1. Generation of short pulses Jörgen Larsson, Fysiska Instutionen Lunds Tekniska Högskola

2. Generation of short pulses Cavity modes Locked cavity modes Time-bandwidth product Active mode-locking Acousto-optic modulation Passive modelocking Hybrid modelocking techniques Kerr lens modelocking SESAM Synchrnously pumped dye lasers Distributed feedback lasers Fiber lasers Short-pulse accelerator sources Group velocity dispersion Group velocity dispersion compensation Prism compressor Chirped mirrors

3. Representation of short pulses Gaussian pulses Carrier EnvelopeAmplitude Frequency

4. Representing ”chirp”

5. Group velocity dispersion

6. Modes in a cavity Gain profile (Gain) bandwidth Mode spacing

8. Fresnel diagrams

9. Time-bandwidth product

10. Time-bandwidth product- How short pulses can we get? FWHM of the intensity in the temporal domain

11. Time-bandwidth product- How short pulses can we get? FWHM of the intensity in the spectral domain Next we determine the width in the spectral plane

12. Time-bandwidth product- How short pulses can we get? Now lets calculate the time-bandwidth product for a gaussian (unchirped) pulse If the pulse is chirped it is wider in the temporal domain

13. Time-bandwidth product- How short pulses can we get? Task for the interested student: A Ti:Sapphire laser operating at 800 nm has a 120 nm FWHM spectrum. What is the shortest pulse we can get from this laser?

14. Classes of methods for modelocking Active modelocking: From an active component in the cavity (typically an optic modulator driven by an RF-frequency) Passive Modelocking From a passive component in the cavity (Saturable absorber, kerr lens......)

15. Active modelocking Acousto-optic modulation

17. Generation of sidebands in an AOM Optical wave Acoustic wave Optical wave in presence of acoustic wave

18. Generation of sidebands in an AOM (travelling wave) If a<<1 Euler’s formulae

19. Generation of sidebands in an AOM (travelling wave-strong Rf- field)

20. Generation of sidebands in an AOM (standing wave) If a<<1 Euler’s formulae

21. Active modelocking Fig 3.7

22. Active modelocking Fig 3.8

23. Passive modelocking Saturable absorber Fig 3.12

24. Passive modelocking Saturable absorber Fig 3.13

25. Gain vs intensity Fig 3.14

26. Passive modelocking

27. Passive modelocking-saturable absorber Fig 3.17

28. Passive modelocking Saturable absorber

29. Passive modelocking Kerr lens

30. Passive modelocking - Saturable semiconductor mirror (SESAM)

31. Synchronous pumping

32. Frequency filtering

33. Passive modelocking-saturable absorber Fig 3.19

34. Hybrid modelocking Fig 3.20

35. Hybrid modelocking Fig 3.21

36. Titanium Sapphire energy level diagram

37. Passive modelocking-Kerr lens (early design)

38. Modern Titanium Sapphire laser