Jacqueline Staromlynska

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.

Evidence for broadband optical limiting in a Pt:ethynyl compound

Results are presented to indicate that the material bis((4-(phenylethynyl)phenyl)ethynyl)bis(tribu- tylphosphine) platinum (II) shows promise as a broadband optical limiter in the visible that will be effective over a large range of pulse lengths from picoseconds to hundreds of nanoseconds.

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 considerations for a liquid crystal tuned Lyot filter for laser bathymetry

The design of a six-stage liquid crystal tuned Lyot filter for operation at a wavelength of 532 nm is described. Design options including material type and factors affecting performance such as material quality are discussed. The proposed narrow-passband filter will have a bandwidth of less than 0.1 nm. To achieve the performance required of the filter, high transmittance polarizers have been developed.

Design criteria for optical power limiters

Factors which affect the design of passive optical power limiters utilizing nonlinear refraction and absorption are discussed. Recent theoretical modelling and experimental studies of the effects produced by varying the thickness and position of the nonlinear medium are reported. Excessive thickness can produce large insertion loss for the limiter in the event of linear absorption or scattering, and also makes retrofitting to existing equipment difficult. Insufficient thickness results in less than optimal limiting. We show that for a third-order refractive nonlinearity a suitable medium thickness is six times the Rayleigh length of the beam inside the medium. Nonlinear absorption can enhance the limiting, allowing for the use of larger apertures or no apertures, and hence greater fields of view. We also show how the optimal position of the medium depends upon the ratio of nonlinear refraction to nonlinear absorption.

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.

High-performance optical filter for the Australian laser airborne depth sounder

The design and performance characteristics of a tunable, six stage Lyot filter for use with the Australian laser airborne depth sounder are described. It is predicted that the filter will significantly reduce the effect of sky reflection from the sea surface thereby allowing an increase in the operational hours of the LADS system by up to six hours per day.

Liquid-crystal electro-optic and nonlinear optical devices

Studies have been carried out across the visible on liquid crystal electro-optic (EO) and nonlinear optical devices. Two geometries were studied, a variable birefringence filter (VBF) and a Fabry Perot (FP) etalon, with a view to using them as (1) EO modulators and (2) EO tunable filters. Restrictions on device design and performance imposed by LC technology are analyzed and discussed. It is shown that for modulators the VBF yields better performance characteristics when employing LC technology, whereas for tunable filters the FP etalon geometry offers advantages. A hybrid spacer layer FP device and a double element VBF, designed to improve the wavelength selectivity of tunable filters, are described. Finally, results on bistable switching in the FP etalon are presented.