Independent control of arbitrary dispersion order of high power ultrashort pulses
M. Kovács1, Á. Börzsönyi1,2, P. Jójárt1,2, K. Osvay1,*
1 Department of Optics and Quantum Electronics, University of Szeged P.O. Box 406, H-6701 Szeged, Hungary
2 CE Optics Kft., Kígyó u. 4, H-6720 Szeged, Hungary
* osvay@physx.u-szeged.hu
Most experiments and applications of chirped pulse amplification (CPA) systems require very high temporal fidelity of the pulses hitting the target. Moreover, in case of few-cycle high intensity lasers, the carrier-envelope phase (CEP) of the pulses also needs to be stabilized. An acousto-optical programmable dispersion filter (AOPDF) can satisfy both requirements, providing dispersion (pre)compensation up to the fourth order of dispersion and CEP shift stabilization as well [1,2]. However, the damage threshold of the AO crystal limits its application for laser pulses of intensities less than 100 MW/cm2, hence it can be used only at the front end of an (OP)CPA laser systems. 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.
A Mach-Zehnder interferometer was illuminated by 80 nm broadband laser pulses centered at 790 nm of a Ti:Sapphire oscillator (Fig. 1). 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 two-dimensional imaging spectrograph. The dispersion can be continously tuned by perpendicular translation of the entire wedge assembly to the laser beam. Four different wedge combinations were designed and examined so far. A doublet similar to [3] for izochronic tuning solely the CEP, a doublet and a triplet for izodispersive tuning of group delay dispersion (GDD) and a triplet for changing thrid order dispersion only. As it is seen from the typical measurement results, here displayed for the GDD-triplet (Fig.2), the wedge assemblies change only the selected spectral phase derivative while the others are practically unaltered within the error of the measurement.
BS W1
W2 Spectro-
graph Programmable
translator stage Delay
line
0 0.4 0.8 1.2 1.6 2
Translation (mm) 0
5 10 15 20 25
GDD (fs2)
Gradient: 11.94 fs2/mm
0 0.4 0.8 1.2 1.6 2
Translation (mm) -80
-40 0 40 80
TOD (fs3)
Fig. 1. A Mach-Zehnder interferometer-based experimental setup
Fig. 1. Measured tuning of GDD and TOD for the GDD-triplet wedge assembly.
We have proved that optical wedge designed on purpose assemblies are 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 PFS and ELI, but also of smaller scale few cycle laboratory systems as LWS 20.
[1] Osvay et al., Appl.Phys.B., submitted
[2] S. Koke et al., Nature Photonics 4, 462-465 (2010) [3] M.Görbe et al., Opt.Lett. 33, 2704-2706 (2008)
