Why don’t you use a complete common path f-to-2f interferometer for stabilization?

The venteon CEP5 f-to-2f interferometer setup is almost common path. A common path interferometer is typically used with amplified pulses, where due to the available pulse energy a lower efficiency all-in-line setup can be used. With typical pulse energies from an oscillator however, the almost common path version is the most stable and efficient solution. Dividing and recombining the IR part only in the interferometer makes no major stability difference here as it is only a short path length built on a monolithic base. Choosing this way, makes the interferometer insensitive to dispersion of the in-line part of the setup, since the delay between both arms can be controlled easily. The frequency doubling and beat signal generation are all done in-line for best long term stability.

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