Time synchronization using laser techniques

The author explains why light pulses are an important tool for time coordination and discuss the activities and the problems in this field. The author reviews the scientific and technical problems propelling the search for very accurate time comparison. A laser comparison method is discussed which is very simple in principle. This is followed by a discussion of the first experiments performed in France, the United States, Spain, and China. A new space based experimental method is presented along with the first results, and some specific problems in laser timing along with the kinds of errors one would expect are discussed