Diffuse reflectivity measurement using cubic cavity

Abstract

A method for measuring diffuse reflectivity using cubic cavity based on the variable port fraction method was developed by measuring oxygen P11 line at 762 nm using tunable diode laser absorption spectroscopy. An experimental method to determine the additional path length l0 was presented. We measured the diffuse reflectivity of a cubic cavity with scattering coatings of different thickness. The error of diffuse reflectivity was reduced from 0.004 to 0.0003 when the diffuse reflectivity increased from 0.867(4) to 0.9887(3). A simulation result manifests that the error of diffuse reflectivity has the potential to be further reduced at higher diffuse reflectivity.

Investigating the Relation between Absorption and Gas Concentration in Gas Detection Using a Diffuse Integrating Cavity

“…It indicates that the theoretical predictions by the beam reflection analysis agreed with the experiments. In fact, the theoretical value of L 0 and L ave were 35 and 23.3 cm respectively for this cavity [21,24]. The fitting results agree with the theoretical values within the measured error ranges.…”

Effective optical path length for tandem diffuse cubic cavities as gas absorption cell

“…The single-pass average path length L ave for a cubic-shaped cavity is a constant of 0.67 times the side length of the cavity a. This has been validated by theoretical deduction of L ave of 4 V/S (V is the volume of the cavity and S is the inner surface area) for an arbitrary-shaped cavity [9] and by experiments [10].…”

“…Here, L ave is the single-pass average path length, which varies with the size and shape of the cavity; ρ is the diffuse reflectivity of the scattering internal coating; f is the port fraction (sum of all port areas/inner surface area), including initial port fraction f 0 and additional port fraction f′; and l 0 is the additional path length considering launch and delaunch conditions [6,10]. Tandem cubic cavities were conformed by two cubic cavities, A and B, shown in figure 1(a).…”

“…The experimental EOPL for each tandem cubic cavities were measured when the diameters of apertures in the middle were 2,4,6,8,10,20,30,40,50,60, and 70 mm. If no baffle was added between the two cubic cavities (f ap = 1/6), a tandem cubic cavity can be seen as a simplified cuboid-shaped cavity.…”