Refractive index measurements of poly(methyl methacrylate) (PMMA) from 0.4-1.6 µm.

Using a transmission-spectrum-based method, the refractive index of a 50 µm thick sample of poly(methyl methacrylate) (PMMA) was measured as a function of wavelength. To mitigate the effects of nonplane-parallel surfaces, the sample was measured at 16 different locations. The technique resulted in the measurement of index at several thousand independent wavelengths from 0.42 to 1.62 µm, with a relative RMS accuracy <0.5×10(-4) and absolute accuracy <2×10(-4).

Thin sample refractive index by transmission spectroscopy.

Transmission spectroscopy and a small number of refractometer index measurements are combined to provide refractive index measurements of transparent samples ~50 um thick at hundreds of wavelengths with absolute accuracies <1 x 10(-4). Key to the technique is the use of independent index measurements to circumvent the need for an independent thickness measurement of the sample. The method was demonstrated on glass samples where fits to Cauchy curves had RMS accuracies <3 x 10(-5) from 415 to 1610 nm. Issues that must be addressed to reach this level of accuracy are discussed.

Optical properties of solid-core photonic crystal fibers filled with nonlinear absorbers.

A theoretical and experimental investigation of the transmission of solid-core photonic crystal fibers (PCFs) filled with nonlinear absorbers shows a sharp change in the threshold for optical limiting and in leakage loss as the refractive index of the material in the holes approaches that of the glass matrix. Theoretical calculations of the mode profiles and leakage loss of the PCF are in agreement with experimental results and indicate that the change in limiting response is due to the interaction of the evanescent field of the guided mode with the nonlinear absorbers in the holes.

Achromatic GRIN singlet lens design.

Gradient refractive index (GRIN) materials are attractive candidates for improved optical design, especially in compact systems. For GRIN lenses cut from spherically symmetric GRIN material, we derive an analogue of the "lens maker's" equation. Using this equation, we predict and demonstrate via ray tracing that an achromatic singlet lens can be designed, where the chromatic properties of the GRIN counterbalance those of the lens shape. Modeling the lens with realistic materials and realistic fabrication geometries, we predict we can make an achromatic singlet with a 19 mm focal length using a matrix of known polymers.

Optical limiting properties of nonlinear multimode waveguide arrays.

An experimental investigation of the transmission of multimode capillary waveguide arrays containing a liquid nonlinear absorber shows an enhanced nonlinear response relative to that found in a single waveguide and to the same length of bulk material. Comparison of the nonlinear response of arrays with different pitch to diameter (d/Lambda) ratios confirm that both the intensity distribution within an individual waveguide and coupling between the elements of the array influence the overall nonlinear response.

Optical properties of a bio-inspired gradient refractive index polymer lens.

The design, fabrication, and properties of one of a new class of gradient-index lenses are reported. The lens is an f/2.25 GRIN singlet based on a nanolayered polymer composite material, designed to correct for spherical aberration. The light gathering and focusing properties of the polymer lens are compared to a homogeneous BK7 glass singlet with a similar f-number. The modulation transfer function of the polymer GRIN lens exceeded that of the homogeneous glass lens at all spatial frequencies and was as much as 3 times better at 5 cyc/mm. The weight of the polymer lens was approximately an order of magnitude less than the homogeneous glass lens.

Nonlinear transmission of a tetrabrominated naphthalocyaninato indium chloride.

The axially substituted complex chloro indium(III) 2-tetrabromo-3-tetra-(3,5-di-tert-butylphenyloxy)naphthalocyanine [Br4(tBu2PhO)4NcInCl (1); MW = 1996] has been synthesized for the first time, and its nonlinear transmission properties have been evaluated with the Z-scan technique in both open and closed aperture configurations at 532 nm for nanosecond pulsed radiation. The tetrabrominated complex 1 displayed a larger positive nonlinear absorption coefficient when compared to an analogous nonbrominated naphthalocyanine [(tBu2PhO)8NcInCl (2); MW = 2498]. The effect of the four Br atoms on the nonlinear optical behavior of 1 is evaluated, discussed, and compared with the nonlinear optical behavior of 2. It is shown that the bromination of the naphthalocyanine ring considerably improves the limiting properties of such a system when high-intensity radiations are produced by nanosecond laser pulses at 532 nm.

Optical limiting properties of nonlinear multimode waveguides.

An experimental investigation of the transmission of multimode capillary waveguides with a nonlinear absorber in the core shows an enhanced nonlinear absorption relative to the same length of bulk material. The results are consistent with partial mode filling within the cores of the waveguides. This study confirms the promising optical limiting capabilities of multimode nonlinear waveguides and implies that the mode structure should be considered in the design and evaluation of capillary array optical limiters.