Improved Open Photoacoustic Helmholtz Cell

Abstract

This paper presents the design of an open photoacoustic Helmholtz cell in which high acoustic volumes with quarter-wave ducts act as high-impedance separators between the main Helmholtz cell structure and the exterior. As a result, penetration of the external acoustic noise into the cell was substantially reduced in comparison to earlier open Helmholtz cell designs. Although the presented cell is not windowless, the photoacoustic background signal resulting from the absorption of the light by the windows is significantly lower in comparison to standard Helmholtz cells. Such an effect was obtained by locating the windows not at the relatively small sample cavity, but at the acoustic buffers, for which the volumes are two orders of magnitude higher. The proposed cell is dedicated for gas or liquid measurements, and its design allows for constant flow of the fluid. Hence, it can be used in continuous, real-time photoacoustic measurements.