Spectrometers that include extended-range linear InGaAs arrays make it possible to measure optical signals to 2500 nm.
Available arrays, however, have more than 100 times the dark current as that of conventional arrays, which are limited to
1700 nm. This behavior leads to non-linearity in a short-wave infrared spectroradiometer used to monitor spectral
radiance of an integrating sphere uniform source. A method of improving linearity in an extended-range InGaAs array is
presented. The non-linearity is corrected using a multi-point calibration at a number of lamp power levels whereby the
calibration factor for each wavelength point depends on the lamp power in the integrating sphere. An algorithm in the
spectroradiometer software chooses the correct calibration factors and reports the system spectral radiance values
accordingly. This method reduced error by more than a factor of two.
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.
A uniform source sphere was designed and built that included both tungsten-halogen and xenon arc lamps. The spectral radiance of the system and arc lamp stability were measured. Results show significant spectral radiance in the blue region of the spectrum, which is greatly improved over conventional systems that use only tungsten-halogen lamps. Short-term stability measurements of the radiance due to one arc lamp show stability of 0.26%. This value is more than ten times greater than that of a tungsten-halogen lamp, which is inherently more stable, but the xenon lamp is sufficiently stable for many applications. Considering the improved blue performance, xenon lamps offer possibilities for uniform source spheres used to calibrate cameras that operate in the blue region of the spectrum, such as remote sensing systems.
Miniature optical systems utilizing arrays of lenses had been conceived by the early part of this century. More recent uses for multi-aperture optics have included Hartmann wavefront sensing and agile beam steering. To support our own research efforts in micro-optics Adaptive Optics Associates, Inc. developed first-order raytrace software that is capable of modeling multi-aperture systems. The graphical user interface at the heart of this software gives a CAD- like utility to the program, which is a powerful tool for the micro-optics design engineer. The article discusses the benefits of such an interface. Several examples of micro-optics systems taken from available literature are analyzed.
Two of the many applications for microlens arrays are fill factor improvement in focal plane arrays and collimation of laser diode arrays. Most lenslet arrays made for fill factor improvement consist of immersion lenses that themselves do not have a 100 fill and the evaluation of such lenses is not representative of their use in an imaging system. Alternative designs are investigated. Anamorphic optics are required to correct for the astigmatism present in laser diode output. An array of micro-optics with toroidal refractive surfaces can be used to collimate or focus the light. We report on the fabrication and evaluation of such anamorphic micro-optics.