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We demonstrate optical limiting for the C(60) fullerene in polymethyl methacrylate (PMMA) as a solid polymer host. It is shown that the optical-limiting behavior is consistent with excited-state absorption (reverse saturable absorption) as a mechanism. We suggest that a higher threshold for optical limiting compared with that of C(60) in toluene is due to nonlinear scattering for the liquid. The performance of C(60) in PMMA is compared with that in chloroaluminum phthalocyanine, N-methylthioacridone, King's complex, and ruthenium King's complex in PMMA. Optical damage thresholds are reported.

We report the characterization of a set of broad-area semiconductor diode lasers with mid-wave infrared (3–5 μm) emission wavelengths. The active region of each laser structure is a 5- or 6-period multiple quantum well (MQW) with Ga0.75In0.25As0.22Sb0.78 barriers and type-II (broken-gap) Ga0.75In0.25Sb/InAs superlattice wells. The cladding layers of each laser structure are n- and p-type InAs/AlSb (24 Å /24 Å) superlattices grown lattice-matched to a GaSb substrate. By tailoring constituent layer thicknesses in the Ga0.75In0.25Sb/InAs superlattice wells, laser emission wavelengths ranging from 3.28 μm (maximum operating temperature=170 K) to 3.90 μm (maximum operating temperature=84 K) are obtained.

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We examine the photophysics of a colloidal suspension of C 60 particles in a micellar solution of Triton X-100 and water, prepared via a new synthesis which allows high-concentration suspensions. The particle sizes are characterized by transmission electron microscopy and dynamic light scattering and found to be somewhat polydisperse in the range of 10-100 nm. The suspension is characterized optically by UV-vis spectroscopy, femtosecond transient absorption spectroscopy, laser flash photolysis, and z-scan. The ground-state absorbance spectrum shows a broad absorbance feature centered near 450 nm which is indicative of colloidal C 60 . The transient absorption dynamics, presented for the first time with femtosecond resolution, are very similar to that of thin films of C 60 and indicate a strong quenching of the singlet excited state on short time scales and evidence of little intersystem crossing to a triplet excited state. Laser flash photolysis reveals that a triplet excited-state absorption spectrum, which is essentially identical in shape to that of molecular C 60 solutions, does indeed arise, but with much lower magnitude and somewhat shorter lifetime. Z-scan analysis confirms that the optical response of this material is dominated by nonlinear scattering. IntroductionSince its discovery, 1 the uniquely symmetrical C 60 molecule has been widely studied, and many applications for it and its derivatives have been proposed, notably lubricants, 2 superconductors, 3 sensors, 4-7 solar cells, 8 and biomedical applications [9][10][11] such as drug delivery and photodynamic therapy. In particular, the photophysical properties of the C 60 molecule have been the subject of intense study. Many authors have reported on the photophysical properties of molecular solutions of C 60 . [12][13][14][15][16][17][18][19][20] Likewise, many authors have studied the photophysical and structural properties of solid films of C 60 . [21][22][23][24][25][26][27][28][29][30][31][32][33][34] Under certain conditions, C 60 forms stable colloidal assemblies in solvents. [35][36][37][38][39][40][41][42][43][44] Colloidal suspensions of C 60 particles can also be formed in binary solvent mixtures, in which one is a good solvent and the other is a poor solvent for C 60 . [45][46][47][48][49] Aqueous suspensions of colloidal C 60 particles are also formed by a number of methods, [50][51][52][53][54][55][56][57][58][59][60][61][62][63][64] including solubilization in micellar solutions. 55,61,[65][66][67][68][69] Some studies have been done of the photophysical properties of these colloidal fullerene suspensions. 67,68,70,71 The photochemical properties, and in particular the generation of reactive oxygen species (ROS) via intersystem crossing to the triplet state, have been of interest both for potential exploitation for photodynamic therapy 9 and regarding concerns about their potential environmental impact, because there have been reports of significant cytotoxicity effects. [50][51][52][53] This work reports on the excited-state dynamics o...