Under a NASA Stennis Space Center (SSC) SBIR, technologies required for an imaging spectral radiometer with wavenumber spectral resolution and milliradian spatial resolution that operates over the 8 micrometers to 12 micrometers (LWIR), and 3 micrometers to 5 micrometers (MWIR) bands, for use in a non-intrusive monitoring static rocket firing application are being investigated. The research is based on a spatially modulated Fourier transform spectral imager to take advantage of the inherent benefits in these devices in the MWIR and LWIR. The research verified optical techniques that could be merged with a Sagnac interferometer to create conceptual designs for an LWIR imaging spectrometer that has a 0.4 cm-1 spectral resolution using an available HgCdTe detector. These same techniques produce an MWIR imaging spectrometer with 1.5 cm-1 spectral resolution based on a commercial InSb array. Initial laboratory measurements indicate that the modeled spectral resolution is being met. Applications to environmental measurement applications under standard temperatures can be undertaken by taking advantage of several unique features of the Sagnac interferometer in being able to decouple the limiting aperature from the spectral resolution.
We have designed and built a number of doublet and triplet lenses intended for focussing laser light. The wavelength range extends from 220 nm to 1550 nm. An ordinary achromat, sometimes called a telescope objective, is suitable for some applications, but its cemented surface will not tolerate high irradiance levels. We discuss the performance of the designs at widely spread wavelengths and show which types of designs can be used without refocussing (achromatic) and which types perform satisfactorily only with refocussing as the wavelength is changed. In particular, we describe the cemented telescope objective, the air-spaced telescope objective, a cemented doublet without axial color correction, an air-spaced objective of a single glass type, an air-spaced doublet for high power lasers, and a three element lens.
We have created a program for the modeling of laser beams to answer systems questions. We have used the IMAGE program for wavefront modeling and far field modeling. In order to answer such questions as 'How much astigmatism is permitted in a Gaussian beam clipped at one-half the one-over-e-squared-radius with an obscuration ratio of 0.3 if 75% of the energy is to lie within 2*lambda*F#?' one might need to use a large lens design program. We have developed the IMAGE program so that the systems engineer has a good tool to answer such questions quickly. In fact, we use a large optical design program for our lens design work and still find that IMAGE is much more convenient and quicker than the more powerful program.
Identification of single reflection and multiple reflection ghosts in high energy laser systems is essential for the safeguard of components, equipment, and personnel. Most ray trace programs require the user to model each path of reflections as an independent optical system. We will describe some of our work on cw and pulsed laser systems with OPTICAD, a program which permits simultaneous display of all ghost paths. We will describe some of its features, such as limiting the search for ghost paths to those which have less than a user specified fraction of the input power.
We shall describe the design, fabrication, testing, and use of lenses achromatized for 633 nm/ 1064 nm and for 532 nm/1064 nm. These lenses are designed to permit easier and more accurate alignment of beams from YAG lasers. Because the 1064 nm light is not visible and because many YAG lasers are pulsed, aligning the beam trains can be frustrating. The achromats we have built permit the use of HeNe (633 nm) and frequency-doubled YAG (532 nm) lasers for alignment of the high powered 1064 beam.
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