Self-compression of an ultraviolet optical pulse assisted by raman coherence induced in the transient regime

An ultrashort laser pulse has recently been used in many types of applications, such as observations of a dephasing process of a molecule and a monitoring of an ultrafast chemical reaction. Several techniques are demonstrated to generate such an ultrashort pulse. One of the techniques utilizes high-order stimulated Raman scattering (HSRS). In this approach, spectrally discrete sidebands are generated, in addition to the original spectral component. The resultant spectrum can be spread from the ultraviolet to the near-infrared regions and is capable of generating a subfemtosecond optical pulse [1]. Impulsive stimulated Raman scattering (ISRS) [2] is a type of stimulated Raman scattering which is used by researchers in Max Born Institute to generate an ultrashort optical pulse [3],[4]. A high-energy laser pulse, whose pulse width is shorter than a period of molecular motion (vibration or rotation), is used to excite coherent molecular motion. The induced coherent motion broadens the spectrum of a temporally delayed pulse (probe pulse). Furthermore, the phases of the newly created spectral components in this regime can easily be controlled, and therefore the pulse width of the temporal profile is compressed [3]. The temporal structure of the modulated probe pulse consists of a train of compressed pulses, when the probe pulse longer than the period of molecular motion is employed [3]. Whereas a single pulse is obtained by decreasing the probe pulse width below this time period [4].