ИСТИНА

The carrier-envelope phase (CEP) of the laser pulse plays an extremely important role in variety of applications when the electric field strength is large enough for such phenomena as high-order harmonic and attosecond pulse generation [1–4], above-threshold ionization [5] and terahertz sub-cycle waveform formation [6]. The time duration of a near single-cycle pulse itself depends on the absolute value of CEP [7]. In our work we used Ti:Saaphire laser system and optical papametric ammplifier to produce tunable pulses in idler wave with an energy of E0 ≈ 180 μJ, central wavelength of λ0 ≈ 2000 nm and duration of τ0 ≈ 60 fs. These pulses couples into anti-resonant hollow-core fiber (AR HCF) filled with argon. The transverse structure of the fiber consists of a hollow core with a diameter of D = 70 μm, surrounded by six hollow tubes with diameters of d = 36 μm and a wall thickness of w ≈ 590 nm and allows to support radiation waveguiding in very wide spectarsl range. The sequence of nonlinear transformations of the femtosecond pump pulse in an AR HCF leads to spectral broadening (supercontinuum generation (SC)) and near single cycle waveform generation. The spectrum broadening follows the soliton selfcompression (SSC) scenario, with additional enhancement from the self-steepening effect and parametric generation of four-wave components in the blue wing of the soliton spectrum [8,9]. In such conditopn it is possible to form very short pulses with the duration less than on cycle of the field, and for such pulses the influence of CEP could play noticeable role. In our investigation we explore the signatures of phase dependence in the visible part of the SC generated during SSC down to single-cycle pulsewidth in an anti-resonant hollow-core fiber (AR HCF) filled with argon. This phenomenon is observed within the small parameter range, when the pulse reaches its maximum compression ratio, but there is still no strong ionization, leading to pulse decay. Theoretical analysis by means of the numerical solution of the generalized nonlinear Schrödinger equation (GNSE) reveals that the phase dependence arises from the broadband third harmonic generation (THG) in the range from 250 nm to 800 nm at the moment of a sub-cycle pulse composition and its spectral interference with the visible part of the SC. The CEP control of this ultrabroadband f-3f interference provides a signature of the sub-cycle pulse synthesis during SSC in the fiber with duration of 0.4 optical cycles and peak power more than 2 GW on the fiber output. The work was supported by Russian Science Foundation grant # 22-12-00149.