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In this paper we calculate the delay of the arrival times of visible photons on the focal plane of a telescope and its fluctuations
as a function of local atmospheric conditions (temperature, pressure, chemical composition, seeing values) and telescope diameter.
The aim of this paper is to provide a model for delay-time fluctuations accurate to the...
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... this section we calculate the delay time for the three Chilean sites of European Southern Observatory (ESO) telescopes. Table 1 shows the characteristics of the sites. We assume an average ground temperature of 288 K and an average ground relative humidity of 20 per cent for the three sites. ...Similar publications
We propose two optimal phase-estimation schemes that can be used for quantum-enhanced long-baseline interferometry. By using distributed entanglement, it is possible to eliminate the loss of stellar photons during transmission over the baselines. The first protocol is a sequence of gates using nonlinear optical elements, optimized over all possible...
Pulsar magnetospheres admit non-stationary vacuum gaps that are characterized by non-vanishing ${\bf{E}} \cdot {\bf{B}}$. The vacuum gaps play an important role in plasma production and electromagnetic wave emission. We show that these gaps generate axions whose energy is set by the gap oscillation frequency. The density of axions produced in a gap...
Context. In the fourth paper in this series, we identified that a pentagonal arrangement of five telescopes, using a kernel-nulling beam combiner, shows notable advantages for some important performance metrics for a space-based mid-infrared nulling interferometer over several other considered configurations for the detection of Earth-like exoplane...
Since a number of years our group is engaged in the design, construction and operation of instruments with very high time resolution in the optical band for applications to Quantum Astronomy and more conventional Astrophysics. Two instruments were built to perform photon counting with sub-nanosecond temporal accuracy. The first of the two, Aqueye+,...
Classical optical interferometry requires maintaining live, phase-stable links between telescope stations. This requirement greatly adds to the cost of extending to long baseline separations and limits on baselines will in turn limit the achievable angular resolution. Here we describe a novel type of two-photon interferometer for astrometry, which...
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... Turbulence in our experiment is relatively weak, as the experiment is accomplished at night from about 11 PM to 6 AM, and the distance is only 220 m. Taking the horizontal channel length, the wind speed, and the receiving aperture into consideration, according to Ref. [34][35][36], the construct function of turbulence C 2 n in our experiment is about 10 −15 − 10 −14 m −2/3 . Turbulence of this strength typically results in about 30% coupling efficiency, and this fairly match with our experimental data. ...
Quantum interference plays an essential role in understanding the concepts of quantum physics. Moreover, the interference of photons is indispensable for large-scale quantum information processing. With the development of quantum networks, interference of photons transmitted through long-distance fiber channels has been widely implemented. However, quantum interference of photons using free-space channels is still scarce, mainly due to atmospheric turbulence. Here, we report an experimental demonstration of Hong-Ou-Mandel interference with photons transmitted by free-space channels. Two typical photon sources, i.e., correlated photon pairs generated in spontaneous parametric down conversion (SPDC) process and weak coherent states, are employed. A visibility of 0.744 ± 0.013 is observed by interfering with two photons generated in the SPDC process, exceeding the classical limit of 0.5. Our results demonstrate that the quantum property of photons remains even after transmission through unstable free-space channels, indicating the feasibility and potential application of free-space-based quantum interference in quantum information processing.
... Downloaded from https://academic.oup.com/mnras/article/512/2/1722/6534919 by guest on 25 February 2024 The CTA requirements are used for the CTA SST and MST (we assume a Gaussian distribution of photon arri v al times for the SST and a rectangular distribution for the MST); for the CTA LST, we refer to a pri v ate communication with D. Mazin. For the 0.5 and 1 m reflector telescopes, at least λ/4 precision is assumed due to their imaging capability, and the time resolution of photons impinging on the detector is dominated by jitter introduced by atmospheric fluctuations (Cavazzani, Ortolani & Barbieri 2012 ). ...
... Telescopes suitable for HTR are located in the lower left-hand corner of the plot providing small collection areas but high isochronicity and thus small optical time spread. Values for their isochronicity are assumed to be dominated by atmospheric turbulence as described in Cavazzani et al. ( 2012 ), since the telescope itself displays imaging capabilities with unisochronicity <λ/4. The time resolution is thus dominated by the single photon detection equipment rather than the optical time spread of the telescope itself. ...
Stellar intensity interferometers correlate photons within their coherence time and could overcome the baseline limitations of existing amplitude interferometers. Intensity interferometers do not rely on phase coherence of the optical elements and thus function without high grade optics and light combining delay lines. However, the coherence time of starlight observed with realistic optical filter bandwidths (>0.1 nm) is usually much smaller than the time resolution of the detection system (>10 ps), resulting in a greatly reduced correlation signal. Reaching high signal to noise in a reasonably short measurement time can be achieved in different ways: either by increasing the time resolution, which increases the correlation signal height, or by increasing the photon rate, which decreases statistical uncertainties of the measurement. We present laboratory measurements employing both approaches and directly compare them in terms of signal to noise ratio. A high time-resolution interferometry setup designed for small to intermediate size optical telescopes and thus lower photon rates (diameters < some meters) is compared to a setup capable of measuring high photon rates, which is planned to be installed at Cherenkov telescopes with dish diameters of >10 m. We use a Xenon lamp as a common light source simulating starlight. Both setups measure the expected correlation signal and work at the expected shot-noise limit of statistical uncertainties for measurement times between 10 min and 23 h. We discuss the quantitative differences in the measurement results and give an overview of suitable operation regimes for each of the interferometer concepts.
... The CTA requirements are used for the CTA SST and MST (we assume a Gaussian distribution of photon arrival times for the SST and a rectangular distribution for the MST), for the CTA LST we refer to a private communication with D. Mazin. For the PW telescopes at least /4 precision is assumed due to their imaging capability, and the timing resolution of photons impinging on the detector is dominated by jitter introduced by atmospheric fluctuations (Cavazzani et al. 2012). ...
... Telescopes suitable for HTR are located in the lower left corner of the plot providing small collection areas but high isochronicity and thus small optical time spread. Values for their isochronicity are assumed to be dominated by atmospheric turbulence as described in Cavazzani et al. (2012), since the telescope itself displays imaging capabilities with unisochronicity < /4. The time resolution is thus dominated by the single photon detection equipment rather than the optical time spread of the telescope itself. ...
Stellar intensity interferometers correlate photons within their coherence time and could overcome the baseline limitations of existing amplitude interferometers. Intensity interferometers do not rely on phase coherence of the optical elements and thus function without high grade optics and light combining delay lines. However, the coherence time of starlight observed with realistic optical filter bandwidths (> 0.1 nm) is usually much smaller than the time resolution of the detection system (> 10 ps), resulting in a greatly reduced correlation signal. Reaching high signal to noise in a reasonably short measurement time can be achieved in different ways: either by increasing the time resolution, which increases the correlation signal height, or by increasing the photon rate, which decreases statistical uncertainties of the measurement. We present laboratory measurements employing both approaches and directly compare them in terms of signal to noise ratio. A high time-resolution interferometry setup designed for small to intermediate size optical telescopes and thus lower photon rates (diameters < some meters) is compared to a setup capable of measuring high photon rates, which is planned to be installed at Cherenkov telescopes with dish diameters of > 10 m. We use a Xenon lamp as a common light source simulating starlight. Both setups measure the expected correlation signal and work at the expected shot-noise limit of statistical uncertainties for measurement times between 10 min and 23 h. We discuss the quantitative differences in the measurement results and give an overview of suitable operation regimes for each of the interferometer concepts.
... Atmospheric turbulence introduces scintillation with a characteristic timescale on the order of microseconds, and a spatial inner scale of approximately 3 mm for typical wind speeds of 10 ms −1 (Dravins et al. 1997), corresponding to delay time variations on the order of tens of picoseconds due to fluctuations in the atmospheric path difference (Dravins & LeBohec 2007;Cavazzani et al. 2012). This sets the lower bound on effective detector timing resolution to be in the 10 ps regime before it is constrained by the atmospheric scintillation. ...
Conventional ground-based astronomical observations suffer from image distortion due to atmospheric turbulence. This can be
minimized by choosing suitable geographic locations or adaptive optical techniques, and avoided altogether by using orbital
platforms outside the atmosphere. One of the promises of optical intensity interferometry is its independence from atmospherically
induced phase fluctuations. By performing narrowband spectral filtering on sunlight and conducting temporal intensity interferometry
using actively quenched avalanche photon detectors (APDs), the Solar g(2)(τ) signature was directly measured. We observe an averaged photon bunching signal of g(2)(τ) = 1.693 ± 0.003 from the Sun, consistently throughout the day despite fluctuating weather conditions, cloud cover and
elevation angle. This demonstrates the robustness of the intensity interferometry technique against atmospheric turbulence
and opto-mechanical instabilities, and the feasibility to implement measurement schemes with both large baselines and long
integration times.
... Typically, the photon bunching signature is observed in a regime where the ratio of the coherence time, τ c , over the photodetector resolution, τ t , is significantly smaller than one, even after an increase of the coherence time via optical filtering. In such a regime, the temporal coherence properties cannot be resolved directly, and the S/N in observing photon bunching is independent of the filter bandwidth (Hanbury-Brown 1974;Foellmi 2009;Rou et al. 2013;Nuñez 2012;Malvimat et al. 2013). ...
Light from thermal black body radiators such as stars exhibits photon
bunching behaviour at sufficiently short timescales. However, with available
detector bandwidths, this bunching signal is difficult to be directly used for
intensity interferometry with sufficient statistics in astronomy. Here 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 in light from blackbody
radiation, including the Sun. Such filtering techniques may revive the interest
in intensity interferometry as a tool in astronomy.
In recent years, a new generation of optical intensity interferometers has emerged, leveraging the existing infrastructure of Imaging Atmospheric Cherenkov Telescopes (IACTs). The MAGIC telescopes host the MAGIC-SII system (Stellar Intensity Interferometer), implemented to investigate the feasibility and potential of this technique on IACTs. After the first successful measurements in 2019, the system was upgraded and now features a real-time, dead-time-free, 4-channel, GPU-based correlator. These hardware modifications allow seamless transitions between MAGIC’s standard very-high-energy gamma-ray observations and optical interferometry measurements within seconds. We establish the feasibility and potential of employing IACTs as competitive optical Intensity Interferometers with minimal hardware adjustments. The measurement of a total of 22 stellar diameters are reported, 9 corresponding to reference stars with previous comparable measurements, and 13 with no prior measurements. A prospective implementation involving telescopes from the forthcoming Cherenkov Telescope Array Observatory’s northern hemisphere array, such as the first prototype of its Large-Sized Telescopes, LST-1, is technically viable. This integration would significantly enhance the sensitivity of the current system and broaden the UV-plane coverage. This advancement would enable the system to achieve competitive sensitivity with the current generation of long-baseline optical interferometers over blue wavelengths.
Using kilometric arrays of air Cherenkov telescopes, intensity interferometry
may increase the spatial resolution in optical astronomy by an order of
magnitude, enabling images of rapidly rotating stars with structures in their
circumstellar disks and winds, or mapping out patterns of nonradial pulsations
across stellar surfaces. Intensity interferometry (pioneered by Hanbury Brown
and Twiss) connects telescopes only electronically, and is practically
insensitive to atmospheric turbulence and optical imperfections, permitting
observations over long baselines and through large airmasses, also at short
optical wavelengths. The required large telescopes with very fast detectors are
becoming available as arrays of air Cherenkov telescopes, distributed over a
few square km. Digital signal handling enables very many baselines to be
synthesized, while stars are tracked with electronic time delays, thus
synthesizing an optical interferometer in software. Simulated observations
indicate limiting magnitudes around m(v)=8, reaching resolutions ~30
microarcsec in the violet. The signal-to-noise ratio favors high-temperature
sources and emission-line structures, and is independent of the optical
passband, be it a single spectral line or the broad spectral continuum.
Intensity interferometry provides the modulus (but not phase) of any spatial
frequency component of the source image; for this reason image reconstruction
requires phase retrieval techniques, feasible if sufficient coverage of the
interferometric (u,v)-plane is available. Experiments are in progress; test
telescopes have been erected, and trials in connecting large Cherenkov
telescopes have been carried out. This paper reviews this interferometric
method in view of the new possibilities offered by arrays of air Cherenkov
telescopes, and outlines observational programs that should become realistic
already in the rather near future.
With its unprecedented light-collecting area for night-sky observations, the
Cherenkov Telescope Array (CTA) holds great potential for also optical stellar
astronomy, in particular as a multi-element intensity interferometer for
realizing imaging with sub-milliarcsecond angular resolution. Such an
order-of-magnitude increase of the spatial resolution achieved in optical
astronomy will reveal the surfaces of rotationally flattened stars with
structures in their circumstellar disks and winds, or the gas flows between
close binaries. Image reconstruction is feasible from the second-order
coherence of light, measured as the temporal correlations of arrival times
between photons recorded in different telescopes. This technique (once
pioneered by Hanbury Brown and Twiss) connects telescopes only with electronic
signals and is practically insensitive to atmospheric turbulence and to
imperfections in telescope optics. Detector and telescope requirements are very
similar to those for imaging air Cherenkov observatories, the main difference
being the signal processing (calculating cross correlations between single
camera pixels in pairs of telescopes). Observations of brighter stars are not
limited by sky brightness, permitting efficient CTA use during also bright-Moon
periods. While other concepts have been proposed to realize kilometer-scale
optical interferometers of conventional amplitude (phase-) type, both in space
and on the ground, their complexity places them much further into the future
than CTA, which thus could become the first kilometer-scale optical imager in
astronomy.
