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Southern African Large Telescope (SALT) Projects

Prime Focus Spectrograph Optics: RSS Collimator Triplet + Doublet Lens Groups

Some of the collimator optics in SALT’s workhorse spectrograph needed replacing. The
individual lenses had been manufactured years previously and in 2021, SALT contracted the
company in California that did the original optical integration to produce a new triplet lens
group. The three extremely fragile, expensive lenses had to be shipped across the world
with the utmost care. Once complete, the new assembly would then have to safely make its
way to South Africa, without SALT incurring additional costs for exporting and importing
lenses that had already been paid for previously. IFS expertly handled this incredibly nerve-
wracking process, including all of the complicated paperwork to ensure that SALT would not
be charged inappropriately for all the back and forth. All of this worked so well for the
triplet lens group that in 2022, SALT decided to do the same for the pair of lenses that
comprise the collimator doublet. The two lenses were shipped to Los Angeles a few months
ago and the new assembly is due to arrive in SA within a couple of weeks. These two new
lens groups will be installed in the spectrograph early next year and will significantly
improve the performance of the instrument.



One of the large Calcium Fluoride lenses that make up the spectrograph’s collimator triplet.


One of the three packing cases used to ship the fragile triplet lenses to California.


Inspecting the beautiful new collimator triplet assembly upon its arrival in Cape Town.

Atmospheric Dispersion Compensator Prisms

In preparation for receiving its new near-infrared spectrograph, SALT had to replace its atmospheric dispersion compensator (ADC).  The original ADC’s lenses (which are actually large, wedge-shaped prisms) had coatings that would not transmit infrared light.  Rather than risk trying to polish off those coatings and then recoat the prisms, a company in Italy was contracted to manufacture new prisms with the required coatings.  IFS was then responsible for safely bringing these precious new prisms into the country and delivering them to the Observatory for integration into the new ADC assembly.



One of the large prisms that make up SALT’s new atmospheric dispersion compensator (ADC).


The second prism being integrated into the new ADC assembly.

New Diffraction Grating

SALT ordered a new volume phase holographic diffraction grating for its prime focus
spectrograph from a company in the United States. The safe arrival of his beautiful but
fragile and rather costly optic was thanks to IFS, who did their usual fantastic job of handling
all of the paperwork and other practicalities.



New volume phase holographic grating for SALT’s prime focus spectrograph.

Near-Infrared Spectrograph: Instrument, Optics + Fibre Cable

For more than a decade, the University of Wisconsin’s Washburn Labs instrumentation group worked to build a near-infrared (NIR) spectrograph for SALT.  Upon the completion of such a task, there can then be few more daunting things than having to pack up such precious cargo and freight it across the world!  IFS took expert care of the logistics and paperwork to ensure that all of the parts – some traveling by ship and others by air – made it safely around the planet and ended up in the requisite number of pieces at the telescope in Sutherland.  



The NIR spectrograph shipping container from Wisconsin being delivered to SALT.


Crates containing all of the intricate NIR optics and the spectrograph’s detector system, stored in the spectrometer room up at SALT after being safely delivered across the world.


Unloading the crate containing the NIR fibre cable from the truck that delivered it directly to the telescope.


The large white cold-room is the thermal enclosure that houses the new NIR spectrograph in the SALT

spectrometer room.


The new NIR spectrograph, fully assembled within its thermal enclosure at SALT.

Laser Frequency Comb Hardware

SALT is working with collaborators in Scotland to build a precision wavelength calibration
device for the telescope’s high-resolution spectrograph. This project involved a great deal
of procurement from vendors located around the world. Since these components are
sensitive, fragile and expensive, great care is required to safely transport them. IFS
successfully handled the importation of all of these orders, but then to add to the
complexity of all this, the main laser for the system turned out to be faulty. The large crate
therefore had to be shipped back to the UK for warranty repairs, after which it will be
returned to SA. Once more, IFS came to the rescue to smooth the way through this
challenging situation. 


The main laser system for the SALT laser frequency comb

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