32 emitters quantum cascade laser phased array

Abstract

We demonstrate a monolithic Quantum Cascade Laser array. We show phase-locking and single-mode emission at λ=8.4µm. It consists of narrow ridges buried into InP:Fe. Phase-locking is provided by evanescent coupling between adjacent ridges. This µ-structuration is simultaneously an answer to the excessive heating and poor beam quality of broad area lasers. First, it increases the surface of exchange between the multi-layer active region and the InP:Fe, which presents a higher thermal conductivity. Secondly, by choosing carefully the width of emitters and the distance between them, we insure phase locking and control of the supermode emission. We have investigated 2µm wide emitters. In order to study the behavior of evanescent coupling, we have chosen spacing from 1 to 8 microns. The number of emitters ranges from 1 to 64. Technological feasibility was demonstrated up to 64 emitters, and lasing operation up to 32 emitters. We have obtained a pure dual-lobe far-field pattern as expected from an anti-symmetrical supermode. The width of each lobes narrows with an increasing array size as expected from the diffraction theory. The beam quality is insensitive to the injective current. The optical power scales linearly with the number of emitters.

Exploiting the time of arrival of Cherenkov photons at the 28 m H.E.S.S. telescope for background rejection: Methods and performance

“…We describe here the shower goodness which is the main hadron rejecter of the Model analysis and attests of the quality of the model adjustment. For more details on its derivation, see [2]. The goodness G of a N pixel image is given by :…”

“…However, several efforts were carried out to make use of the arrival time information of the Cherenkov photons as an additional, independent variable. In 2007, [1] exploited the timing information of the first MAGIC telescope using a template-based reconstruction method that resembles the one of [2]. Two years later the MAGIC collaboration presented several ways to improve the single-telescope performance by introducing several time-based variables [3].…”

“…In this contribution, we present the status of the background rejection study using the Time of Maximum information of the CT5 camera. The variables commonly used by the Model reconstruction [2] are firstly reminded. Then the Time of Maximum, its calibration and its potential for background suppression are described.…”