Laser Launch Telescope

A big milestone arrived this week. The launch telescope arrived from the manufacturer. It is an impressive instrument itself, a half meter aperture, an extraordinarily short focal length, made to very exacting precisions, even for optics. It is a cassegrain design with an focal ratio of f/1. The primary is coated with a custom coating designed for maximum reflectance at the 589nm sodium D line, where the laser will operate. This gives the primary a notably orange cast that is quite beautiful. The entire telescope is enclosed in an airtight aluminum shell with the optics supported on a carbon fiber frame within.

Laser Launch Telescope
Kenny Grace inspecting the Keck 1 laser launch telescope during incoming inspection after unpacking
This is one of the key components in creating a laser for the Keck 1 adaptive optics system. An enormous amount of work has gone into preparing for the laser… modifications to the structure of the Keck 1 telescope, cabling, electrical power and liquid cooling plumbing. An insulated room built on the side of the telescope to house the laser and a safety system to comply with laser safety regulations. All of this in preparation for the arrival of two key components, the laser itself and the launch telescope that will focus this light into a clean beam rising into the night sky over Mauna Kea.

The entire assembly will mount behind the secondary of K1. This is different than the current laser in Keck 2 that is emitted from a launch telescope along the side of the main telescope. Having the laser on the side creates some problems for the AO wavefront controller, the artificial guidestar can be elongated by parallax when seen from the other side of a ten meter telescope. Having the laser launched from the center of the main telescope is a far more optimal solution. But doing that takes a far more difficult to design and build launch telescope as it has to be extraordinarily compact.

We expect delivery of the laser itself in May. Our laser engineer has been working with the laser manufacturer to insure it meets all specifications. Reports indicate it is not only meeting those specifications, but surpassing them. When we take delivery there will be a period of testing before the equipment is trucked to the mountain for installation in its final position.

The coming week will be fun, need to string a new set of cables to the Keck 1 secondary mirror. This means 150 feet of cabling from the Nasmyth Deck, up the tubular structure of the telescope and across the spider to the secondary. On a ten meter telescope this means a lot of high work from the personnel bucket of the jib crane among the girders of the telescope. This is going to be fun!

Author: Andrew

An electrical engineer, amateur astronomer, and diver, living and working on the island of Hawaiʻi.

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