Three-octave-spanning supercontinuum generation and sub-two-cycle self-compression of mid-infrared filaments in dielectrics

Significance statement

The high-energy, ultrabroadband, few-cycle mid-infrared (mid-IR) supercontinuum (SC) is a very attractive source not only for detecting biomedical materials and air pollutants with the resonant fingerprints of the common molecules, such as H2O, CO2, CO, and NH4, because of sharp and strong resonances with molecules at mid-IR wavelengths, but also for probing the strong-field ultrafast event of the fundamental dynamics in physics and chemistry owing to the large ponderomotive energy to the electrons in the strong-field ionization process at mid-IR wavelengths. Compared to supercontinuum generation (SCG) in the nonlinear fibers, SC from filamentation in bulk dielectrics has the advantages such as no alignment sensitivity issue, flexible materials available in normal and anomalous GVD regimes, no limitation of confinement loss at long wavelengths, high adaptable pump power, and high throughput. This makes the filament in bulk dielectrics an emerging technique for SCG.

We systematically investigate mid-IR SCG from filaments in different dielectrics in both normal and anomalous GVD regimes. CaF2, BaF2, and ZnS, which have relatively flat dispersion around 2 µm were chosen as bulk dielectric materials. The bulk dielectrics were pumped by a homebuilt, 2.1 µm, 27 fs, 1 kHz optical parametric chirped pulse amplifier (OPCPA). With the pump wavelength at 2.1 µm, the continuum spectrum is extended to wavelengths up to ~3.4 µm in CaF2. Moreover, we performed SCG in a ZnS crystal with normal GVD, for the first time. The generated SC spans from 500 nm to 4.5 µm, corresponding to 3.1 octaves. Stable and robust single filaments with conical far-field profiles were formed. The SC from the filaments not only has broad spectrum, it also has few-cycle pulse width and good temporal profile. The temporal profile of the generated mid-IR SC was characterized using a second-harmonic generation frequency-resolved optical gating technique. For the SC from CaF2 in the anomalous GVD regime, pumped at 8.5 µJ, the pulse is self-compressed to 13.5 fs in full width at half maximum, corresponding to ~1.8 cycles, at ~2.25 µm central wavelength. The pulse is close to transform limited because of the balance between self-phase-modulation, and anomalous GVD. Such a mid-IR broadband source with µJ pulse energy and few-cycle pulse duration is a promising tool for molecular motion studies.

 

 

Three-octave-spanning supercontinuum generation and sub-two-cycle self-compression of mid-infrared filaments in dielectrics. Advances In Engineering

 

 

 

 

 

 

 

 

 

 

 

Journal Reference

Optical Letter Volume No 6, 1069, 2015. Houkun Liang1, Peter Krogen1, Ross Grynko2, Ondrej Novak1, Chun-Lin Chang1, Gregory J. Stein1, Darshana Weerawarne2, Bonggu Shim2, Franz X. Kärtner,1,3,4 and Kyung-Han Hong1,*

1Department of Electrical Engineering and Computer Science and Research Laboratory of Electronics, Massachusetts Institute of Technology (MIT), Cambridge, Massachusetts 02139, USA.

2 Dept. of Physics, Applied Physics and Astronomy, Binghamton University, State University of New York, Binghamton, New York 13902, USA.

3Center for Free-Electron Laser Science, DESY and Department of Physics, University of Hamburg, Hamburg, Germany.

4The Hamburg Center for Ultrafast Imaging, Luruper Chaussee 149, 22761 Hamburg, Germany.

*Corresponding author: [email protected]

Abstract

Stable and robust mid-infrared (mid-IR) filaments with several µJ of pulse energy is formed in bulk dielectrics. More than 3-octave-spanning supercontinuum from ZnS in the normal group velocity dispersion (GVD) regime and self-compression of the mid-IR pulse to sub-2-cycle duration in CaF2 in the anomalous GVD regime are demonstrated.

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