Abstract
An accurate readout of low-power optical higher-order spatial modes is of increasing importance to the precision metrology community. Mode sensors are used to prevent mode mismatches from degrading quantum and thermal noise mitigation strategies. Direct mode analysis sensors (MODAN) are a promising technology for real-time monitoring of arbitrary higher-order modes. We demonstrate MODAN with photo-diode readout to mitigate the typically low dynamic range of CCDs. We look for asymmetries in the response of our sensor to break degeneracies in the relative alignment of the MODAN and photo-diode and consequently improve the dynamic range of the mode sensor. We provide a tolerance analysis and show methodology that can be applied for sensors beyond first order spatial modes.
Highlights
Two fundamentally limiting noise sources in ground based interferometric gravitational wave (GW) detectors and optical clocks are thermal noise [1,2] and quantum noise [3,4,5]
We look for asymmetries in the response of our sensor to break degeneracies in the relative alignment of the mode analysis sensors (MODAN) and photo-diode and improve the dynamic range of the mode sensor
This paper demonstrates MODAN with commercial low noise, high dynamic range, high bandwidth photo-diodes and 1064 nm wavelength light
Summary
Two fundamentally limiting noise sources in ground based interferometric gravitational wave (GW) detectors and optical clocks are thermal noise [1,2] and quantum (projection) noise [3,4,5]. There are proposals to use a spatial Higher-Order Mode (HOM) as the carrier beam to mitigate thermal noise [9,10,11]. Recent proposals [30,31,32] encode witness diffraction orders onto the diffractive optical element (DOE) and use a CCD as a light-sensor. This allows calibration of the relative alignment of between the CCD and DOE but limits the dynamic range. We note that our methodology is similar to mode division multiplexing with Multi-Mode Fibers [33], which is of increasing interest for increasing communications bandwidth [34]
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