I understand this is common in femtosecond fiber lasers. This is because of instability in the soliton formed due to the long nonlinear interaction lengths in fibers. But what if I observe similar sideband from the Ti:Sapphire laser oscillator. Is this detrimental to the laser performance ?
Together with the weak periodic disturbance due to the discrete nature of dispersion and nonlinearity, in a bulk soliton mode-locked laser additional disturbances can result from the periodically occurring losses and amplification in the laser resonator. When the laser is driven too far into the soliton mode-locking regime, the pulses become unstable. Kelly sidebands thus indicate that the pulse duration is near the minimum possible value.
I would say that Kelly sidebands in Ti:Sa case mean that the cavity dispersion is too close to zero.
The lowest-order Kelly sidebands actually appear in a Kerr-lens mode-locked Ti:sapphire laser, where the overall cavity dispersion crosses zero. In my experience, they are not detrimental to the laser performance unless they are too close to the wavelength range where the laser is above threshold. Then, slight fluctuations of the pulse energy might move them in and out of the spectrum, leading to leaps in the pulse energy (interestingly not in the average power). Of course, they drain power out of the pulses into the cw spike(s) but this is usually negligible. Also, according to Haus (IEEE Journal on Sel. Topics in QE, vol. 6 (2000) p.1173), they limit the pulse width that can be achieved by KLM from a certain cavity configuration.
Matthias, it's nice to hear from you! You remember such details, wow
Sorry, this should read: "... too close to the edges of the wavelength range ....".
Thank you Matthias and others. This information is important as my Quatronix oscillator is displaying a side-band. The problem is if i try to walk the cavity and get rid of this band or do other minor changes like slit-size or prism movement, i lose the over all stability as well as the output power. Now i can concentrate on other things.
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