Thu-Lan Kelly

White-light performance of a polarization-independent liquid-crystal phase modulator

The broadband performance of a polarization-insensitive liquid-crystal phase modulator is analyzed, and its effect on an adaptive optics system is quantified.

Ultra-sensitive wavefront measurement using a Hartmann sensor

We describe a Hartmann sensor with a sensitivity of lambda /15,500 at lambda= 820nm. We also demonstrate its application to the measurement of an ultra small change in wavefront and show that the result agrees with that expected to within lambda/3,300.

Phase-aberration correction with dual liquid-crystal spatial light modulators

A phase-aberration-correction system that uses high-resolution, twisted nematic liquid-crystal spatial light modulators in a Mach-Zehnder interferometer is presented. A correction algorithm is described and experimentally verified by use initially of one liquid-crystal panel. Phase aberrations are successfully removed by a single liquid-crystal panel, but unacceptably high amplitude variation is introduced into the wave front because of the phase-amplitude coupling of the spatial light modulator. A second panel is used to remove the amplitude modulation. The modified optical system with a multiplicative architecture is described, and results are presented that show the correction of phase aberrations with an amplitude variation of less than 10%.

Focusing of astigmatic laser diode beam by combination of adaptive liquid crystal lenses

Abstract An experimental liquid crystal compensator of laser diode astigmatism is described. This compensator consists of two adaptive liquid crystal lenses. The compensator performs focusing of an astigmatic laser beam from infinity to 0.5 m. Numerical and experimental results of focusing for laser diode beam with 0.82 μm wavelength are represented. Dispersion properties of the compensator in 0.633–0.85 μm region of wavelengths and transmission at 0.82 μm are investigated experimentally.

ACIGA's high optical power test facility

Advanced laser interferometer detectors utilizing more than 100 W of laser power and with ~106 W circulating laser power present many technological problems. The Australian Consortium for Interferometric Gravitational Astronomy (ACIGA) is developing a high power research facility in Gingin, north of Perth, Western Australia, which will test techniques for the next generation interferometers. In particular it will test thermal lensing compensation and control strategies for optical cavities in which optical spring effects and parametric instabilities may present major difficulties.

Dual-conjugate wavefront generation for adaptive optics

We present results of the isoplanatic performance of an astronomical adaptive optics system in the laboratory, by using a dual layer turbulence simulator. We describe how the performance of adaptive correction degrades with off--axis angle. These experiments demonstrate that it is now possible to produce quantifiable multi-layer turbulence in the laboratory as a precursor to constructing multi-conjugate adaptive optics.

Wavelength dependence of twisted nematic liquid crystal phase modulators

Many twisted nematic liquid crystal spatial light modulators suffer from limited phase modulation capability and coupled amplitude modulation. In particular, a phase modulation capability of less than 2π radians is a severe limitation. Phase modulation is wavelength dependent. We examine the effect of changing the operating wavelength on the phase and amplitude modulation characteristics of a commercial liquid crystal spatial light modulator. Comparisons are made with a double pass configuration which can also increase the phase modulation capability.

Technology developments for ACIGA high power test facility for advanced interferometry

The High Optical Power Test Facility for Advanced Interferometry has been built by the Australian Consortium for Interferometric Gravitational Astronomy north of Perth in Western Australia. An 80 m suspended cavity has been prepared in collaboration with LIGO, where a set of experiments to test suspension control and thermal compensation will soon take place. Future experiments will investigate radiation pressure instabilities and optical spring effects in a high power optical cavity with ~200 kW circulating power. The facility combines research and development undertaken by all consortium members, whose latest results are presented.

Australia's Role in Gravitational Wave Detection

An enormous effort is underway worldwide to attempt to detect gravitational waves. If successful, this will open a new frontier in astronomy. An essential portion of this effort is being carried out in Australia by the Australian Consortium for Interferometric Gravitational Astronomy (ACIGA), with research teams working at the Australia National University, University of Western Australia, and University of Adelaide involving scientists and students representing many more institutions and nations. ACIGA is developing ultrastable high-power continuous-wave lasers for the next generation interferometric gravity wave detectors; researching the problems associated with high optical power in resonant cavities; opening frontiers in advanced interferometry configurations, quantum optics, and signal extraction; and is the worlds leader in high-performance vibration isolation and suspension design. ACIGA has also been active in theoretical research and modelling of potential astronomical gravitational wave sources, and in developing data analysis detection algorithms. ACIGA has opened a research facility north of Perth, Western Australia, which will be the culmination of these efforts. This paper briefly reviews ACIGAs research activities and the prospects for gravitational wave astronomy in the southern hemisphere.

Improved kinoforms on spatial light modulators with less than π phase modulation capability

A novel method of encoding a phase hologram that uses less than p radians of phase is described. The technique is based on Lees delayed sampling method for amplitude holograms. It was devised for use with liquid crystal spatial light modulators with limited phase modu- lation capability. Results are compared with Lees method and binary phase holograms and show improved image quality.