Periodic Reporting for period 1 - MOAI (MethOds And Instrumentation for laser guide star wavefront sensing)
Período documentado: 2020-09-01 hasta 2022-08-31
One of the biggest problems for telescopes placed on the ground are the optical aberrations produced by the atmospheric turbulence when observing sky objects. Fortunately, technological progress made possible the development of Adaptive Optics, a technique which enables real-time correction of the atmospheric distortions, hence providing improved image quality to the scientific instruments in the telescope. Thanks to adaptive optics we are capable to identify planets outside the solar system and also to observe the motion of stars around the black holes in the center of our galaxy.
A key technology in adaptive optics are lasers that can produce bright spots of light in the upper atmosphere, also called laser guide stars. Laser guide stars are essential to extend the observable sky where adaptive optics can be employed, providing astronomer with more and better information about the universe.
In this project, we investigated methods and technologies that tackle the fundamental limitations of laser guide stars in current and future adaptive optics systems. We studied how a multi-color laser guide star can be generated and evaluated how this could enable an adaptive optics system to correct for the fast lateral motion (jitter) of stars arising from atmospheric turbulence. We contributed to the development of the PAPYRUS adaptive optics bench, which has been in operation at the Observatoire de Haute-Provence in southern France, providing a pyramid-based adaptive optics system to the whole community for experimenting new concepts and technology. In addition, we developed a prototype of a laser guide star wavefront sensor for one of the first instruments of the Extremely Large Telescope. This prototype helped to validate a new wavefront sensor camera and to test the optical design of the wavefront sensor for the first time in a controlled environment. This part of the work provided valuable information for the final design of the laser guide star wavefront sensor.
A key technology in adaptive optics are lasers that can produce bright spots of light in the upper atmosphere, also called laser guide stars. Laser guide stars are essential to extend the observable sky where adaptive optics can be employed, providing astronomer with more and better information about the universe.
In this project, we investigated methods and technologies that tackle the fundamental limitations of laser guide stars in current and future adaptive optics systems. We studied how a multi-color laser guide star can be generated and evaluated how this could enable an adaptive optics system to correct for the fast lateral motion (jitter) of stars arising from atmospheric turbulence. We contributed to the development of the PAPYRUS adaptive optics bench, which has been in operation at the Observatoire de Haute-Provence in southern France, providing a pyramid-based adaptive optics system to the whole community for experimenting new concepts and technology. In addition, we developed a prototype of a laser guide star wavefront sensor for one of the first instruments of the Extremely Large Telescope. This prototype helped to validate a new wavefront sensor camera and to test the optical design of the wavefront sensor for the first time in a controlled environment. This part of the work provided valuable information for the final design of the laser guide star wavefront sensor.
The first work package (WP1) consisted of investigating the feasibility of measuring tip tilt from multi-wavelength laser guide star. For this, the following activities were carried out.
• Reviewed full literature and previous work on this topic. Created a database shared among researchers involved in this work.
• Evaluated the photon-return flux with an upgraded version of the LGSBloch package for Mathematica including two-photon excitation (589 nm + 569 nm) from 3S1/2 level to 4D5/2 in atomic sodium.
• Determined the maximum achievable return flux on each detection wavelength for state-of-the-art sodium lasers (20W and 50W output power).
• Determined the fundamental sensitivity of tip-tilt detection with polychromatic laser guide star as a function of the aperture of the receiver telescope.
Results were discussed among peers and the possibility of elaborating research projects dedicated to exploring this application was proposed. Simulation code and documentation with results were produced and are available on demand.
The purpose of WP2 was to study and explore alternative wavefront sensing methods for laser guide stars and laser guide star generation. Activities carried out in this context were:
• Using the LOOPS bench at LAM to evaluate the options to emulate a laser guide star with spatial light modulator.
• Development of a laser guide star proxy. Two original lab demonstrators were developed: one based on a Rhodamine 6G capillary tube, and a second one with an engraved glass cube. These proxies were incorporated in the LGS Bench (see WP3).
• Modeling of LGS wavefront sensing with a pyramid wavefront sensor. This activity was carried out by a supervised exchange Msc student who will continue this work as a PhD student of LAM.
• A collaborative project with ESO on mirror phasing with pyramid wavefront sensor was started. Preliminary results were presented at several workshops.
The purpose of the WP3 was to develop a new LGSWFS prototype, incorporating innovative and validating new technology such as microlens array, detectors, spatial light modulator and light sources. The following activities were carried out:
• Performed the optical design of a test bench.
• Characterized and validated a new CMOS sensor for LGS wavefront sensing.
• Developed analysis code.
• Characterized a spatial light modulator (SLM) for emulating the extremely large telescope primary mirror. The use of SLM is becoming very attractive in the AO community to emulate/calibrate optical systems. We have shared our findings with our colleagues as well as provided feedback to the manufacturers who were unaware of this type of specific applications with SLMs.
• Characterized light sources, including laser and LED.
• Contributed to the design, tests, and commissioning of the PAPYRUS pyramid bench.
Regarding outreach and dissemination of the MSCA, the following activities were carried out:
• Chaired one session of workshop on AO4Astro2 (remote).
• Organized laboratory seminars at LAM.
• Participated in the scientific organizing committee AO4ELT8 Workshop in Valparaiso.
• Participated in Fête de la Science and Science is Wonderful outreach activities.
• Supervised international student visitors at LAM.
• Reviewed full literature and previous work on this topic. Created a database shared among researchers involved in this work.
• Evaluated the photon-return flux with an upgraded version of the LGSBloch package for Mathematica including two-photon excitation (589 nm + 569 nm) from 3S1/2 level to 4D5/2 in atomic sodium.
• Determined the maximum achievable return flux on each detection wavelength for state-of-the-art sodium lasers (20W and 50W output power).
• Determined the fundamental sensitivity of tip-tilt detection with polychromatic laser guide star as a function of the aperture of the receiver telescope.
Results were discussed among peers and the possibility of elaborating research projects dedicated to exploring this application was proposed. Simulation code and documentation with results were produced and are available on demand.
The purpose of WP2 was to study and explore alternative wavefront sensing methods for laser guide stars and laser guide star generation. Activities carried out in this context were:
• Using the LOOPS bench at LAM to evaluate the options to emulate a laser guide star with spatial light modulator.
• Development of a laser guide star proxy. Two original lab demonstrators were developed: one based on a Rhodamine 6G capillary tube, and a second one with an engraved glass cube. These proxies were incorporated in the LGS Bench (see WP3).
• Modeling of LGS wavefront sensing with a pyramid wavefront sensor. This activity was carried out by a supervised exchange Msc student who will continue this work as a PhD student of LAM.
• A collaborative project with ESO on mirror phasing with pyramid wavefront sensor was started. Preliminary results were presented at several workshops.
The purpose of the WP3 was to develop a new LGSWFS prototype, incorporating innovative and validating new technology such as microlens array, detectors, spatial light modulator and light sources. The following activities were carried out:
• Performed the optical design of a test bench.
• Characterized and validated a new CMOS sensor for LGS wavefront sensing.
• Developed analysis code.
• Characterized a spatial light modulator (SLM) for emulating the extremely large telescope primary mirror. The use of SLM is becoming very attractive in the AO community to emulate/calibrate optical systems. We have shared our findings with our colleagues as well as provided feedback to the manufacturers who were unaware of this type of specific applications with SLMs.
• Characterized light sources, including laser and LED.
• Contributed to the design, tests, and commissioning of the PAPYRUS pyramid bench.
Regarding outreach and dissemination of the MSCA, the following activities were carried out:
• Chaired one session of workshop on AO4Astro2 (remote).
• Organized laboratory seminars at LAM.
• Participated in the scientific organizing committee AO4ELT8 Workshop in Valparaiso.
• Participated in Fête de la Science and Science is Wonderful outreach activities.
• Supervised international student visitors at LAM.
The work performed in WP1 advanced the knowledge on the mechanisms of tilt correction with polychromatic laser guide star and to better understand the conditions at which this technique could bring real benefits to adaptive optics observations. In addition, we calculated numerically the photon return flux with multi-wavelengths laser guide stars using continuous wave lasers currently available, which so far has been done only with pulsed lasers. Corrections to previous models (transition cross sections in sodium) were also included. This study can serve as the basis for the design of a major project that demonstrates the polychromatic laser guide star concept with continuous wave lasers.
The exploratory worked in WP2 enabled the development of two original laser guide star proxies which can be used as a light source for laser guide star wavefront sensor benches. The access for experimentation and testing with laser guide stars is often very difficult, therefore the availability of a proxy that adequately scale the size and properties of an LGS in a laboratory will benefit any research activities on laser guide star wavefront sensing.
In WP3, a new sensor dedicated to laser guide star wavefront sensing was characterised and validated in the optical bench. As a result, this new sensor will be used in one of the AO instrument for the Extremely Large Telescope. Furthermore, the successful commissioning of the PAPYRUS optical bench will enable for the first time, community-wide on-sky access to a pyramid-based adaptive optics system. PAPYRUS is also aimed as a tool for education, allowing engineering and astronomy students to learn from a real AO system.
The exploratory worked in WP2 enabled the development of two original laser guide star proxies which can be used as a light source for laser guide star wavefront sensor benches. The access for experimentation and testing with laser guide stars is often very difficult, therefore the availability of a proxy that adequately scale the size and properties of an LGS in a laboratory will benefit any research activities on laser guide star wavefront sensing.
In WP3, a new sensor dedicated to laser guide star wavefront sensing was characterised and validated in the optical bench. As a result, this new sensor will be used in one of the AO instrument for the Extremely Large Telescope. Furthermore, the successful commissioning of the PAPYRUS optical bench will enable for the first time, community-wide on-sky access to a pyramid-based adaptive optics system. PAPYRUS is also aimed as a tool for education, allowing engineering and astronomy students to learn from a real AO system.