Reverse saturable absorbers have shown great potential to attenuate laser radiation. Good candidate molecules and various particles have successfully been incorporated into different glass matrices, enabling the creation of self-activated filters against damaging laser radiation. Although the performance of such filters has been impressive, work is still ongoing to improve the performance in a wider range of wavelengths and pulse widths. The purpose of this tutorial is, from an optical engineering perspective, to give an understanding of the strengths and weaknesses of this class of smart materials, how relevant photophysical parameters are measured and influence system performance and comment on the pitfalls in experimental evaluation of materials. A numerical population model in combination with simple physical formulas is used to demonstrate system behavior from a performance standpoint. Geometrical reasoning shows the advantage of reverse saturable absorption over nonlinear scattering due to a fraction of scattered light being recollected by imaging system optics. The numerical population model illustrates the importance of the optical power limiting performance during the leading edge of a nanosecond pulse, which is most strongly influenced by changes in the two-photon absorption cross section and the triplet linear absorption cross section for a modeled Pt-acetylide. This tutorial not only targets optical engineers evaluating reverse saturable absorbing materials but also aims to assist researchers with a chemistry background working on optical power limiting materials. We also present photophysical data for a series of coumarins that can be useful for the determination of quantum yields and two-photon cross sections and show examples of characterization of molecules with excited triplet states.
Optical limiting materials are developed for applications in protection of optical sensors against laser aggressions. We have studied functionalised macrocycles (thiacalixarenes) and alkynylplatinum(II) derivatives for optical limiting applications. Glass materials based on alkynylplatinum(II) derivatives and macrocycles were prepared through the sol-gel process. The molecular species were grafted to the matrix in order to maximise the concentration and the stability of the final solid-state material. The glass materials were cut and polished to approximately 1.5 mm. The glass materials show broadband optical limiting in the visible wavelength region, for nanosecond laser pulses.
Preliminary results on the optical power limiting properties of platinum(II) acetylides containing triazole units are presented. It is shown that the triazole units give a positive contribution to the limiting abilities of the platinum(II) acetylide and that this modified chromophore could have potential use in sensor protection devices. Moreover, this paper discusses how the versatile building block 2,2-bis(methylol)propionic acid (bis-MPA) can be used advantageously to functionalize nonlinear optical (NLO) platinum(II) acetylides. The bis-MPA units can be used to prepare dendritic substituents offering site isolation to the chromophore leading to improved clamping. The bis-MPA functionalization also improves the solubility of the platinum(II) acetylides in many organic solvents. The preparation of solid-state optical power limiters, where the NLO chromophore is inserted in an optically transparent matrix, is addressed. Again, the bis-MPA unit can be employed to increase the number of accessible end-groups to which matrix-compatible species can be attached. It is concluded that the hydroxy-functional platinum(II) acetylides can be modified to fit almost any matrix, organic or inorganic. Finally, depending on functionalization, it is possible to prepare doped glasses where the chromophore is either embedded in the matrix, or covalently bonded to the matrix.
The market demand for bright laser pointers has led to the development of readily available devices that can pose a threat
to road safety. Laser pointers can be involved in accidents caused by laser users who do not realise the dangers involved,
but laser pointers can also enable deliberate criminal activity. There are technologies available that can counter the threat
in different ways. A number of protective principles are outlined below. Some technologies built upon Liquid Crystal
Devices are described in greater detail.
Without any knowledge of what laser pointers a potential aggressor has access to, a frequency agile filter seems to be the
most promising way to avoid the most severe consequences of dazzle from laser pointers. Protective systems
incorporating suitable glasses or visors holding frequency agile filters of this kind however, are not commercially
We present a sol-gel derived photonic structure of beryllium oxide. A new low temperature synthesis route has been developed to produce beryllium oxide from beryllium alkoxide. The beryllium alkoxide was prepared from beryllium metal, methyl mercury and butyl alcohol as starting materials. The samples have been mathematically modelled and their IR reflectance characteristics in the 2-18 μm wavelengths rang has been measured.
Alkynyl platinum derivatives and thiacalixarenes were trapped in solid transparent matrices prepared by the sol-gel process. By using functionalyzed silicon alkoxides, molecular species were grafted to the gel matrix giving a high doping concentration and chemically stable materials. In this communication we present broadband optical limiting performance in the visible wavelength region observed in the prepared materials.
This report presents preliminary optical limiting and spectroscopic characterization of dendrimer capped Pt-ethynyls. Preliminary OPL and spectroscopic characterization revealed that these have better OPL properties than the non-capped analogue. The excited state properties in terms of luminescence for emission at ca 400 nm and 525 nm is in the nanosecond and microsecond range, respectively. The site isolation provided by the dendrimer capping also give rise to strong phosphorescence involving the same emission bands near 525 nm. The decay time for this was found to be in the range 0.2 ms, considerably longer than for other similar Pt-complexes, and we tentatively assign this to a site-isolation effect that prevents quenching of the triplete state. It was shown how the dendron capping also makes it feasible to blend the dye with e.g. MMA monomers and carry out polymerization to obtain a solid OPL device with good performance.