Our focus is in the development and exploration of experimental techniques for the study of ultrafast physical and chemical processes. A large variety of research projects are being developed in our laboratory ranging from ultra-powerful laser sources, fiber lasers, laser micromachining, photo-induced chemical reactions in solution (proton, electron or energy transfer) solvation dynamics, or chemical dynamics in confined and crowded media. Our multidisciplinary team composed of chemists and physicists, maintains collaborations with several laboratories around the globe. The following are snapshots of some of the mentioned research lines and set-ups.
We have designed and built a time resolved fluorescence spectrometer in which we observe fluorescence emitted by molecules exited by an ultra-short pulse. In our setup we can follow spectral changes of that fluorescence with time resolution of 60 fs, while registering full emission spectra. The setup is powered by home build 5 kHz Ti:sapphire amplifier. It is followed by two independent NOPA amplifiers. This gives us a possibility to continuously scan the excitation pulse wavelength. Fluorescence emitted by the sample is collected by low time dispersion all reflective objective in Schwarzschild configuration. Ultrafast gating is based on up-conversion in BBO crystal mounted on a swinging shaft. Fast rotation of the crystal during measurement and signal collection by an imaging spectrograph allow us to register full fluorescence spectrum at each time delay. Recorded up-conversion data are treated with unique global analysis software, which is allows for a real time data analysis. These features give us a great opportunity to uncover earliest stages of ultrafast chemical reactions by collecting simultaneous full emission spectra and kinetics.
Our field of interest focuses on reactions such as: proton transfer, tautomerization, bimolecular reactions, electron and energy transfer. Moreover in our research we also include a femtosecond pulse shaping to study coherent control of chemical reactions.
We constructed the unique broadly tunable system for the time resolved Raman spectroscopy. The system utilizes stimulated Raman process to probe the chemical system as it evolves after excitation to the upper electronic level. Our setup is based on Yb femtosecond source (1030 nm) which opens new possibilities in terms of tunability as compared to the widely used Ti:sapphire counterpart. Our custom built noncollinear optical parametric amplifier gives us an access to virtually any excitation wavelength in the UV-VIS range with the time duration down to 15 fs. A novel scheme for the generation of narrowband Raman pulses provides energetic tunable pulses in the 305-985 nm range with the spectral bandwidth as small as 5 cm-1 [Opt. Express 20, 2136 (2012)]. We see what others cannot see thanks to improved time resolution, sensitivity and tunability.
The ultrafast time-resolved infrared transient absorption spectroscopy is a technique complementary to our two other setups: time-resolved fluorescence and time-resolved Raman spectrometer. It is based on interaction of two ultrashort (about 100 fs duration) pulses with interrogated sample. The first – a 400 nm pump pulse – is used for electronic excitation. The second – a widely tunable (3-10 μm) infrared pulse – is used for probing. With controlled time delay between the pulses we can observe time evolution of infrared absorption spectra of samples in the most interesting spectral regions: hydrogen bonds stretching near 3000 cm-1, carbonyl bonds stretching at 1600 cm-1 and so called "fingerprint region" between 1000 and 1500 cm-1.
Both pulses are derived from a 150 kHz repetition rate Ti:Sapphire oscillator-amplifier system by means of parametric processes in nonlinear crystals. An in-house developed infrared MCT camera with a 2D focal plane array is used in the detection stage (see J. Electron. Imaging. 22, 043020 (2013) for more information). The camera enables acquisition of multiple spectra at the same time and thus to monitor both transient and stationary infrared spectra during the measurement.
The setup is used to investigate several phenomena: nonradiative relaxation, electron and proton transfer processes, isomerisation. In the coming months the setup will be upgraded to enable polarization-resolved IR pump – IR probe measurements This modification will allow us to study vibrational lifetimes and molecular reorientational lifetimes. We will measure both values in aqueous solutions of “smart” polymers in order to analyze intermolecular interactions between a polymer and a solvent.
We have completed the construction of high average power femtosecond fiber laser which now provides more than 60W of average power at 1030 nm, 500 fs of laser pulse duration and the diffraction limited beam quality. The beam is steered by the high speed scanner (up 4 m/s) on work area. The system can provide second and third harmonics output on request. We encourage other groups or scientists to use our station in their research.
In this 3 year project Dr Yuriy Stepanenko and his team is going to extend recently developed OPCPA system and reach 10 TW with high hopes for even greater powers. One of the long-term objectives of the project is to produce laser pulses with peak power of 100 TW and higher. Such powerful light pulses is used for compact elementary particles accelerators with energies that are useful for instance in medical therapies. At these intensities, the wakefield created by the electromagnetic field of the laser pulse accelerates electrons to relativistic energies. At even higher intensities, ion acceleration also becomes relativistic paving the road to table top heavy ions accelerators. The research on the parametric OPCPA system is funded by the National Centre for Research and Development (Project NR02001910).
In the frame of my project I am trying to understand intermolecular interactions in aqueous solutions of “smart” polymers. In these systems polymer chains undergo very fast conformational change in response to an external stimulus (eg. change in temperature or pH). As a result the macroscopic phase separation in the systems is observed. With use of femtosecond infrared spectroscopy I hope to observe early (of the order of picoseconds) stages of this type of phase transition. Web page: https://www.researchgate.net/profile/Marcin_Pastorczak/ Funding: NCN ‘Fuga’ grant – „Femtosecond infrared spectroscopy of aqueous polymer solutions”
One of the major problems in the description of chemical reactions in intracellular media is that the diffusion between partners is restricted by the presence of large molecules (crowding). Additionally, the complex topology of the cytoplasm incorporates space restrictions to the molecular movement (confinement). Our objective is to provide with model and controlled experimental data for a deeper and better understanding of intracellular reaction. In liquid crystals (LCs) the movement of reactants is restricted to directions driven by the phase organization of the liquid. The influence of this restriction has scarcely been investigated. Interesting features in the kinetics are to be expected. For example, it is known that the kinetics differ from 3D strongly when reducing the dimensions available to the diffusing species. Moreover, though by themselves LCs have many applications, they can also be regarded as similar to cell membranes. Both lines are strongly connected through the common treatment of diffusion under crowding and confinement conditions, as reveals the literature on the theoretical investigations so far performed. Major questions remain open regarding the relevance of anomalous diffusion under these conditions and the interplay with chemical reactions. This work is funded by NCN through the program SONATA BIS.
The key idea of this research is that photo-induced reactions strongly depend on the photon-flux of excitation. Obviously, the amount of photochemical products does, but it has been theoretically predicted by the Encounter Theory that the rate of the reaction itself also does. This counter-intuitive effect has never been observed before. The consequences of this effect are beyond those of pure scientific curiosity. Many other experimental techniques used in a large variety of fields do make use of large excitation intensities. Just to name two of the most important: fluorescence confocal microscopy (with very important applications in the study of biological systems, single molecules, nanostructures…) and ultrafast time resolved laser spectroscopy (applied to the study of chemical reactions in any field). In both cases, usually knowledge is required from other conventional methods in order to interpret the results under the assumption that the rate of the processes is not affected by the different extent of the excitation intensity. In case of demonstrating that this is not in general the case, far reaching implications can be expected from our work in these mentioned methods. We are developing this project in collaboration with the group of Prof. Günter Grampp from the Graz University of Technology and under the auspices of the Narodowe Centrum Nauki program Harmonia, grant number 2012/06/M/ST4/00037.