Ultrafast Lasers Benefit Optical Experiments

Until now, time-resolved optical experiments have been taking advantage of external moveable optical delay lines or two synchronized pulsed laser systems in order to achieve a defined pulse delay between two partial beams.

Sueddeutsche Kunststoff-Zentrum (SKZ), provider of independent contracting services to the plastics industry, has now developed a procedure using only a single pulse source for the creation of a defined and variable pulse delay, thus eliminating the need for any external moveable components.

The procedure, dubbed the Oscat principle (Optical Sampling by Cavity Tuning), uses the possibility to change the laser repetition rate for generating a defined pulse delay with an almost scaleable range at will.

Time-resolved experiments with ultrashort laser pulses need a variable and adjustable pulse delay. (Image: Thomas Hochrein, SKZ)

Delay lines are required for most setups in time-resolved experiments with femtosecond lasers. The areas of application, for example, are pump-probe experiments in femtochemistry, time-domain terahertz spectroscopy, and stimulated emission of x-ray pulses in attophysics or interferometric methods.

Time-domain characteristics of these investigations require partial beams to be provided with an adjustable time delay. To achieve this, a wide range of different methods are used. Adjustable mechanical delay lines, among them linear delay stages, are the most frequently used.

In practice, the disadvantages are the usually substantial adjustment effort, the low mechanical stability and susceptibility to vibrations as well as deviations due to temperature fluctuations caused by thermal expansion effects. To avoid these negative effects, femtosecond laser systems consisting of two synchronized lasers have been developed during the past years. But the very complex technology, the high costs and the twofold construction volume are disadvantages of such systems.

SKZ developed the Oscat procedure based on a simple functional principle using the features of ultra-short pulse lasers available today. Due to the adjustment of laser the repetition rate and an additional scaling value the temporal resolution or the scan range is almost scaleable at will, respectively. The scan width is adjustable from the femtosecond to the nanosecond range in a complete fiber-coupled setup.

Preliminary theoretical considerations and experimental results give evidence to the simple implementation possibilities even in commercial devices. Experiments have shown an excellent conformity with the measuring data of the new procedure in comparison to the conventional delay line.

The procedure is suitable for the implementation in free-space setups, but particularly for applications in fully fiber-coupled systems. The conventional delay line or a synchronized two-laser system is no longer required. The procedure falls extensively back on already existing technological possibilities of modern femtosecond laser systems. Outside the laser, it is only possible to use fiber-coupled and immoveable components. This makes the setup very robust and easy to adjust.

SKZ is a service provider for industry and research and hence itself not interested in a direct commercial exploitation of the procedure. Interested parties are welcome to address themselves to the SKZ.

For more information, visit: www.skz.de