National HE STEM Programme

Transcription

1 National HE STEM Programme Telescopes to Microscopes:- Adaptive Optics for Better Images Prof John Girkin Department of Physics, Durham University, Durham This project developed a practical adaptive optics system to demonstrate the role that optics plays in modern astronomy and microscopy. The practical demonstration was supported with posters and a discussion with the attendees with post graduate, post doctoral and academic staff. The system was demonstrated, within the time available, to several groups of children and their responses logged and based upon this minor modifications have been made to the display which will subsequently be used at the Durham Science Festival (October 2012), British Association Science Festival in Newcastle and Chelmsford in 2013 and an application will be made to the Royal Society Summer Event for 2013.

2 Background Despite the totally different scale of the objects that they are observing astronomical telescopes and optical microscopes have a great deal in common and developments in both fields have led to advanced discoveries in the basic principles of optics over hundreds of years. One specific challenge in both imaging systems is that to observe their targets the light has to travel through a wide range of materials which affect the optical properties of the light. In the case of ground based telescopes these aberrations are caused by the air and the associated local changes in refractive indices, in microscopy as one images more deeply one has to observe through more tissue and the structure of the sample causes aberrations. Over the past twenty years significant resource has been provided to research and overcome these problems in astronomy and a number of active optical elements have been developed to remove the aberrations. These adaptive optics are now so advanced that ground based telescopes can now frequently produce higher quality images than those from space bourn systems. Recently the cost and size of such systems has fallen dramatically and the methodology has now been applied to optical microscopes where there has also been a rapid advance in new imaging modalities (multi- photon microscopy, sub- diffraction limited imaging, high speed microscopy). Using adaptive optics it is now possible to image at depth (in excess of 1 mm) with sub- micron resolution. Thus adaptive optics is linking two areas of general scientific interest, astronomy and the life sciences, through the use of advanced optical technology. The aim of the demonstration was to show how basic optics is linked with advanced technology to solve a wide range of problems thus showing the importance of core STEM science to advanced research in other fields. The specific objectives during the limited initial time of the project were to 1) Develop a small breadboard system showing the basics of adaptive optics. 2) Show the system to groups of school children from local schools in the Northeast for feedback. 3) Based upon the feedback improve the system for use in the coming year at several scientific outreach events. 4) Build best practice for such demonstrations.

3 Demonstration System Images of the system, without the cover, are shown below. The object being imaged in the above configuration is a photographic slide (in this case of the Mona Lisa) but the system is flexibly designed and the slide (which can be of an galaxy, star system or biological sample) can also be replaced with a microscope objective and real biological sample. The image from the sample is then relayed via the lenses and optics onto the active optical element, in this case a deformable mirror (top right in the upper image) before being directed onto a science camera. In addition to demonstrate the use of a laser guide star a low power laser diode can follow a related optical path, go onto the object and be reflected back through the imaging optical system, off the deformable mirror and into a wavefront sensor which measures the optical

4 aberrations. A computer then controls the mirror to remove the aberrations present. In the above system the aberrations can be added in two ways. In the first a rotating plate, with poor optical quality, is placed in the imaging path. As this is activated the image on the science camera degrades. The adaptive optics can then be switched on and this image degradation is removed in a closed loop manner. It is also possible for closed loop system to be switched off, the aberrating plate removed and the mirror shape controlled manually. Thus the participants (children in the evaluations to date) can manually change the shape of the mirror and see the effect on the image quality. The system provides some level of quantification if the audience are older and can thus be presented with more advanced concepts. The aberrations added can be described as Zernicke terms (the mathematical representation of such aberrations) as well more simple qualitative descriptions such as astigmatism. Such effects can clearly be seen on the image and links made through to ophthalmic correction (although a clear distinction has to be made with defocus). Several image quality metrics are also displayed (such as contrast, brightness) and these are monitored in real time as the closed loop system, or manual alterations, are made. This is then used to demonstrate to the audience that it is possible to quantify many abstract quantities including image quality an important general concept in STEM subjects. Results and Outcomes The optical demonstration, as shown above, has been built and operates. It is robust enough to be moved around both the Durham University site and also off campus either by hand or in a car. It is controlled with a laptop computer but for demonstration purposes this has now been linked to a larger display monitor. The majority of the audience appreciated the closed loop control though a clear interest was the ability to adjust the mirror manually to alter the image. This was not unexpected and it is hoped that by playing with the system some aspect of the science registered not just the fact you can distort an image. A follow- up questionnaire could have been undertaken to determine this but it was felt that this was well beyond the scope of the project. A basic questionnaire was produced and completed by the students in which they assessed the presentation, demonstration and there was space for comments. The feedback is summarised in graph 1. This is taken from 178 children with 86% saying that the display and demonstration was very good or excellent. The decision was made to make the questionnaire as simple as possible so that we had completed forms thus a more detailed analysis is not applicable at this stage. There were individual variations between the different demonstrators but the variation was at the level of one of five responses in 178! It was thus felt that the demonstration was helping the different demonstrators, who had significantly different levels of experience in outreach (from first timers to somebody with 20 years experience) convey the meaning and excitement of optical systems in the different applications. The demonstrators, although all

5 working in optical instrumentation were a mixture of astronomical instrumentation and optical microscopy developers thus the system appears to help both branches of science as a tool for outreach. 50% 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% Poor Okay Good Very Good Excellent Graph 1 Showing the student view on the overall presentation and display Discussion and Improvements The following are in the process of being improved as a result of the initial demonstrations:- 1) At future larger events (ie not directly with small groups in schools) a larger TV monitor will be used to demonstrate the images. This means a slight loss of resolution but significantly increases the impact of the display in a larger venue. 2) An improved banner is required. The original version contained images and a little explanatory text. This is being split into two items. A larger banner with both biological and astronomical images with a large title to catch the attention and then a smaller desktop poster explaining the demonstration in a few bullet points if the demonstrator is otherwise engaged. In a small venue the combined banner worked but logistics of talking through the system using the banner in a larger space were not suitable. Thus having the option of both formats is important so the demonstration can be adjusted to the venue, and audience. 3) A wider range of object slides is required. This requires some thought as having 35mm slides produced now is becoming increasingly difficult! We have identified one source however. 4) The system was used by a wide range of demonstrators and their experiences have been collected. One mistake that was made early on was not giving the demonstrators sufficient time to play with the system before they met their audience and all said that the third and fourth

6 explanations were much better! It also became clear that the flexibility in the system was a real benefit as different people could then explain the concepts in different ways. 5) An attempt will be made to enable the mirror to be controlled through an ipad touch screen so that the audience can alter the mirror shape more easily and perhaps in a manner that is easier and more accessible than sliders on a computer controlled via a mouse drag. 6) Additional supporting images of AO in use in astronomy and microscopy will be provided in future as supporting material as questions along these lines were asked frequently. 7) A consideration is being given to the production of post cards with interesting images, some text on the back and links to appropriate web site. These are low cost and are being used in other areas within Durham though as yet not for outreach. In summary the demonstration was well received and the initial feedback was positive. All the users felt that the audience gained an appreciation of how optical systems work and how they can be used to advance instrumentation in a wide range of fields. The aesthetic appeal of a large number of optical components on a confined board space was not initially considered as being important but gave the demonstration a certain wow factor. This was improved in the lab using some dry ice but although improving the visual appearance the condensation degraded the performance of the display (we can not deal with scattering which is another important point about adaptive optics but can confuse the audience) and will generally not be used in future. The post graduates and post doctoral researchers who had previously undertaken some outreach felt that the demonstration helped attract attention and those that had not previously tried outreach all enjoyed the experience. With the described improvement the system will be used in the coming year at the meetings proposed, and also is available internally within Durham for other events that may take place. John Girkin, 19 th July 2012