1. The Technique of Time-Resolved Pump-Probe Speaker: Ho- Jay Ton Advisor: Jia-Hon Lin

2. Outline The Principle of Pump-Probe Experiment Device Two-Photon Absorption Data fitting

3. The Principle of Pump-Probe Case of Photograph Slow shutter Fast shutter For the object of higher speed faster shutter is required to catch the image or it would be indistinct But the shorter time the shutter open the seldom sensitization the CCD got Method: in the dark open the shutter and control the time of flashlight short enough

4. The Principle of Pump-Probe Synchronization ( ): In this case the moment of flashlight and motion of object have the same period and time delay In order to know the full states of motion of object we could control the time delay between flashlight and object motion Case of Pump-Probe Two laser beams with synchronization one of them called pump-beam excited the physical system to produce phenomenon we want to observe Another beam called probe-beam which have fixed time delay to the pump-beam just like the flashlight mentioned before Femtosecond pump pulses induce changes in the transmittance the material and femtosecond probe pulse are used to detect those change

5. The Principle of Pump-Probe So-called differential transmission spectra (DTS) often yield sensitive and reliable information on the semiconductor transmission spectra DTS is the difference between the probe transmission with and without the pump

6. Experiment Device Probe beam controlled by motorized stage varying the time delay Δt between the pump and probe pulse pump power : probe power 10 : 0.5 (in order to produce the minimum disturbance in the sample)

7. Two-Photon Absorption T and T 0 transmission of probe beam ΔT= T-T 0 Under pumping condition carriers move to high energy level Sample α (absorption) decrease ΔT increase If consider the two-photon absorption (TPA) pump and probe beam supply one photon to generate carrier caused measured transmission (ΔT) decreasing

8. Data fitting

10. Pump power=10mw Pump power=30mw Pump power=20mw