Abstract
We generate temporally modulated optical pulses with a beat frequency of 255 GHz, a duration of 360 ps, and a repetition rate of 2 MHz. The temporal envelope, beat frequency, and repetition rate are computer-programmable. A frequency comb serves as a phase and frequency reference for the locking of two laser lines. The system enables beat frequencies that are adjustable in steps of the frequency comb's repetition rate and exhibit Hz-level precision and accuracy. We expect the optical beat pulses to be well suited for versatile multi-cycle terahertz-wave generation with controllable carrier-envelope phase. We demonstrate that the inherent synchronization of the frequency comb's ultra-short pulse train and the synthesized optical beat (or later the multi-cycle terahertz) pulses enables rapid and phase-sensitive sampling of such pulses.
Highlights
Terahertz waves offer capabilities unavailable through conventional radio frequency (RF) or optical methods
We focus on the development of a laser frontend emitting optical beat pulses optimized for terahertz generation with shapeable envelope and picosecond durations
We have demonstrated a laser system producing optical beat pulses with hundreds of picosecond duration
Summary
Terahertz waves offer capabilities unavailable through conventional RF or optical methods. The limited availability of adequate terahertz coherent sources and detection schemes imposes limitations on the utility of terahertz waves in applications In this contribution, we propose and demonstrate a frequency-comb-based laser source producing a phase-stable optical beat signal of which the envelope is a pulse with a picosecond durations. To facilitate locking between the single frequency lasers and the frequency comb as well as to enable the generation of a frequency difference with high accuracy and precision, the oscillator’s repetition rate, frep, as well as its carrier-envelope offset (CEO) frequency (fCEO) must be fixed. The frequency difference is an exact integer (N) multiplier of the ultra-short pulse laser’s repetition rate (frep) It exhibits sub-Hz frequency precision and accuracy.
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