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Laser Pointing Camera - Telescope

The LPC-TLS is a compact system, including a telescope and a smart camera (with CCD detector on its first implementation and CMOS next cameras), that is used to assist a single or multiple Laser Guide Stars (LGS) Adaptive Optics (AO) system to precisely (1") pointing the guide stars to the expected sky position, with a precision that is very difficult or impossible to obtain in open loop. This is achieved by taking images of the pointed area with the LPC-TLS and using the on board astrometric software to find the real position of the LGS in the sky, thus allowing to communicate to the laser launch telescopes the ALT-AZ offsets to be applied to put the LGS in the correct position.

 

The LPC-TLS allows to have a fast pointing of single or multiple LGS on the AO wave-front sensor (WFS) during the initial acquisition phase of the telescope preset, thus reducing considerably the overheads currently experienced in most LGS-AO systems in operation.

 

By recognizing via astrometric software the field stars as well as the multiple LGS, LPC-TLS is insensitive to flexures of the laser launch telescope or of the receiver telescope opto-mechanics.

 

Moreover, LPC-TLS gives regularly the photometry and fwhm of the LGS, as well as the scattering of the uplink beams at the height of 10-15km, thus monitoring the presence and evolution of cirrus clouds.

 

Finally, besides eliminating the overhead of the LGS acquisition in the AO WFS during operation, the LPC-TLS is a very powerful tool during the calibration of the lasers pointing and WFS wobbling during LGS AO systems commissioning.

Several LPC-TLS implementations are currently installed at ESO VLT in Chile, Gemini North at Hawaii and IAC ORM at La Palma - Spain.

LPC-TLS main features

The LPC-TLS is composed by a mounted telescope coupled with an AST492 ‘smart’ camera including an integrated filter wheel and on-board computing processor, based on Linux OS running special customized software.

  • Telescope:

    • Maksutov 150mm f/12

    • INVAR mounted for thermal stability

    • Field of view of ~35x25 arcmin

    • Fixed focus up to 20°C delta T, option for electrical focuser

    • Field derotator

    • Customizable mechanical interface to the observatory telescope

    • Wind and dust protection box with motorized cover

    • Dimensions: 70x45x45cm

    • Total instrument weight: 35Kg

  • CMOS Sensor:

    • Sony IMX492 Monochrome, 46 Mpxl

    • 8192 pxl (H) x 5648 pxl (V)

    • Quantum Efficiency (peak) 80%

    • Readout noise 1.7e-

    • Pixel size 2.315 um (H) x 2.315 um (V)

    • Binning 1x1 and 2x2 (hi-res) and 4x4 (normal operation)

    • 12 bit ADC, 14 bit bin 2, 16 bit bin 4

    • 2 fps (download time only, no post processing)

  • Processing Unit:

    • microprocessor Intel ATOM E3940 quad core 1.8GHz

    • 4GB DDR3L

    • 32GB eMMC + SSD 256 GB

    • industrial temperature range

    • LINUX operating system

    • RTC Battery

    • 3x Companion Microchip SAM3S microcontrollers for realtime system management

    • Internal USB connectors

  • Connectors on Panel:

    • Supply 24V @ max 2700mA with remote On/Off input 

    • Opto-isolated 24V Discrete INPUT: IN_1, IN_2

    • Opto-isolated 24V Discrete OUTPUT: Watchdog, Laser_Trigger

    • Single or dual fiber/LAN Gigabit Ethernet

  • Cooling:

    • Peltier Cell controlled by uP

    • Sensor operating temperature setpoint: 0 to 10°C

    • Options for air, liquid or surface contact dissipation

  • Filter Wheel:

    • Integrated 7 positions

    • Filter size 1.25” mounted

  • Integrated Software:

    • LPC software suite for LGS position identification and offset calculation (3σ error ≤1 arcsec in ALT AZ with ~5s + exposure calculation time)

    • LGS return flux (phot/s/m2), LGS fwhm in arcsec and the uplink scattering intensity (phot/s/sec/arcsec2)

    • Simple TCP/IP commands interface
  • Complete support service: customization, commissioning and maintenance during operation

Ordering Information

p/n LPC-TLS-01

Please contact info@astrel-instruments.com for price, delivery time, documentation and any further customization requests.

LPC-TLS application: ESO Paranal UT4 telescope 4 LGS unit

LPC-TLS has been developed by Astrel Instruments and INAF-OAR (Italian National Institute of Astrophysics - Rome Observatory) for the 4LGSF of the ESO Adaptive Optics Facility, and installed on the UT4 telescope at ESO Paranal Observatory. The LPC-TLS commissioning followed the standard ESO path for the installation and verification of new instrumentation and has been timed by the commissioning phases of the main project, the 4LGSF. LPC-TLS passed provisional acceptance tests in Garching ESO Headquarter (November 2014) and it was then delivered to Paranal for local acceptance and installation on UT4 during April 2015.

LPC-TLS is currently a fully operational instruments on UT4.

LPC-TLS commissioning started after the control software integration with the 4LGSF workstation, with its alignment to UT4 optical axis and preliminary astrometry verification of plate scale, focus and sensitivity. During the 6 following nights it was thoroughly tested using the return signal from the first of the four LGS of the new 4LGSF already activated. After two commissioning runs all the design requirements of LPC-TLS are fully satisfied. The main results are highlighted in the following list:

  • LPC-TLS is functional on the 100% of the sky (full sky coverage), including  empty or crowded star field areas

  • The average time to return the pointing correction to the 4LGSF is about 60 seconds including the exposure time, with the exception of the 47 Tuc field where, due to the paramount number of stars, it takes about 2 minutes

  • End to end budget error for pointing correction is within 1” per axis

  • The average astrometric precision is < 1 arcsec at 3 sigma

  • The photometric precision when exposing for 4 seconds the LGS using a calibrated V-band filter is better than 0.1 mag.

  • The system is operative with Na return flux from 1Mphot/m2/s to 45Mphot/m2/s

  • The passive fan-less heat dump system of the camera Peltier cooler works for a full night without overloading

  • LPC-TLS is ready to be operative from a cold start in less than 5 minutes

Images Copyright by ESO