Thermal light such as blackbody radiation including starlight has been known to exhibit photon bunching behaviour. This is the characteristic property of thermal photons to propagate closer together than as described by random Poissonian timing statistics. Although first theorised in the 1960s, attempts to directly probe the temporal coherence of starlight has remained challenging due to the very short timescales required. This work aims to address that by using narrowband spectral filtering to increase the timescale sufficiently for a direct measurement. We present calibration tests using laboratory light sources towards an observatory measurement.
Pseudothermal light exhibits photon bunching, like thermal light, but it does not originate from randomly phased emission. As photon bunching is common in both pseudothermal and thermal light, the analysis of photon bunching is insufficient to differentiate pseudothermal light and thermal light. However, thermal light obeys the Siegert relation, which connects the interferometric visibility ∥g(1)(τ )∥ and second-order photon correlation g(2)(τ ). In this work, we present a direct test test for Siegert relation by a single-shot measurement. Using our technique, we demonstrate that laser light scattered off a rotating ground glass, violates the Siegert relation, which provides further evidence that it is a pseudothermal light source.
KEYWORDS: Signal to noise ratio, Single mode fibers, Light sources, Astronomical imaging, Beam splitters, Light sources and illumination, Interferometry
Dark-field techniques are successfully used in microscopy for increasing the contrast of almost transparent objects, and for edge detection by removing image components with low spatial frequencies. A removal of image components with little interesting information but high intensity yields a higher signal-to-noise ratio for the image components of interest. Here, we present a technique to enhance the signal-to-noise ratio of an image signature contained in a spatial asymmetry. While being an interferometric technique based on image inversion, it will work with incoherent light sources, and thus be applicable in many practical imaging scenarios. We experimentally demonstrate an increase of the signal-to-noise ratio in asymmetry detection by an order of magnitude in a proof-of-principle experiment.
Conventional optical ranging techniques require timing modulated light sources to provide for the time-of-flight information, which may allow for detection, jamming or decoy by a third-party with information to the modulation pattern. Quantum ranging techniques, or quantum lidar, use spontaneous parametric down converted light sources to provide the timing correlation, where entanglement is not necessarily exploited in the simplementation, and is complex and expensive. Here we propose the use of stationary broadband light generated from a laser diode operating below threshold to provide the timing correlation, as extracted from thermal photon bunching.
Classical sensing techniques such as range finding and clock synchronization use timing modulated light sources to provide the timing correlations needed for their implementation. Corresponding quantum schemes utilise spontaneous parametric down converted light sources to provide the timing correlations without the need for timing modulation, although entangled states are too fragile to be fully exploited presently. Here we demonstrate the use of thermal light as an alternative source for timing correlations, via the photon bunching generated from a laser operating below threshold, and showcase its practical viability by successful range finding measurements.
KEYWORDS: Single photon, Photons, Ultrafast phenomena, Quantum networks, Phase shift keying, Modulators, Modulation, Four wave mixing, Dispersion, Chemical species
We report an experimental demonstration of spectral compression performed on heralded 795 nm single photons with narrow spectral bandwidths about 3 times larger than the corresponding atomic transitions, generated through four-wave mixing in cold Rubidium-87 atoms. This scheme uses an asymmetric cavity as a dispersion medium to spread out the photon temporally, and subsequently a phase modulator, to modify the spectral energy distribution of the photons. The spectral bandwidth of the photons was compressed by a factor of 2.6, from 20.6 MHz to less than 8 MHz, almost matching the corresponding atomic transition linewidth of 6 MHz. The spectral compression scheme can potentially be adapted to a wide range of wavelengths and spectral widths.
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