In this experiment, an intensity autocorrelator is set up in order to measure the pulse duration of a passively mode-locked Titanium-Sapphire laser with a power of 267mW producing femtosecond pulses. Then this measurement, as well as a measurement of the laser’s spectrum, is used to test the Uncertainty Principle. Intensity autocorrelation is a well-established technique for measuring pulse duration, and is among the more intuitive techniques for this purpose, which is why it was selected for this experiment. The experimental setup was computerized. The delay of one half of the pulse was controlled by a motorized translation stage which was itself controlled by a computer which could scan across the zero delay point of the pulse, and the data from the detector went to a digital oscilloscope and was then saved by a computer. Dispersion was compensated for by negative dispersion mirrors in the laser itself. To calculate the duration of the pulse, it was assumed that the pulses took the shape of sech^2(x). The duration of the laser pulses was determined to be 12.9 fs. The standard deviation of the pulse in time was found to be 6.6 fs, and the standard deviation of the pulse in energy was 1.15*10^(-20) J. When multiplied, the standard deviations give a value of 7.6*10^(-35) Js or 0.72 ħ, which is greater than the theoretical minimum limit given by the Uncertainty Principle of 0.50 ħ.
Relic, Ross N.
"Measuring the Pulse Duration of a Femtosecond Laser Using Intensity Autocorrelation,"
Macalester Journal of Physics and Astronomy: Vol. 11:
1, Article 11.
Available at: https://digitalcommons.macalester.edu/mjpa/vol11/iss1/11