Polymer Materials Design for Optical Limiting
- PDF / 1,431,833 Bytes
- 7 Pages / 414.72 x 648 pts Page_size
- 7 Downloads / 206 Views
ABSTRACT Phthalocyanines (PC's) containing heavy metal central atoms have recently been recognized as leading candidates for reverse saturable absorption and optical limiting (OL) applications in the visible spectrum. Strong triplet excited state absorption brought about by a large intersystem crossing rate is responsible for the excellent limiting performance of these molecules. Moreover, devices which maximize the excited state population along the light path will demonstrate maximum limiting efficiency. A non-homogeneous distribution of indium tetra(tert-butyl) phthalocyanine chloride (InC1PC) has been shown to be very effective in attenuating 532 nm nanosecond laser pulses. This was accomplished by approximating a hyperbolic distribution of chromophores using discrete elements of fixed dye concentration. Greater OL should be achieved by fabricating materials containing a continuous concentration gradient of chromophore. This paper focuses on issues concerning the preparation of solid polymeric materials that contain such a chromophore gradient. This design is achieved by diffusing chromophore-containing solutions into partially polymerized poly(methyl methacrylate) (PMMA). INTRODUCTION The attenuation of high-intensity laser pulses is very important for the protection of human eyes and optical sensors both in the laboratory and in the field. It is also important to maintain high transparency under ambient lighting conditions. Different techniques have been employed to obtain strong optical limiting performance, but among these, the property of reverse saturable
absorption is very promising. This approach utilizes molecules that have weak ground state absorption but moderate to strong excited state transitions, resulting in a linear regime with high transparency and a highly attenuating non-linear response. Phthalocyanines (PC's) are one class of organic molecules that exhibit reverse saturable absorption. The structures of the compounds studied in this paper are shown in Figure 1.
/ tBu/\ S\
t-Bu
N
N
N
,,,O-Si(n-hexy1)3
N----
,.M-N IN N
N,I,
Nt-Bu
(n-hexyi) 3Sj-O
N
.
Figure 1. Chemical structure of phthalocyanines under study in this work. M=InCl for the lefthand structure, and M=Sn for the right-hand structure. In fact, these molecules have a moderate excited-state singlet (SI -> Sn) transition and a strong excited-state triplet (T1 -> Tn) transition. Heavy metal atom substitution on the PC results in a higher intersystem crossing rate due to spin-orbit coupling and therefore a higher triplet state 89 Mat. Res. Soc. Symp. Proc. Vol. 479 01997 Materials Research Society
population. The resulting optical limiting performance is over three times higher than PC's with light atom substitutions such as AlCl [1]. Additionally, the performance of a homogeneous solution of InC1PC is 6 times that of C60 a commonly reported optical limiting material [I]. Although heavy atom substitution of PC's improves their performance significantly, the materials are still under-utilized in focusing optical systems. Chr
Data Loading...
