26th Australian Institute of Physics Congress and the Australian and New Zealand Conference on Optics and Photonics

Method of Passive Acoustic Noise Suppression for High-Resolution Optical Spectroscopy

Not scheduled

20m

Belinda Hutchinson Building (The University of Sydney )

Poster AIP | Quantum Science and Technology (QST)

Speaker

Aidan Dugdale (The University of Sydney)

Description

Laboratory environments emanate acoustic noise from a variety of sources that can affect the amplitude and frequency stability of optical elements (especially lasers) in high-resolution spectroscopy experiments. Examples of noise sources include talking, doors closing, or from lab-specific sources such as the pulse tube of a dilution refrigerator. Here, I will present a template for the design, fabrication, and characterisation of a passive acoustic isolation enclosure to suppress the effects of acoustic noise. Acoustic noise coupling into laser systems is a common pathway for generating laser frequency noise. Laser frequency noise broadens its optical linewidth, which can obscure or artificially broaden spectroscopic measurements. Therefore, achieving high-resolution spectroscopy requires acoustic isolation to suppress spectral broadening, motivating the construction of the enclosure.

The enclosure is custom-fabricated, made from high-density polyethylene (HDPE) with two layers of mass-loaded vinyl and a layer of convoluted foam. The HDPE reflects acoustic noise via acoustic impedance mismatch with air, whilst the layers of mass-loaded vinyl absorb acoustic noise due to being a high density material. Finally, convoluted foam is a measure to avoid internal resonances from building up. Since convoluted foam has low density, it also provides minor decoupling of the laser system from direct contact with the rigid exterior of the enclosure, thereby suppressing direct transmission of mechanical waves to the laser.

The noise suppression capability of the enclosure was quantified using a fibre delay-line interferometer, a method chosen due to its high sensitivity to perturbations. The speaker was calibrated such that the frequency-dependent outputs held a flat volume profile, allowing an accurate measurement of the spectral response. Each subsequent layer showed reduced acoustic sensitivity across the 50 Hz to 20,000 Hz acoustic band, demonstrating the usefulness of passive isolation.