Reproducing the Velador Experiment
Filter Selection
In Osadchey’s original experiment, an attenuating filter was installed at the laser. The CCD camera lens was removed and the attenuated laser was projected directly onto the CCD chip.
Low resolution CCD cameras are not typically equipped with shutters, and can provide effectively continuous image feeds. Image capture can be performed via remote computer control on many models, and the camera used should be selected for this feature.
Removal of the camera lens should be unnecessary. Internal reflection within the camera will occur if the lens is not removed. However, this can be compensated, and proper alignment of the reflected image artifact can amplify motion effects.
Drifting of the laser beam can be exaggerated by tilting the plane of incidence. In Osadchey’s original experiment, the plane of incidence is the CCD chip surface. Tilting this surface can exaggerate motion, but also exaggerates the angular width of the laser beam. A more practical alternative may be to interpose a translucent screen at an angle between the CCD chip and laser, and measure drift by photographing that screen. This should eliminate interference patterns within the CCD chip surface, but may create difficulties with internal reflection within the beam path. The screen should preferably cover the camera aperture completely, and not allow any clear line of sight to the beam path cavity wall. Leaving the lens in place will also affect the resolution limit, and thermal behavior of the screen must also be considered.
One sheet of 20# white cotton copy paper is sufficient to block the majority of the laser light, depending on screen position. Positioning the camera at a distance of a few centimeters behind the screen will allow a full screen view of the diffuse light transmitted through the screen. The selected screen should be as flat and as light weight as possible. Paper compressed between two sheets of glass is optimal, but a more lightweight configuration may be a sheet of paper stretched across a 2.0 cm aperture in a wood frame. The screen is constructed of a material which has a limited service life (paper), and so should be constructed with eventual replacement in mind.
The optimal position of the screen can be calculated, based on an observed width of 1/3 of the camera field of view.
The vertical field of view is less than the horizontal. Thus, elevational shifting of the incident laser may require greater separation between screen and camera to view the full range of motion.
Ink markings on the paper screen should be visible at this separation distance, and can be used for reference.
(Update 7/8/07)
Phase 1 of my experiment has been completed without use of a filter. I found that internal reflection inside the filter was creating additional image noise, and leaving the camera lens in place was creating false images due to internal reflection in the camera. I removed the lens from the camera, and reduced the power supplied to the laser, decreasing its intensity. The laser light is only 6 times the intensity of the sun, and the camera CCD is able to accomodate this level of illumination without burning out - particularly if the laser power level is reduced.
