Optics allow distant places to be seen in focus but Rob Coppinger peers into the universe of astronomy where the vision of deep space is also the past
Optics have been important to astronomy ever since Galileo Galilei built his first telescope and peered into the night sky in the late 16th and early 17th centuries. Galileo could not have conceived of the space-based observatories now encircling the Earth or that some of their components come for Chelmsford, England.
Kimberly Loft is an astrophysicist and technical sales engineer for Chelmsford-based Laser Components: ‘We are able to provide stock astronomical filters as well as custom filters. We also supply lenses to remove aberration. We do have a range of products useful for astronomy, other than optics.’
Laser Components’ products have been used for the US Naval observatory and the International European Southern Observatory, which is actually based in Chile. Laser Components’ products have also gone in to space-based observatories where they have to be operational at a wide range of temperatures. They also need to be radiation resistant, owing to the extreme environment present in space. For the products to withstand these extreme conditions, Laser Components’ suppliers and filter partners use ion beam sputtered coatings. ‘We use methods such as this to sustain the launch stress and to provide a long stable performance afterwards,’ explains Loft.
Laser Components’ partner, Omega Optical, uses hydrogen alpha and beta filters. These isolate the alpha or beta line of the spectrum respectively and block out the rest. ‘With hydrogen beta you can view faint nebulas with hydrogen beta emissions,’ adds Loft. Other filters will block out all wavelengths except double or triple ionised oxygen and, with these, astronomers can look at the Ring Nebula and the dark sky, where there are apparently no stars until examined more closely. The main issue with terrestrial observatories is the Earth’s atmosphere. As well as distorting light, causing the stars to appear to twinkle, the atmosphere absorbs ultraviolet and infrared light. ‘The key improvement would be to find solutions to the difficulties caused by the Earth’s atmosphere, allowing for better resolution images from terrestrial observatories to be taken,’ says Loft. The atmospheric aberration can be diminished with the right optics but solving the issue of key wavelength absorption is more difficult, according to Loft.
One answer is to put the observatory into space. The Hubble space telescope being the most well-known of the space-based observatories, it and others are looking for extra-solar planets. In particular, the French Corot spacecraft and NASA’s Kepler are both looking for possible new Earths. Loft explained that: ‘The main resources are the space programmes’ efforts to find extra solar planets and the different methods used. These methods include examining the radial velocity and observing the gravitational micro lensing of distant objects. All these techniques require sensitive optics and a greater blocking of unwanted light to improve the signal to noise ratio.’ So, extra-solar planets present a challenge that will require scientists to find better techniques to detect the different objects in space with new solutions and new optics.
Analysing the light from extra-solar planets will enable scientists to determine the make-up of the atmospheres and therefore if the planet harbours life. To ensure the detectors are only getting the correct light and not stray light from other sources, such as the Earth’s Sun, the space agencies use special software to understand how different optic systems will deliver light to the detector sensor. Michael Gauvin is vice president for sales and marketing at Lambda Research. He says: ‘We started TracePro under a small business innovation research [SBIR] phase one and two contract for NASA for stray light studies. We did two different SBIRs for NASA. The first was to develop TracePro and what they required was a product they could quickly use to analyse and remove stray light in any ground or space based telescope or satellite system.’ Lambda Research works with almost all of the Fortune 500 companies that do stray light projects. ‘These companies are constantly doing projects all the time [with TracePro] and in many of these projects the customer works without our support,’ adds Gauvin.
TracePro, and Lambda’s other product Oslo, are tools for designing and analysing optical systems. ‘We created TracePro, which is a CAD optical modeller based on the Acis kernel from Spatial Corporation, which is now owned by Dassault Systemes and gives us our CAD capability. Lambda added the optical ray tracing capabilities to create a complete 3D opto-mechanical modeler,’ says Gauvin.
Both TracePro and Oslo have been used to design and analyse various NASA optical systems, including the James Webb Space Telescope and the Terrestrial Planet Finder Coronagraph, and the optical design for the ground-based Large Synoptic Survey Telescope (LSST), which is based in Chile. Oslo has 900 systems in its database and these have been created and patented during the course of Oslo’s many years in the market. ‘Oslo is a spreadsheet-based programme where you define your surfaces and materials that you want to use for each one of the different lenses and mirrors in the system and then you specify what parameters you want to optimise for these mirrors and lenses,’ explains Gauvin. ‘And based on optical algorithms Oslo then defines the best optimal system based on the merit function and image you’re requesting.’
TracePro has been used to simulate optical systems operating at wavelengths ranging from the extreme ultraviolet, through the visible and infrared, and out to millimetre waves. It has an interface that makes it possible to pick up the program after a brief period working on user-based projects.
‘The LSST used Oslo to design the telescope’s mirrors. The LSST rapidly scans the entire sky every few nights taking 15-second exposures every 20 seconds. To achieve this exposure rate they have to move the entire camera the size of a Volkswagen bus extremely quickly around on a gimbal since it’s a ground based telescope,’ says Gauvin.
The LSST will produce a wide-field astronomical survey of the universe using its 8.4-metre mirror. The LSST uses a 3,200 Megapixel camera with its primary and tertiary mirrors and their two aspherical optical surfaces. All of the data generated by the digital camera will require 30 Terabytes of data management every night.
Hubble, which has a 2.4-metre primary mirror, does not encounter the atmospheric problem. Dr Emile Schyns is a product manager with Photonis, which has technology onboard Hubble. ‘We recieved a NASA award for our custom made MCPs for the Cosmic Origin Spectrograph. It was installed on Hubble in May 2009, the last service mission of NASA,’ explains Schyns. ‘It worked about 1,000 times better than the previous one.’ For space projects Photonis’ main customers are the European Space Agency, NASA, universities, the Jet Propulsion Laboratory, and other national space agencies such as the Netherlands, France and the UK.
Space-based or ground-based, ring nebula or extra-solar planet, optics is always going to play a crucial part in the analysis of light from deep space that can tell us more about how the universe evolved and what its future holds.