Characterization of ultrashort pulses

The spectacular development of ultra-short pulse lasers raises a very specific metrology problem, insofar as the light pulses produced are the shortest events known to man. It is therefore not possible to use an even briefer phenomenon to characterize the ever-shortening pulses produced by such lasers. As a result, ultra-short lasers could only be developed in conjunction with new characterization methods, which are the subject of this article.

The extraordinary diversity of methods devised over the last few decades cannot be covered exhaustively here, so a number of sometimes arbitrary –– choices have had to be made. First of all, by short or ultra-short pulse we mean a pulse whose duration is between a few femtoseconds and a few picoseconds. For longer pulses, electronic measurement methods may be preferable. Conversely, the sub-femtosecond (or attosecond) range is the subject of very specific measurement methods not developed here, even if these methods often derive from concepts that will be discussed in this article. Moreover, aspects such as pulse contrast or carrier phase with respect to the envelope will not be discussed, despite the essential role they play in particular in the field of high-intensity physics.

After a reminder of the fundamental principles that enable us to distinguish two main classes of measurement methods, the article will deal successively with so-called non-stationary methods (most often linear), and then with so-called non-linear methods, which exploit second- or third-order optical non-linearity.