Principle of an intensity autocorrelator

1. Principle of an intensity autocorrelator The incident beam is divided by the beam splitter into two equal parts and a variable time delay τ is put on one arm by a translation stage. The two beams of intensity I(t) and I(t-τ) are focused into a second-harmonic generation crystal to generate a signal.

2. incident light translation stage concave mirror BS time delay BBO silver mirror iris PMT Fig 1. Schematic diagram of an intensity autocorrelator BS: 50:50 beam splitter BBO: β-Barium borate, a second harmonic generation crystal PMT: photomultiplier tube

3. Delay = 0

4. Delay = 0.5

5. Delay = 1

6. Delay = 2

7. Delay = 3

8. Delay = 4

9. Delay = 5

10. Simulated signal intensity vs. delay

11. Plot acquired by labview directly The plot was acquired by measuring the Ti- Sapphire laser in Tom Weinacht’ lab.

12. Plot with a portion of data • The pulse duration is 232.0159 fs.

13. Discussion about the pulse length The group-velocity dispersion for C7980 fused silica at a wavelength of 780nm is 384.6154 /cm, the path length in the glass is about 2.2cm and the initial pulse length is about 60 fs. The is 71.6 fs. If the GVD for SF10 is used instead, which is 1615 /cm, the calculated is 174.8033 fs. All the parameters are in the document “Optical cast plastic filters” from CVI website.