RP DisCav – Advanced Laser Resonator Design and Optimization
RP DisCav is a powerful software for calculations on optical resonators, in particular on laser cavities. It has been developed by Dr. Rüdiger Paschotta. So far, RP DisCav is not for sale, but allows RP Photonics to do laser designs and the like within consulting contracts, requiring a rather limited amount of time. Dr. Paschotta has great experience in resonator design.
Main Features
- RP DisCav can calculate a wide range of properties of such cavities, such as the variation of the beam radius, the sensitivity of the resonator mode e.g. to thermal lensing and misalignment, dispersion from geometric effects, etc.
- It also facilitates sophisticated optimizations. A figure of merit of arbitrary kind can be easily defined, and refined algorithms are used for minimizing this figure of merit by adjusting resonator properties. If necessary, arbitrary boundary conditions can be observed such as preserving certain symmetries, limiting the difference of certain quantities, etc.
- The software can draw (to scale) the resulting resonator setup and provide basically arbitrary plots showing all its properties.
Examples of Graphical Output
The following graphs have all been made with RP DisCav and illustrate some of its features. They all apply to the example of a femtosecond Ti:sapphire laser with a prism pair for dispersion compensation and a SESAM for passive mode locking. The software is very flexible. Design graphs of new kinds can be easily defined; the given examples do not represent a fixed set of choices.
The first graph shows the resonator setup. The Ti:sapphire crystal is located between two curved mirrors with radii R1 and R2. Such graphs allow for a convenient check for the correctness of the resonator structure and parameters.
The next graph shows the evolution of the beam radius in tangential (red) and sagittal (blue) direction. The beam is collimated on the left-hand side (the one of the output coupler mirror) and shows two peaks at the positions of the prisms. It then goes through a sharp focus in the Ti:sapphire crystal, and is later again focused on the saturable absorber mirror (SESAM) on the right-hand side.
Now we consider the variation of the beam radii when the length e (the distance between the mirror with radius R1 and the Ti:sapphire crystal) is varied. (The default value is e = 3.31 cm.) The dotted curve shows the horizontal shift of the beam in the laser crystal which would be caused by a tilt of 0.1 mrad of the output coupler. This demonstrates that for e near 3.35 cm the resonator would be very sensitive to misalignment. This effect would not occur in the second stability zone (e = 3.46 cm to 3.55 cm).
Finally, we investigate the influence of the focusing power of the thermal lens in the laser crystal on the mode radii. For a weak thermal lens, the mode size will slightly increase on the output coupler and decrease in the laser crystal and on the SESAM. The Kerr lens also tends to decrease the mode size in the laser crystal, but the effect is too weak for Kerr lens mode locking. The stability range would have to be shifted to the right in order to achieve this. (The corresponding optimization is of course also possible with RP DisCav.)
