Abstract
The dependence of the carrier-envelope (CE) phase of the pulses from a hollow-core fiber on the input laser energy was studied using two f-to- 2f interferometers. The CE phase in the in-loop f-to-2f interferometer was measured with the octave spanning white-light spectrum from the hollow-core fiber, whereas the out-of-loop interferometer was based on a sapphire plate. By modulating the input power of the in-loop interferometer and measuring the out-of-loop CE phase at the same time, the coupling coefficient between the measured CE phase and the laser energy for the hollow-core fiber was determined to be 128 mrad per 1% energy change .
Highlights
Carrier-envelope (CE) phase controlled, high power few-cycle pulses are an indispensable tool for generating single isolated attosecond pulses and studying other high field physics processes [1,2]
A least-square linear fit in Fig. 5(c) shows the 1% power fluctuation introduced a 128 mrad CE phase error. This value is smaller than the 160 mrad for sapphire plate based f-to-2f interferometers [12], which can be related to the fact that the white-light generation in the hollow-core fiber is produced by the self-phase modulation all the way through the 0.9 m long gas-filled waveguide rather than the strong self-focusing process combined with filamentation in a 2.3 mm sapphire plate [14]
Due to the dispersion the CE phase changes during the process of propagation, as expressed: Fig. 5. (a) In-loop CE phase locked by a hollow-core fiber based f-to-2f interferometer; (b) Outof-loop CE phase measured by a sapphire plate based f-to-2f interferometer and the in-loop power modulation; (c) CE phase change to laser power coupling coefficient by a least-square fitting
Summary
Carrier-envelope (CE) phase controlled, high power few-cycle pulses are an indispensable tool for generating single isolated attosecond pulses and studying other high field physics processes [1,2] To produce such pulses, CE phase stabilized multi-cycle pulses from a chirped-pulse amplifier (CPA) are focused into a hollow-core fiber filled with a noble gas to broaden the spectrum. When the bandwidth of the white-light from the hollow-core fiber covers an octave, it can be used directly to perform f-to-2f measurements [10] This approach is more appealing because of the simplicity and the removal of the CE phase noise introduced by the sapphire plate. The increase of the CE phase noise is likely caused by the laser power fluctuation inside the hollow-core fiber or the sapphire-based interferometers. We study the influence of the laser energy fluctuation on the precision of the f-to-2f measurements using the octave-spanning white-light from the hollow-core fiber
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