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  • September 2012

Optics InfoBase > Spotlight on Optics > Pulse synthesis in the single-cycle regime from independent mode-locked lasers using attosecond-precision feedback

Pulse synthesis in the single-cycle regime from independent mode-locked lasers using attosecond-precision feedback

Published in Optics Letters, Vol. 37 Issue 17, pp.3579-3581 (2012)
by J. A. Cox, W. P. Putnam, A. Sell, A. Leitenstorfer, and F. X. Kärtner

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Spotlight summary: In quantum mechanics, the Heisenberg uncertainty principle limits the minimum uncertainty of the measurements of energy and time. This fundamental principle demands that a pulse’s temporal width times its frequency width should be larger than a certain numerical constant, and eventually requires a broader gain bandwidth for the generation of a shorter pulse in time. However, intrinsically, the spectral bandwidth of gain medium of individual lasers is not broad enough to produce pulses with a nearly single cycle in duration. To date, there have been several attempts to overcome this fundamental limit using coherent combination of multi-branch nonlinear spectral generation from a single master oscillator. Unfortunately, it has been shown that this method has no long-term stability and often renders spectral gaps in the output.

In this letter, the authors achieve for the first time the coherent synthesis of few cycle pulses generated from two independent lasers into a nearly single optical cycle pulse with long-term stability. A brief description of the authors' method is as follows: The authors employ two few-cycle laser sources. One is a Kerr lens mode-locked Ti:sapphire laser with a wavelength range of 700-1000 nm. The other is a fiber supercontinuum laser source driven by a stretched pulse, passively mode-locked, erbium fiber laser with a wavelength range of 950-1400 nm, where the fiber laser wavelength below 1400 nm is filtered with a knife edge. To coherently synthesize these two few-cycle pulses, the authors synchronize their sources with attosecond precision. This requires accurate control of timing jitter and carrier envelope phase of the fiber laser by using two novel feedback mechanisms given by a waveguide lithium niobate electro-optic timing shifter and an acousto-optic frequency shifter, in addition to feedback through an intracavity piezo-actuated mirror. All three feedback signals are obtained from either the balanced optical cross-correlator or balanced homodyne phase detector.

Through this attosecond synchronization of two few cycle sources, the authors clearly show the generation of a pulse with 1.1 optical cycles in duration with a wavelength range of 700-1400 nm by retrieving the envelope of the synthesized pulse retrieved using two-dimensional spectral shearing interferometry. The authors also claim that this pulse synchronization can be achieved for at least several minutes even in an uncontrolled laboratory environment. Therefore, as the authors note, the generation of a single-cycle of the carrier wave through coherent synthesis of individual laser sources can possibly open up a new path of studies such as phase sensitive nonlinear optics including optically driven field emission, carrier wave Rabi flopping, and high harmonic generation.

--Taek Yong Hwang

Technical Division: Optoelectronics
ToC Category: Lasers and Laser Optics
OCIS Codes: (140.7090) Lasers and laser optics : Ultrafast lasers
(270.2500) Quantum optics : Fluctuations, relaxations, and noise
(140.3425) Lasers and laser optics : Laser stabilization

Posted on September 11, 2012

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