Frequency Stabilization of Four Cascaded Optical Cavities

This research covers the development and application of multiple low- noise high-bandwidth lockboxes to position the mirrors of four cascaded optical cavities using piezo actuators for frequency locking with a preci- sion of 40 Hz. The design and fabrication of a custom printed circuit board that hosts two ARM-based microcontrollers for signal processing are elucidated. By measuring the impedance of the piezo actuators over a large range of frequencies, we found several electromechanical resonances ranging from a few kHz to a main resonance at 80 − 100 kHz. It was found that these resonances greatly impact the ability to lock the cavity to the laser source and thereby impose bandwidth limitation on the feedback. By avoiding excitation of such resonances by reducing the feedback bandwidth to below the first prominent resonance at 2.5 kHz, we were able to achieve a high quality lock of a single optical cavity. Using a reduced bandwidth of 250 Hz and a reduced modulation frequency of 1...Show moreThis research covers the development and application of multiple low- noise high-bandwidth lockboxes to position the mirrors of four cascaded optical cavities using piezo actuators for frequency locking with a preci- sion of 40 Hz. The design and fabrication of a custom printed circuit board that hosts two ARM-based microcontrollers for signal processing are elucidated. By measuring the impedance of the piezo actuators over a large range of frequencies, we found several electromechanical resonances ranging from a few kHz to a main resonance at 80 − 100 kHz. It was found that these resonances greatly impact the ability to lock the cavity to the laser source and thereby impose bandwidth limitation on the feedback. By avoiding excitation of such resonances by reducing the feedback bandwidth to below the first prominent resonance at 2.5 kHz, we were able to achieve a high quality lock of a single optical cavity. Using a reduced bandwidth of 250 Hz and a reduced modulation frequency of 1.9 kHz, we demonstrated the locking of four cascaded cavities and achieved an optical transmission of T ≈ 40%, limited mostly by optical alignment. Finally, we show an initial lock freeze procedure for three cascaded cavities in which 90% of the transmission during the locked state is retained for a period of 4.9 seconds, while providing no feedback on the piezos.Show less

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Frequency Stabilization of Four Cascaded Optical Cavities