- Conference date: 19-24 September 2005
- Location: Varenna (Italy)
Autocorrelators based on Michelson interferometer using a nonlinear element are commonly used for measuring ultra‐short laser pulses. In principle it is possible to use any nonlinear interaction, for example wave mixing (second harmonic generation), photodiodes with two‐photon absorption, etc. But each of them has its disadvantages. The speed of nonlinear interactions might restrict their application for measurement of ultra‐short pulses. Another disadvantage of most autocorrelators with nonlinear elements is the need for relatively high laser power. Also various factors such as laser instability, quality of nonlinear crystal, and in the first place geometrical factors influence the nonlinear interaction: a little change of the alignment in a scheme with wave mixing can bring to considerable variation in two waves interaction.
In this work we consider an autocorrelator without nonlinear elements. The mirror in one arm of a Michelson interferometer was moved along the optical axis, and the change of interference maxima and minima was registered with a slow IR photodiode. Signal from photodiode (correlation function) was observed by digital oscilloscope. The sech2 laser pulse temporal shape was selected being in a good agreement with the obtained correlation function. The experiments were performed at the University of Milano‐Bicocca using the two laser front ends of the multi‐stage Nd:glass “ATILLA” laser system. The first one was a Quantronix Nd:YLF master oscillator with pulse duration of ∼ 100 ps, the second one a Timebandwidth Nd:glass femtosecond oscillator with pulse duration of ∼ 200 fs.
In conclusion, this technique is very simple, not limited by speed of nonlinear interaction, and in principle it could be used for measuring of pulses with any duration and with very low energy. The quality of optics, mechanics and other elements of the scheme is not essential, but results of measurements are quite precise.
- Michelson interferometers
- Correlation functions
- Ultrafast measurements
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