1. Vladimer Chavchanidze Institute of Cybernetics
of the Georgian Technical University
Gia Petriashvili
Cholesteric Liquid Crystal Structures as the Basic Elements of the Novel Adaptive Optics System
EC funded GEO-RECAP project networking and IDEALIST project twinning
meetings Georgian Technical University
Tbilisi, Georgia

2. As the light from distant celestial objects enters our atmosphere, it gets disturbed by our ever-moving atmosphere. Adaptive optics corrects for the distortions in an image, caused by this atmospheric turbulence. The distortion of incoming light is shown schematically in Fig.1.
Fig.1. As uniform waves of starlight reach Earth, they distort due to the temperature variations in atmospheric cells. As light travels slightly faster in less dense warm air, the resultant refraction is non-uniform. This accounts for the 'twinkling' of stars when seen from the Earth's surface. (Images: Gemini Observatory press release) 1

3. Since the adaptive optics was suggested by Babcock [1], a great number of wavefront correctors have been proposed, realized and used to improve the performance of the adaptive optics in science, medicine, and industry. To understand how adaptive optics works, imagine the light from the star as waves arrive at the top of the Earth's atmosphere Fig.2. The wavefronts are essentially perfectly flat. The turbulent atmosphere crumples the wavefront.
Fig.2 Light propagation through the adaptive optics system

4. The Shack-Hartman Sensor (Fig
The Shack-Hartman Sensor (Fig.3) is the most common wavefront sensor used today due to its simplicity and manufacturability. Using an array of miniature lenses called “lenslets,” the sensor splits light into a number of small beams which is then focused onto a CCD camera. Compensating a wavefront brings us to the truly adaptive element in adaptive optics, the wavefront corrector. The most prevalent technology used for this function is a deformable mirror (Fig.3), a thin, flexible, reflective surface whose shape is controlled through a variety of competing technologies. The selection criteria for a deformable mirror are application based. Fundamental specifications for deformable mirror systems are spatial resolution, spatial frequency, speed, stroke, and surface finish.
Fig.3. Deformable mirror and Shack-Hartmann wavefront sensor

5. In this presentation we propose a new concept of adaptive optics systems, in which two basic components: shack-Hartmann’s wave front sensor and the deformable mirror are assembled by use of liquid crystal structures. In particular: as the wave front sensor is utilized a “liquid crystal micro lenses array” [2, 3], Fig.4, and as the deformable mirror - a ”Cholesteric liquid crystal mirror” Fig.5.
Fig.4. Array of liquid crystal lenses. The average diameter of each lens is 150 microns in size, and this size can be varied over the wide range of dimensions ( micron)

6. Fig.5. Image correction and light propagation through the cholesteric liquid crystal mirror based adaptive optics system

7. Expected parameters of the proposed systems are next:
Our approach is quite different from now existing concepts and we hope it significantly will improve the properties of modern adaptive optics systems. The liquid crystal materials could make possible novel devices for numerous applications, in particular: improving night time astronomical imaging, enhance the performance of free space optical communication systems. Medical applications include imaging of the biological tissues, where it can be combined with the optical coherence tomography. It is also expected to play a military role by allowing ground-based and airborne laser weapons to reach and destroy targets at a distance including satellites in orbits.
In contrast to the now existing systems, the proposed technology is very cheap, capable of reducing noise and correcting the distorted images from all forms of distortions and also allow much higher pixel density, hence improvement in the image fidelity after the processing.
Expected parameters of the proposed systems are next:
Response time: ≤1 millisecond
Size of correcting element: from 100µ to 10 cm
Number of correcting elements: 10³ and more
1. H. W. Babcock. The Possibility of Compensating Astronomical Seeing. PASP, 65, October 1953.
2. R.Hamdi1, G.Petriashvili, G.Lombardo, R.Barberi Liquid Crystal bubble structures as the basic element
for the building of novel electro optical devices 23 International Liquid Crystal Conference 11th-16thJuly
2010, Krakòw, Poland.
3. R.Hamdi, G.Petriashvili, G.Lombardo, R.Barberi Liquid crystal bubbles forming a tunable-focus
micro-lens array, 11th ECLC , 6-11th February 2011, Maribor-Slovenia.