DIN 58175-2:2013-07

For temporal characterization of ultra-short laser pulses, different methods have been proposed in literature. Due to their short duration and the much longer response times of all known electronic detector systems a direct measurement of the temporal shape of ultra-short laser pulses is impossible, indirect methods must be applied, with the sampling of the pulse being carried out by a physical event of at least comparable duration. One alternative to comply with this requirement is the use of the pulse to be measured itself as the event of comparable duration. A robust method that is often used for the temporal characterization of ultra-short laser pulses is the optical autocorrelation technique. The output of this measurement is the autocorrelation signal, which does not reflect the temporal shape of the electric field itself but mathematical corresponds to a correlation of the pulse with itself. Thus the autocorrelation function is always symmetrical. As an essential result the full width at half maximum of the autocorrelation function can be determined; however, the full width at half maximum of the autocorrelation function only allows derivation of the temporal full width of half maximum of the pulse shape when certain assumptions about the temporal pulse shape are necessary. This standard specifies the test methods for the determination of the autocorrelation function for ultra-short pulses. This standard addresses the measurement of the temporal characteristics of ultra-short laser pulses, that is, a possible transverse structure of the electric field is ignored. This restriction appears acceptable for a range of practically relevant ultra-short laser pulses, because the beam can often be regarded as nearly homogeneous with respect to its spectral and temporal properties. Furthermore, many applications are not sensitive against a transverse structure because averaging over the beam diameter automatically takes place due to the specific arrangement. The autocorrelation technique can be used in all cases where a direct measurement of the temporal behavior of ultra-short laser pulses is not possible due to their short duration and the substantially longer response times of electronic detector systems. Practical prerequisites are the availability of a suitable non-linear effect and a suitable detector in the relevant wavelength range. The result of this measurement is the autocorrelation function. While the autocorrelation function must neither be confused with the temporal pulse profile nor does it enable to unambiguously reconstruct the latter without further knowledge, it delivers useful yet limited information on the pulse structure of an ultra-short pulse laser. This also means that the half width of the autocorrelation does not allow unambiguous information of the actual pulse duration. Yet, it allows estimation of the pulse duration when a certain pulse shape is assumed, which is frequently found sufficient in applications where the pulse shape is known, for example, from theoretical considerations. More complex measuring techniques that provide additional information allow for the determination of the actual pulse duration under certain conditions. These techniques, however, are beyond the scope of this standard. The committee responsible for this standard is NA 027-01-18 AA "Laser" ("Laser") at DIN.