Abstract
We study in detail the compression of high-energy ultrashort laser pulses to the few-cycle regime in gas-filled planar hollow waveguides. In this scheme, the laser beam is guided in only one transverse dimension, whereas the other dimension is free to adjust, allowing scalability to high pulse energies. We report on various practical aspects of the planar hollow waveguide compression scheme and characterize the dependence of the performance of the method on several experimental parameters: (i) we evaluate different materials for the construction of planar waveguides; (ii) we investigate the dependence of the pulse duration on gas type and pressure; (iii) we measure the spatial intensity and phase; (iv) we characterize the pulse duration along the transverse beam direction; and (v) we investigate the focusability. An output pulse energy of 10.6 mJ at a duration of 10.1 fs (FWHM) in the beam center after compression is demonstrated. A careful estimation reveals that the radiation should be focusable to a relativistic intensity exceeding 1019 W cm−2 in the few-cycle regime. The experimental results are supported by numerical modeling of nonlinear pulse propagation inside planar hollow waveguides. We discuss energy up-scalability exceeding the 100 mJ level.
Highlights
Nonlinear frequency mixing of stretched low-energy seed pulses with high-energy pump pulses
Since SPM and, spectral broadening are determined by the light intensity in the waveguide, the compressed pulse duration may vary along the non-guided dimension, at least if the transverse beam profile is different from a top-hat
The experimental results used in this comparison can be found in Akturk et al [21], where we reported a compressed pulse duration of 13.6 fs at an output pulse energy of 8.1 mJ
Summary
The experimental setup of the planar hollow waveguide pulse compression scheme is illustrated in figure 1. The planar hollow waveguide is placed inside a gas cell, which can be filled with different noble gases (Ar, Kr and Xe) at adjustable pressure. A cylindrical mirror is used to focus the laser beam to a line at. The cylindrical axis of the focusing mirror needs to exactly coincide with the free transverse axis of the waveguide (where no guiding occurs). At the output of the cell, the beam is re-collimated by using a second cylindrical mirror, placed one focal distance away from the end of the waveguide. We use broadband dielectric cylindrical mirrors (Eksma, CVI) of focal length f = 1.3 m, both for coupling the beam to the waveguide and for collimation. A CCD camera (IDS) monitors the laser transverse spatial mode on a white screen placed close to the collimating cylindrical mirror
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