Reconstruction of Transmitted Cherenkov Lights Spectra from the RGB Camera Image
Abstract
Purpose
To develop a computational method for the reconstruction of the spectra of the Cherenkov light transmitted through a fluorescent material from the RGB image data taken by digital color cameras.
Methods
The desired solution of the transmitted photon spectrum, X, can be obtained by solving the following minimization problem: min||X-X0||2 subject to QX = C (1) Here, X0 is the Cherenkov photon spectrum emitted by the MV photon. Q is the camera's sensitivity to RGB colors. C consists of the measured pixel values of three colors. The solution was achieved using the LSQLIN function in MATLAB. For experimental tests of the algorithm, a water bath was irradiated with a 5 x 5 cm2 10 MV FFF beam from the side. A cotton cloth with fluorescein dye was placed on the front wall of the bath. A Canon EOS 6D digital camera captured photos of the beam generated by the transmitted Cherenkov light.
Results
The original Cherenkov light spectrum peaked at 300 nm and decreased gradually with increasing wavelength. The reconstructed spectra showed that without the dye, the transmitted light intensity decreased in the range of 500 to 560 nm but increased in the range of 560 to 660 nm, due to the photon transmission characteristic of cotton, which strongly absorbs photons below 550 nm but effectively transmits those above 550 nm. Meanwhile, when the cloth contained the dye, there was a slight decrease in the photon intensity below 500 nm (blue), but an increase in the range of 500 to 550 nm (green). These changes were caused by fluorescence induced by the fluorescein dye, which absorbs blue light and emits green, fluorescent photons.
Conclusion
The proposed reconstruction method is simple and could successfully reproduce the spectrum of Cherenkov light transmitted through a thin cotton cloth containing a fluorescent dye.