The negative effects of the Earth’s atmosphere severely limits ground based high precision photometry. Scintillation noise cannot easily be corrected as it is produced by high altitude turbulence, and therefore the range of angles over which it is correlated is very small. Comparison stars can be used to correct for atmospheric transparency variations, however, the shot noise of the comparison star, as well as differences in the airmass along the lines of sight for each star, add noise to the calibration. We propose a new technique to correct for these effects by projecting a laser guide star (LGS) directly on top of the target star, therefore creating an artificial reference point that passes along the same line of sight. The measured LGS photometry can then be used to calibrate the photometry of the target star. We will present preliminary results from an on-sky test of this experiment conducted in May 2024 at the Roque de los Muchachos Observatory, La Palma, Spain using a simple instrument to separate the LGS and the target star light sources onto two separate detectors. It is expected that this technique could provide very high precision ground based photometry.
CaNaPy is an experimental Laser Guide Star Adaptive Optics facility designed to demonstrate pre-compensation of a sodium LGS uplink beam, and to investigate wavefront sensing on the pre-compensated LGS using a Pyramid wavefront sensor. CaNaPy was installed at the 1m ESA OGS telescope at the Observatorio del Teide, Tenerife, in autumn 2023. Here we report on the commissioning phase activities followed by the first on-sky results on LGS uplink pre-compensation. CaNaPy is developed at ESO in collaboration with ESA, Durham University, IAC, INAF, and Microgate, with scientific collaborators from ANU and the RICAM institute.
The CaNaPy project pioneers a novel configuration in Visible Wavelength Laser Guide Star Adaptive Optics (LGS-AO). Collaboratively established by ESA and ESO, it hosts a 70 W CW 589nm laser, employing upward propagation pre-compensation on sodium LGS via a pyramid wavefront sensor (Py-WFS). Operating at Teide Observatory, its aim is to demonstrate the benefits of pre-compensating the LGS upward propagation path, reducing LGS spot size in the mesosphere. This enhances Sodium optical pumping effects and significantly boosts Py-WFS sensitivity. Early on-sky experiments, using Natural Guide Stars, are underway, comparing results with simulation predictions using PASSATA. These trials mark a critical milestone in advancing visible wavelength LGS-AO, promising better resolution and sensitivity with reduced laser power requirements.
The role played by the LPC (Laser Pointing Camera, produced by ASTREL Instruments in collaboration with INAF-OAR) within the CANAPY-ALASCA project (an experimental LGS-AO system, achieved thanks to a synergy between INAF, ESO, ESA, Microgate, Durham University, IAC) is described, emphasizing his cruciality during commissioning, and describing their usefulness not only in the purely astronomical context (VLT/E- ELT) but also in the context of the use of adaptive optics for satellite communications tests.
We present the design and implementation of an adaptive optics test bench recently built at the School of Electrical Engineering of the Pontificia Universidad Católica de Valparaíso in Chile. The flexible design of the PULPOS bench incorporates state-of-the-art, high-speed spatial light modulators for atmospheric turbulence emulation and wavefront correction, a deformable mirror for modulation, and a variety of wavefront sensors such as a pyramid wavefront sensor. PULPOS serves as a platform for research on adaptive optics and wavefront reconstruction using artificial intelligence techniques, as well as for educational purposes.
We propose a design of an adaptive optics (AO) system for the high-resolution fiber-fed echelle spectrograph installed at the Nasmyth focus of the 6-m BTA telescope at the Special Astrophysical Observatory (SAO) of the Russian Academy of Sciences (RAS). The system will be based on a pyramid wavefront sensor and benefit from the experience of the Laboratoire d’Astrophysique de Marseille team in the field of adaptive optics. The AO will operate in the visible domain of 430-680 nm, in an f/30 input beam and provide correction for the on-axis source only. The main challenges in this particular design are insetting inserting the AO into an existing optical system and maintaining the focal and pupil planes configuration, fitting within the instrument’s flux budget as well as limitations on the total cost of the AO bench. According to the current design, the AO bench will use an additional relay consisting of 2 spherical mirrors to re-collimate the beam and project the pupil onto a small deformable mirror. A dichroic splitter will be used to longwave component to the pyramid wavefront sensor branch based on refractive optics only. Using off-the-shelf components only we can reach the instrumental wavefront error of 0.016 waves PTV with a 20 nm bandpass filter at 700 nm. Using folding mirrors and refocusing of the fiber’s microlens we restore the nominal geometry of the beam feeding the spectrograph. The final goal for the AO system is to increase the energy concentration in spot at the spectrograph’s entrance, and our preliminary modelling shows that we can gain by factor of 69.5 with the typical atmospheric conditions at SAO RAS.
HARMONI is the first light visible and near-IR integral field spectrograph for the ELT. It covers a large spectral range from 450 nm to 2450 nm with resolving powers from 3500 to 18000 and spatial sampling from 60 mas to 4 mas. It can operate in two Adaptive Optics modes - SCAO (including a High Contrast capability) and LTAO - or with no AO mode. To prepare the final design reviews, we have built an optical bench to emulate and characterize the performance of the laser guide star (LGS) wavefront sensor (WFS) to be used in HARMONI. The WFS is a classic Shack-Hartmann, nonetheless pushed to the extreme due to the size of the primary mirror of the ELT (39 m). The WFS is composed of a 80×80 double side microlens array (MLA), an optical relay made of 6 lenses in order to re-image the light coming from the MLA on the detector, and a CMOS camera using a Sony detector with 1608×1104 pixels, RON< 3e, and a frame rate of 500Hz. The sensor has a large number of pixels to provide a field-of-view wider than 15 arcsec per subaperture over the full pupil, which is required to image the elongated LGS spots. An innovative feature of our bench is the use of a spatial light modulator (SLM) which allows us to emulate the M4 deformable mirror (DM) and the real position of its actuators, together with the projected spiders in the pupil plane. We report on the design and performance of our bench, including the first interaction matrices using the ELT-M4 influence functions and a non-elongated source. We expect to implement a system to emulate an elongated source in order to grasp a better understanding of its effects on wavefront sensing.
HARMONI is the first light visible and near-IR integral field spectrograph for the ELT covering a large spectral range from 450nm to 2450nm with resolving powers from 3500 to 18000 and spatial sampling from 60mas to 4mas. It can operate in two Adaptive Optics modes - SCAO and LTAO - or with no AO. The project is preparing for Final Design Reviews. The laser Tomographic AO (LTAO) system provides AO correction with very high sky-coverage thanks to two systems: the Laser Guide Star Sensors (LGSS) and the Natural Guide Star Sensors (NGSS). LGSS is dedicated to the analysis of the wavefront coming from 6 laser guide stars created by the ELT. It is made of 6 independent wavefront sensor (WFS) modules mounted on a rotator of 600mm diameter to stabilise the pupil onto the microlens array in front of the detector. The optical design accepts elongated spots of up to 16 arcsec with no truncation using a CMOS detector from SONY. We will present the final optical and mechanical design of the LGSS based on freeform lenses to minimize the numbers of optical components and to accommodate for the diversity of sodium layer configurations. We will focus on rotator design, illustrating how we will move 1 tons with 90” accuracy in restrictive environment. Finally, we will present the strategy to verify the system in HARMONI context. The main challenge for the verification being how to test an AO system without access to the deformable mirror, part of the ELT.
HARMONI is the first light, adaptive optics assisted, integral field spectrograph for the European Southern Observatory’s Extremely Large Telescope (ELT). A work-horse instrument, it provides the ELT’s diffraction limited spectroscopic capability across the near-infrared wavelength range. HARMONI will exploit the ELT’s unique combination of exquisite spatial resolution and enormous collecting area, enabling transformational science. The design of the instrument is being finalized, and the plans for assembly, integration and testing are being detailed. We present an overview of the instrument’s capabilities from a user perspective, and provide a summary of the instrument’s design. We also include recent changes to the project, both technical and programmatic, that have resulted from red-flag actions. Finally, we outline some of the simulated HARMONI observations currently being analyzed.
Laser Guide Star wave-front sensing [LGSWFS] is a key element of tomographic Adaptive Optics system. For classical Shack-Hartmann Wave-Front Sensor, necessary trade-offs have to be made between the pupil spatial sampling, the sub-aperture field-of-view and the pixel sampling. For Extremely Large Telescope [ELT] scales, these trade-off are also driven by strong technical constraints, especially concerning the available detectors. We propose a sensitivity analysis, and we explore how these parameters impacts the final performance. We introduce the concept of super resolution, which allows to reduce the pupil sampling and allows proposing potential LGSWFS designs providing the best performance for ELT scales.
Laser guide star (LGS) wave-front sensing (LGSWFS) is a key element of tomographic adaptive optics system. However, when considering Extremely Large Telescope (ELT) scales, the LGS spot elongation becomes so large that it challenges the standard recipes to design LGSWFS. For classical Shack–Hartmann wave-front sensor (SHWFS), which is the current baseline for all ELT LGS-assisted instruments, a trade-off between the pupil spatial sampling [number of sub-apertures (SAs)], the SA field-of-view (FoV) and the pixel sampling within each SA is required. For ELT scales, this trade-off is also driven by strong technical constraints, especially concerning the available detectors and in particular their number of pixels. For SHWFS, a larger field of view per SA allows mitigating the LGS spot truncation, which represents a severe loss of performance due to measurement biases. For a given number of available detectors pixels, the SA FoV is competing with the proper sampling of the LGS spots, and/or the total number of SAs. We proposed a sensitivity analysis, and we explore how these parameters impacts the final performance. In particular, we introduce the concept of super resolution, which allows one to reduce the pupil sampling per WFS and opens an opportunity to propose potential LGSWFS designs providing the best performance for ELT scales.
The adaptive optics systems of future Extremely Large Telescopes (ELTs) will be assisted with laser guide stars (LGS) which will be created in the sodium layer at a height of ≈90 km above the telescopes. In a Shack–Hartmann wavefront sensor, the long elongation of LGS spots on the sub-pupils far apart from the laser beam axis constraints the design of the wavefront sensor (WFS) which must be able to fully sample the elongated spots without undersampling the non-elongated spots. To fulfill these requirements, a newly released large complementary metal oxide semiconductor sensor with 1100 × 1600 pixels and 9 μm pixel pitch could be employed. Here, we report on the characterization of such a sensor in terms of noise and linearity, and we evaluate its performance for wavefront sensing based on the spot centroid variations. We then illustrate how this new detector can be integrated into a full LGS WFS for both the European Southern Observatory’s ELT and the Thirty Meter Telescope.
The Provence Adaptive optics Pyramid Run System (PAPYRUS) is a pyramid-based Adaptive Optics (AO) system that will be installed at the Coude focus of the 1.52m telescope (T152) at the Observatoire de Haute Provence (OHP). The project is being developed by PhD students and Postdocs across France with support from staff members consolidating the existing expertise and hardware into an RD testbed. This testbed allows us to run various pyramid wavefront sensing (WFS) control algorithms on-sky and experiment on new concepts for wavefront control with additional benefit from the high number of available nights at this telescope. It will also function as a teaching tool for students during the planned AO summer school at OHP. To our knowledge, this is one of the first pedagogic pyramid-based AO systems on-sky. The key components of PAPYRUS are a 17x17 actuators Alpao deformable mirror with a Alpao RTC, a very low noise camera OCAM2k, and a 4-faces glass pyramid. PAPYRUS is designed in order to be a simple and modular system to explore wavefront control with a pyramid WFS on sky. We present an overview of PAPYRUS, a description of the opto-mechanical design and the current status of the project.
HARMONI is the adaptive optics assisted, near-infrared and visible light integral field spectrograph for the Extremely Large Telescope (ELT). A first light instrument, it provides the work-horse spectroscopic capability for the ELT. As the project approaches its Final Design Review milestone, the design of the instrument is being finalized, and the plans for assembly, integration and testing are being detailed. We present an overview of the instrument’s capabilities from a user perspective, provide a summary of the instrument’s design, including plans for operations and calibrations, and provide a brief glimpse of the predicted performance for a specific observing scenario. The paper also provides some details of the consortium composition and its evolution since the project commenced in 2015.
The return flux from a sodium laser guide star suffers, at large angles between the geomagnetic field and the laser beam, from the reduction in optical pumping due to spin-precession of sodium atoms. This detrimental effect can be mitigated by modulating the circular polarization of a continuous-wave laser beam in resonance with the Larmor frequency of sodium atoms in the mesosphere. We present an investigation based on numerical modeling to evaluate the brightness enhancement of a laser guide star with polarization modulation of a continuous-wave laser beam at different observatories.
In this work we discuss a mechanism for generation of a coherent source of light from the mesosphere as a new concept of directional laser guide star. In contrast to the near-isotropic spontaneous emission, nonlinear processes in atomic vapors like amplified spontaneous emission can yield highly directional emission in the forward and backward directions. Along with directional emission, excited sodium atoms also radiate at different wavelength creating a polychromatic laser guide star (PLGS). If feasible, a directional PLGS would provide a net gain in the return flux of several orders of magnitude compared to traditional LGS schemes, making possible laser-guided tip/tilt-correction in adaptive optic systems.
Recent numerical simulations and experiments on sodium Laser Guide Star (LGS) have shown that a continuous wave (CW) laser with circular polarization and re-pumping should maximize the fluorescent photon return flux to the wavefront sensor for adaptive optics applications. The orientation and strength of the geomagnetic field in the sodium layer also play an important role affecting the LGS return ux. Field measurements of the LGS return flux show agreement with the CW LGS model, however, fluctuations in the sodium column abundance and geomagnetic field intensity, as well as atmospheric turbulence, induce experimental uncertainties. We describe a laboratory experiment to measure the photon return flux from a sodium vapor cell illuminated with a 589 nm CW laser beam, designed to approximately emulate a LGS under controlled conditions. Return flux measurements are carried out controlling polarization, power density, re-pumping, laser linewidth, and magnetic field intensity and orientation. Comparison with the numerical CW simulation package Atomic Density Matrix are presented and discussed.
We report on the comparison between observations and simulations of a completed 12-month field observation campaign at Observatorio del Teide, Tenerife, using ESO's transportable 20 watt CW Wendelstein laser guide star system. This mission has provided sodium photon return flux measurements of unprecedented detail regarding variation of laser power, polarization and sodium D2b repumping. The Raman fiber laser and projector technology are very similar to that employed in the 4LGSF/AOF laser facility, recently installed and commissioned at the VLT in Paranal. The simulations are based on the open source LGSBloch density matrix simulation package and we find good overall agreement with experimental data.
The aim of this research is to experimentally validate a Gauss-Markov model, previously developed by our
group, for the non-uniformity parameters of infrared (IR) focal plane arrays (FPAs). The Gauss-Markov model
assumed that both, the gain and the offset parameters at each detector, are random state-variables modeled by a
recursive discrete-time process. For simplicity, however, we have regarded here the gain parameter as a constant
and assumed that solely the offset parameter follows a Gauss-Markov model. Experiments have been conducted
at room temperature and IR data was collected from black-body radiator sources using microbolometer-based
IR cameras operating in the 8 to 12 μm. Next, well-known statistical techniques were used to analyze the offset
time series and determinate whether the Gauss-Markov model truly fits the temporal dynamics of the offset. The
validity of the Gauss-Markov model for the offset parameter was tested at two time scales: seconds and minutes.
It is worth mentioning that the statistical analysis conducted in this work is a key in providing mechanisms for
capturing the drift in the fixed pattern noise parameters.
In this paper the effects of the internal temperature on the response of uncooled microbolometer cameras have
been studied. To this end, different temperature profiles steering the internal temperature of the cameras have
been generated, and black-body radiator sources have been employed as time and temperature constant radiation
inputs. The analysis conducted over the empirical data has shown the existence of statistical correlation between
camera's internal temperature and the fluctuations in the read-out data. Thus, when measurements of the
internal temperature are available, effective methods for compensating the fluctuations in the read-out data can
be developed. This claim has been tested by developing a signal processing scheme, based on a polynomial
model, to compensate for the output of infrared cameras equipped with amorphous-Silicon and Vanadium-Oxide
microbolometers.
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