S. Yeremenko

Hydrogen-bond dynamics in water explored by heterodyne-detected photon echo

Results of heterodyne-detected photon echo experiments on the OH stretching mode of water are reported and discussed. Two vibrational dynamical processes with time constants of 130 and 900 fs were identified. The former is attributed to bond breaking dynamics of a single hydrogen bond, the latter to rearrangement of the hydrogen-bond network.

Frequency-resolved pump–probe characterization of femtosecond infrared pulses

A novel method for ultrashort IR pulse characterization is presented. The technique utilizes a frequency-resolved pump-probe geometry that is common in applications of ultrafast spectroscopy, without any modifications of the setup. The experimental demonstration of the method was carried out to characterize 70-fs IR pulses centered at 3 microm .

Infrared Photon-Echo Spectroscopy of Water: The Thermalization Effects

The larger part of the nonlinear response in IR photon-echo and transient-grating spectroscopy on HDO-D2O mixtures at >l-ps delays is found to originate from the D2O refractive index modulation due to local volume thermalization.

Vibrational energy relaxation in water-acetonitrile mixtures

IR pump-probe spectroscopy is used to study the effect of hydrogen bonding on the vibrational energy relaxation pathways. Hydrogen bonding accelerates the population relaxation from 12ps in diluted acetonitrile solution to 700fs in bulk water.

2D photon-echo spectroscopy of hydrogen-bond dynamics in liquid water

The complexity of the physical properties of liquid water is largely determined by the presence of a three-dimensional hydrogen bond (HB) network. The HB’s undergo continuous transformations that occur on ultrafast timescales. The molecular vibrations are especially sensitive to the presence of the HB network. For example, the spectrum of the OH-stretch vibrational mode is substantially broadened and shifted towards lower frequencies if the OH-group is involved in the HB. Therefore, the microscopic structure and the dynamics of water are expected to manifest themselves in the IR vibrational spectrum, and, therefore, can be studied by methods of ultrafast infrared spectroscopy. It has been shown in a number of ultrafast spectroscopic experiments and computer simulations that dephasing dynamics of the OH-stretch vibrations of water molecules in the liquid phase occurs on sub-picosecond timescales. The technique of photon echo peak shift (EPS) allows obtaining the most direct information about the frequency fluctuation correlation function. This chapter presents a study of ultrafast dynamics in liquid water employing heterodyne-detected TG and EPS techniques. Heterodyne detection allows one to separate the genuine photon echo signal that contains information on water dynamics, from thermal effects. The analysis of the experimental EPS data that includes thermal effects yields a 700-fs time constant for the slowest component. This value is in perfect agreement with our previous findings from heterodyne-detected photon echo experiments.

Phase-amplitude retrieval: SHG FROG vs. SPIDER

Summary form only given. Frequency resolved optical gating (FROG) and spectral phase interferometry for direct electric-field reconstruction (SPIDER) are nowadays leading techniques that provide access to phase-amplitude pulse retrieval. Each of these techniques has a number of outstanding features that establish the method applicability under certain experimental conditions. For instance, FROG is perfectly suited for pulse characterization precisely at the position of the sample in most spectroscopic applications because it utilizes similar excited-probe geometry. On the other hand, SPIDER has the advantage of real-time pulse measurement at high repetition rates. While in an ideal case both methods allow the precise amplitude-phase reconstruction of an ultrashort pulse, in practice specific experimental conditions such as phase-matching, detector noise etc. affect the reconstruction quality. For instance, experimental comparison of the techniques in the case characterization of a single pulse has shown some discrepancies in the retrieved parameters. We present a comparative study of SPIDER and second-harmonic generation (SHG) FROG techniques. Two main sources of errors are analyzed: the limited phase matching bandwidth of the nonlinear medium and the detector noise. We show that under similar experimental conditions SPIDER performs somewhat better than SHG FROG.