Abstract
In visual diffuse transmission density measurement, it is hard to measure optical density (OD) up to 6.0 because the signal to noise is more than 10E-06. Thus, there are only two methods to find the measurement. One is using a highly sensitive detector with low background noise, and the other is improving the incident light flux with a wide spectrum, including visual scope. A new diffuse optics emitter was designed to realize OD measurements up to 6.0. It uses 235 optical fibers on a hemisphere to collect and feed in the incident flux, then emits this flux by a diffuse opal. Thus, an incident light with a high diffuse coefficient and high incident flux was realized for high OD measurement. This emitter has been used in the new national reference of National Institute of Metrology, China (NIM) for diffuse transmission optical density. According to the measurement result in this reference, the OD can be measured up to 6.6.
Highlights
Diffuse transmission optical density is an important optical property of many materials, such as exposed films, special filters, etc. [1,2,3,4]
How to expand the measurement range and decrease uncertainty at the same time is the new challenge in diffuse optical spectroscopy [23,24,25]
The diffuse coefficient β of the diffuse light source based on diffuse optics emitter (DOE) is calculated by the radiance distribution Li (θ, φ, λ) of the bottom surface of the opal, which is shown in Figure 1. β can be given by
Summary
Diffuse transmission optical density is an important optical property of many materials, such as exposed films, special filters, etc. [1,2,3,4]. It is used to evaluate photographs and achieve optical density (OD) calibration, including non-destructive testing (NDT), DNA microarrays in Biosensors and Bioelectronics, human bone image, fMRI cortical mapping, etc. With the rapid development of Biosensors and Bioelectronics and fMRI, the precise request for OD measurement is changing. The measurement range has expanded and the precision has improved at the same time [17,18,19,20,21,22]. Many old diffuse optical instruments, including most national standard density instruments in many countries, cannot satisfy these new measurement demands. How to expand the measurement range and decrease uncertainty at the same time is the new challenge in diffuse optical spectroscopy [23,24,25]
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