Circularly polarized pump pulses

When a circularly polarized probe pulse is introduced at a time delay of At after the pump laser pulse, new features with a pair of straight distributions running parallel to the horizontal and vertical axes emerge [29], as... 

The experimental set-up we used is shown in Fig. 2, A synchronously pumped mode-locked and cavity-dvunped dye laser, which can be timed to the D or Dj line of Cs, generates pulses of about 20 ps duration at a pulse rate of U MHz and peak powers of several hundred watt. They are split into linearly polarized pump pulses and stronger circularly polarized probe pulses, which pass an optical delay line. Both beams are focussed into a common interaction region where they act on the Cs vapor, which is contained in a cell at room temperature. The radiated wave propagating in pump pulse direction is detected by a photomultiplier, which measures the transmitted average intensity behind a crossed polarizer as a function of the delay time. 

The laser output is split into a strong pump beam with circular polarization and a weak probe beam with linear polarization. Both beams are focussed into a common interaction region where they overlap within a few cm. The pump pulses act on the Na atoms with an input piUse area 0 w fr / 100 rad 6ind induce coherence in the vapor which is contained in a heated cell with a number density of approximately 10 cm . 

It is the advantage of the cholesteric phase that its pitch and thereby the wavelength of the emitted laser light can be tuned by various external stimuli (usually the temperature). Lasers relying on a cholesteric feedback medium have usually a very narrow line width and their emission is circularly polarized. With this concept, rather small lasers can be constructed [97, 98]. They are usually pumped by pulsed solid-state lasers although, after first attempts [99], continuous pump conditions were recently successfully established [100]. Lasing has been mostly observed from low molar mass cholesteric mixtures because they show excellent alignment. The state of the art is reviewed in [98, 101, 102]. 

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