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Fiber‐Optic Probes for Small‐Scale Measurements of Scalar Irradiance
Author(s) -
Rickelt Lars Fledelius,
Lichtenberg Mads,
Trampe Erik Christian Løvbjerg,
Kühl Michael
Publication year - 2016
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/php.12560
Subject(s) - irradiance , optical fiber , optics , scale (ratio) , scalar (mathematics) , physics , mathematics , geometry , quantum mechanics
A new method for producing fiber‐optic microprobes for scalar irradiance (=fluence rate) measurements is described. Such fine‐scale measurements are important in many photobiological disciplines. With the new method, it is possible to cast spherical 30–600 μm wide light integrating sensor tips onto tapered or untapered optical fibers. The sensor tip is constructed by first casting a clear polymethyl methacrylate ( PMMA ) sphere (~80% of the size of the final probe tip diameter) onto the optical fiber via dip‐coating. Subsequently, the clear sphere is covered with light diffusing layers of PMMA mixed with TiO 2 until the fiber probe exhibits a satisfactory isotropic response (typically ±5–10%). We also present an experimental setup for measuring the isotropic response of fiber‐optic scalar irradiance probes in air and water. The fiber probes can be mounted in a syringe equipped with a needle, facilitating retraction of the spherical fiber tip. This makes it, e.g . possible to cut a hole in cohesive tissue with the needle before inserting the probe. The light‐collecting properties of differently sized scalar irradiance probes (30, 40, 100, 300 and 470 μm) produced by this new method were compared to probes produced with previously published methods. The new scalar irradiance probes showed both higher throughput of light, especially for blue light, as well as a better isotropic light collection over a wide spectral range. The new method also allowed manufacturing of significantly smaller scalar irradiance microprobes (down to 30 μm tip diameter) than hitherto possible, and such sensors allow minimally invasive high‐resolution scalar irradiance measurements in thin biofilms, leaves and animal tissues.