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Submitted on 23 Nov 2020
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Sub-20 fs pulse train synthesis using transient SRS in H2-filled IC HC-PCF
David Kergoustin, Foued Amrani, Benoît Debord, Frédéric Gérôme, Fetah Benabid
To cite this version:
David Kergoustin, Foued Amrani, Benoît Debord, Frédéric Gérôme, Fetah Benabid. Sub-20 fs pulse
train synthesis using transient SRS in H2-filled IC HC-PCF. Conference on Laser and Electro-Optics
/Europe (CLEO/Europe-EQEC 2019), Jun 2019, Munich, Germany. Paper CF-P.49. �hal-02329754�
Sub-20 fs pulse train synthesis using transient SRS in H
2-filled IC HC- PCF
D. Kergoustin1, F. Amrani1, B. Debord1, F. Gérôme1 and F. Benabid1 1. GPPMM group, Xlim research institute, CNRS UMR 7252, University of Limoges, France
Transient Stimulated Raman Scattering (TSRS) in gas-filled Hollow-Core Photonic Crystal Fibers (HC-PCF) has proven to be an efficient platform in generating several octaves wide coherent Raman frequency combs thanks to a very high Rama net gain [1, 2]. In such a configuration, the Stokes field is initiated from the quantum noise and amplified along the Raman medium as it propagates to then trigger with the pump field the generation of ultra- wide Raman comb via Raman coherence. Despite the quantum-noise onset of such phenomenon, the resulted optical comb can exhibit strongly phase-locked spectral components [2]. This is done by the amplification of a unique temporal and spatial mode (TSM) of the spontaneous Stokes field continuum [3]. A practical realization of the selection and amplification of this TSM wave-packet is achieved by the use of a single-mode HC-PCF, which acts as a spatial filter, and by the choice of a pump pulse whose duration is sufficiently short to act as a temporal filter. So far, the experimental demonstration of the Raman comb coherence was done using nanosecond pulses to ensure a high Raman gain [4].
Here, we report on the generation of several octave wide Raman comb from a H2-filled Inhibited-Coupling HC-PCF pumped with 10 ps pulses, and the synthesis of a pulse train using a small portion of the generated comb.
Fig. 1 summarizes the set-up (Fig.1a) and the results (Figs.1b-f) of the pulse train synthesis. The pump laser emits 1030 nm wavelength and 10 ps pulses at 250 kHz repetition frequency, with 8 W average power. The beam is coupled into a 3 meters-long H2-filled Kagome HC-PCF, with an inner diameter of 57 µm and gas pressure of 20 bars. The output beam is characterized by a frequency resolved optical gating (FROG) with an optical bandwidth of ~850-1200 nm and an OSA. Fig. 1 shows the recorded optical spectrum of the comb. It shows ro- vibrational Raman lines with two frequency spacings: 17.6 THz and 125 THz for respectively the rotational and vibrational lines sharing the same pump. The FROG sensitive bandwidth is highlighted in the dashed yellow box.
Fig. 1(c) shows a typical FROG spectrogram. The pink curves in Fig.1 (d) and (e) represent the retrieved autocorrelation and spectrum trace respectively. The autocorrelation trace shows a train of 15 fs wide pulses with a period 56 fs, which corresponds to the 17.6 THz rotational Raman resonance and to the frequency spacing of the retrieved spectrum. The blue curves represent numerical reconstruction of the experimental spectrum and autocorrelation by interpolating an expression made of a linear combination of the fields at the measured frequencies. Fig. 1(f) shows the reconstructed temporal profile of the pulse detected by the FROG from the measured spectrum and autocorrelation. The temporal distribution shows a pulse train with comparable amplitude.
This pulse train synthesis was also observed with pump pulse duration ranging from 10 ps to 1 ps. The present results represent an important milestone towards the arbitrary optical waveform synthesizer.
The authors acknowledge support from “Région Nouvelle-Aquitaine”, Σ_LIM Labex Chaire and DGA.
References
[1] A. Benoit et al., Optics Express 23(11) (2015).
[2] Y. Y. Wang et al. Phys. Rev. Lett. 105, 123603 (2010).
[3] M.G. Raymer and I.A.Walmsley, Progress in Optics. 28 (1990).
[4] M. Alharbi PhD Thesis (2014).
Fig. 1: (a) experimental scheme, (b) ultra-wide Raman frequency comb and the lines seen by our detection, (c) measured spectrogram, (d) experimental (purple) and reconstructed (blue) autocorrelation trace, (e) experimental (purple) and reconstructed (blue) corresponding spectrum and (f) equivalent femtosecond pulse train.
