Intense self-compressed carrier-envelope phase-locked few-cycle pulses at 2 µm C.P. Hauri 1 , C.I. Blaga 2 , E. Power 3 , J. Cryan 2 , R. Chirla 2 , P. Colosimo 2 , G. Doumy 2 , A.M. March 2 , C. Roedig 2 , E. Sistrunk 2 , J. Tate 2 , J. Wheeler 2 , R. López-Martens 1 , K.D. Schultz 4 , L.F. DiMauro 2 1 Laboratoire d’Optique Appliquée, École Polytechnique - CNRS, F-91761 Palaiseau Cedex, France Phone: +33 169 319733, email:hauri@ensta.fr 2 Physics Department, Ohio State University, Columbus, USA 3 Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, Michigan 48109, USA 4 Department of Physics, Austin Peay State University, Clarksville, TN. Abstract: We demonstrate filamentation at 2 µm using carrier-envelope phase (CEP) stabilized 55 fs, 330 µJ pulses from an OPA. The ultra-broadband output is self-compressed below 3-optical cycles with 270 µJ and preserves the CEP offset. OCIS codes: We demonstrate the use of self-guided filamentation for spectral broadening and pulse compression of a mid- infrared pulse. The pulse originating from a carrier-envelope phase stabilized optical parametric amplifier is artificially broadened in a xenon cell and self-compressed to 0.27 mJ, 17 fs pulses at 2 µm. This pulse duration corresponds to less than 3 optical cycles at this center wavelength. The high peak power, good spatial beam profile and excellent CEP stability preserved during filamentary propagation provides an attractive source for investigating strong-field physics at mid-infrared wavelengths. The experimental setup is shown in Fig. 1. The femtosecond optical parametric amplifier (OPA) pumped by a multi- millijoule Ti:sapphire CPA system delivers multi-cycle pulses in the mid-IR with sufficient peak power to investigate the efficacy of the nonlinear pulse compression techniques developed at shorter wavelengths. An optical filament is produced by weakly focusing the mid-IR light with an 0.5 m focal length spherical mirror into a 1 m long cell filled with xenon (2.15×10 5 Pa). Filamentary propagation is verified by recording the plasma fluorescence (Fig. 1) and reveals the presence of two consecutive nonlinear focusing-defocusing cycles within the roughly 10 cm long filament. During filamentation the beam undergoes extreme spectral broadening due to self-phase modulation and plasma effects (Fig. 2, left). Fig. 1: Experimental setup with Ti:sapphire pumped OPA system, gas cell for filamentation and diagnostic tools. The photograph shows the plasma channel generated by non-linear propagation of the intense 2 µm pulse in xenon. Temporal characterization of the ultra-broadband 270 µJ mid-IR pulses was performed using an interferometric autocorrelation technique. A 2 micron thick pellicle with a broadband coating at 2 µm acts as a 50/50 beamsplitter in a Michelson interferometer. An interferogram (Fig 2, inset) was recorded using the linear response of an InGaAs photodiode to reconstruct the spectrum of the ultrabroadband pulse (Fig 2). A pulse duration of 17 fs is measured using a 2 nd -order autocorrelator based on a 2-photon induced photocurrent from a saturated InGaAs diode and is shown in Fig. 2 (right). The pulse is reconstructed from the measured spectrum and 2 nd -order autocorrelation using the PICASO method [2] with an adaptive genetic algorithm [3] as our functional minimization routine. JWD4 JWE4.pdf