Tim McKay

Linear and nonlinear optical properties of platinum-ethynyl

We report an experimental investigation of absorption, fluorescence, and nonlinear absorption in a platinum-ethynyl complex. We have observed strong singlet absorption at 355 nm, and a weaker triplet absorption at 520 nm. Photoluminescence measurements show a fluorescence band at 400 nm and a phosphorescence band at 520 nm. Pump–probe nonlinear absorption measurements confirmed that S0→T1 followed by excited triplet-state absorption corresponds to the dominant excitation path in the region between 513 and 532 nm.

Platinum ethynyl compound for optical limiting

Nanosecond and picosecond studies have been carried out on a platinum ethynyl compound dissolved in tetrahydrofuran. Nonlinear absorption was observed at 532 nm using nanosecond pulses and at 1064 nm using picosecond pulses. The nonlinear absorption observed at 532 nm was found to have a long time constant associated with it indicating the presence of excited state absorption. A possible route for this excited state absorption may be single photon absorption from the ground state to the T1 excited state followed by excited state absorption from the T1 state. Strong nonlinear scattering was observed at 532 nm using nanosecond pulses and at 1064 nm using picosecond pulses. Optical limiting studies using 532 nm, nanosecond pulses revealed that below input fluences of 6 J/cm2 nonlinear absorption is the dominant limiting mechanism whereas above 6 J/cm2 there is significant nonlinear scattering. Picosecond experiments indicated that the scattering may, in part, be attributed to strongly absorbing scattering centers present in the solution, possibly originating from laser induced breakdown of the platinum ethynyl material. Excite-probe studies indicated that the time constant associated with the scattering is of the order of tens of milliseconds suggesting that this platinum ethynyl compound is a good candidate for use against picosecond to microsecond pulses.

Design of low-haze holographic notch filters

We have studied the optical quality of holographic notch filters and have identified that stray illumination during the exposure stage and substrate scatter are the limiting factors. We propose and analyze a novel holographic recording scheme in which the substrate is rotated during exposure. Using this method, we have produced high-uniformity, flare-free dichromated gelatin notch filters with optical density greater than 5 and with scatter comparable with that from polished substrates.

Numerical modeling of z-scans of thick nonlinear absorbers

A numerical scheme for modeling of z-scans with samples ranging from thin samples to beyond the thick sample limit was introduced in our previous work (A. Eriksson et al., J. Opt. Soc. Am. B15, pp. 810-816, 1998). The method relies on a multilayer approach, where all layers are treated as independent, and may have different linear and nonlinear optical properties. The theoretical scheme can be used for irradiance as well as fluence, dependent absorbers. It allows for an arbitrarily shaped aperture in front of the detector. Here the method is tested and compared with the results of analytical thick sample theory and previously published numerical simulations. Ways of optimizing the performance of an optical limiting device are modeled and discussed. Preliminary experimental z-scan results of both thin and thick sample chloro-aluminum phthalocyanine were analyzed.

Success factors for urgent technology insertion into military systems of systems

New or improved technologies are frequently inserted into existing military capabilities (socio-technical systems of systems) in order to address emerging threats or to exploit latest scientific and technological developments. Urgent technology insertion projects, which are aimed at addressing critical capability gaps, pose a particular challenge for Defence organisations as any delays and/or suboptimal execution may negatively impact on mission success, potentially resulting in the loss of life. As a result, identifying the success factors for timely and effective insertion of urgently required technologies is imperative. Based on a one-year-long ethnographic study of urgent technology insertion project strengths, weaknesses, opportunities, and threats in the Australian Defence Organisation (ADO), this paper presents eight success factors for urgent technology insertion and uses them to evaluate a recent case study.

Fibre Laser Doppler Vibrometry System for Target Recognition

Vibrations from a target provide a difficult to mask target signature. Vibrometry shows potential for long-range target identification whilst a fibre implementation may lead to a smaller, more compact system when compared with an equivalent solid-state source solution. A prototype fibre LDV system and electronic demodulation scheme using low-cost telecommunications components is described and tested. The aim of the system is to remove the velocity component of a target signature for target identification purposes. Signal processing methods and signature measurements are described which demonstrate the utility of the system for target recognition.