Transient absorption

In the transient absorption experiment a strong pump laser is used in order to excite the sample. Another pulse, called probe, enters the sample at different time delays with respect to the pump incidence. In the experiment the change in the probe pulse spectrum due to absorption in the sample is measured. The final signal is obtained as a difference in the absorption with the pump pulse on and off. The obtained absorption change, due to the pump pulse interaction with the sample, evolves in time. This evolution allows to extract valuable information on the excited state dynamics, including its lifetime and decay pathways. Our setup has a wide bandwidth supercontinuum probe and a pump at 400 or 800  nm. The setup contains also an optical parametric amplifier (OPA), which allows to tune the pump or probe pulse in the 2000-350 nm range. We use the setup for investigation of the quantum dots systems.

Optical Kerr Effect

We have constructed setup for Heterodyne Detected Optical Kerr Effect Spectroscopy, which we are using for analysis of the ultrafast dynamics in liquids and solids. The setup utilizes a balanced detector, designed in our laboratory, which gives S/N ratio of 1 000 to 10 000. The chopper free configuration and a fast scanning delay line, allows for rapid signal acquisition. Therefore, measurement conditions for a given sample can be optimized with the live feedback from the setup. The measurement is controlled by dedicated software, created in our laboratory. The key problems here are the proper synchronisation of the delay position with photodiode signal and elimination of background distortions. Wee have used the setup so far for investigation of molecular liquids like carbon tetrachloride, chloroform, bromoform, hydrogen bonded mixtures like methanol/acetone and ethanol/water and crystalline samples like alexandrite and Nd/Pr doped YAG.

Long cavity Ti:Sapph laser

Longer cavity means larger energy per pulse. Our oscillator was already running with 27m long cavity. Highest achieved energy was found to be 50 nJ for cavity length of 11m. The cavity is elongated with so called Herriott cell, which conserves beam parameters, while having some non zero length. Stability of this construction is now the object of our studies.

Quantum dots

Quantum dots show properties, which are different from those of the bulk substrate. For example the plasmon frequency of metal quantum dots shows different values depending on the dot size. We are mainly interested in the mechanisms of excitation relaxation for such systems and its dependence on the environment.

Molecular Dynamics

We are running molecular dynamics simulations in parallel with experiments, which then allows us to better understand the processes which contribute to the experimental signal. We use DL_POLY and Gromacs packages combined with our own software. At the time we are targeting at predicting the Kerr effect signal, with all of its contributions, holding information about the ultrafast structure of the analysed liquids. Part of the software is written for calculations on NVIDIA graphical processors

Laser stability numerical analysis

We are studying the stability of lasers. Previously alexandrite continuous wave laser was the subject and some periodic behavior, modulating the output power, was found experimentally and theoretically. Now we are heading for acquiring the Ti:Sapphire mode locking laser as our next object of studies.