Experimental Insights on Factors Influencing Sensitivity of Thin Film Narrow Band-Pass Filters

First time study for development of relationship between design and fabrication of thin film narrow-pass filters simulated using the Essential Macleod optical coating design program and verified through experimental data. In thin film narrow band-pass filter's design, can design better filter by changing some parameters, but the theoretical designs are often difficult to achieve. The sensitivity of thin film narrow band-pass filters are mainly influenced by the refractive index of cavity layers, number of mirror layers, interference order and number of cavities. Based on analysis of all these aspects, laws of influence are obtained. A narrow band-pass filter with super wide rejection band was designed and fabricated to verify the simulation results, showing a good agreement between the experimental and theoretical observations.

Attention and the Contextual Interference Effect for a Continuous Task

Many studies have shown that practicing several motor tasks in a random (high contextual interference) order promotes motor learning relative to practicing the same tasks in a blocked order (low contextual interference). The facilitative effect of high contextual interference has been attributed to more frequent intertask comparisons, greater difficulty in recalling task solutions between trials, and the dissimilarity among the various tasks. Each of these explanations suggests that task difficulty is increased by high contextual interference. The hypothesis of this study was that this increase in task difficulty during practice would be associated with a higher attention load during practice. This hypothesis was supported; however, high contextual interference promoted only a transient increase in retention. The short-lived effect was attributed to the continuous nature of the task and was discussed in terms of the necessary conditions for contextual interference to emerge.

Low Order Fabry-Perot Low Dispersion Multicolor Large Field Survey System

Crossing a low interference order Fabry-Perot etalon with an objective prism on a Schmidt telescope leads to a simple large field multiband spectrophotometric survey system well-adapted to the study of the spectral energy distribution of faint galaxies and redshift estimates.

A long-term radial velocity program of high accuracy with a small telescope

We are making accurate observations of the change in Doppler shift of stellar absorption lines. The purpose is to detect the oscillatory reflex motion due to planets orbiting stars. The scrambling of incident light by an optical fiber and the stability of wavelength calibration by a Fabry-Perot etalon provide immunity to systematic errors. Selecting several echelle diffraction orders in the vicinity of 4250–4600 A, which are imaged on a CCD, about 350 points on the profile of the stellar spectrum are sampled by successive orders of interferometric transmission through the etalon. At 4300 A each interference order is 47 milliangstroms wide and the sample points are 0.64 A apart, causing distinct, widely-spaced monochromatic images of the entrance aperture to be formed in the focal plane of the camera. Changes in Doppler shift modify the relative intensities of these images, according to the slope of the spectral profile at each point sampled. To simplify operation and enhance sensitivity, the instrument is being operated as a null-measurement accelerometer, responding only to changes in radial velocity. With an argon emission line lamp the interferometer is calibrated to two parts in 100 million; this corresponds to ± 6 meters/sec in Doppler shift. These calibrations show instrumental variations of ± 27 meters/sec on a time scale of months; observations of stars are corrected for such changes. The internal repeatability of observations of the differential Doppler shift of Arcturus (K1 IIIb; B=1.19) is ± 6 meters/sec for each exposure of 600 square meter-seconds. These exposures are obtained in 15–20 minutes with a 0.9-meter telescope. The external repeatability (day-to-day differential accuracy) of nightly averages of stellar observations is ± 20 meters/second.

The LPL Radial Accelerometer

We have begun to observe radial velocities of stars with an optical spectrometer designed for unusually high accuracy. Light from a star image in the focal plane of a telescope is fed to the entrance aperture of the spectrometer by a single optical fiber. Wavelengths are calibrated by transmission of collimated light through a tilt-tunable Fabry-Perot interferometer. The scrambling of incident light rays by the optical fiber and the intrinsic stability of the Fabry-Perot etalon provide immunity to the sources of systematic errors that plague conventional radial velocity meters. The spectrum is dispersed by an echelle grating crossed with another plane reflection grating. Several echelle orders in the vicinity of 4250-4600 Å are imaged in a two-dimensional format on a charge-coupled (CCD) array of detectors. About 350 distinct points on the profile of the stellar spectrum are sampled by successive orders of interferometrie transmission through the etalon. In the vicinity of 4300 Å each interference order is 47 milliangstroms wide and the sample points are 0.64 Å apart, resulting in distinct , widely-spaced monochromatic images of the entrance aperture to be formed in the focal plane of the camera. Changes in Doppler shift cause changes in the relative intensities of these images, according to the slope of the spectral profile at each point sampled. The instrument is being operated as a null-measurement accelerometer, sensitive only to changes in radial velocity, which simplifies operation and enhances sensitivity. With an argon-filled, iron hollow cathode emission line lamp, the interferometer can be calibrated to two parts in 100 million; this corresponds to ± 6 meters/sec in Doppler shift. Calibrations of the interferometer show variations of ± 27 meters/sec on a time scale of months; observations of stars are corrected for such changes. The internal repeatability of observations of the differential Doppler shift of light from the integrated disk of the Sun is ± 6 meters/sec. The corresponding result from about 70 observations of Arcturus (Kl IIIb; B=1.19) is ± 40 meters/sec internal repeatability for each exposure of 20 square-meter seconds. The external repeatability (day-to-day differential accuracy) of nightly averages of stellar observations is ± 20 meters/second. Since the internal precision on the sun and the argon lamp is much better than it is with short exposures on Arcturus, the quality of our observations of stars is limited by the rate of detected photons. This justifies averaging a number of short exposures of a star to approach “laboratory” precision.