Photon Statistics of Semiconductor Light Sources
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Date
2011-01-21
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Abstract
In recent years, semiconductor light sources have become more and more interesting
in terms of applications due to their high efficiency and low cost. Advanced designs like
lasing without inversion make it possible to approach the ideal so-called thresholdless
laser. However, the drawback of such highly efficient light source lies in the rather
complicated techniques needed to characterize the emission properties. While common
laser emission above and below the lasing threshold can easily be distinguished just
by analyzing the output power, the more sophisticated technique of characterizing the
emission in terms of their coherence properties by Hanbury Brown-Twiss interferometry must be applied to characterize semiconductor lasers. This poses several problems.
Coherence properties manifest in the emission photon statistics, but only on timescales
shorter than the coherence time of the emission. While typical coherence times are
still in the nanosecond range for common lasers operated below threshold, they are as
short as a few tens of picoseconds for semiconductor lasers. This poses a problem as
the most commonly used detectors to measure photon statistics are photodiodes which
offer a temporal resolution of hundreds of picoseconds at best. This work discusses an
alternative experimental approach to measure photon statistics using a streak camera.
The best possible time resolution using this setup is shown to be on the order of two
picoseconds and therefore sufficient for measurements on semiconductor lasers.
This experimental technique is applied to several kinds of semiconductor-based light
sources, including quantum-dot vertical-cavity surface-emitting lasers, planar microcavity lasers and so called polariton-condensates. The thresholds of these devices are
identified by analysis of the emission photon number statistics and a transition from
thermal light towards coherent emission is evidenced. Also, unexpected features like antibunching from a quantum dot ensemble or scattering between the condensate ground
state and its excitation spectrum are discussed.
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Keywords
Quantum optics, Semiconductor light sources, Optical coherence, Polariton condensate, Laser