Long-term maintenance of the carrier-envelope phase coherence of a femtosecond laser

Abstract

The long-term carrier-envelope phase (CEP) coherence of a femtosecond laser with same pulse-to-pulse CEP value, obtained using the direct locking method, is demonstrated by employing a quasi-common-path interferometer (QPI). For the evaluation of the CEP stability, the phase noise properties of a femtosecond laser with the CEP stabilized using a QPI are compared with those obtained using a Mach-Zehnder f-2f interferometer, for which the phase power spectral density and the Allan deviation were calculated from the beat signals of the interferometers. With the improved CEP stability, the long-term CEP coherent signal with an accumulated phase noise well below 1 radian can be maintained for more than 56 hours, i.e., the CEP coherence is preserved without a phase cycle slip for more than 1.6 × 10(13) pulses at a repetition rate of 80 MHz. The relative stability is also estimated to be approximately 1.4 × 10(-22) at a central wavelength of 790 nm.

Carrier-envelope phase control of Yb:KGW laser and parametric amplifiers

“…The achieved result is a significant improvement to the previously published results on CEP locking in femtosecond oscillators with ytterbium doped active elements [7,8] and is comparable to the best reported values for the Ti:sapphire oscillator CEP stabilized using servo-loop schemes [28][29][30].…”

On the origin of flicker noise in carrier-envelope phase stabilization

“…Despite the different experimental arrangements, both measurements show nearly identical white frequency noise levels in the range below ≈10 Hz. We additionally inspected the OOL measurements from other groups [6,10,12,13], which exhibit a similar 1∕f noise contribution, with noise levels that are equal to or slightly higher than those in Fig. 2, cf.…”

Carrier envelope phase stabilization with a true common-path collinear ƒ–2ƒ interferometer

“…18) Other than the conventional methods with an ƒ-2ƒ interferometer, there are a number of stabilization methods, e.g. a 0-ƒ interferometer that uses difference-frequency generation with a periodicallypoled magnesium-oxide-doped lithium niobate (PP-MgO: LN) crystal instead of a conventional SHG crystal, 23,24) an octave spanning oscillator that expands the spectral bandwidth by one octave or more, 25) an active ƒ-2ƒ interferometer that amplifies the long wavelength component, 26) direct locking that stabilizes the CEP in the time domain, 27,28) and feed-forward control instead of feedback control where loop noise is inevitable in principle. 18,19) According to the calculation of the effect of shot noise by Borchers et al, the phase noise can be reduced by increasing the signal-to-noise (SN) ratio and increasing the number of photons, and an SN ratio of at least 30 dB is required for CEP stabilization.…”