Nonlinear optics and quantum optics, IAP, WWU Münster

Group of Lange and Ackemann Nonlinear optics and quantum optics Institute of Applied Physics WWU Münster

Research

Current projects

Discontinued projects

-	Overview
-	Coupled lasers
-	Radiation trapping
-	Dynamics of driven nonlinear resonators

Publications

Coupled lasers

Field of Research

Experimental setup

Experimental observations

Team members

Publications

Field of Research

Arrays of spatially coupled lasers, especially semiconductor laser arrays, are of considerable technical importance for a number of applications. For some purposes it is desirable that all lasers are synchronized in phase, e.g., for the generation of high power coherent sources operating at a stationary intensity. For other purposes, one may want to operate each element of an array at its own variable power level, e.g., for display applications or optical data processing. From a more fundamental point of view, the study of coupled nonlinear oscillators reveals a fascinating wealth of dynamical phenomena; here, coupled lasers -- or coupled modes of one laser -- are systems well suited for theoretical and experimental investigation of these phenomena.
Both experiment and theory have shown that already two single-mode lasers that are stable individually can exhibit a chaotic instability when coupled. Studying only two lasers can thus be considered a preliminary step to the investigation of larger numbers of coupled lasers.

Neodymium-doped yttrium orthovanadate (Nd:YVO4) is a fairly novel laser material that can provide much higher gain per unit volume than the well-established materials like Nd:YAG. Using very thin laser crystals (down to 100µm), so-called microchip or microcavity lasers can be created. Owing to the large mode spacing, these lasers can operate on a single frequency without any additional selection elements. Our studies involve a system of two or three coupled lasers in a semimonolithic Nd:YVO4 microchip resonator, pumped by a titanium-sapphire laser.

When the lasers are coupled, intensity instabilities occur that are caused by the interaction between the phase dynamics and the intensity dynamics. The instabilities can be synchronous oscillations or pulses of the intensities of all lasers, or can strong oscillations in one laser only (so called localized synchronization). In our experiments we observe these phenomena and identify and classify their parameter regimes. The experimental observations are compared to numerical simulations of suitable dynamical models.

Experimental setup

Experimental setup
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Laser system (Detail)
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Experimental Observations

The figures show a setup of three coupled lasers. Their distances are chosen such that their mutual coupling strenghts are roughly equal. While the near field is unchanged, different changes in the frequency detuning betwenn the three lasers lead to different states of phase coupling, which can be discriminated in the far field images: an uncoupled state (the gaussian distribution shows the addition of the single-laser intensities), phase coupling between two lasers (interference stripes) or the coupling of all three lasers with relative phase differences of 120° (hexagonal pattern).