Abstract
Sub-single-cycle pulses in the mid-infrared (MIR) region were generated through a laser-induced filament. The fundamental (ω1) and second harmonic (ω2) output of a 30-fs Ti:sapphire amplifier were focused into nitrogen gas and produce phase-stable broadband MIR pulses (ω0) by using a four-wave mixing process (ω1 + ω1 - ω2 → ω0) through filamentation. The spectrum spread from 400 cm-1 to 5500 cm-1, which completely covered the MIR region. The low frequency components were detected by using an electro-optic sampling technique with a gaseous medium. The efficiency of the MIR pulse generation was very sensitive to the delay between the fundamental and second harmonic pulses. It was revealed that the delay dependence of the efficiency came from the interference between two opposite parametric processes, ω1 + ω1 - ω2 → ω0 and ω2 - ω1 - ω1 → ω0. The pulse duration was measured as 6.9 fs with cross-correlation frequency-resolved optical gating by using four-wave mixing in nitrogen. The carrier-envelope phase of the MIR pulse was passively stabilized. The instability was estimated as 154 mrad rms in 2.5 h.
Highlights
Coherent light sources in the mid-infrared spectral region (MIR, 3–20 μm) are highly important for studies in molecular science since a number of molecular vibrations have resonance in this wavelengthAppl
It may result in shorter attosecond pulse generation via high harmonic generation
We report the detail of the performance of the MIR pulses generated by using four-wave mixing (FWM)
Summary
Coherent light sources in the mid-infrared spectral region (MIR, 3–20 μm) are highly important for studies in molecular science since a number of molecular vibrations have resonance in this wavelength. In contrast to the third harmonic generation process, FWM does not suffer from phase mismatch caused by Gouy phase shift [12] This means that the conversion efficiency of FWM can be significantly improved with a filamentation effect. Ultrabroadband MIR pulse generation by using FWM of the fundamental and second harmonic output of a Ti:sapphire amplifier is one of the most attractive applications of the filamentation effect. Such MIR pulses with more than one octave at full width at half maximum are very attractive. The fundamental (ω1 ) and second harmonic (SH, ω2 ) output of a 30-fs Ti:sapphire amplifier were focused into a nitrogen gas and produced phase-stable broadband MIR (ω0 ) pulses through. The stability of the carrier-envelope phase was significantly improved with the inline scheme
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