Two Photon Absorption

Setup

This is layout of our test in laser room. Input beam is split into two arms: fixed(we call it “probe beam”) and with delay stage(we call it “injection beam”). One set of polarizer and half-wave plate is installed before beam splitter to control input energy. The other set is installed on the probe beam path to equalize energy of two beams.

Signal on photodiode

The photodiode G1962 from Hamamatsu was connected to scope via circuit board designed by Radiabeam. The plot below shows the signal level of two single beam arms and when they are overlapping and non-overlapping respectively. A significant increase of signal was observed when they are correlated.

Scan

We started the scan from far away where signal level did not respond to scan and ended when signal went back to same level. We do not fully understand the distribution of the scan. My guess is it is the convolution of two pulse profile, but it does not appear as Gaussian. Maybe you have a better idea. If we know the distribution, we can estimate the pulse duration.