# Real-Time Measurement of Photodissociation with a Static Modulated Fourier Transform Spectrometer
## 2 Methods
### Experimental Setup  
Rhodamine-6G (Rh-6G), the solid dye, was fabricated in the laboratory to investigate the fast decaying fluorescence due to photodissociation when it was irradiated by the intense absorbing photon energy. In a polymerized solid dye, the sufficient pumping photon energy can affect the bond energy between solid dye and nanomaterials, and it can be measured using the proper inspection method that is proposed in this study. As the host material, 20 mL of methacrylate (MMA) having high transmittance in the absorption and fluorescence wavelength band of the dye was prepared. Since Rh-6G has low solubility in MMA, it was first dissolved in methanol of 3 mL for 2 mM molarity and then mixed with MMA. Rh-6G was prepared at a molar concentration of 2 mM. In order to induce the polymerization reaction, 1, 1\({}^{\prime}\) Azobis (crychlohexa-necarbonitrile) was used as a directing agent, and 1 wt% of MMA was appropriate. Molecular sieves of 40 mg were inserted into the solution in the form of granules with diameters and pores of 1.6 mm and 0.4 nm, respectively.  
The polymerization was initiated at high temperature for active chemical reaction. It is very crucial to keep the temperature of the solution constant during the polymerization process. A mold containing the dye solution was put into a 100 mL water bath and heated until it retained the ambient temperature. In the initial state, the temperature of the water bath was adjusted to 90 \({}^{\circ}\)C until the dye solution became viscous. This procedure took about 2 h. Then, the temperature of the water bath was lowered to 70 \({}^{\circ}\)C and maintained for 5 h. In the initial state, several pores were formed in the solution but all disappeared after 5 h. In order to harden the solid dye sample, the temperature of the water bath was raised to 80 \({}^{\circ}\)C and maintained for 5 h. Figure 2 shows the produced solid dye sample. The thickness and the diameter of the sample were 3.3 and 13.5 mm, respectively. Its surfaces were cut and polished to the optical level.  
A diode laser of 1 W output at 530 nm was used as a pumping light source to excite the solid dye. In order to analyze the photodissociation of the solid dye, the pulse width of the pumping laser was adjusted to 2.5, 5, and 10 ms with pulse width modulation. The pulse repetition rate of the diode laser was fixed to 10 Hz. Evaluating the optical properties of the solid dye, we used a static modulated Fourier transform spectrometer based on a modified Sagnac interferometer. In order to transmit the fluorescence from the solid dye to the interferometer, a flat-convex lens with focal length and diameter of 100 mm and 2 inches was used. Two mirrors in the interferometer are square and 2 inches wide. The surfaces of the mirrors were coated with silver. The beamsplitter was coated to have a transmittance of 50% from 488 to 694 nm. The beamsplitter was tilted 45\({}^{\circ}\) from the optical axis, and the two mirrors were each tilted 22.5\({}^{\circ}\) from the optical axis. The displacement of M2 was 1 mm. To collect the light passing through the interferometer to the detector, a planar lens with a focal length of 100 mm and a diameter of 2 inches was used. The measurement wavelength range of the one-dimensional array detector was 200 to 1100 nm, and the effective number of pixels was 2048. The width of a single pixel in the detector was 14 \(\upmu\)m. By combining a thermal imaging camera with 320 and 240 pixels in the horizontal and vertical directions with a spectrometer, the temperature change in the solid dye along with the change in the spectral signal were obtained simultaneously. Figure 3 shows the spectrometer in this study.  
Figure 3: The experimental setup used to investigate the spectral and thermal properties.  
Figure 2: A synthesized solid-state dye.