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Temporal Intensity Interferometry

Peng Kian Tan

Published Jul 17, 2020• 0 citations
Publisher

Abstract

Working in experimental quantum optics with focus on instrumentation for temporal intensity interferometry. Have successfully measured and resolved the temporal photon bunching effect from Sunlight in Singapore despite the tropical, humid, and urban environment. Our lab measurements have successfully identified the presence of coherent laser light even when embedded in a blackbody radiation background. Measurements also differentiated coherent laser light from thermal light that are both narrowband emission lines which could otherwise be mis-identified.

DOI
10.1002/essoar.10503708.1

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Working in experimental quantum optics with focus on instrumentation for temporal intensity interferometry. Have successfully measured and resolved the temporal photon bunching effect from Sunlight in Singapore despite the tropical, humid, and urban environment. Our lab measurements have successfully identified the presence of coherent laser light even when embedded in a blackbody radiation background. Measurements also differentiated coherent laser light from thermal light that are both narrowband emission lines which could otherwise be mis-identified.
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.
Photons emitted by incoherent sources exhibit temporal bunching, a fundamental manifestation of Bose-Einstein statistics first observed by Hanbury Brown and Twiss (HBT). While intensity correlation measurements originated in astronomy and are now central across quantum technologies, biophysics, and spectroscopy, observing temporal bunching in broadband thermal light remains limited by detector temporal resolution. Conventional approaches - such as streak cameras or optical upconversion - introduce severe trade-offs in efficiency, bandwidth, or setup versatility. Here, we propose and demonstrate a third route: pre-detection temporal magnification of the optical field prior to measuring its intensity autocorrelation function in a conventional HBT setup. Using an electro-optic time lens with a temporal magnification of 660, we resolve the temporal intensity autocorrelation of broadband thermal light generated via non-degenerate spontaneous parametric down-conversion with a bandwidth of 250 GHz. This enables direct observation of thermal photon bunching on sub-3.5 picosecond timescales without narrow spectral filtering, establishing pre-detection temporal imaging as a general platform for broadband statistical optics, with applications spanning ultrafast quantum optics, biophysical imaging, and potentially stellar intensity interferometry.
Temporal photon bunching is the phenomena in which photons tend to cluster together on a short time scale. This effect can be quantified using the second order coherenceg(2)(τ)g^{(2)}(\tau)g(2)(τ)of the light. Photon bunching has been utilized in LIDAR, ghost imaging and simulating star light. In these applications, bunched light is typically generated inefficiently by sending coherent laser light through a phase randomization media, such as a rotating ground glass [1] or a liquid suspension of microspheres [2].
Light from thermal blackbody radiators such as stars exhibits photon bunching behavior at sufficiently short timescales. However, with available detector bandwidths, this bunching signal is difficult to observe directly. We present an experimental technique to increase the photon bunching signal in blackbody radiation via spectral filtering of the light source. Our measurements reveal strong temporal photon bunching from blackbody radiation, including the Sun. This technique allows for an absolute measurement of the photon bunching signature g (2) (0), and thereby a direct statement on the statistical nature of a light source. Such filtering techniques may help revive the interest in intensity interferometry as a tool in astronomy.