Clouds cover approximately 70% of the Earth's surface and therefore play a crucial rule in governing both the climate system and the hydrological cycle. The microphysical properties of clouds such as the cloud particle size distribution, shape distribution and spatial homogeneity contribute significantly to the net radiative effect of clouds and these properties must therefore be measured and understood to determine the exact contribution of clouds to the climate system. Significant discrepancies are observed between meteorological models and observations, particularly in polar regions that are most sensitive to changes in climate, suggesting a lack of understanding of these complex microphysical processes. Remote sensing techniques such as polarimetric LIDAR and radar allow microphysical cloud measurements with high temporal and spatial resolution however these instruments must be calibrated and validated by direct in situ measurements. To this end a low cost, light weight holographic imaging device has been developed and experimentally tested that is suitable for deployment on a weather balloon or tower structure to significantly increase the availability of in situ microphysics retrievals.
We report on a numerical model and supporting experiments to show that a high peak power, pulse
burst, Na guide-star waveform, suitable for use with adaptive optics systems requiring dynamic
refocusing to avoid guide star elongation, is capable of producing a return comparable to
conventional guide star laser of comparable output power. The predictions from our numerical
model using coherent pumping by short, high peak power pulses, or
so-called π-pulse pumping,
indicate that very bright fluorescence returns can be achieved in this regime. This is supported by
experimental results where fluorescence is observed in alkali atoms (cesium) using variable input
power and pulse lengths. The model is used to predict very bright Na guide stars, using short pulses
to excite most of the Na atoms available, followed by sufficient time to let them decay.
We demonstrate for the first time the practical feasibility of a new sodium guide star laser with a
pulsed burst output of sufficient energy at 589nm to be useful for current applications and readily
scalable to meet future requirements. We describe complete experimental design verification results
of the pulse burst laser concept, optimized to eliminate guide-star elongation issues and to meet all
requirements for Multi Conjugate Adaptive Optics (MCAO) for future extremely large ground-based
telescopes (ELTs). It makes use of sum frequency generation (SFG) of two, Q-switched, injection
mode-locked, wavelength stabilized Nd:YAG lasers, producing a
macro-micro, pulse-burst output
which is optimized in power and bandwidth to maximize the fluorescence from the high altitude
We report on the development of a low-cost differential absorption lidar (DIAL) for profiling water vapour in the lower
atmosphere. It uses diode lasers in the 830nm region, differing from previously constructed water DIAL systems in
having a double master laser design with active stabilisation of both wavelengths. We present measurements of
backscatter coefficients of aerosols over Adelaide that feed into a sensitivity analysis, as well as initial DIAL
We describe a new, improved approach for sodium guide-star lasers for the correction of atmospheric aberrations in
telescopes, which satisfies all current requirements for advanced pulse burst waveforms. It makes use of sum frequency
generation (SFG) of two pulsed, Q-switched, injection mode-locked Nd:YAG lasers, resulting in a macro-micro pulse-burst
output, optimized in power and bandwidth to maximize the fluorescence from the high altitude sodium layer. The
approach is robust and power scalable and satisfies the requirements for Multi Conjugate Adaptive Optics (MCAO) for
current and future telescopes, including extremely large ground telescopes (ELTs). It is also adaptable for advanced
design options. Here we describe the approach in detail, the results from critical design verification experiments, the
current status and plans for further work required to demonstrate a complete sodium guide-star laser.
The Australian Consortium for Gravitational Astronomy has built a High Optical Power Test Facility north of Perth, Western Australia. Current experiments in collaboration with LIGO are testing thermal lensing compensation, and suspension control on an 80m baseline suspended optical cavity. Future experiments will test radiation pressure instabilities and optical spring in a high power optical cavity with ~200kW circulating power. Once issues of operation and control have been resolved, the facility will go on to assess the noise performance of the high optical power technology through operation of an advanced interferometer with sapphire tests masses, and high performance suspension and isolation systems. The facility combines research and development undertaken by all consortium members, which latest results are presented.
Interference resulting from the measurement of four-time fourth-order correlation functions of a wave field is discussed. The fringes that are observed are peculiar because they have a statistical origin, and show the greatest contrast when the coherence time of the field is finite. This is demonstrated with a simple acoustic experiment. Random telegraph phase noise is used in this experiment to vary the field coherence in order to highlight the problem of interpreting this interference; for this noise the Gaussian moment theorem may not be invoked to reduce the description of the interference to one in terms of first order interference. A second example using the pseudorandom phase fluctuations that are encoded on GPS satellite transmissions is also presented.
The Australian Consortium for Interferometric Gravitational wave Astronomy (ACIGA) is carrying out research on the detection of gravitational waves using laser interferometry. Here we discuss progress on each of the major sub systems: data analysis, lasers and optics, isolation suspension and thermal noise, and configurations, and report on the development of a high optical power test facility in Gingin, Western Australia.