I have a SESAM and a rare-earth doped fiber (Nufern-TDF-25/400) to do experiment, actually the SESAM is from Batop, its modulation depth is about 20%, the linear cavity is used. I also use the lens to focus the spot on the SESAM, the spot is also 25 um in diameter (the spot is from signal light not pump light), then I got a Q-switched pulses (About μs level). If I want to realize mode-locking. I personally think, in this situation, whether to realize Q-switching or mode-locking depends on the laser spot size. If I could reduce the laser spot on SESAM largely, it is possible to realize mode-locking. Is it right?
Dear Xinyang, passive Q-switching takes place in both cases as in time of "giant" pulse generation so in time of mode locking. However in first case there are lasing in one mode operation meanwhile in the second case lasing develops in many mode operation. Last depends from relaxation time of the saturated absorber in laser cavity. Mode locking needs the saturated absorber with relaxation time less then round trip time in the given cavity while the giant pulse generation develops better with slow relaxing absorber. Besides many mode oscillation needs cavity without any plane parallel elements to exclude accidental interferometers that can depress some modes from the all mode spectra.
There are two differences on the conditions to realize passive mode-locking and passive Q-switching.
1. The modulation depth of SA for Q-switching usually should be larger than the one for mode-locking.
2. The response time of the SA for Q-switcing shoul much shorter than the life time of doped ions on the metastable level. The response time of the SA for mode-locking should be shorter than round-trip time.
The detailed explanation can be found in our papers.
Journal of Lightwave Technology 33(23):4857,2015
Optics Letters 40(16):3699,2015
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Optics