We propose to use the rare-earth-doped silica as the IR-to-visible converter. Its principle of operation employs the up-conversion on pumping with the near-IR radiation. A time-dependent 3-D heat transfer model for fiber geometry, incorporating the finite element method appropriate to the fiber geometry, is developed to perform the resolution analysis. The simulation results of the study demonstrate the spatial and temporal resolution of this transducer for the constant and impulse irradiation profile, confirming the concept feasibility. The performance in terms of temporal and spatial resolution is appreciably improved when the Er-doped silica fiber is in contact with a cold reservoir. The cold sink also enhances the speed of device response, as the latent image is quickly erased.
Many studies, based mostly on ultra-sensitive length measurements, have revealed dimensional micro-instabilities in various optical materials. In some components, probe arrays and interferometric methods have also revealed changes in surface figure over time. Both types of measurements have shown that creep can be observed over periods of days, to months, and years. The typical asymptotic form of the aging curve points to the relaxation of structural or embedded stress. However, details of the mechanisms involved are not well understood. Additionally, the results of an interferometric study of an optical flat over a period of several years have provided some specific indicators for further studies in this area. For example, the extremely small change in shape of the surface was found to be rotationally symmetric, and hence apparently unrelated to the large amount of internal strain non-uniformly distributed throughout the flat substrate. This change in shape approached a limiting value after a period of eight years. The form of this curve suggests that the activation of the change was initiated at the time of the component fabrication, and not at the time of material manufacture. Some scenarios for possible sources of the observed change are discussed and some critical tests are suggested with the aim of clarifying the role of possible mechanisms responsible for long-term changes. Finally, a practical method for using an oil film as a reference standard of flatness in a Fizeau-type interferometer is presented.
We present preliminary results on the feasibility demonstration of using the rare-earth-doped silica as the IR-to-visible converter. Its principle of operation employs the up-conversion upon pumping with the near IR radiation. The simulation results of the time-dependent 3-D heat transfer study demonstrate the spatial and temporal resolution of this transducer for the constant and impulse irradiation profile, confirming the concept when the Er-doped silica fiber is in contact with a cold reservoir. The preliminary experimental results confirm the feasibility of using the converter for room temperature applications, that correspond to about 10-μm radiation. The error arising from the rare-earth dopant non-uniformity is estimated at +/- 1.5 C.
We propose to use the rare-earth-doped silica as the IR-to-visible converter. We describe its principle of operation employing the up-conversion upon pumping with the near IR radiation. We developed a time-dependent 3-D heat transfer model for fiber geometry with finite element method. We present results of the study to determine spatial and temporal resolution of this transducer for the constant and impulse irradiation profile. We conclude that better temporal and spatial resolution is achieved when the fiber is in contact with a cold reservoir. The cold sink also assists in the rapid response of the device, as the latent image is quickly erased.
A pair of thin prisms may be used to deviate the light beam without changing the image orientation in a vectorial shearing interferometer. The prism rotations determine the position of the wave front and the amount of its tilt. The separation between the prisms and their orientation determine the direction and the magnitude of the beam displacement. We designed a high precision mechanism with a fine resolution to rotate and displace each of two thin prisms. The device incorporates a two-axis calibration system. The angular resolution is 18 arc sec, with a periodic error of 3 arc sec, and a cumulative error of 10 arc sec is predicted.
A pair of thin prisms is used to deviate the light beam without changing the image orientation in a vectorial shearing interferometer. The relative angle between prisms determines the position of the wave front and its tilt. This system is employed to control the displacement of a sheared wave front as a vector quantity and to introduce a controlled amount of tilt in a novel interferometric shearing system. The predicted performance of this wave-front director is confirmed experimentally.