Diffraction from Embedded Reflectors in Li-Baker HFGW Detector

Abstract

Abstract Recent experimentation and speculation about the design of a sensitive detector for high-frequency gravitational waves (HFGW) has centered around a number of principles. Those detectors that have been built so far have not yet realized sensitivity sufficient to investigate the cosmic high-frequency relic gravitational wave background, analogous to the cosmic microwave background. A proposal for a more sensitive HFGW detector due to Baker and based upon a principle first enunciated by Li and co-workers has become known as the Li-Baker detector. Its possible design details are currently the subject of scientific debate. One significant aspect concerns the design of the reflector(s) needed to direct the photons produced by the incident HFGW towards a set of microwave receivers. If the reflector(s) is(are) placed within a Gaussian microwave beam, then they become sources of diffraction that can potentially overpower the required signal because the diffracted power will not be distinguishable from photons produced by interaction with the HFGW. This means that diffraction is potentially a source of shot noise at the microwave receivers and, if extreme, may also swamp the receivers. In this paper some estimates of this diffraction are obtained and the design of the reflector(s) is discussed. The Li-Baker detector must be designed in such a way that the diffraction reaching the microwave receivers is reduced as far as possible by employing a suitable geometry and highly absorbent walls for the interaction volume.