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Laser Guide Star Launch Telescopes

By illuminating the sodium vapor layer at the top of the atmoshpere, laser launch telescopes are used to create artifical guide stars for adaptive optics systems for astronomy. The laser launch telescope must maintain spectral quality while expanding and collimating the sodium vapor frequency beam. A wavefront sensor examines the artificial star to measure atmospheric disturbance, and control a deformable mirror to correct the telescope's vision.

TNO has delivered 5 laser launch telescopes with a thermally insensitive design, currently in operation at the VLT. The combination of  large field of view (FOV) and  small wavefront error (< 50 nm) led to the use of a large (Ø 380 mm) convex aspherical L2 lens. This L2 is particularly difficult to manufacture and measure. TNO provided an L2 which met and exceeded requirements thanks to the use of its unique in-house NANOMEFOS machine, which allows the surface form to be measured directly, giving feedback to computer controlled deterministic polishing at TNO.

Laser launch telescope assembly ready for delivery to ESO (for VLT)



A wavefront sensor examines the artificial star to measure atmospheric disturbance, and control a deformable mirror to correct the telescope's vision.

The key techical specifications of the design include:

Schematic overview showing main components
  • Athermal design to minimize defocus due to thermal effects
  • Input source beam diameter: 15 mm
    (source provided by ESO, key components supplied by Toptica and MPBC)
  • Beam expander ratio: 20x (300 mm diameter collimated output beam)
  • Transmitted wavefront error: 17-23 nm rms (required < 50 nm rms)
  • Thermally induced defocus: 0.15 waves PV (required <0.2 waves rms)
  • Pointing accuracy on-sky: < 0.2” at 3x rms (required 0.3” at 3x rms)
  • Polarization extinction ratio: > 99.5 % (required > 98 %)
  • Throughput: 97.7 % (required > 95 %)
  • Field selector mechanism: 4.8 arcmin radius FOV (design can accomodate larger FOV)

Use of this pre-existing design, with minimal modifications, can imply significant cost savings versus a new development. TNO's VLT Laser Launch Telescope design has also been considered as a baseline approach for both the ELT and GMT telescope systems.

Please contact us to discuss adapting the Laser Launch Telescope to your requirements.

mr. Matthew Maniscalco MSc, JD, LLM

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mr. Matthew Maniscalco MSc, JD, LLM

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