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Radiometric and Photometric Measurements
Published in Lazo M. Manojlović, Fiber-Optic-Based Sensing Systems, 2022
An integrating sphere is an optical device that consists of a spherical shell in which inner walls are covered with a diffuse, white, and highly reflective coating. To be able to perform the measurements, there are small holes at the sphere for entrance and exit ports. The main function of an integrating sphere is to spatially integrate the radiant flux by a uniform scattering or diffusing effect that occurs at its inner walls. Light rays, which are incident at any point on the integrating sphere inner walls, are due to the multiple scatterings, distributed evenly to the all other points at the inner sphere surface. An integrating sphere is typically used with some light source and a detector for radiant flux measurement and it has become a standard instrument in optical radiometry and photometry. It has a unique function of the total flux measurement of any light source in a single measurement. Typical integrating sphere arrangement is presented in Figure 2.15. The light, which radiant flux ΦI is to be measured, enters the integrating sphere through the input hole with the area of entrance opening of AI. Due to the multiple scatterings at the inner highly reflective and diffusive walls, the light emanating from the source illuminates the inner walls with uniform irradiance E.
Light Detection
Published in Araz Yacoubian, Optics Essentials, 2018
To measure total optical power from a source that has a wide range of angles, such as emission from an LED, an apparatus called an integrating sphere can be used to collect the total light emission. A basic diagram of on integrating sphere is shown in Figure 3.3. Measurements made with an integrating sphere are insensitive to detector position, and is therefore suitable for nonuniform and diverging source measurements. By the time light is received at the photodetector, it is scattered from the inside walls of the integrating sphere and is hightly attenuated, which is a useful feature for making high-power laser measurements.
Colorimetry
Published in John G. Webster, Halit Eren, Measurement, Instrumentation, and Sensors Handbook, 2017
In the most common diffuse geometry, the illuminator includes an integrating sphere. An integrating sphere is a hollow metal sphere coated with a highly reflecting white coating with openings for the light source, the sample, and the receiver. The instrument’s light source projects a beam of light onto the integrating sphere’s wall. The light is reflected many times by the sphere’s wall, and the sample is illuminated from all angles. When measuring in the diffuse/normal mode, d/0, the receiver views the sample along its normal. When the receiver is positioned in this manner, the specular reflection is directed back toward the light source and is not measured.
The upconversion quantum yield (UCQY): a review to standardize the measurement methodology, improve comparability, and define efficiency standards
Published in Science and Technology of Advanced Materials, 2021
Callum M. S. Jones, Anna Gakamsky, Jose Marques-Hueso
Optics are used to align the source with the UC sample, which is placed inside the IS. The integrating sphere possess walls made of material (e.g. SpectralonTM) that is highly reflective (>99%) across a broad range of wavelengths. A baffle is places inside the integrating sphere for ensuring all sample emission is isotropic and subject to similar loss effects due to contact with the reflective walls [31]. It accomplishes this by blocking emission light from making direct contact with the measurement detector. The light from the integrating sphere exits through an emission port, where additional optics guide it through an emission monochromator and towards the detector. Photon-multiplying tubes (PMTs) and charge-couple devices (CCDs) detectors are ideal for detecting light in the UV/visible/NIR range. Careful consideration should be given to the detector as it defines the measurement range, resolution, noise level, speed, and cost of the setup. For example, CCDs typically provide greater sensitivity at longer wavelength ranges compared to PMTs [53]. Additional equipment includes the short-pass and long-pass filters required for minimizing second order effects, as well as the bandpass filters used for optimizing the bandwidth of the excitation. Optical density filters are also utilized for controlling the excitation light intensity, in addition to the emission light intensity, to protect the detectors from oversaturation damage. Finally, although used in relative UCQY analysis, polarizers are not needed for absolute methods [73].
Manufacture and characterization of a 3D-printed integrating sphere
Published in Instrumentation Science & Technology, 2021
Luismar Barbosa da Cruz Junior, Luciano Bachmann
The integrating sphere theory assumes that the internal wall has uniform and high diffuse reflectivity. It also requires a small sample port area, compared to the total internal surface area of the integrating sphere, typically less than 4%.[9] The coating must not display fluorescence. A baffle is also required to avoid direct radiation from being reflected or transmitted from the sample to the detector.[10]