Investigations of photoluminescence and of photo-induced absorption have been carried out on ZnSe... more Investigations of photoluminescence and of photo-induced absorption have been carried out on ZnSe and ZnSe:Te crystals. The parameters of deep levels and their connection with radiative properties of the crystals have been determined. The annealing of ZnSe:Te crystals in halogen vapor causes creation of IR-radiative centers of rapid hole capture which quench the red luminescence.
Spectroscopy of PbMo0 4 Single Crystals Indirect Interband 'fransitions By 697 SIl. EFENDIEV (a) ... more Spectroscopy of PbMo0 4 Single Crystals Indirect Interband 'fransitions By 697 SIl. EFENDIEV (a) , V. GAVRYUSHll'< (b), G. RACIUKAITlS (b) , G. PUZONAS (b), A. KAZLAUSKAS (b), N. DARVISHOV (a) , and S. SHAKHDGAN (a) Two-photon inter band absorption sp ectra are obtained first in PbMo0 4 crystals. They are shown to be attributed to indirect two-photon absorption (TPA) with the assistance of phonons to exciton sta tes formed band transitions with the extrema in different points of the Brillouin zone. The energy parameters of excitons E~x = 3.56 (80 K) and 3.53 eV (300 K), Eb = 50 meV, of phonons (65, 180, lmd 270 meV), and of the interband absorption edge E~ = 3.61 (80 K) and 3.58 eV (300 K) are obtained. Anomalously hi gh effi cien cy of electron-phonon interaction is found in crystals' studied. The phonon energy observed in TP A at indirect transitions is shown to be determined probably by joint participa ti on of severa l active phonon modes of MOO:;-2 tetrahedral group in PbMoO J crystal. B nplIcTa" " ax PbMoO. BllepBbIe 1I0:IY'leHhI cnenTpbI nByx.poToHHoro MemaOHI-lOro norJ' OLl(eHHfl . Ilonaa aHo , 'lTO OHI-! .p0IDIHPYIOTCfl HerrpfliVIbIiVIH nBYX.pOTOHHbIiVIH rrorJIO-Ll(eHHfl~'lI1 (JJ:<DIl) C Y'laCTIICM (POHOHOB B 3ECHTOHHhlC COCTOflHHfl, o6paayeMbIc Ha aOHHblX C paaHeceHHbDm no HMnY;Ibcy 3 1-; cTpe~Iy~IaMIf. IlOJIY'leI-lhl 3ReprCnI'IeCHHC rrapaMeTpbl 3ECHTOHOB E~x = 3,56 (80 K) 11 3 ,53 eV (300 K), EL = 50 meV, .pOHOHOB (65, 180 H 270 meV) H ~Iert{aOHHoro Epafl nOrJIOLl(eHHfl E~ = 3,61 (80 K) H 3,58 eV (300 K). 06HapymcHa aHOlVIaJIbHO BblCOnafl 3(P(IJCETHBHocTb :'lJICHTPOH-.poHOIII-lOrO BaaHMOneMcT-BlIfl 11 lICCJICnYCMbIX EPllCTCJIJIax. IloHaaaHo, 'ITO 3I-lCprllH .pOI-lOHOB, Ha6JIIonaCMbIX B J-lCrrpflMOaOHHOM JJ:<I)Il, nO-BHnllMOMY, onpCnCJIflIOTCH HOJIJI eHTlIBHbIM Y'IaCTHCM HeCHOJIh-I-nIX aHTlIBHbIX (POHOHHbIX MOn TCTpa:-JnpWICCHOM rpynnhl MOO:;-2 B MOJIH6naTC CBHI-IUa.
The European Physical Journal Applied Physics, 2010
The thin-film technology is the most promising technologies to achieve a significant cost reducti... more The thin-film technology is the most promising technologies to achieve a significant cost reduction in solar electricity. Laser scribing is an important step to preserve high efficiency of photovoltaic devices on large areas. The high-repetition-rate laser with the pulse duration of 10 ps was applied in selective ablation of multilayer thin-film a-Si solar cells deposited on flexible and rigid substrates. Two types of solar cells with flexible and rigid substrates had been investigated. The first type of solar cells was made of 400 nm a-Si layer coated on both sides with 2 μm transparent ZnO:Al contact layers deposited by CVD technique on the glass plate. The second type of solar cells was made of a flexible polyimide substrate coated with the Al back-contact, a-Si light absorbing layer and the ITO top-contact. Selection of the right laser wavelength is important to keep the energy coupling in a well defined volume at the interlayer interface. Well-defined shapes of scribes were produced by laser ablation through layers of the solar cell on the glass substrate. Localization of the coupled energy at inner interface led to the "lift-off" type process rather than evaporation of the top ITO layer when the 355 nm radiation was applied. All laser scribes did not indicate any material melting or other thermal damage caused by laser irradiation. Ultra-short picosecond pulses ensured the high energy input rate into absorbing material therefore peeling of the layers was possible without the influence on the remaining material.
The process of nanoparticle generation during nanosecond and picosecond laser ablation of various... more The process of nanoparticle generation during nanosecond and picosecond laser ablation of various metals (Ni, Al, W and stainless steel) in ambient air and argon gas was investigated. The number concentration of nanoparticles generated by laser ablation in argon gas was up to 100 times higher compared to the concentration in ambient air. Three stable separate size peaks of nucleation, Aitken and accumulation modes of nanoparticles were observed in case of argon gas, while in ambient air particles of a wide size spectrum (8-200 nm) were generated. The natural precursors in ambient air can have an effect on size spectrum of the particles composed of various chemical compounds with target material during the ablation process. The influence of laser process parameters and properties of investigated metals on the number concentration and size distribution of nanoparticles generated during ns-and ps-laser ablation was observed.
2013 38th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2013
Search of novel breakthrough concepts of room temperature compact terahertz (THz) imaging systems... more Search of novel breakthrough concepts of room temperature compact terahertz (THz) imaging systems remains as one of sensitive topics in THz photonics. As a rule, a particular attention is attributed to the development of compact THz sources and detectors, however, compact optic componentssuch as focusing lenses, mirrors, beam splitters, etcas well plays important role in reducing size of the systems. Preferences here are usually given to inexpensive and relatively simple technology-based approaches, for instance, binary lenses [4], focusing elements of a combined design structures or narrow-band laser-ablated filters . These solutions can be found well-suited in THz heterodyne [7] and spectroscopic imaging when only several specific spectral lines are used to record image, but still enabling to indentify an object under test. Very recently, terahertz zone plate with integrated resonant filters (TZP) was proposed and experimentally demonstrated for efficient radiation focusing and spectral selection in a single device at selected THz frequency .
ABSTRACT The thin-film Cu-chalcopyrite-based solar cell technologies are becoming more attractive... more ABSTRACT The thin-film Cu-chalcopyrite-based solar cell technologies are becoming more attractive due to their lower cost and optimal performance. High efficiency of small cells might be maintained with the transition to larger areas if small segments are interconnected in series in order to reduce photocurrent in thin films and resistance losses. Interconnect formation is based on three step scribing processes and use of laser is thus crucial for performance of the device. For the first time we demonstrate the possibility to scribe the CZTSe thin-film solar cell structures with picosecond lasers. Investigations on the material lift-off effect in the CZTSe thin film were performed and the method was approved for the damage-free front-side scribing processes. Single pulse ablation and scribing experiments in the thin-film solar cell structures together with theoretical modeling of laser energy coupling in the complex CZTSe structure are presented. We found that the absorber layer removal process was triggered by a micro-explosive effect induced by high pressure of sublimated material due to temperature increase in molybdenum-CZTSe interface. This facilitated to minimize the remaining thermal effects since the laser-affected material was removed by thermo-mechanical process.
Laser micromachining has been proven an excellent technique for patterning many engineering mater... more Laser micromachining has been proven an excellent technique for patterning many engineering materials. The emitted photon energy from a UV laser is high enough to break the chemical bonds of the target reducing the heat effects on surrounding material. We ...
The laser-induced backside wet etching (LIBWE) is an advanced laser processing method used for st... more The laser-induced backside wet etching (LIBWE) is an advanced laser processing method used for structuring transparent materials. LIBWE with nanosecond laser pulses has been successfully demonstrated for various materials, e.g. oxides (fused silica, sapphire) or fluorides (CaF 2 , MgF 2 ), and applied for the fabrication of microstructures. In the present study, LIBWE of fused silica with mode-locked picosecond (t p = 10 ps) lasers at UV wavelengths ( 1 = 355 nm and 2 = 266 nm) using a (pyrene) toluene solution was demonstrated for the first time. The influence of the experimental parameters, such as laser fluence, pulse number, and absorbing liquid, on the etch rate and the resulting surface morphology were investigated. The etch rate grew linearly with the laser fluence in the low and in the high fluence range with different slopes. Incubation at low pulse numbers as well as a nearly constant etch rate after a specific pulse number for example were observed. Additionally, the etch rate depended on the absorbing liquid used; whereas the higher absorption of the admixture of pyrene in the used toluene enhances the etch rate and decreases the threshold fluence. With a 1 = 266 nm laser set-up, an exceptionally smooth surface in the etch pits was achieved. For both wavelengths ( 1 = 266 nm and 2 = 355 nm), LIPSS (laser-induced periodic surface structures) formation was observed, especially at laser fluences near the thresholds of 170 and 120 mJ/cm 2 , respectively.
Recent progress in the development of diode-pumped mode-locked (picosecond) lasers has increased ... more Recent progress in the development of diode-pumped mode-locked (picosecond) lasers has increased interest in their industrial application, especially in microfabrication. The theoretical modelling and experimental results of static and dynamic characteristics of a microactuators developed for micro/nanorobotics and manufactured by laser micro-machining are presented in this paper. The laser micromachined flexures based silicon membrane was used as a moving part of the actuator. The static and dynamic characteristics of designed actuator were simulated using finite element method (Ansys package). The developed microactuator demonstrates the possibility to drive the object up to 40 lm with control voltage 200 V.
35th International Conference on Infrared, Millimeter, and Terahertz Waves, 2010
ABSTRACT Resonant mesh filters for THz region were fabricated using ultrashort pulse UV laser rad... more ABSTRACT Resonant mesh filters for THz region were fabricated using ultrashort pulse UV laser radiation. The arrays of cross-shaped holes were processed in the stainless steel foil and the molybdenum film on polyimide. The spectral performance of the filters was investigated experimentally and numerically.
Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XVII, 2012
ABSTRACT During the recent few years picosecond lasers have been proved as a reliable tool for mi... more ABSTRACT During the recent few years picosecond lasers have been proved as a reliable tool for microfabrication of diverse materials. We present results of our research on structuring of thin films and surfaces using the direct laser writing and the laser beam interference ablation techniques. The processes of micro-pattering were developed for metallic, dielectric films as well as complex multi-layer structures of thin-film solar cells as a way to manufacture frequency-selective surfaces, fine optical components and integrated series interconnects for photovoltaics. Technologies of nano-structuring of surfaces of advanced technical materials such as tungsten carbide were developed using picosecond lasers as well. Experimental work was supported by modeling and simulation of energy coupling and dissipation inside the layers. Selectiveness of the ablation process is defined by optical and mechanical properties of the materials, and selection of the laser wavelength facilitated control of the structuring process. Implementation of the technologies required fine adjustment of spatial distribution of laser irradiation, therefore both techniques are benefiting from shaping the laser beam with diffractive optical elements. Utilization of the whole laser energy included beam splitting and multi-beam processing.
Journal of Micromechanics and Microengineering, 2012
In this paper we demonstrate femtosecond laser fabrication of micro-tubes with a height of severa... more In this paper we demonstrate femtosecond laser fabrication of micro-tubes with a height of several tens of micrometers in the photopolymer SZ2080 by three different methods: direct laser writing, using the optical vortex beam and holographic lithography. The flexibility of direct laser writing and dramatic increase of production efficiency by applying the vortex-shaped beam and four-beam interference approaches are presented. Sample arrays of micro-tubes were successfully manufactured applying all three methods and the fabrication quality as well as efficiency of the methods is compared. The processing time of a single micro-tube with 60 μm height and 3 μm inner radius is reduced 400 times for the holographic lithography technique and 500 times for the optical vortex method compared with the direct laser writing technique. The processing time of a micro-tube array containing 400 micro-tubes is the shortest for the holographic lithography method but not for the optical vortex method as in the case of a single micro-tube, because the holographic lithography method does not require time for sample translation. Additionally, the holographic lithography enables manufacturing of the whole micro-tube array by a single exposure. Although point-by-point photo-structuring ensures unmatched complexity of manufactured microstructures, employing nowadays high repetition rate amplified femtosecond lasers combined with beam shaping or several beam interference can envisage industrial applications for practical demands.
ABSTRACT In this work we present the latest results in the application of multi-photon polymeriza... more ABSTRACT In this work we present the latest results in the application of multi-photon polymerization for tissue engineering, by fabricating microstructured artificial 3D scaffolds for stem cell growth. Microstructuring of large scale 3D scaffolds is investigated and the direct laser writing technique is supplemented by fabrication by multi-beam interference and micromolding of large scale structures. Within the limitation of our study, we conclude that the proposed nonlinear direct laser writing technique offers rapid and flexible fabrication of biomedical components with required shape, pore size and general porosity. The applications could target biostable and biodegradable implants applied for bone or tissue replacement as well as drug delivery or release agents.
Investigations of photoluminescence and of photo-induced absorption have been carried out on ZnSe... more Investigations of photoluminescence and of photo-induced absorption have been carried out on ZnSe and ZnSe:Te crystals. The parameters of deep levels and their connection with radiative properties of the crystals have been determined. The annealing of ZnSe:Te crystals in halogen vapor causes creation of IR-radiative centers of rapid hole capture which quench the red luminescence.
Spectroscopy of PbMo0 4 Single Crystals Indirect Interband 'fransitions By 697 SIl. EFENDIEV (a) ... more Spectroscopy of PbMo0 4 Single Crystals Indirect Interband 'fransitions By 697 SIl. EFENDIEV (a) , V. GAVRYUSHll'< (b), G. RACIUKAITlS (b) , G. PUZONAS (b), A. KAZLAUSKAS (b), N. DARVISHOV (a) , and S. SHAKHDGAN (a) Two-photon inter band absorption sp ectra are obtained first in PbMo0 4 crystals. They are shown to be attributed to indirect two-photon absorption (TPA) with the assistance of phonons to exciton sta tes formed band transitions with the extrema in different points of the Brillouin zone. The energy parameters of excitons E~x = 3.56 (80 K) and 3.53 eV (300 K), Eb = 50 meV, of phonons (65, 180, lmd 270 meV), and of the interband absorption edge E~ = 3.61 (80 K) and 3.58 eV (300 K) are obtained. Anomalously hi gh effi cien cy of electron-phonon interaction is found in crystals' studied. The phonon energy observed in TP A at indirect transitions is shown to be determined probably by joint participa ti on of severa l active phonon modes of MOO:;-2 tetrahedral group in PbMoO J crystal. B nplIcTa" " ax PbMoO. BllepBbIe 1I0:IY'leHhI cnenTpbI nByx.poToHHoro MemaOHI-lOro norJ' OLl(eHHfl . Ilonaa aHo , 'lTO OHI-! .p0IDIHPYIOTCfl HerrpfliVIbIiVIH nBYX.pOTOHHbIiVIH rrorJIO-Ll(eHHfl~'lI1 (JJ:<DIl) C Y'laCTIICM (POHOHOB B 3ECHTOHHhlC COCTOflHHfl, o6paayeMbIc Ha aOHHblX C paaHeceHHbDm no HMnY;Ibcy 3 1-; cTpe~Iy~IaMIf. IlOJIY'leI-lhl 3ReprCnI'IeCHHC rrapaMeTpbl 3ECHTOHOB E~x = 3,56 (80 K) 11 3 ,53 eV (300 K), EL = 50 meV, .pOHOHOB (65, 180 H 270 meV) H ~Iert{aOHHoro Epafl nOrJIOLl(eHHfl E~ = 3,61 (80 K) H 3,58 eV (300 K). 06HapymcHa aHOlVIaJIbHO BblCOnafl 3(P(IJCETHBHocTb :'lJICHTPOH-.poHOIII-lOrO BaaHMOneMcT-BlIfl 11 lICCJICnYCMbIX EPllCTCJIJIax. IloHaaaHo, 'ITO 3I-lCprllH .pOI-lOHOB, Ha6JIIonaCMbIX B J-lCrrpflMOaOHHOM JJ:<I)Il, nO-BHnllMOMY, onpCnCJIflIOTCH HOJIJI eHTlIBHbIM Y'IaCTHCM HeCHOJIh-I-nIX aHTlIBHbIX (POHOHHbIX MOn TCTpa:-JnpWICCHOM rpynnhl MOO:;-2 B MOJIH6naTC CBHI-IUa.
The European Physical Journal Applied Physics, 2010
The thin-film technology is the most promising technologies to achieve a significant cost reducti... more The thin-film technology is the most promising technologies to achieve a significant cost reduction in solar electricity. Laser scribing is an important step to preserve high efficiency of photovoltaic devices on large areas. The high-repetition-rate laser with the pulse duration of 10 ps was applied in selective ablation of multilayer thin-film a-Si solar cells deposited on flexible and rigid substrates. Two types of solar cells with flexible and rigid substrates had been investigated. The first type of solar cells was made of 400 nm a-Si layer coated on both sides with 2 μm transparent ZnO:Al contact layers deposited by CVD technique on the glass plate. The second type of solar cells was made of a flexible polyimide substrate coated with the Al back-contact, a-Si light absorbing layer and the ITO top-contact. Selection of the right laser wavelength is important to keep the energy coupling in a well defined volume at the interlayer interface. Well-defined shapes of scribes were produced by laser ablation through layers of the solar cell on the glass substrate. Localization of the coupled energy at inner interface led to the "lift-off" type process rather than evaporation of the top ITO layer when the 355 nm radiation was applied. All laser scribes did not indicate any material melting or other thermal damage caused by laser irradiation. Ultra-short picosecond pulses ensured the high energy input rate into absorbing material therefore peeling of the layers was possible without the influence on the remaining material.
The process of nanoparticle generation during nanosecond and picosecond laser ablation of various... more The process of nanoparticle generation during nanosecond and picosecond laser ablation of various metals (Ni, Al, W and stainless steel) in ambient air and argon gas was investigated. The number concentration of nanoparticles generated by laser ablation in argon gas was up to 100 times higher compared to the concentration in ambient air. Three stable separate size peaks of nucleation, Aitken and accumulation modes of nanoparticles were observed in case of argon gas, while in ambient air particles of a wide size spectrum (8-200 nm) were generated. The natural precursors in ambient air can have an effect on size spectrum of the particles composed of various chemical compounds with target material during the ablation process. The influence of laser process parameters and properties of investigated metals on the number concentration and size distribution of nanoparticles generated during ns-and ps-laser ablation was observed.
2013 38th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), 2013
Search of novel breakthrough concepts of room temperature compact terahertz (THz) imaging systems... more Search of novel breakthrough concepts of room temperature compact terahertz (THz) imaging systems remains as one of sensitive topics in THz photonics. As a rule, a particular attention is attributed to the development of compact THz sources and detectors, however, compact optic componentssuch as focusing lenses, mirrors, beam splitters, etcas well plays important role in reducing size of the systems. Preferences here are usually given to inexpensive and relatively simple technology-based approaches, for instance, binary lenses [4], focusing elements of a combined design structures or narrow-band laser-ablated filters . These solutions can be found well-suited in THz heterodyne [7] and spectroscopic imaging when only several specific spectral lines are used to record image, but still enabling to indentify an object under test. Very recently, terahertz zone plate with integrated resonant filters (TZP) was proposed and experimentally demonstrated for efficient radiation focusing and spectral selection in a single device at selected THz frequency .
ABSTRACT The thin-film Cu-chalcopyrite-based solar cell technologies are becoming more attractive... more ABSTRACT The thin-film Cu-chalcopyrite-based solar cell technologies are becoming more attractive due to their lower cost and optimal performance. High efficiency of small cells might be maintained with the transition to larger areas if small segments are interconnected in series in order to reduce photocurrent in thin films and resistance losses. Interconnect formation is based on three step scribing processes and use of laser is thus crucial for performance of the device. For the first time we demonstrate the possibility to scribe the CZTSe thin-film solar cell structures with picosecond lasers. Investigations on the material lift-off effect in the CZTSe thin film were performed and the method was approved for the damage-free front-side scribing processes. Single pulse ablation and scribing experiments in the thin-film solar cell structures together with theoretical modeling of laser energy coupling in the complex CZTSe structure are presented. We found that the absorber layer removal process was triggered by a micro-explosive effect induced by high pressure of sublimated material due to temperature increase in molybdenum-CZTSe interface. This facilitated to minimize the remaining thermal effects since the laser-affected material was removed by thermo-mechanical process.
Laser micromachining has been proven an excellent technique for patterning many engineering mater... more Laser micromachining has been proven an excellent technique for patterning many engineering materials. The emitted photon energy from a UV laser is high enough to break the chemical bonds of the target reducing the heat effects on surrounding material. We ...
The laser-induced backside wet etching (LIBWE) is an advanced laser processing method used for st... more The laser-induced backside wet etching (LIBWE) is an advanced laser processing method used for structuring transparent materials. LIBWE with nanosecond laser pulses has been successfully demonstrated for various materials, e.g. oxides (fused silica, sapphire) or fluorides (CaF 2 , MgF 2 ), and applied for the fabrication of microstructures. In the present study, LIBWE of fused silica with mode-locked picosecond (t p = 10 ps) lasers at UV wavelengths ( 1 = 355 nm and 2 = 266 nm) using a (pyrene) toluene solution was demonstrated for the first time. The influence of the experimental parameters, such as laser fluence, pulse number, and absorbing liquid, on the etch rate and the resulting surface morphology were investigated. The etch rate grew linearly with the laser fluence in the low and in the high fluence range with different slopes. Incubation at low pulse numbers as well as a nearly constant etch rate after a specific pulse number for example were observed. Additionally, the etch rate depended on the absorbing liquid used; whereas the higher absorption of the admixture of pyrene in the used toluene enhances the etch rate and decreases the threshold fluence. With a 1 = 266 nm laser set-up, an exceptionally smooth surface in the etch pits was achieved. For both wavelengths ( 1 = 266 nm and 2 = 355 nm), LIPSS (laser-induced periodic surface structures) formation was observed, especially at laser fluences near the thresholds of 170 and 120 mJ/cm 2 , respectively.
Recent progress in the development of diode-pumped mode-locked (picosecond) lasers has increased ... more Recent progress in the development of diode-pumped mode-locked (picosecond) lasers has increased interest in their industrial application, especially in microfabrication. The theoretical modelling and experimental results of static and dynamic characteristics of a microactuators developed for micro/nanorobotics and manufactured by laser micro-machining are presented in this paper. The laser micromachined flexures based silicon membrane was used as a moving part of the actuator. The static and dynamic characteristics of designed actuator were simulated using finite element method (Ansys package). The developed microactuator demonstrates the possibility to drive the object up to 40 lm with control voltage 200 V.
35th International Conference on Infrared, Millimeter, and Terahertz Waves, 2010
ABSTRACT Resonant mesh filters for THz region were fabricated using ultrashort pulse UV laser rad... more ABSTRACT Resonant mesh filters for THz region were fabricated using ultrashort pulse UV laser radiation. The arrays of cross-shaped holes were processed in the stainless steel foil and the molybdenum film on polyimide. The spectral performance of the filters was investigated experimentally and numerically.
Laser Applications in Microelectronic and Optoelectronic Manufacturing (LAMOM) XVII, 2012
ABSTRACT During the recent few years picosecond lasers have been proved as a reliable tool for mi... more ABSTRACT During the recent few years picosecond lasers have been proved as a reliable tool for microfabrication of diverse materials. We present results of our research on structuring of thin films and surfaces using the direct laser writing and the laser beam interference ablation techniques. The processes of micro-pattering were developed for metallic, dielectric films as well as complex multi-layer structures of thin-film solar cells as a way to manufacture frequency-selective surfaces, fine optical components and integrated series interconnects for photovoltaics. Technologies of nano-structuring of surfaces of advanced technical materials such as tungsten carbide were developed using picosecond lasers as well. Experimental work was supported by modeling and simulation of energy coupling and dissipation inside the layers. Selectiveness of the ablation process is defined by optical and mechanical properties of the materials, and selection of the laser wavelength facilitated control of the structuring process. Implementation of the technologies required fine adjustment of spatial distribution of laser irradiation, therefore both techniques are benefiting from shaping the laser beam with diffractive optical elements. Utilization of the whole laser energy included beam splitting and multi-beam processing.
Journal of Micromechanics and Microengineering, 2012
In this paper we demonstrate femtosecond laser fabrication of micro-tubes with a height of severa... more In this paper we demonstrate femtosecond laser fabrication of micro-tubes with a height of several tens of micrometers in the photopolymer SZ2080 by three different methods: direct laser writing, using the optical vortex beam and holographic lithography. The flexibility of direct laser writing and dramatic increase of production efficiency by applying the vortex-shaped beam and four-beam interference approaches are presented. Sample arrays of micro-tubes were successfully manufactured applying all three methods and the fabrication quality as well as efficiency of the methods is compared. The processing time of a single micro-tube with 60 μm height and 3 μm inner radius is reduced 400 times for the holographic lithography technique and 500 times for the optical vortex method compared with the direct laser writing technique. The processing time of a micro-tube array containing 400 micro-tubes is the shortest for the holographic lithography method but not for the optical vortex method as in the case of a single micro-tube, because the holographic lithography method does not require time for sample translation. Additionally, the holographic lithography enables manufacturing of the whole micro-tube array by a single exposure. Although point-by-point photo-structuring ensures unmatched complexity of manufactured microstructures, employing nowadays high repetition rate amplified femtosecond lasers combined with beam shaping or several beam interference can envisage industrial applications for practical demands.
ABSTRACT In this work we present the latest results in the application of multi-photon polymeriza... more ABSTRACT In this work we present the latest results in the application of multi-photon polymerization for tissue engineering, by fabricating microstructured artificial 3D scaffolds for stem cell growth. Microstructuring of large scale 3D scaffolds is investigated and the direct laser writing technique is supplemented by fabrication by multi-beam interference and micromolding of large scale structures. Within the limitation of our study, we conclude that the proposed nonlinear direct laser writing technique offers rapid and flexible fabrication of biomedical components with required shape, pore size and general porosity. The applications could target biostable and biodegradable implants applied for bone or tissue replacement as well as drug delivery or release agents.
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Papers by Gediminas Raciukaitis