LAMPI DI LUCE: DAI MILLISECONDI AGLI ATTO SECONDI

Mankind has always been interested in studying the movement of ever faster objects upon using ever shorter light pulses. As a first example of a study of macroscopic samples, mention will be made about the study of a horse, while galloping, as obtained by the photographer Eadweard Muybridge around the end of years ‘800. He was in fact able to obtain a complete recording of the horse movement upon using an ingenious system of several cameras, placed along the horse racing, equipped with shutters with a record opening time of about 2 millisecond (1 ms=10–3 s). About 50 years later (1930) the introduction of flashlamps allowed the achievement of light pulses with duration of about one microsecond (1 μs=10–6 s). Upon using flashlamps in a repetitive mode, it was then possible to record the movement of much smaller and hence much faster objects (e.g. a bullet while crossing an apple or the fast movement of a golf player while hitting the golf ball). It was, however, only after the invention of the laser (T.H. Maiman, 1960) that people became able to generate much shorter light pulses. From initial pulse durations (middle of years ‘60) of about 10 picosecond (1 ps= 10–12 s), one could then generate (during years ’90) laser light pulses of a few femtoseconds (1 fs=10–15 s) down the present values of about 70 attoseconds (1 as=10–18 s). During all these years after laser invention, the research group at the Physics Department of Politecnico di Milano, leaded by the author of the present paper, has always been at the forefront of the international research to generate and utilize laser pulses of ever shorter duration. After the introduction of the first laser at the Politecnico di Milano at the beginning of 1963 (more than 50 years ago!), the research group was able to obtain light pulses of about 5 picoseconnds in 1969, a record value for that time. The same group then obtained record values of light pulses of about 4,5 femtoseconds, at the end of years ’90, and of only 130 attoseconds around the middle of years 2000. Ultrashort laser pulses have been used, throughout all these years, by a large number of international groups to investigate the ultrafast dynamic behavior of molecules, molecular complexes, and solid state nanoscopic materials (such as quantum wells and quantum dots). As a representative example, some discussion will be presented about a recent work made by the research group of Politecnico about the retinal contained in the rodospin protein, a basic element for human vision.