In Bohr's model of the hydrogen atom, the electron takes about 150 attoseconds (1 as = 10(-18) s) to orbit around the proton, defining the characteristic timescale for dynamics in the electronic shell of atoms. Recording atomic transients in real time requires excitation and probing on this scale. The recent observation of single sub-femtosecond (1 fs = 10(-15) s) extreme ultraviolet (XUV) light pulses has stimulated the extension of techniques of femtochemistry into the attosecond regime. Here we demonstrate the generation and measurement of single 250-attosecond XUV pulses. We use these pulses to excite atoms, which in turn emit electrons. An intense, waveform-controlled, few cycle laser pulse obtains 'tomographic images' of the time-momentum distribution of the ejected electrons. Tomographic images of primary (photo)electrons yield accurate information of the duration and frequency sweep of the excitation pulse, whereas the same measurements on secondary (Auger) electrons will provide insight into the relaxation dynamics of the electronic shell following excitation. With the current approximately 750-nm laser probe and approximately 100-eV excitation, our transient recorder is capable of resolving atomic electron dynamics within the Bohr orbit time.

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A study of using a single crystal photo-elastic modulator for active Q-switching of a fiber laser is presented. The modulator, which oscillates in a longitudinal eigenmode, was realized with LiTaO(3). This induces due to the photo-elastic effect a modulated artificial birefringence which modulates the polarization of passing light. When used together with a polarizer inside a laser cavity the laser photon life time is strongly modulated and the laser may start to emit laser pulses. We realized this with a fiber laser based on a 5m long double clad Nd-doped fiber. The pulse repetition frequency was 400 kHz and the pulse duration 300ns.

Time-multiplexing is a method to increase the brilliance of diode lasers, i.e. a sequence of laser pulses emitted from different laser diodes at different times is guided onto a common optical path via a cascade of polarizing cube beam splitters and polarization switches. The latter are made of piezo-electric crystals oscillating in resonance and making use of the photo-elastic effect to obtain the desired modulation of polarization. We realized a demonstrator for time multiplexing of four laser diodes with such self-excited photo-elastic modulators. The latter is a new alternative to conventional photo-elastic modulators used in ellipsometers.

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