*2.1. Spectrometer Development*

Figure 1 shows the schematic and prototype of the spectrometer designed in this study, which includes a collimator, an optical fiber, a connector, a reflective diffraction grating, a focusing mirror, and a complementary metal-oxide-semiconductor (CMOS) linear sensor. The optical fiber, through which the light enters, is connected to the collimator with an SMA (SubMiniature version A) connector. Since the round-to-linear fiber optic bundle (model No.: BFL200HS02, Thorlabs Inc., Newton, MA, USA) is used as the optical fiber, there is no need to add a separate slit as an entrance aperture. This indicates that the output terminal of the fiber optic bundle, i.e., the linear bundle, acts as the slit. The collimator (model No.: PAF2S-7A, Thorlabs Inc., Newton, MA, USA) is used to collimate the light, coming from the fiber optic bundle, and then send a collimated beam towards the grating. The reflective diffraction grating (model No.: GR13-0605, Thorlabs Inc., Newton, MA, USA) splits the photons coming from the collimator, depending on the wavelength, and then spreads the light across the focusing mirror (concave). The focusing mirror directs the light, at each wavelength, onto the CMOS linear image sensor. The line camera (model: USB line camera 8M, Coptonix GmbH, Berlin, German) which consists of a main circuit board, and the CMOS linear image sensor (model No.: S11637-1024Q, Hamamatsu, Hamamatsu City, Japan) is used as the detector. Each pixel of the CMOS linear image represents a portion of the spectrum that is translated into a measurable value, by a spectroscopy software. A dedicated software was also developed to operate the spectrometer, display the measured data, and store measurement results. The spectral response range of the developed spectrometer was 225–975 nm, and its sampling frequency was 5 kHz.

**Figure 1.** Configuration of the developed spectrometer: (**a**) schematic; (**b**) designed prototype.
