Ultrafast measurements of optical spectral coherence by single-shot time-stretch interferometry.

Yiqing Xu,Kevin K Tsia,Kenneth K Y Wong,Zhibo Ren,Xiaoming Wei

doi:10.1038/srep27937

Yiqing Xu, Kevin K Tsia + Show 3 more

Open Access

https://doi.org/10.1038/srep27937

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Journal: Scientific Reports	Publication Date: Jun 13, 2016
Citations: 22	License type: CC BY 4.0

Affiliation: University of Hong Kong

Abstract

The palette of laser technology has significantly been enriched by the innovations in ultrafast optical pulse generation. Our knowledge of the complex pulse dynamics, which is often highly nonlinear and stochastic in nature, is however limited by the scarcity of technologies that can measure fast variation/fluctuation of the spectral phase (or coherence) and amplitude in real-time, continuously. To achieve this goal, we demonstrate ultrafast interferometry enabled by optical time-stretch for real- time spectral coherence characterization with microsecond-resolution. Accessing the single-shot interferograms continuously, it further reveals the degree of second-order coherence, defined by the cross-spectral density function, at high speed-a capability absent in any existing spectroscopic measurement tools. As the technique can simultaneously measure both the high-speed variations of spectrally resolved coherence and intensity, time-stretch interferometry could create a new arena for ultrafast pulse characterization, especially favorable for probing and understanding the non-repetitive or stochastic dynamics in real-time.

Highlights

While the evaluation of the degree of coherence is still based on ensemble of pulses, the key feature of the present technique is its capability of accessing large population of single-shot interferograms within a short time scale, thanks to the high-repetition rate operation (>1 0’s MHz)
The most practical approach to obtain the spectral coherence experimentally is Young’s type interferometry, in which single pulses interfere with the adjacent pulses
Taking the advantage of its capability to quantify the high-speed broadband spectral coherence in real-time, single-shot time-stretch interferometry is useful for probing the stochastic or noise-sensitive systems in which the amplitude and phase fluctuation dynamics are in short-time scale

Summary

Introduction

Our approach hinges on high-speed evaluation of the measured visibility of ultrafast single-shot interferograms continuously-generated by interfering the neighboring pulses. While the evaluation of the degree of coherence is still based on ensemble of pulses, the key feature of the present technique is its capability of accessing large population of single-shot interferograms within a short time scale, thanks to the high-repetition rate operation (>1 0’s MHz). This is in contrast to the traditional Young’s type interferometric methods in which the spectral acquisition speed is limited by the imaging sensor employed in the classical spectrometers. The technique, which can simultaneously measure broadband spectral intensity in real-time, represents a powerful tool for comprehensive characterization of ultrafast pulses, in terms of tracking the intensity and coherence variation at an unprecedentedly high speed

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