A simple analytical model for the signal acquisition range for a laser guided mortar is presented. The signal consists of a
repetitively pulsed laser of fixed pulse duration and fixed pulse repetition frequency. The pulses are detected by a seeker
consisting of a quadrant photodiode and a trans-impedance amplifier. Noise is introduced from solar irradiance and
from the detector/amplifier electronics. The model maximizes the acquisition range by optimizing trans-impedance
amplifier circuit components. A comparison of integrating multiple low energy pulses (MPLD) versus detecting each
pulse individually (conventional) is made.
In recent years, infrared (IR) spatial light modulators (SLM) have found applications in areas such as scene simulation and dynamic spatial frequency filtering. To help meet these requirements, we have developed two novel methods of SLM fabrication. Both SLM designs deposit a vanadium dioxide (VO2) thin film on a thermal array. VO2 films exhibit a temperature dependent hysteresis about their transition from dielectric to conductor. Accompanied with this transition is a change from a state of low to high reflectivity in the 3 - 5 micrometers band. Our two SLM designs exploit this temperature dependent hysteresis through the use of thermal arrays. The first SLM design deposits the VO2 thin film on a planar diode array. Each diode constitutes a `pixel' of the SLM. Power provided to a diode permits accurate thermal control about the film's hysteresis. Initial biasing of the diode array is required to the base of the VO2's hysteresis curve. The second SLM design deposits VO2 on a thermoelectric array. These pixels have the ability to both heat and cool the VO2 film, thereby allowing the array to be operated in a bistable mode. Bistable operation requires external biasing to the center of the VO2's hysteresis curve.
The temperature coefficients of refractive index for various crystalline and polycrystalline materials, Al203
(ordinary ray), Y203, LaO3-dOped Y203, ALON, and MgA12O4 were determined from measurements of optical
thickness as a function of temperature using a Michelson interferometer operating at 0.633 pm. For the temperature
range of 23°C to 500°C, the first order coefficients ranged from 8.28x10I0C for pure yttria to 14.6x10/°C for
ALON. Measurements of NaC1 and A1203 samples using this technique are in agreement with published data.
Knowledge of the scatter characteristics of candidate infrared sensor dome materials is necessary for the evaluation of
image quality and susceptibility to bright off-axis sources. For polycrystalline materials in particular, the scattering levels
are high enough to warrant concern. To evaluate the effects of scatter on image quality, estimates of the window Point
Spread Function (PSF), or its transform, the Optical Transfer Function (OTF) are required. Additionally, estimates of the
material scatter cross-section per unit volume are essential for determining flare susceptibility. Experimental procedures and
models in use at JHU/APL allow the determination of each.
Measurement results are provided for samples of A1203 (ordinary ray), Y203, LaO3-doped Y203, MgAL2O4, and ALON.
Applications of these results are illustrated for planar windows having arbitrary orientations with respect to the optical axis.