Clock technology development is of significant interest in NASA applications for navigation, tracking, and information distribution. Experiments are currently under way to develop a compact, high-precision vapor cell frequency standard using Ramsey interference in rubidium vapor.
Optical pumping in alkali atoms, and microwave resonance techniques have been used as standard techniques in early developments of vapor cell clocks. During last few decades, new concepts and technologies have emerged, particularly in developing precision frequency standards using atomic vapor cells. The phenomenon of all-optical Ramsey interference using pulsed coherent population trapping (CPT) beams provides a new avenue for such a development. Our recent studies have shown that frequency narrowed Ramsey interference can be produced in rubidium vapor without the effect of power broadening. Ramsey fringes can be generated using pulsed CPT fields in a vapor medium as opposed to using spatially separated fields in an atomic beam. Fringes of width as narrow as 1.8 kHz using a buffer-gas filled rubidium cell have been observed.
Frequency stability is an important criterion for implementation of a vapor cell frequency standard. Currently, we are investigating this aspect which is closely associated with the ac Stark effect in Ramsey interference. Our studies indicate that this effect can be reduced significantly and higher frequency stability can be achieved for the clock application. Experiments are done to identify all major sources of error that affect the short-term and long-term frequency stability performances of the clock.
Polarization Imaging LADAR
Polarization imaging can produce high-specificity images from optically backscattered light and offer distinct advantage for a wide range of detection and classification problems. It can provide information related to target composition and geometry. Polarization imaging has been used to detect targets by exploiting the reflective characteristics of man-made objects in multispectral imaging. It has been also used in optical coherence tomography (OCT) for complete polarimetric characterization of biological samples. We are developing a polarization imaging scanning laser radar system to extract additional information than intensity-only imaging. The system uses the principle of Stokes and Mueller matrix imaging and uses a high pulse repetition frequency laser system combined with appropriate sensor electronics and systems control.
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