# Real-Time Measurement of Photodissociation with a Static Modulated Fourier Transform Spectrometer
## 3 Results and Discussions  
Photodissociation of the polymerized solid dye can be caused by the pumping light of a diode laser. The pumping light with sufficient photon energy can affect the chemical bonds of the polymerized solid dye [16; 17; 18], and the effectiveness of absorbed photon depends on the absorption spectrum of polymerized solid dye. Since the pumping light at 530 nm, which was the absorption peak of the Rh-6 polymerized solid dye, was used, the photodissociation proceeded rapidly. Furthermore, the low thermal conductivity of the polymerized solid dye accelerates the heat accumulation by absorbing the pumping light. Photodissociation appeared as a result of the fluorescence decreasing as the pumping power was absorbed. Since the Fourier transform spectrometer has a high signal-to-noise ratio, it is possible to measure the spectrum even if the fluorescence intensity of the solid dye was lowered by photodissociation. Figure 4 shows the interferogram for the fluorescence of the solid dye with respect to the pulse width change of the pumping laser. Figure 4a is an interferogram obtained when the laser with a pulse width of 2.5 ms was irradiated to the dye, and the strongest intensity of fluorescence was obtained, resulting in a highly visible interference pattern. In this case, the signal-to-noise ratio of the interferogram was calculated to be 15.4. Figure 4b is the interferogram after irradiating the dye with a laser of 2.5 ms pulse width for 15 min. In that case, the signal-to-noise ratio was measured to be 12.6. Figure 4c is the interferogram after adjusting the laser pulse width to 5 ms and irradiating the solid dye for 15 min. The signal-to-noise ratio is 10.9. Figure 4d is the interferogram after irradiating the solid dye after adjusting the laser pulse width to 10 ms, and the signal-to-noise ratio was calculated as 5.5. The signal-to-noise ratio becomes worse along with increasing pulse width. In the comparison of Figure 4d to Figure 4a, the pulse width widened by 4 times and the signal to noise ratio deteriorated by 74%. The fluorescence-related interference pattern gradually deteriorated as the signal-to-noise ratio became worse. Figure 5 demonstrates the investigation on the spectral change of fluorescence from the solid dye along with the pulse width of the laser irradiated. Figure 5a shows the Fourier-transformed fluorescence spectrum when the solid dye was irradiated by 2.5 ms pulse width of the laser. It could be seen that the fluorescence decreased due to photodissociation over time. The fluorescence peak wavelength was measured 590 nm at 60 s. When the solid dye was irradiated with the laser for 900 s, the peak wavelength was shifted to 586 nm. Figure 5b is the Fourier-transformed fluorescence spectrum when the pulse width of the laser was adjusted to 5 ms. It could be seen that the decrease in fluorescence over time is larger than in the case of Figure 5a. The peak wavelength was measured to be 590 nm after 60 s irradiation. When the laser irradiation time was extended to 900 s, the peak wavelength shifted to 586 nm. Figure 5c shows the fluorescence spectrum obtained when the pulse width of the laser was 10 ms. It could be seen that the fluorescence decreased the most rapidly. The fluorescence peak wavelength was measured 590 nm. After it was irradiated for 900 s, the peak wavelength was shifted to 580 nm. Figure 5d shows the relative intensity of the fluorescence spectrum with respect to the pulse width of the pumping laser. The fluorescence intensity of the solid dye after 60 s irradiation was assumed to be 1 for comparison. When the pulse width was 2.5 ms, the fluorescence intensity after 900 s irradiation was reduced by 44% of the initial one. When the pulse width was 5 ms, the fluorescence intensity decreased by 53% after 900 s irradiation from the initial.