Modelocked oscillator question

[johng23]

I have a Ti:Sapphire oscillator which outputs something like 25 fs pulses at 100 MHz (KM-labs if anyone is familiar). The laser has two curved mirrors on either side of the Ti:Sapphire which direct the fluorescence to the end mirrors. Once it is lasing in CW, you translate one focusing mirror closer to the crystal to achieve Kerr lens modelocking.

This laser kit was purchased many years ago and the central assembly came "pre-aligned", so that the precise tilts of these focusing mirrors were defined with respect to the crystal. The manual included precise caliper measurements of all these tilts. It gives detailed procedures for tweaking every single thing in the laser, except for these angles. One gets the sense that they are extremely difficult to align and it needs to be done by the laser gurus who sold you it.

Well, years later I came along and screwed with it, and then in trying to get back to the lasing configuration, I found that those initial measurements were completely wrong. I then went about aligning it in a very simple way by making sure that the fluorescence from the crystal was going to the right places in the laser, etc. It seemed to work OK, but if that's really all there is to it, why would they make it sound like a magical component in the documentation?

So my question is, IS there anything "magic" about the precise angles of the focusing mirrors in a laser resonator of this kind? Either in terms of power, or higher order effects on the pulses, stability, etc?

 

[Valerie Park]

Or is it really just a matter of making sure the fluorescence from the crystal goes to the right places?The answer is yes, there is something magical about the precise angles of the focusing mirrors in a laser resonator of this kind. The angles of the focusing mirrors determine the shape and size of the laser resonator, which in turn affects the power and quality of the laser output. Precisely controlling the angles of the focusing mirrors ensures that the laser resonator is optimally matched to the gain medium, providing maximum output power and stability. It also allows for higher-order effects such as modelocking, which can further improve the pulse quality and stability of the laser output.