TEM Messtechnik Gmbh

Date: Tuesday 6th of August 2024
Time: 13:00 - 14:00
Place: HPF G6
Host: Cornelius Hempel

Frequency-agile laser stabilization techniques and lasers

Thomas Kinder - Development of optical measurement technology, TEM Messtechnik Gmbh (external page LinkedIn)

Abstract: The most sophisticated applications of laser technology typically require a precise knowledge, if not stability, of the laser oscillation frequency. This is especially the case in quantum optics and precision spectroscopy as well as in interferometric metrology.

Methods to frequency-lock a laser to a fixed reference are covered well in the existing literature. In contrast, the more challenging applications are those where the laser must change its frequency, be it continuously or stepwise, preferably whilst remaining locked to some reference. To this end, RF offset locks and cavity locks have spread widely. However, both methods provide very limited agility: RF locks will typically lose the lock upon every quick change of the control frequency, and the frequency range that can be addressed with a single modulator device is quite small compared to the laser tuning range. When locking the laser to an optical cavity, a continuous change of the resonance frequency requires changes of the cavity length – an approach that contradicts the idea of a stable reference. Even a combination of both methods does not lead to a freely and widely tunable locked laser.

To fill this gap, TEM Messtechnik developed the iScan method and system.
It uses a quadrature (I/Q, sine/cosine) signal pair from dedicated interferometers that encode changes of the optical frequency into the phase angle of the quadrature signal pair. Crucially, this removes the need for moving parts, making the measurement scheme both fast and allowing the interferometers to be built with good passive stability. To stabilize the target laser to a fixed frequency, the corresponding locking electronics minimizes deviations from a fixed target phase angle. More interestingly, this target phase angle can also be stepped, allowing for quick (within a few us) and large frequency jumps (many tens of GHz) of the laser, now primarily limited by the properties of the laser as opposed to the instrumentation. Similarly, the target phase angle can also be ramped, allowing the laser to be stabilized during a frequency sweep, for example enabling extremely linear scan profiles.

The talk will cover the theory and practical methods to generate such signals, the respective locking schemes, example configurations and their achievements. It will then discuss the remaining error sources and ideas on how to overcome them.

Webpage: external page TEM Messtechnik GmbH