Generation of Phase-Stable Sub-Cycle Mid-Infrared Pulses from Filamentation in Nitrogen

Abstract

Sub-single-cycle pulses in the mid-infrared (MIR) region were generated through a laser-induced filament. The fundamental (ω 1 ) and second harmonic (ω 2 ) output of a 30-fs Ti:sapphire amplifier were focused into nitrogen gas and produce phase-stable broadband MIR pulses (ω 0 ) by using a four-wave mixing process (ω 1 + ω 1 − ω 2 → ω 0 ) 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, ω 1 + ω 1 − ω 2 → ω 0 and ω 2 − ω 1 − ω 1 → ω 0 . 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.

Frequency-resolved optical gating capable of carrier-envelope phase determination

“…The absolute phase at 3.3 mm was obtained as À 0.51p. The phase shift at B5 mm (2,000 cm À 1 ) is due to interference between two different parametric processes at the generation of the infrared pulse 18 .…”

“…It is known that the intensity of the infrared pulse generated by four-wave mixing changes with a period of B200 nm by changing the delay between the fundamental and the SH of the Ti:sapphire laser output pulses 18 . The situation is similar to terahertz generation with gas plasma 22,23 .…”

“…The detail of the system is described in the Methods section. The test pulse was a phasestable sub-single-cycle infrared pulse (E test (t)) generated by using four-wave mixing through filamentation 18 . The reference pulse was a 30 fs 800 nm pulse (E ref (t À t)) from a Ti:sapphire amplifier.…”

“…1. We generated phase-stable infrared sub-single-cycle pulses (E test (t), 500 nJ, o 0 ) by using four-wave mixing (FWM, o 1 þ o 1 À o 2 -o 0 ) of the fundamental (700 mJ, 800 nm, o 1 ) and the SH (15 mJ, 400 nm, o 2 ) of Ti:sapphire amplifier (Femtopower compactPro, FEMTOLASERS) output through filamentation in nitrogen 18 . The centre wavelength of the generated infrared pulse was B3.3 mm.…”

Development and Application of Sub-Cycle Mid-Infrared Source Based on Laser Filamentation

“…They succeeded in generating 1.3-cycle MIR pulses by using the scheme [1]. The technology has been further developed by several groups [2][3][4][5][6][7][8], in particular, Fuji and Nomura have succeeded in generating sub-cycle MIR pulses by using the same scheme with nitrogen [7]. The spectrum spreads from 2 to 50 µm and the pulse duration is 6.9-fs with the central frequency of 3.3 µm.…”