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[en] Under intense optical excitation, the polarizability of transparent optical materials has a significant third order, nonlinear contribution. This manifests itself in a wide variety of effects, which, under certain conditions, are collectively referred to as white light continuum generation. We report on a new approach that isolates, for the first time, some of these effects
[en] Complete test of publication follows. In the quest for a way to generate ultrashort, high-power, few-cycle laser pulses the discovery of optical parametric amplification (OPA) has opened up to the path towards a completely new regime, well beyond that of conventional laser amplification technology. The main advantage of this parametric amplification process is that it allows for an extremely broad amplification bandwidth compared to any known laser amplifier medium. When combined with the chirped-pulse amplification (CPA) principle (i.e. OPCPA), on one hand pulses of just 10 fs duration and 8 mJ pulse energy have been demonstrated. On the other hand, pulse energies of up to 30 J were also achieved on a different OPCPA system; the pulse duration in this case, however, was 100 fs. In order to combine ultrashort pulse durations (i.e. pulses in the few-cycle regime) with high pulse energies (i.e. in the Joule range) we propose tu pump on OPCPA chain with TW-scale short pulses (100 fs - 1 ps instead of > 100 ps of previous OPCPA systems) delivered by a conventional CPA system. This approach inherently improves the conditions for generating high-power ultrashort pulses using OPCPA in the following ways. Firstly, the short pump pulse duration reduces the necessary stretching factor for the seed pulse, thereby increasing stretching and compression fidelity. Secondly, also due to the shortened pump pulse duration, a much higher contrast is achieved. Finally, the significantly increased pump power makes the use of thinner OPCPA crystals possible, which implies an even broader amplification bandwidth, thereby allowing for even shorter pulses. We carried out theoretical investigations to show the feasibility of such a set-up. Alongside these studies we will also present preliminary experimental results of an OPCPA system pumped by the output of our Ti:Sapphire ATLAS laser, currently delivering 350 mJ in 43 fs. An insight into the planned scaling of this technique to petawatt levels (i.e. the Petawatt-Field-Synthesizer project at the MPQ) will also be given.
[en] An analysis has been completed to provide guidelines for producing planar microwave resonators with Q-factors of the order of 106-108 at a temperature of 4 K and a frequency of 1-20 GHz using high-Tc superconducting thin films on sapphire shielded by suitable buffer layers. Buffer layers not only overcome the problems of film-substrate interactions and reduction of microcracks, but can also confine the field into the sapphire which enhances the Qr and Qc of the resonator. (author)
[en] Complete text of publication follows. One of the most crucial issues in chirped pulse amplification (CPA) systems is the precise temporal recompression of the pulses hitting the target. In case of few cycle high intensity lasers, the stabilization of the carrier-envelope phase (CEP) of the pulses is also required. An acousto-optical programmable dispersion filter can satisfy both aims, providing dispersion (pre)compensation up to the fourth order of dispersion and make the CEP shift stable. Its use is, however, limited to a pulse intensity of 100 MW/cm2, hence its application is restricted to the front end of the (OP)CPA laser systems. A simple optical arrangement consisting of wedges with different materials and different apex angles was proposed recently for isochronic control of CEP of a pulse train. In this paper we show that assembly of wedges can be specifically designed to tune only one of the dispersion coefficients, while all the others, including CEP, remain practically unchanged. Wedge pairs changing solely the zeroth (CEP) and second order (group delay) dispersion (GDD) are experimentally presented along with a triplet of wedges tuning the third order dispersion (TOD) only. The experiment was carried out with the use of spectrally resolved interferometry (SRI). A Michelson-interferometer was illuminated by 100 nm bandwidth laser pulses of a Ti:Sapphire oscillator. The sample arm of the interferometer contained the wedge assembly, set to near Brewster-angle incidence at each surfaces, designed for tuning the required order of dispersion. At the output of the interferometer the spectral interference between the pulses from the sample and reference arms was resolved with a spectrograph. The dispersion was tuned by perpendicular shift of the entire wedge assembly to the laser beam. In the measurements spectral interferograms were recorded and evaluated at each spatial position of the assembly. Three different wedge combinations, two doublets and a triplet were designed and examined carefully. The first doublet consisted on an N-PK51 and a Lithosil-Q1E193 wedge and was designed to CEP tuning, the second one from N-SSK2 and N-LaK7 aimed to change the GDD only. The measured tuning slopes were 1.66 rad/nm and 3.6 fs2/mm, respectively. The triplet compiled of N-LaK7, N-LaSF46 and NSF57 wedges was made for TOD tuning: 130 fs3/mm was measured. All wedge assemblies only changed the selected spectral phase derivative while keeping the others practically zero. The residual angular dispersion was also measured, and found to be well below the detection limit of 0.2 μrad/nm. We have proved that a combination of optical wedges is capable to control the required order of dispersion, including CEP, independently to all the other orders. Since the loss is negligible and the (bulk) damage threshold is high, we believe that such specially designed wedge combinations can significantly contribute to the fine tuning of dispersion and CEP just prior to the compressor of high power laser systems like Petawatt Field Syntheser (PFS), Extreme Light Infrastructure (ELI), but also of smaller scale laboratory few cycle systems.
[en] In this paper, we report the operation of transversely excited Ti:sapphire laser in a cavity length of 44 mm with plane mirrors. From initial measurements we obtained a slope efficiency of 5.8% for input and output power measurements and threshold energy of 11 mJ. Buildup time between the 532 nm output and the output pulse of Ti:sapphire is approx 38.6 ns