Papers by Robertas Kananavicius
PhotonicsViews, Jun 1, 2021
Sum frequency generation (SFG) spectroscopy is a powerful technique for characterization of vibra... more Sum frequency generation (SFG) spectroscopy is a powerful technique for characterization of vibrational bonds of molecules at surfaces and interfaces [1]. The principle of SFG is based on resonant nonlinear mixing of two optical pulses — typically one in MIR range and another visible (VIS). There are two main SFG spectroscopy techniques. Narrowband SFG (NB-SFG) is based on picosecond MIR and picosecond VIS source. Full spectral information is obtained by tuning MIR pulses through vibrational lines of the molecules. The typical resolution in NB-SFG is a few cm−1 [2]. In broadband SFG (BB-SFG) femtosecond MIR pulses with spectrum spanning a few hundred cm−1 are used. This allows for simultaneous recording of complete SFG spectra and reduces systematic errors due to sample degradation during the measurement. However in most experimental BB-SFG setups the same femtosecond laser source is used to produce narrowband VIS pulses. Therefore typical resolution obtained with BB-SFG is ∼10–20 cm−1 which limits ability to analyze vibrational line-shapes [2]. Finally a hybrid system was demonstrated where two separate laser sources — femtosecond and picosecond — were synchronized to achieve both very high spectral resolution (<1cm−1) and simultaneous spectral recording [3]. However the system required two complex independent synchronized laser systems which would be difficult to implement in most laboratories.
Nonlinear Frequency Generation and Conversion: Materials and Devices XXII
PhotonicsViews, 2021
Vibrational sum frequency generation (SFG) spectroscopy offers detailed molecular level informati... more Vibrational sum frequency generation (SFG) spectroscopy offers detailed molecular level information on the structure, ordering, and orientation of molecular groups, and the function of monolayers at various interfaces, including buried ones, without noticeable contribution from the bulk phases.
Chemical Physics Letters, 2009
Chlorosomes from green photosynthetic bacteria Chloroflexus aurantiacus have been studied by time... more Chlorosomes from green photosynthetic bacteria Chloroflexus aurantiacus have been studied by timeresolved femtosecond transient absorption spectroscopy. The fastest kinetics of 200-300 fs resolved, was interpreted to stem for intra-chlorosomal excitation energy transfer. Energy transfer from the antenna to the baseplate appeared as a major 9.2 ps rise component detected at the baseplate probe wavelength. Excitation energy transfer rates were evaluated for a model chlorosome. Calculated rod to rod, and rods to baseplate rate constants of 200-400 fs and 10-20 ps, respectively, are in accord with the experimental results.
Photosynthesis Research, 2006
Energy transfer of the light harvesting complex LHC-II trimer, extracted from spinach, was studie... more Energy transfer of the light harvesting complex LHC-II trimer, extracted from spinach, was studied in the Q y region at room temperature by femtosecond transient absorption spectroscopy. Configuration interaction exciton method [Linnanto et al. (1999) J Phys Chem B 103: 8739-8750] and 2.72 Å structural information reported by Liu et al. was used to calculate spectroscopic properties and excitation energy transfer rates of the complex. Site energies of the pigments and coupling constants of pigment pairs in close contact were calculated by using a quantum chemical configuration interaction method. Gaussian random variation of the diagonal and off-diagonal exciton matrix elements was used to account for inhomogeneous broadening. Rate calculations included only the excitonic states initially excited and probed in the experiments. A kinetic model was used to simulate time and wavelength dependent absorption changes after excitation on the blue side of the Q y transition and compared to experimentally recorded rates. Analysis of excitonic wavefunctions allowed identification of pigments initially excited and probed into later. It was shown that excitation of the blue side of the Q y band of a single LHC-II complex results in energy transfer from chlorophyll b's of the lumenal side to chlorophyll a's located primarly on one of the monomers of the stromal side.
Optics Letters
We present a broadband optical parametric chirped pulse amplification (OPCPA) system delivering 4... more We present a broadband optical parametric chirped pulse amplification (OPCPA) system delivering 4 J pulses at a repetition rate of 5 Hz. It will serve as a frontend for the 1.5 kJ, <150 fs, 10 PW laser beamline currently under development by a consortium of National Energetics and Ekspla. The spectrum of the OPCPA system is precisely controlled by arbitrarily generated waveforms of the pump lasers. To fully exploit the high flexibility of the frontend, we have developed a 1D model of the system and an optimization algorithm that predicts suitable pump waveform settings for a desired output spectrum. The OPCPA system is shown to have high efficiency, a high-quality top-hat beam profile, and an output spectrum demonstrated to be shaped consistently with the theoretical model.
2017 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC)
Sum frequency generation (SFG) spectroscopy is a powerful technique for characterization of vibra... more Sum frequency generation (SFG) spectroscopy is a powerful technique for characterization of vibrational bonds of molecules at surfaces and interfaces [1]. The principle of SFG is based on resonant nonlinear mixing of two optical pulses — typically one in MIR range and another visible (VIS). There are two main SFG spectroscopy techniques. Narrowband SFG (NB-SFG) is based on picosecond MIR and picosecond VIS source. Full spectral information is obtained by tuning MIR pulses through vibrational lines of the molecules. The typical resolution in NB-SFG is a few cm−1 [2]. In broadband SFG (BB-SFG) femtosecond MIR pulses with spectrum spanning a few hundred cm−1 are used. This allows for simultaneous recording of complete SFG spectra and reduces systematic errors due to sample degradation during the measurement. However in most experimental BB-SFG setups the same femtosecond laser source is used to produce narrowband VIS pulses. Therefore typical resolution obtained with BB-SFG is ∼10–20 cm−1 which limits ability to analyze vibrational line-shapes [2]. Finally a hybrid system was demonstrated where two separate laser sources — femtosecond and picosecond — were synchronized to achieve both very high spectral resolution (<1cm−1) and simultaneous spectral recording [3]. However the system required two complex independent synchronized laser systems which would be difficult to implement in most laboratories.
Physical Review B, 2002
Transient absorption of methyl substituted ladder-type poly(para-phenylene) has been studied by m... more Transient absorption of methyl substituted ladder-type poly(para-phenylene) has been studied by means of picosecond pump-probe spectroscopy in the presence of an applied electric field. A transient Stark shift of the absorption band was observed and related to kinetics of generated excitons and electron-hole pairs. We demonstrate that dynamics of the Stark shift provide unique information on the charge redistribution in excited states, in particular, it allows us to monitor the charge separation distance during the exciton dissociation into electron-hole pairs.
Optics express, 2021
In this work, we present the development of a femtosecond tunable middle infrared (mid-IR) radiat... more In this work, we present the development of a femtosecond tunable middle infrared (mid-IR) radiation source for the realization of a hybrid concept compact broadband high-resolution sum-frequency generation (SFG) spectroscopy system. For the realization of the new concept, we used a two-channel picosecond fiber laser as a seed for narrowband (∼1.5 cm-1) and broadband ultrafast radiation sources operating at 1 kHz repetition rate. In order to achieve >500 cm-1 bandwidth widely tunable microjoule level pulses in the mid-IR spectral region (2-10 µm), broadband femtosecond source optimization was performed. Numerical simulations with different nonlinear crystals and optical parametric amplification layouts at given fixed initial conditions paved a way to experimentally realize an optimal scheme for a femtosecond mid-IR channel. Fully operating SFG spectrometer setup was assembled and tested. The developed SFG spectrometer demonstrates a unique combination of parameters: excellent spe...
We report on the status of the re-commissioning of a high energy OPCPA laser system with programm... more We report on the status of the re-commissioning of a high energy OPCPA laser system with programmable spectrum that serves as a frontend for a 10 PW laser at ELI-Beamlines. The OPCPA chain was developed by a consortium of National Energetics and Ekspla along with scientists of ELI-Beamlines.1 The laser system, consisting of three picosecond OPCPA stages, pulse cleaner, Offner stretcher, and 5 nanosecond OPCPA stages pumped by Nd:YAG lasers with programmable pulse shape (NL944, Ekspla), allows for precise spectral shaping while achieving high nonlinear conversion efficiency. Employing a subsequent Nd:glass power amplifiers (PA), the system was demonstrated to yield>1 kJ of energy, while maintaining broad spectrum of > 13 nm (FWHM). After recommissioning the OPCPA frontend in Dolní Břežany, an output energy of 4.3 J, flat beam-profile and good far-field quality has been demonstrated. The spectral shape has been optimized to support > 15 nm bandwidth and >1.5 kJ, consistent...
Photosynthesis Research, 2011
Exciton model for description of experimentally determined excitation energy transfer from carote... more Exciton model for description of experimentally determined excitation energy transfer from carotenoids to chlorophylls in the LHC-II trimer of spinach is presented. Such an approach allows connecting the excitonic states to the spatial structure of the complex and hence descriptions of advancements of the initially created excitations in space and time. Carotenoids were excited at 490 nm and at 500 nm and induced absorbance changes probed in the Chl Q(y) region to provide kinetic data that were interpreted by using the results from exciton calculations. Calculations included the 42 chlorophylls and the 12 carotenoids of the complex, Soret, Q(x) and Q(y) states of the chlorophylls, and the main absorbing S(2) state of the carotenoids. According to the calculations excitation at 500 nm populates mostly a mixed Lut S(2) Chl a Soret state, from where excitation is transferred to the Q(x) and Q(y) states of the Chl a&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s on the stromal side. Internal conversion of the mixed state to a mixed Lut S(1) and Chl a Q(y) state provides a channel for Lut S(1) to Chl a Q(y) energy transfer. The results from the calculations support a picture where excitation at 490 nm populates primarily a mixed neoxanthin S(2) Chl b Soret state. From this state excitation from neoxanthin is transferred to iso-energetic Chl b Soret states or via internal conversion to S(1) Chl b Q(y) states. From the Soret states excitation proceeds via internal conversion to Q(y) states of Chl b&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s mostly on the lumenal side. A rapid Chl b to Chl a transfer and subsequent transfer to the stromal side Chl a&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s and to the final state completes the process after 490 nm excitation. The interpretation is further supported by the fact that excitation energy transfer kinetics after excitation of neoxanthin at 490 nm and the Chl b Q(y) band at 647 nm (Linnanto et al., Photosynth Res 87:267-279, 2006) are very similar.
The Journal of Physical Chemistry a, Apr 1, 2007
Optical Organic and Semiconductor Inorganic Materials, 1997
The Journal of Physical Chemistry A, 2007
Transient mid-infrared spectroscopy is used to probe the dynamics initiated by excitation of liga... more Transient mid-infrared spectroscopy is used to probe the dynamics initiated by excitation of ligand-to-metal (400 nm) and metal-to-ligand (345 nm) charge transfer states of FeIII complexed with acetylacetonate (Fe(acac)3, where acac stands for deprotonated anion of acetylacetone) in solution. Transient spectra in the 1500-1600 cm-1 range show two broad absorptions red-shifted from the bleach of the nu(CO) (approximately 1575 cm-1) and nu(C=C) (approximately 1525 cm-1) ground state absorptions. Bleach recovery kinetics has a time constant of 12-19 ps in chloroform and tetrachloroethylene and it decreases by 30-40% in a 10% mixture of methanol in tetrachloroethylene. The transient absorptions experience band narrowing simultaneously with blue-shifting of the absorption maxima. Both phenomena have time constants of 3-9 ps with no evident dependence on the solvent. The experimental observations are ascribed to fast conversion of the initially excited charge transfer states to the ligand field manifold, and subsequent vibrational cooling on the lowest ligand field excited state prior to electronic conversion to the ground state. The analysis of time dependent bandwidths and positions of the transient absorptions provides some evidence of mode specific vibrational cooling.
Journal of the American Chemical Society, 2007
. Time evolution of the bleach recovery of the νCdC (1521 cm -1 ) band of Cr(acac)3 in TCE upon e... more . Time evolution of the bleach recovery of the νCdC (1521 cm -1 ) band of Cr(acac)3 in TCE upon excitation at 400 nm. The solid line represents biphasic fit with time constants τ1 ) 15 ps and τ2 ) 760 ps. The inset shows the correlation between the bleach and the excited state absorption (ESA) at 1509 cm -1 (with reversed sign). The sharp feature near zero delay is a coherent artifact.
Photosynthesis Research, 2006
Energy transfer of the light harvesting complex LHC-II trimer, extracted from spinach, was studie... more Energy transfer of the light harvesting complex LHC-II trimer, extracted from spinach, was studied in the Q(y) region at room temperature by femtosecond transient absorption spectroscopy. Configuration interaction exciton method [Linnanto et al. (1999) J Phys Chem B 103: 8739-8750] and 2.72 A structural information reported by Liu et al. was used to calculate spectroscopic properties and excitation energy transfer rates of the complex. Site energies of the pigments and coupling constants of pigment pairs in close contact were calculated by using a quantum chemical configuration interaction method. Gaussian random variation of the diagonal and off-diagonal exciton matrix elements was used to account for inhomogeneous broadening. Rate calculations included only the excitonic states initially excited and probed in the experiments. A kinetic model was used to simulate time and wavelength dependent absorption changes after excitation on the blue side of the Q(y) transition and compared to experimentally recorded rates. Analysis of excitonic wavefunctions allowed identification of pigments initially excited and probed into later. It was shown that excitation of the blue side of the Q(y) band of a single LHC-II complex results in energy transfer from chlorophyll b&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s of the lumenal side to chlorophyll a&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;#39;s located primarly on one of the monomers of the stromal side.
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Papers by Robertas Kananavicius