Device for determining the speed of an object

摘要

The invention relates to a device for determining the speed of an object (2), having a transmitter (1) which emits monochromatic light in the direction of the object (2), and an interferometer (4) in which the radiation scattered by the object is guided along two paths having different optical path lengths and is finally brought to interference. The changes in the path differences which are caused by movement of the object are perceived as frequency changes with the aid of a photodetector arrangement (11). The aim of the invention is to simplify the design of such a Doppler interferometer (4), and to prevent it from becoming maladjusted by external influences. According to the invention it is proposed for this purpose firstly to polarise the scattered radiation linearly in a polariser (8) and subsequently to split it up into the two components of different optical path lengths with the aid of a birefringent (double reflecting) crystal (9), and thus to combine the two optical paths geometrically. After renewed polarisation, the frequency changes can be established using a photodetector arrangement (11) and subsequently evaluated. <IMAGE>