LCD backlighting applications require diffuse illumination over an extended area of a display unit while maintaining
high luminance levels. Since such applications involve multiple reflections within a reflective cavity, the efficiency of
the cavity can be affected significantly by relatively small changes in the reflectance of the cavity material. Materials
with diffuse rather than specular (or mirror-like) reflectance scatter light, averaging out hot spots and providing a
uniform field of illumination. Reflectors with specular components tend to propagate non-uniformities in the illuminator
system. The result is a spatial variation in brightness visible to the viewer of the display. While the undesirability of
specular materials for such applications has been widely recognized, some diffuse materials in common use exhibit a
significant specular component. This paper describes a method for measuring the specular component of such
materials, and presents a simple approach to evaluating the effect of such secondary specular behavior on the
performance of a backlight cavity. It is demonstrated that significant differences exist among available diffuse
reflectance materials, and that these differences can lead to significant differences in the performance of the displays in
which these materials are used.
The demand for progressively more powerful lasers has caused those employing side-pumped laser designs to become
acutely aware of pumping efficiency and performance. Additionally, precision applications demand beam stability and
uniformity for the lifetime of the laser flash lamp. The use of highly diffuse, high reflectance pump chamber reflectors
such as Spectralon<sup>(R)</sup>‡ have been shown to amplify overall power and performance. Spectralon is used in a wide range of
side-pumped applications for its superior optical characteristics and design flexibility but stated damage thresholds of
approximately 4 J/cm<sup>2</sup> have limited it to lower power applications. To increase energy tolerances, initial damage
thresholds are defined through mathematical simulation. A general form of the heat equation is studied numerically to
develop a theoretical model of Spectralon's damage threshold. The heat equation is discretized using the Euler method.
Secondly, process modifications are performed to test for increased material durability and to physically reproduce
initially defined theoretical parameters.
The use of diffuse reflectance materials in laser pump reflector design can lead to significant improvements in laser
performance over reflectors employing more traditional, specular (or mirror-like) reflectors. Diffuse reflectors provide a
more predictable and uniform beam profile, and reduced susceptibility to parasitic oscillations. Since laser pumping
involves multiple reflections within the pump chamber, the efficiency of a laser pump chamber can be significantly
affected by relatively small changes in reflectance. For example, a chamber with a reflectance factor of approximately
99% over the 400 to 1000 nm range, can provide a 15% gain in performance over a comparable 98% reflective
chamber, even though the reflectance factor is only 1-2% lower. Much larger gains are possible over typical ceramic
reflectors. This paper will examine high performance PTFE as a reflector in laser pump chambers compared to other
materials. Gains in performance through reflectance and diffuseness are shown through mathematical models,
experimental results and real world case studies.