What would you say are the biggest challenges and trends underway in astronomy right now?
It is unquestionable that only within this decade our understanding of the Cosmos has been transformed in an extraordinary fashion and astronomy, has contributed enormously towards this and in many different directions. This has opened a number of new opportunities but also generated a number of new challenges.
For example, using ESA’s Planck space telescope, in 2013, scientists were able to retrieve data and construct the most detailed map ever created from the cosmic microwave radiation (CMR). The significance of this lies on the fact that microwave background radiation carries specific signature patterns as they were imprinted on the sky at the very early Universe. Remarkably, these observations match to an amazing degree the theoretical predictions of inflation models about the beginning of the Universe, and which, if proven to be correct (by further support from other indirect observations), it could mean that we will have managed to gain an insight to the first tiny fractions of a second (10-39 seconds) after its creation - by indirect observations alone. In order to make any meaningful measurements, and to be able to detect the tiny fluctuations present into an impressively isotropic universe, the telescope required to have a resolution of better than 10 ppm, a target that was previously thought to be a nearly unattainable pursuit.
Even more recently, in September 2015, the LIGO (Laser Interferometer Gravitational-wave Observatory) allowed scientists to detect, for the first time, ripples (gravitational waves) in the fabric of spacetime generated by the violent collision between two massive black holes. This observation has confirmed a major prediction of Einstein’s general theory of gravity, that was made 100 years earlier (100-year anniversary), and has opened a brand new window of opportunity for observing areas of the Universe where spacetime is warped by exotic heavenly bodies and to study phenomena that were previously inaccessible to our detection instruments.
The success of LIGO (USA), essentially constitutes the birth of a new type of astronomy where the fabric of space and time itself, and not just the heavenly bodies, is observed and analysed. This is obviously a fascinating and an incredible new quest. In order to achieve this tremendous task, the instrument required to realise a resolving power that equates - in terms of change in the lengths of the arms - to an astounding one-ten-thousandth of the diameter of a proton (10-19 metre)! Efforts are currently directed towards combining a number of such observatories around the world, such as the LIGO (USA), VIRGO (Italy), LIGO (India), and others, to spawn an interconnected network of observatories that will hopefully allow detection and analysis of new phenomena and give an insight to the cosmos that otherwise would not be possible.
Another exciting area of work, is the detection, mapping and analysis of exoplanets. Exoplanets are remote planets which are outside our planetary system and are orbiting other stars. Such planets are very difficult to detect as they are masked by the strong light emitted by their nearby star. Since the first scientific observation of an exoplanet back in 1988, several more such bodies have been detected, now reaching to be several thousand. The discovery of such planets has intensified the interest among scientists in their search for extra-terrestrial life and earth-like planets that orbit around what is known to be, a ‘star’s habitable zone’. There is a particular interest, in those planets that are likely to hold liquid water on their surface since water is considered to be a vital component for the existence and support of life. The Keppler Space telescope is one such example of an instrument that has been very successful in discovering many exoplanets in the recent years amounting to date to more than two thousand.
Considering the aforementioned, it becomes apparent that the general trends and challenges in astronomy is to access and study areas of the Cosmos, either directly or indirectly, that were previously thought to be inaccessible by conventional astronomy, either because events are beyond of what is considered to be our horizon of observation or, because objects are invisible, obscured, or too remote, making their observation particularly tricky. In almost all these pursuits, the field of optics has played, and remains to play, a pivotal role in advancing science in general and astronomy in particular.
Have the demands of astronomy increased over the years with the advancement of optical technologies?
I believe that there has been a two-way interaction between the two. The demands of astronomy have pushed significantly towards the advancement of optical technologies, but also the advancement of optical technologies has inspired scientists involved with astronomy to pursue greater goals.
Over the past few years, it is unquestionable that there have been great advances in several areas that relate to optical manufacturing such as testing, quality of materials available and also, coatings.
It is now possible for example, to acquire high quality technical glasses and ceramics that exhibit very high homogeneity and possess many other desirable properties weather these are physical, optical or mechanical. Polishing compounds have also improved substantially allowing improved manufacturing while, at the same time, a range of technical coatings performed at very tight manufacturing tolerances has become available even on large optics. These tolerances are achieved using different coating technologies allowing us to attain improved reflective or, anti-reflective, performances, homogeneities, and enhanced environmental stability, protection and durability.
However, I think that at the heart of the advancement of optics has been the wide availability of new generation interferometers, which make it possible to measure the accuracy of the manufactured optics to an incredible level and with great reliability. These new interferometers use advanced measuring techniques and sophisticated analysis software at their core. It is not very long time ago that opticians used to say: ‘if I can measure it, I can make it’. Now it is possible to measure it, and much more than that. It is also possible to measure parameters such as slope errors, mid-spatial frequencies, waviness, micro-roughness, and many other data and to an astounding level of accuracy.
Today, optical technologies allow you to manufacture complex optical surfaces to an accuracy that is comparable to a tiny fraction of a wave, or in other terms, to an accuracy that it is within few 10’s of the diameter of an atom, and indeed have the confidence to make this claim as it is backed by reliable measurements and analysis data. Many other sophisticated optical technologies such as sensitive spectrometers, other measuring equipment, coating chambers, advanced optical and mechanical design software have all contributed in raising the bar in the expectations of manufacturing optics and optical assemblies as a whole, inclusive those related with astronomy applications.
Are there any current hindrances in manufacturing capability that are preventing the advancement of optics for astronomy?
In pursue of expanding the boundaries of our existing knowledge and understanding of the cosmos, the current trends in astronomy optics are, as someone would expect it, to go for larger, more complex and, of course better. However, although testing, as well as manufacturing capabilities have improved greatly, and available manufacturing technology options such as MRF (magneto rheological finishing) and robotic polishing, have increased significantly over the past few years, such projects still pose major difficulties and are extremely costly and difficult to realise. Even if the costs and the related difficulties in achieving high optical performances at these scales is momentarily ignored, it is difficult to ignore the extraordinary manufacturing capacity requirements and the demanding and mind blowing needs in manufacturing speeds to produce the high number, large and demanding multi-segment mirrors, that are required for such complex telescope arrays.
Despite these great hindrances, the pursuit of realising massive telescope arrays is justified by the fact that such super structures allow us to detect and study habitable exoplanets or massive black holes by tracing the perturbed orbital path of the nearby stars (such as the one present in the centre of our galaxy), to achieve amassing angular resolutions, and to be able to observe remote stars that were born in the earliest era of star formation of our Universe – just to name few.
Some examples of such massive super-structures (other than the LIGO) are, the currently under construction ELT (Extremely Large Telescope) which, is expected to become operational by 2024, or the VLT (Very Large Telescope) array that became fully operational back in 2000 and with some additional capabilities having been added to it between 2004 and 2007.
Have any advancements in astronomical optics in recent years been driven by other applications areas of photonics? Alternatively, do you think advancements in astronomical optics could benefit other photonics application areas?
That is quite a tricky question. There is no doubt that there are some application areas in photonics that there may be a more apparent connection with astronomical optics and vice versa. Most likely nearly all fields of optics could benefit with advances in another application area since, as more optical tools emerge and become available, they can easily turn into a source of inspiration and know-how for scientists, optical designers and engineers that work in apparently diverse fields.
However, it is difficult to ignore that there are naturally few application areas that do display a stronger correlation with challenges that are also present in astronomical optics and these are more likely to benefit from advancements made to one field of application or the other. Such applications could be, for example, areas of photonics that relate with surveillance or satellite earth-observations. Such satellite telescopic cameras are often used for mapping of the earth’s resources or to study and monitor climatic changes or for other more general purpose meteorological applications. Similar optical technologies are often used for defence purposes as well. Another relevant defence application may be the development of novel advanced tactical weapons such as LAWS (lAser Weapon Systems) – just to name few.
Many of these applications, often need to deal with similar problems as in astronomical optics, and these may be for example the larger size of optics involved or dealing with similar issues such as; varying gravity effects (or lack), atmospheric perturbations that can affect the quality of the observations, adverse operating environments and thermal loads, requirements for special type of mounting, dealing with extreme dynamic loads, vibrations, shock effects, and generally parameters that increase the needs for resilience, stability, reliability and environmental durability.
It is obvious that such applications that share more similarities and have common challenges to resolve (such as the ones described above) are the most likely to benefit the greatest by optical advancements made to one application or the other.
