Max-Planck-Institut für Kernphysik Heidelberg

Atoms and molecules in ultra-short laser pulses

Priv.-Doz. Dr. Robert Moshammer and Dr. Claus Dieter Schröter

  Research topics:  |  Ions in Traps  |  Electrons in Collisions  |  Lasers in Time  |  
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Dispersion Management

To create few-cycle laser pulses, special techniques have to be employed. One possibility is the spectral broadening of a light pulse by self-phase-modulation (SPM) in a glass capillary tube filled with a noble gas. The dispersion, caused by optical elements, has severe impact on the temporal shape of a few-cycle laser pulse and leads to temporal broadening. Dispersion control is therefore indispensable in such a laser system. [Here we] delineate an efficient method of simulating the effects of dispersion caused by an optical path, affecting the laser pulse. Using this simulation it is possible to interactively design a pulse compressor, which can quickly be calculated and put into operation. For this method it is vital to precisely know the dispersive behavior of each element. [...] First applications of the simulation, namely the interactive design of a pulse compressor consisting of dispersive mirrors, seem to yield very promising results. [1]

White Light Interferometer

In order to simulate the dispersion effects onto a laser pulse, one has to have precise knowledge of the Group Delay Dispersion (GDD) of each element in a given setup. For some optical elements, such as glass or a grating compressor, the GDD functions are simply calculated. But there are other elements, i.e. chirped mirrors, which have to be measured. The measurement is done interferometrically by using a white light Michelson-interferometer.

Fig 1: Schematic of the interferometer [1]

From the measured interferogram one can retrieve the GDD function of the chirped mirrors.

Pulse Simulation

After having retrieved the GDD function of each element in the optical path, one can start to simulate the the temporal shape of a laser pulse. The simulation process consists of three major steps. First the GDD functions of all elements are added up to a total GDD function. After that the total GDD function is integrated twice to gain a phase. Secondly, the phase funtion is used to carry out a fast fourier transform in order to obtain a temporal profile of the laser pulse. The third and last step is the calculation of an autocorrelation function. This enables the user to compare calculated temporal impulse profiles with the exoeriment. A schematic of the principle of operation of the program is shown in (Fig. 2).

Fig 2: Schematic of pulse simulation [1]

[1] Andreas Fischer, Erzeugung und Dispersionskontrolle von Femtosekundenlaserimpulsen, Diploma thesis Sep. 2010
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