser ignition (LI) research, in particular that targeting laser sources (or laser spark plugs) with dimensions and properties suitable for operating directly on engines. Some of the envisaged solutions for design and implementation are introduced. The path taken, from the first approach to build a compact laser suitable for engine ignition, to the practical realization of a laser spark plug, is described. Some results obtained from LI of test engines with devices resembling classical engine spark plugs are discussed, emphasizing the technological advances which have brought LI close to application in automobile gasoline engines. Scientific and technical advances have led to the realization of laser devices with multiple beam outputs, but many other important aspects such as integration, thermal endurance and vibration resilience are still to be solved. Recent results of multi-beam LI of a single-cylinder test engine are encou...
A diode-pumped, passively Q-switched, compact and monolithic Nd:YAG/Cr 4+ :YAG ceramic laser with... more A diode-pumped, passively Q-switched, compact and monolithic Nd:YAG/Cr 4+ :YAG ceramic laser with four-beam output is presented. The energy of each laser pulse could be increased up to 5.9 mJ at pulse duration around 1 ns. The system is seen as a solution for a laser spark with multiple-point ignition. In comparison with ignition by electrical spark plugs, the laser ignition of a gasoline direct injected engine offers several potential benefits; often discussed are the no quenching of the combustion flame kernel, the ability to focus a laser beam at any location of interest in the combustion chamber, or the possibility to deliver beams in different positions, simultaneously or with temporal control. The first report on an automobile that was fully ignited by laser sparks was presented in 2013 [1]; also, a Renault vehicle was run only by laser sparks recently, in 2015 [2]. Better engine stability and reduced CO and HC emissions were measured for the engine ignited by laser sparks. A ...
2021 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 2021
An optical vortex (OV) has a number of intrinsic properties, such as spiral phase structure, holl... more An optical vortex (OV) has a number of intrinsic properties, such as spiral phase structure, hollow-core intensity distribution or orbital angular momentum, which leads to many interesting applications in the field of frontier research, like cold atom trapping [1] , [2] , laser-plasma interaction [3] , or communications and quantum-information coding [4] , [5] . The determination of topological charge (TC) is an important aspect for OV’s characterization. In this work, we present a procedure to determine TC of an OV by probing the spiral phase plate (SPP) element with a laser beam of a different wavelength than the one for which SPP was designed.
2021 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC), 2021
Vector beams (VB) are optical beams with a variable polarization state on the transversal section... more Vector beams (VB) are optical beams with a variable polarization state on the transversal section of the beam. The more standard VB are composed of two complex conjugated modes with orthogonal polarization states. Specific applications of VB are beginning to emerge, for instance in StED Microscopy [1] or laser material processing [2] . It has been demonstrated that a particular category of VB that are composed of modes that are not complex conjugated, exhibit a rotation of the transversal profile with the propagation to the focal plane [3] . This effect is caused by the accumulation of a different amount of Gouy phase between the composing modes. This kind of beams will be further called hybrid vector beams (HVB). A recent study on the propagation of HVB demonstrated that far-field diffraction pattern may considerably change depending on the mode composition and/or polarization state [4] . We showed in [5] that a change in the mode composition of the HVB can be realized by an adjustment of the incoming polarization state on a system consisting from a spiral phase plate (SPP) and a uniaxial crystal that acts as a radially symmetric quarter waveplate.
Abstract A spiral phase plate (SPP) represents one of the most efficient and cost-effective optic... more Abstract A spiral phase plate (SPP) represents one of the most efficient and cost-effective optical devices used for vortex beam generation. In this work, we studied, both experimentally and theoretically, the effect of illumination of an SPP with a laser beam of a different wavelength than the one for which it was designed. We visualized the transversal intensity profile without any additional focusing element and the spatial phase of the beam was investigated using a Sagnac interferometer. SPPs with topological charges from 1 to 8 were used in these investigations. The results of the study revealed that the characteristic diffraction patterns which show rotational symmetry of order m, but no inversion symmetry, can be used to determine the absolute value m and the sign of the topological charge of the SPP. In addition, the same technique has the potential to be used for singularity manipulation and shaping the intensity distribution of vortex beams.
We report on the design, realization, and output performance of a diode-pumped high-peak-power pa... more We report on the design, realization, and output performance of a diode-pumped high-peak-power passively Q-switched Nd:YAG∕Cr 4 :YAG composite medium monolithic laser with four-beam output. The energy of a laser pulse was higher than 3 mJ with duration of 0.9 ns. The proposed system has the ability to choose independently the focus of each beam. Such a laser device can be used for multipoint ignition of an automobile gasoline engine, but could also be of interest for ignition in space propulsion or in turbulent conditions specific to aeronautics.
A laser configuration made of a thin-disk Nd:YAG/YAG composite medium that consists of a circular... more A laser configuration made of a thin-disk Nd:YAG/YAG composite medium that consists of a circular Nd: YAG core bonded by diffusion to a circular undoped YAG and that has the shape of a plane-concave lens is presented. The pump is done through the undoped YAG edge, in a threefold scheme, directly from the diode-laser optical fibers. Such a laser was built employing a Nd:YAG/YAG ceramics made of a 1.0-at.% Nd:YAG core of 2.0-mm diameter surrounded by a 10 mm in diameter YAG. The thickness was 180 lm at the center of Nd:YAG and 500 lm at the YAG edge. The Nd:YAG/YAG medium was attached to a water-cooled copper finger. At 2 Hz repetition rate the laser yielded pulses at 1.06 lm with energy E p = 31.8 mJ under the pump at 807 nm with total energy E pump = 114.6 mJ; the slope efficiency was 0.31. A decrease of laser pulse energy with the repetition rate was observed. This indicates that a better thermal management, which could be made through metallic bonding of Nd:YAG/YAG to the cooling system, is necessary.
ABSTRACT Two methods for multiple high energetic THz pulse generation by two-color filamentation ... more ABSTRACT Two methods for multiple high energetic THz pulse generation by two-color filamentation in air with controllable energy ratio and delay ranging from one to hundreds of ps were investigated. In the first method the laser pulse is split into two inside the optical stretcher of a CPA laser system, the resulting consecutive filaments occur in the same region and allows the study of the influence of the first plasma filament on the THz emission of the delayed filament. Based on a polarization sensitive thin film beam splitter placed in front of a 45° mirror, the second method produces multiple parallel consecutive filaments. Above a certain total pump level the THz energy delivered by multiple pulses exceeds the value given by a single filament for the same pump energy, thereby overcoming the THz emission saturation of the single filament.
Uploads
Papers by Oana Grigore