|M.Sc Student||Assaf Lazar|
|Subject||A Method to Improve the Accuracy of Velocity|
|Department||Department of Physics||Supervisors||Professor Emeritus Ron Amiram|
|Dr. Amit Ben-Kish|
|Full Thesis text - in Hebrew|
The velocity history of a moving object can be concluded by measuring the frequency shift of light reflected from it (Doppler shift). The frequency shift can be measured with a velocity interferometer, which translates frequency change to a change in the interference pattern. The Frequency per Fringe constant (FPF) is the ratio between the frequency change and the change in the interference pattern, and accordingly its accuracy has a major influence on the accuracy of the measurement. It is usually calculated from the interferometer optical parts specifications, and then confirmed in an experiment which includes other velocity diagnostics or another interferometer. The calculation uses many parameters, some of them difficult to be measured directly. Accordingly, a measured accuracy of few percents is usually achieved. We suggest here two original methods to measure the FPF directly with high accuracy by measuring the changes in the interference pattern caused by a well known frequency shift of the light. The FPF of two velocity interferometers were measured by a calibration system which was built according to one of the suggested methods. The FPFs were found to be 0.5% different from the FPF values that were calculated previously from the interferometer optical parts specifications. From an experiment in which the two interferometers took part, we concluded that replacing the calculated FPF with the measured FPF reduced significantly the difference between the velocities.