Michael R. Jacobson

Spectral Selectivity Applied To Hybrid Concentration Systems

The efficiency of conversion of concentrated solar energy can be improved by separating the solar spectrum into portions matched to specific photoquantum processes and the balance used for photothermal conversion. The basic approaches of spectrally selective beam splitters are presented. A detailed simulation analysis using TRNSYS is developed for a spectrally selective hybrid photovoltaic/photothermal concentrating system. The analysis shows definite benefits to a spectrally selective approach.

New Christiansen filters

A number of new optical filters that are based on the well-known Christiansen effect of scattering light in a heterogeneous medium have been fabricated. In addition to the conventional solid-in-liquid systems, we fabricated some solid-in-solid filters, which we refer to as solid Christiansen filters. Here we report on their fabrication, performance, and applications. From our experiments we have also derived the dispersion curve for a liquid styrene monomer in the visible region.

2007 Topical Meeting on Optical Interference Coatings:Manufacturing Problem

Measurements are described on the experimental filters submitted to the Third Optical Thin Film Manufacturing Problem in which the object was to produce multilayers with a measured colorimetric performance that is as close as possible to that specified. The perceived colors of the coating, when illuminated with randomly polarized light incident at 7 degrees by a source representing average daylight with a correlated color temperature of approximately 6500 K, were to be yellow and blue, respectively, in light reflected from its two surfaces, and the color was to appear white when viewed in transmission mode. Eleven teams from 7 different countries submitted a total of 18 samples.

Thin-Film Multilayer Filter Designs For Hybrid Solar Energy Conversion Systems

The efficiency of hybrid photothermal/photovoltaic energy conversion can be increased by separating the solar spectrum into portions matched to the photothermal and photovoltaic processes. Thin-film multilayer filters can implement this concept; five such filters consisting of all-dielectric or metal-dielectric layers have been designed. The transmission profile of each design is calculated by computer, considering dispersion, absorption, and angle of incidence effects. These profiles are compared and evaluated with respect to the desired spectral performance. The most successful candidate design is an optical minus filter consisting of Ti02, Zr02, and Si02. Results show very sharp selection of the targeted photovoltaic spectral region and low ripple in the transmission region outside the bandstop.

Development of an automated scanning monochromator for monitoring thin films.

A scanning monochromator system for the monitoring of thin-film deposition in a box coater is described. The system employs data from both a quartz crystal oscillator and a wideband transmission spectrometer. The spectrometer uses a holographic grating as its dispersive element and a CCD array to collect the data. All data are sent to a microcomputer where the information is displayed, stored, and analyzed. Several applications, including measurement of optical constants of inhomogeneous films and characterization of moisture adsorption, are discussed.

Water penetration fronts in thin films deposited at oblique incidence

Abstract Water penetration spots in thin films deposited at oblique incidence are shown to be nearly elliptical in shape. Water spreads laterally at greatest speed in the direction normal to the plane of incidence of the evaporant molecules. The ratio of the maximum and minimum speeds increases with the angle of incidence of the vapour and, for magnesium fluoride, is about 1.5 for an angle of 60°. The primary cause of the anisotropic water penetration effect is believed to be self-shadowing which occurs during the deposition of thin films, leading to a columnar microstructure with intermediate voids which act as sinks for penetrating liquids.

2004 Optical Society of America's Topical Meeting on Optical Interference Coatings: manufacturing problem

Results are presented for the second Optical Society of Americas Optical Interference Coatings Manufacturing Problem. The participants were asked to produce multilayer coatings which, in the 450-650 nm spectral region and for light incident at 60 degrees, would have transmittances of 0.7 and 0.3 for p- and s-polarized light, respectively. Three different teams each submitted four solutions. Three different deposition processes were used to produce these coatings. The smallest average departure from the target transmission values was 0.79%. A number of interesting conclusions can be drawn from this exercise.

Multiple analysis of an unknown optical multilayer coating

Results are given of the analysis at five different laboratories of an unknown optical multilayer coating. In all, eleven different analytical and laboratory techniques were applied to the problem. The multilayer nominally consisted of three dielectric and two metallic layers. It was demonstrated convincingly that with present day techniques it is possible to determine the basic structure of such a coating.

2010 topical meeting on optical interference coatings: manufacturing problem.

For the 2010 Manufacturing Problem, the participants were required to produce a filter that had normal incidence transmittances of 0.001, 0.01, 0.1, and 0.96, respectively, in four separate 60 nm wide bands in the 400 to 700 nm wavelength region. The problem is not unlike those that need to be routinely solved in the telecommunication industry. Nine groups submitted a total of 11 different filters for the contest. The number of layers in the filters received ranged from 28 to 678, and the total metric thicknesses varied between 4,038 and 22,513 nm. The transmittances of the filters were measured at two independent laboratories. Some of the performances were quite close to the specifications.

Study Of Surface Contamination By Surface Plasmons

In the Kretschmann arrangement of coupling light into surface plasmon resonances, the base of a prism is coated with a metal film and the light is incident on that film internally. If the thickness of the film is correctly chosen, then light incident at particular angle will be coupled completely into the plasmons. Thus coupling leads to a narrow, deep dip in the internal reflectance of the prism base as a function of incidence angle. Any change in the character of the metal surface results in measurable changes in the incidence angles; thus, the phenomenon is an extremely sensitive indicator of surface conditions. In particular, the effect can detect and monitor very small amounts of surface contamination. The metal layer can also be overcoated with a thin dielectric layer, so that changes induced in contamination of the latter can be observed. The surface plasmon phenomenon and the experimental arrangement employed for contamination detection will be described; experimental results on residues left by strippable coatings will also be presented.